DIYABC v2.0: a software to make approximate Bayesian computation inferences about population history using single nucleotide polymorphism, DNA sequence and microsatellite data

The Divergence History of Two Japanese Torreya Taxa (Taxaceae): Implications for Species Diversification in the Japanese Archipelago

The Japanese archipelago as a continental island of the Eurasia continent and harboring high levels of plant species diversity provides an ideal geographical setting for investigating vicariant allopatric speciation due to the sea-level fluctuations associated with climatic oscillations during the Quaternary. In this study, three chloroplast DNA regions and 14 nuclear loci were sequenced for 31 individuals from three populations of Torreya nucifera var. nucifera and 52 individuals from three populations of T. nucifera var. radicans. Population genetic analyses (Network, STRUCTURE and phylogeny) revealed that the genetic boundaries of the two varieties are distinct, with high genetic differentiation (FST) of 0.9619 in chloroplast DNA and 0.6543 in nuclear loci. The relatively ancient divergence times between the two varieties were estimated to 3.03 Ma by DIYABC and 1.77 Ma by IMa2 when dated back to the late Pliocene and the early Pleistocene, respectively. The extremely weak gene flow (2Nm = 0.1) between the two varieties was detected by IMa2, which might be caused by their population expansion since the early Pleistocene (~2.0 Ma) inferred in the Bayesian skyline plots and DIYABC. Niche modeling showed that the two varieties had significant ecological differentiation (p < 0.001) since the Last Interglacial even earlier. These results demonstrate that vicariant allopatric speciation due to sea-level fluctuations may be a common mode of speciation in the Japanese archipelago. This finding provides insights into the understanding of species diversification in the Japanese Archipelago and even East Asian flora under climatic oscillations during the Quaternary.

Genomic signature and evolutionary history of completely cleistogamous lineages in the non-photosynthetic orchid Gastrodia

Despite a long-standing interest since Darwin's time, the genomic implications of obligate self-fertilization remain elusive. Complete cleistogamy-the obligate production of closed, self-pollinating flowers-represents an extreme reproductive strategy. Here, we present the genomic profiles and evolutionary history of two lineages of the mycoheterotrophic orchid Gastrodia, both of which independently acquired complete cleistogamy, based on detailed sampling and a combination of simple sequence repeat (SSR), multiplexed ISSR genotyping by sequencing (MIG-seq) and RNA-seq data. Our analysis reveals clear species delimitation, with no evidence of introgression between the completely cleistogamous species and their co-occurring allogamous sisters. Intriguingly, all analyses indicate that both the completely cleistogamous Gastrodia species and their allogamous sisters exhibit genetic profiles typical of self-pollinating plants. This pattern suggests that their ancestors, probably bearing allogamous flowers, had already evolved mechanisms to mitigate the deleterious effects of selfing, potentially facilitating the emergence of complete cleistogamy through benefits such as reproductive assurance, enhanced colonization ability and species reinforcement. Meanwhile, further analyses suggest that complete cleistogamy evolved very recently (possibly within the last 1000-2000 years) in these two Gastrodia lineages. Combined with the scant evidence of complete cleistogamy outside Gastrodia, our findings imply a limited and ephemeral role for complete cleistogamy in plant speciation.

Comparison of unique Dong Tao chickens from Vietnam and Thailand: genetic background and differences for resource management

BACKGROUND

Rare Dong Tao (DT) chickens are a unique and highly productive poultry breed introduced from Vietnam to Thailand ~ 30 years ago. It has a very peculiar appearance, including enormously enlarged feet with reddish scales, and considered local and culturally significant to both countries. Their adaptability and distinct genetic traits have attracted global interest, underscoring their potential for breeding programs and a need for their thorough genetic makeup assessment.

OBJECTIVE

To assess the genetic diversity and differentiation within the Dong Tao chicken breed, comparing two populations introduced in Thailand with a native population in Vietnam.

METHODS

Three Dong Tao chicken populations from Thailand and Vietnam-along with 54 other indigenous, local chicken, and red junglefowl populations from Thailand, were analyzed using 28 microsatellite markers.

RESULT

High genetic variability and low inbreeding levels were observed in these populations, indicating their effective management despite historical bottlenecks. Genetic similarities between DT-U and DT-HY and indigenous breeds, as well as the closer alignment of DT-L with red junglefowl, highlighted existing introgression and adaptation processes. Two markers, MCW0098 and MCW0216, showed a variation pattern due to potential impact of directional selection, possibly driven by environmental adaptation pressures. These findings emphasize the importance of DT chickens as genetic resources for breeding programs that focus on climate resilience and productivity enhancement.

CONCLUSION

Dong Tao chickenshared genetic similarities with indigenous and local chicken breeds, and red junglefowl, with potential influence of directional selection driven by environmental adaptation pressures.

The Intertidal North-South Split: Oceanographic Features and Life History Shape the Phylogeography of Chiton Acanthochitona rubrolineata

The genetic structure and demographic history of marine organisms are shaped by a variety of factors including biological and ecological characteristics, ocean currents, and the palaeogeological effects of sea-level fluctuations. Here we present a comprehensive method combining population genomics, laboratory experiments, and ocean modelling in 13 populations of the chiton Acanthochitona rubrolineata along the coast of China. Based on demographic and population genomic analyses, significant divergence was observed between the Northern and Southern population groups, which are separated by the Yangtze River Estuary. The numerical circulation model simulation showed that gene flow and population connectivity were strongly influenced by ocean currents and the larval dispersal ability of chiton A. rubrolineata. These data thus clearly revealed the presence of two separately evolving lineages in chiton-A. rubrolineata northern and A. rubrolineata southern. Our study highlights that a robust understanding of organisms in the intertidal zone requires a comprehensive consideration of factors that influence gene flow and genetic structure, including the life-history traits, coastal currents, geographic isolation, and habitat suitability. The life history of marine organisms, together with local oceanographic features, could ultimately drive the population divergence and lead to speciation. These findings provide a guideline for future analyses of non-model and potentially threatened species and will aid in the conservation of biodiversity.

Intraspecific character displacement in oaks

Character displacement refers to the process by which species diverge more in sympatry due to competition for resources. This competition-driven speciation can also occur within populations, known as intraspecific character displacement (ICD). ICD can promote divergence within species by influencing intraspecific competition or encouraging the evolution of alternative phenotypes. Despite its significance, ICD remains understudied and requires further exploration. In this study, we investigate how competition influences genetic and morphological differentiation within species in sympatric and allopatric populations. We focused on Quercus serrata (in China and Japan) and Q. serrata var. brevipetiolata (found only in China), which belong to a small monophyletic group of oak species nested within Section Quercus (white oaks). Using genetic markers, we detected divergence between Chinese and Japanese populations and further diversification within China, with asymmetric historical gene flow primarily from Q. serrata (the earlier diverged species) to Q. serrata var. brevipetiolata (the later variety). Although genetic differentiation did not differ between sympatric and allopatric populations, leaf morphological variation, analyzed through the geometric morphometric method (GMM) and traditional morphological method, revealed greater trait variation in sympatry. In addition, we found an allometric growth relationship between leaf size and leaf mass of Q. serrata and Q. serrata var. brevipetiolata, with the leaf area of Q. serrata var. brevipetiolata decreasing more disproportionately to leaf mass. This suggests a resource trade-off, where Q. serrata var. brevipetiolata, the later diverged variety, adopts more resource-conservative traits in sympatry. Further analysis of trait variation with environmental factors supports these findings, while genetic variation along climate gradients showed significant responses primarily in Q. serrata, regardless of sympatric or allopatric conditions. Although neutral genetic markers are insufficient to capture selection-driven adaptive differentiation, we inferred that Q. serrata var. brevipetiolata is progressing towards ecological divergence from Q. serrata. Overall, our results highlight the role of ICD in driving morphological diversification and resource-use strategies within species in response to competitive pressures.

Maternal and paternal lineage analysis of Island Southeast Asian goats reveals continental propagation routes and introgression through the Indian ocean

The Philippines and Indonesia, located at the crossroads of historical human migrations in the Asia-Pacific region, lie in the southeasternmost part of Mainland Southeast Asia. Both countries are recognized as mega-diverse nations, hosting a wide variety of species. However, the history of goat propagation in Island Southeast Asia remains unclear due to limited molecular studies and the absence of archaeological evidence in this region. This study conducted phylogeographic analyses of mtDNA hypervariable region 1 and SRY 3'UTR sequences of goats from the Philippines and Indonesia, comparing them with Old World domestic goats. Philippine goat mtDNA haplotypes were classified into haplogroups B (152/206, 73.8%) and A (54/206, 26.2%), whereas all Indonesian goat mtDNA haplotypes belonged to haplogroup B (72/72, 100%). The distribution of mtDNA haplogroup B and regional differences suggest two propagation routes: one from China/Taiwan to the Philippines and another from Mainland Southeast Asia to Indonesia. The distribution of five SRY haplotypes demonstrated that haplotype Y2A, absent in Mainland Southeast Asia, was present in Island Southeast Asia, indicating gene introgression through the Indian Ocean from the African continent and/or southern Europe. This introgression may have been driven by human activities, such as European migrations between the 16th and 19th centuries.

Integrative Analysis of Diphasiastrum digitatum Holub: Unveiling Genetic Variation and Ecological Adaptations for Sustainable Ecosystem Management

Understanding the diversity and ecological evolutionary history of plant species is crucial for addressing the current biodiversity crisis and comprehending the processes by which organisms fill ecological and geographic spaces. In this study, we present a comprehensive analysis of the diversity and evolutionary history of Diphasiastrum digitatum Holub from the lycophyte lineage of plants, using microsatellite genotyping data and biogeographic analyses. Based on the available transcriptome assembly, we generated numerous markers and utilized 13 robust microsatellite markers to genotype a collection of 402 specimens from the Eastern US (VT; VA; NC; TN). In accordance with the accepted phylogeny, cross-amplification tests demonstrated a closer relationship between D. digitatum and Diphasiastrum spp. compared with Lycopodium spp. Furthermore, the population genetics analyses identified two genetic clusters within the D. digitatum collection and suggested ongoing divergence and expansion. Isolation-by-distance analysis indicated that geographic distance had a minimal effect on differentiation, whereas environmental variables related to water regime were strongly associated with the genetic variance. Ecological niche modeling showed a post-Last Glacial Maximum expansion of D. digitatum from southern refugia, corroborating a similar evolutionary scenario based on our microsatellite data. Overall, this study provides valuable insights into the evolutionary history of clubmosses and highlights the migration events and the environmental factors that shaped their current distribution.

The genetic trail of the invasive mosquito species Aedes koreicus from the east to the west of Northern Italy

BACKGROUND

Aedes koreicus is native to Far East Asia and recorded in Europe since 2008. In Italy, Ae. koreicus is widespread throughout the Northern part of the peninsula, highlighting its invasive potential and spread. However, no clear clues about the dispersal patterns of the species have been collected so far.

METHODOLOGY/PRINCIPAL FINDINGS

Population genetic analyses were performed to assess the genetic structure of populations of Ae. koreicus and to make hypotheses about its dispersal patterns in Northern Italy. Ten microsatellite markers specific for Ae. koreicus were used to genotype 414 individuals from 13 populations in the pre-alpine area of Italy, and neighboring Slovenia. Basic and Bayesian population genetic analyses were performed to evaluate patterns of genetic variation, genetic structure, and demography of selected mosquito populations. While presenting a certain degree of structuring, the Italian and Slovenian populations of Ae. koreicus were poorly differentiated. Moreover, demographic analysis supports the expansion of a single population propagule of Ae. koreicus in Italy and Slovenia and provides evidence of the presence of overwintering populations in the studied area.

CONCLUSIONS/SIGNIFICANCE

Our results highlight a common origin, and stable colonization of Northern Italy and Slovenia, as a probable consequence of the expansion of a unique population. This stresses out the importance of continuous monitoring of Ae. koreicus, to finally uncover the geographic origins and entrance pathways of invasive populations and to prevent or limit further introductions.

Genetic Differentiation of Abies alba Outside Its Main Range Under Warm Meso- and Sub-Mediterranean Conditions in Italy and Switzerland

Abies alba is an important European tree species currently mostly found at cool and humid sites in the montane zone. In the past, it grew under markedly warmer and drier climates during the Eemian and mid-Holocene, and cryptic Mediterranean populations confirm the species' capacity to grow under warm, summer-dry conditions. However, it is unknown if warm-loving Mediterranean occurrences are related to specific genetic properties (e.g., subspecies or ecotypes). Investigating the genetics of cryptic warm-loving populations is crucial for a better understanding of past and future population dynamics of A. alba. We genotyped 478 A. alba samples at 174 single-nucleotide polymorphisms (SNP), covering a broad latitudinal range from Southern Italy to Switzerland while accounting for local altitudinal gradients, and combined these newly introduced genotypes with those of other European Abies populations from the literature. Population genetic structure analyses grouped the warm-loving meso- and sub-Mediterranean populations into the same genetic cluster as the mountain populations of each region. The occurrence of three genetic clusters from Northern to Southern Italy is in line with the glacial refugia history. The inferred evolutionary and demographic history suggests a northward expansion of A. alba after glaciation, as well as a trans-Adriatic gene flow between Balkan and Southern Italian populations. Collectively, the combined genotypic data from individuals across the species' range demonstrate that cryptic Mediterranean populations of A. alba align with the local and large-scale genetic structure of populations from its main range, suggesting that the species is able to thrive in a warmer and drier environmental range than hitherto anticipated. This finding implies that it is unneeded to postulate extinct subspecies or ecotypes to explain the occurrence of meso- and sub-Mediterranean Eemian or mid-Holocene silver fir forests, with important implications for future A. alba population dynamics.

The Genetic Architecture of Local Adaptation and Reproductive Character Displacement in Scutiger boulengeri Complex (Anura: Megophryidae)

Speciation is a continuous process driven by barriers to gene flow. Based on genome-wide SNPs (single nucleotide polymorphisms) of 190 toads from 31 sampling sites of Scutiger boulengeri complex, we found evidence for monophyly which represented a continuous speciation process of at least six lineages in S. boulengeri, which radiated and exhibited varying degrees of divergence and gene flow. The SNP-based phylogenetic tree was largely discordant with the multilocus mitochondrial tree (i.e., S. mammatus and S. glandulatus nested in the lineages of S. boulengeri) published before. The Min Mountains (MM) and Qinghai-Tibet Plateau (QTP) lineages differ fundamentally in habitat (i.e., elevation) and morphology (i.e., SVL), we detected signatures of potential high-altitude and cold adaptation genes in QTP (vs. MM). We found the evidence of reproductive trait disparity (i.e., SVL and nuptial pads) is key to promoting sympatric rather than allopatric species pairs. In addition, we identified selection signals for genes related to sympatric character displacement, genes linked to obesity-related traits, nuptial spines morphology and enlarged chest nuptial pads in S. mammatus (vs. QTP group of S. boulengeri). Our study provided new insight and paradigm for a varied speciation pattern from local adaptation of allopatry to sympatric character displacement in the S. boulengeri complex.

Evolutionary Histories of Camellia japonica and Camellia rusticana

The genus Camellia is widely distributed, primarily in East Asia. Camellia japonica is located at the northern limit of this genus distribution, and understanding changes in its distribution is crucial for understanding the evolution of plants in this region, as well as their relationship with geological history and climate change. Moreover, the classification of sect. Camellia in Japan has not been clarified. Therefore, this study aims to understand the evolutionary history of the Japanese sect. Camellia. The genetic population structure was analysed using SNP data and MIG-seq. The relationship between the Japanese sect. Camellia, including the related species in China, was further inferred from the phylogeny generated by RA x ML, SplitsTree and PCA. Population genetic structure was inferred using a Bayesian clustering method (ADMIXTURE). We subsequently employed approximate Bayesian computation, which was further supported by the coalescent simulations (DIYABC, fastsimcoal and Bayesian Skyline Plots) to explore the changes in population, determining which events appropriately explain the phylogeographical signature. Ecological niche modelling was combined with genetic analyses to compare current and past distributions. The analyses consistently showed that C. japonica and C. rusticana are distinct, having diverged from each other during the Middle to Late Miocene period. Furthermore, C. japonica differentiated into four major populations (North, South, Ryukyu-Taiwan and Continent). The Japanese sect. Camellia underwent speciation during archipelago formation, reflecting its ancient evolutionary history compared with other native Japanese plants. C. rusticana did not diverge from C. japonica in snow-rich environments during the Quaternary period. Our results suggest that both species have been independent since ancient times and that ancestral populations of C. japonica have persisted in northern regions. Furthermore, the C. japonica population on the continent is hypothesised to have experienced a reverse-colonisation event from southern Japan during the late Pleistocene glaciation.

Population genetics of the freshwater red alga Batrachospermum gelatinosum (Rhodophyta) II: Phylogeographic analyses reveal spatial genetic structure among and within five major drainage basins in eastern North America

The freshwater red alga Batrachospermum gelatinosum has a well-documented distribution spanning historically glaciated and unglaciated eastern North America. This alga has no known desiccation-resistant propagule; thus, long-distance dispersal events are likely rare. We predicted strong genetic structure among drainage basins and admixture among sites within basins. We predicted greater genetic diversity at lower latitude sites because they likely serve as refugia and the origin of northward, post-Pleistocene range expansion. We used 10 microsatellite loci to investigate genetic diversity from 311 gametophytes from 18 sites in five major drainage basins: South Atlantic Gulf, Mid-Atlantic, Ohio River, Great Lakes, and Northeast. Our data showed strong genetic partitioning among drainage basins and among sites within basins, yet no isolation by distance was detected. Genetic diversity varied widely among sites and was not strictly related to latitude as predicted. The results from B. gelatinosum provide strong support that each stream site contributes to the unique genetic variation within the species, potentially due to limited dispersal and the prevailing reproductive mode of intragametophytic selfing. Simulations of migration suggested post-Pleistocene dispersal from the Mid-Atlantic. Batrachospermum gelatinosum potentially persisted in refugia that were just south of the ice margins rather than in the southernmost part of its range. Research of other taxa with similar ranges could determine whether these results are generally applicable for freshwater red algae. Nevertheless, these results from B. gelatinosum add to the growing literature focused on the patterns and genetic consequences of post-Pleistocene range expansion by eastern North American biota.

Insular environment-dependent introgression from an arid-grassland orchid to a wetland orchid on an oceanic island

Adaptive introgression plays a vital role in allowing recipient species to adapt and colonize new environments. However, our understanding of such environment-dependent introgressions is primarily limited to specific plant taxa in particular settings. In Japan, two related orchid species, the autonomously self-pollinating Pogonia minor and the outcrossing Pogonia japonica, typically inhabit dry grasslands and wetlands, respectively. Intriguingly, an island ecotype of P. japonica exists in arid, wind-swept, open sites on volcanic mountain slopes on Kozu Island, in the oceanic Izu Islands. To investigate potential introgression and its implications between P. japonica and P. minor on Kozu Island, we applied a comprehensive approach that included examining morphological traits, genome-wide SNP data, and plastid DNA sequences. We also examined the breeding systems of these species on Kozu Island through artificial pollination experiments to determine if introgression from P. minor has endowed the P. japonica ecotype with selfing capabilities. Extensive sampling on Kozu Island revealed that all P. japonica specimens exhibit signs of introgression from P. minor, suggesting the absence of pure P. japonica populations on the island. Furthermore, the chloroplast haplotypes of the insular P. japonica ecotype consistently match those of P. minor, indicating a predominantly asymmetrical initial hybridization with P. minor acting mainly as the maternal parent in the formation of F1 hybrids. Despite the advantages of self-fertilization in isolated environments, the insular P. japonica does not exhibit autogamy. Consequently, the scarcity of moist habitats, rather than selection pressure for selfing, likely contributes to the observed widespread introgression. Our study strongly suggests that the arid-environment-adapted P. minor has introgressed into the insular ecotype of P. japonica, enabling its successful colonization of arid volcanic mountain slopes of the oceanic island.

Computational Genomics and Its Applications to Anthropological Questions

The advent of affordable genome sequencing and the development of new computational tools have established a new era of genomic knowledge. Sequenced human genomes number in the tens of thousands, including thousands of ancient human genomes. The abundance of data has been met with new analysis tools that can be used to understand populations' demographic and evolutionary histories. Thus, a variety of computational methods now exist that can be leveraged to answer anthropological questions. This includes novel likelihood and Bayesian methods, machine learning techniques, and a vast array of population simulators. These computational tools provide powerful insights gained from genomic datasets, although they are generally inaccessible to those with less computational experience. Here, we outline the theoretical workings behind computational genomics methods, limitations and other considerations when applying these computational methods, and examples of how computational methods have already been applied to anthropological questions. We hope this review will empower other anthropologists to utilize these powerful tools in their own research.

Tracking the North American Asian Longhorned Beetle Invasion With Genomics

Biological invasions pose significant threats to ecological and economic stability, with invasive pests like the Asian longhorned beetle (Anoplophora glabripennis Motschulsky, ALB) causing substantial damage to forest ecosystems. Effective pest management relies on comprehensive knowledge of the insect's biology and invasion history. This study uses genomics to address these knowledge gaps and inform existing biosurveillance frameworks. We used 2768 genome-wide single nucleotide polymorphisms to compare invasive A. glabripennis populations in North America, using genomic variation to trace their sources of invasion and spread patterns, thereby refining our understanding of this species' invasion history. We found that most North American A. glabripennis infestations were distinct, resulting from multiple independent introductions from the native range. Following their introduction, all invasive populations experienced a genetic bottleneck which was followed by a population expansion, with a few also showing secondary spread to satellite infestations. Our study provides a foundation for a genome-based biosurveillance tool that can be used to clarify the origin of intercepted individuals, allowing regulatory agencies to strengthen biosecurity measures against this invasive beetle.

Population connectivity and size reductions in the Anthropocene: the consequence of landscapes and historical bottlenecks in white forsythia fragmented habitats

BACKGROUND

White forsythia (Abeliophyllum distichum) is an endangered Korean Peninsula endemic that has been subjected to recent population genomics studies using SNPs via RAD sequencing. Here, we primarily employed the often underutilized haplotype information from RAD loci to further describe the species' previously uninvestigated haplotype-based genomic variation and structure, and genetic-geographic characteristics and gene flow patterns among its five earlier identified genetic groups. We also inferred the time of past events that may have impacted the effective population size of these groups, as well as the species' potential future distribution amidst the warming climate and anthropogenic threats.

RESULTS

Our findings emphasized the recognition of the species' regional patterns of genetic structure, and the role of topography and its associated gene flow patterns as some of the possible factors that may have influenced the species' present-day fragmented population distribution. The inferred bottleneck events during the Anthropocene, some of which aligned with the time of historical catastrophic events on the Peninsula (e.g., the Korean War), were revealed to have contributed to the generally low effective population size of its five lineages, particularly those with marginal distributional range. Future distribution under both optimistic and pessimistic climatic scenarios suggests unlikely suitable habitats for these populations to expand from their current range limits, at least in the next 80 years.

CONCLUSIONS

The small effective population size and landscape-driven limited gene flow among white forsythia populations will remain a big challenge for the conservation management of the species' already fragmented population distribution. To help mitigate these impacts, the merging of various research approaches and the use of genomic data to their full potential is recommended to provide the optimized knowledge-based tools for the conservation of this endangered species, and other similar plants under pressure.

First genetic evaluation of a wild population of Crocodylus intermedius: New insights for the recovery of a Critically Endangered species

During the second third of last century, the Orinoco Crocodile (Crocodylus intermedius) underwent a hunting process driven by the demand from the North American, European, and Japanese leather industry, resulting in a sharp decline of its populations. Currently, only two known remaining populations of this Critically Endangered species persist in the Colombian Orinoquía: in the Guayabero-Duda-Lozada and the Cravo Norte-Ele-Lipa River Systems. The latter has been the only population subject of study, including recent surveys and local conservation initiatives such as egg and hatchling ranching. Despite suggestions for population recovery based on the observed increase in clutches in the area, information regarding its genetic status has been pending assessment. This research aims to provide a genetic characterization of this remaining population and to evaluate the diversity recovered during a period of the egg ranching initiative. For this purpose, we utilized variable molecular markers, specifically 17 microsatellite loci, nuclear DNA. Despite revealing intermediate levels of genetic diversity, we identified an effective population size of 11.5-17, well below the minimum values proposed for short-term subsistence. While no evidence of inbreeding was found, it is acknowledged as a potential risk based on the population's history. Additionally, we detected a historical bottleneck possibly influenced by arid periods affecting the region since the Pleistocene. While the evaluated population presents a unique opportunity for C. intermedius conservation, it also exposes a high risk of entering the extinction vortex. The primary action to be taken is to support the egg and hatchling ranching program, which successfully recovered most of the genetic diversity present in the population.

Genetically- and environmentally-dependent processes drive interspecific and intraspecific divergence in the Chinese relict endemic genus Dipteronia

China is a hotspot of relict plant species that were once widespread throughout the Northern Hemisphere. Recent research has demonstrated that the occurrence of long-term stable refugia in the mountainous regions of central and south-western China allowed their persistence through the late Neogene climate fluctuations. One of these relict lineages is Dipteronia, an oligotypic tree genus with a fossil record extending to the Paleocene. Here, we investigated the genetic variability, demographic dynamics and diversification patterns of the two currently recognized Dipteronia species (D ipteronia sinensis and D . dyeriana). Molecular data were obtained from 45 populations of Dipteronia by genotyping three cpDNA regions, two single copy nuclear genes and 15 simple sequence repeat loci. The genetic study was combined with niche comparison analyses on the environmental space, ecological niche modeling, and landscape connectivity analysis. We found that the two Dipteronia species have highly diverged both in genetic and ecological terms. Despite the incipient speciation processes that can be observed in D. sinensis, the occurrence of long-term stable refugia and, particularly, a dispersal corridor along Daba Shan-west Qinling, likely ensured its genetic and ecological integrity to date. Our study will not only help us to understand how populations of Dipteronia species responded to the tectonic and climatic changes of the Cenozoic, but also provide insight into how Arcto-Tertiary relict plants in East Asia survived, evolved, and diversified.

Reconstructing the Global Migration History of Phytophthora infestans Toward Colombia

The evolution of new variants of plant pathogens is one of the biggest challenges to controlling and managing plant diseases. Of the forces driving these evolutionary processes, global migration events are particularly important for widely distributed diseases such as potato late blight, caused by the oomycete Phytophthora infestans. However, little is known about its migration routes outside North America and Europe. This work used genotypic data from population studies to elucidate the migration history originating the Colombian P. infestans population. For this purpose, a dataset of 1,706 P. infestans genotypes was recollected, representing North and South America, Europe, and Asia. Descriptive analysis and historical records from North America and Europe were used to propose three global migration hypotheses, differing on the origin of the disease (Mexico or Peru) and the hypothesis that it returned to South America from Europe. These scenarios were tested using approximate Bayesian computation. According to this analysis, the most probable scenario (posterior probability = 0.631) was the one proposing a Peruvian origin for P. infestans, an initial migration toward Colombia and Mexico, and a later event from Mexico to the United States and then to Europe and Asia, with no return to northern South America. In Colombia, the scenario considering a single migration from Peru and posterior migrations within Colombia was the most probable, with a posterior probability of 0.640. The obtained results support the hypothesis of a Peruvian origin for P. infestans followed by rare colonization events worldwide.

Population genetic structure and historical demography of the population of forest elephants in Côte d'Ivoire

The population of forest elephant (Loxodonta cyclotis) has continuously declined in Côte d'Ivoire and, the remaining population largely consists of subpopulations that are fragmented and isolated. No data actually exist on the level of genetic diversity and population genetic structure of current forest elephant populations in Côte d'Ivoire. In this sense, determining genetic diversity and the underlying mechanisms of population differentiation is crucial for the initiation of effective conservation management. A total of 158 dung samples of forest elephants were collected at stage 1 of decompositions (dung pile intact, very fresh) in three Classified Forests (CF) (Bossématié, Dassioko and Port-Gauthier) in Côte d'Ivoire. A total of 101 sequences of the mitochondrial DNA control region measuring 600 base pair and 26 haplotypes were obtained. A haplotypic diversity ranging from 0.655 ± 0.050 at Bossématié and 0.859 ± 0.088 at Port Gauthier was obtained. Fifteen (15) out of 26 haplotypes observed were singletons and only the Dassioko and Port Gauthier CFs shared the same haplotypes. The strong genetic connectivity between forest elephant populations of the Dassioko and Port Gauthier CFs is supported by the grouping of these populations into a single cluster by Bayesian analysis. Although populations of L. cyclotis exhibit relatively high genetic diversity, habitat fragmentation could affect the genetic variability of current populations. Urgent measures including the reinforcement/establishment of genetic corridors and the strengthening of protection measures need to be undertaken to save the remaining populations of forest elephants in Côte d'Ivoire.

A Comparative Genetic Analysis of Phoenix atlantica in Cape Verde

The Cape Verde palm tree, Phoenix atlantica, holds significant ecological and cultural importance within the Cape Verde archipelago. However, its genetic distinctiveness has been questioned due to its close relationship and morphological similarity to the date palm (Phoenix dactylifera). In this study, we used an expanded sample set, 18 simple sequence repeat (SSR) markers, and a plastid minisatellite to characterize P. atlantica in Cape Verde and investigate its relationship with other Phoenix species. Our findings identify genetic markers that differentiate the P. atlantica genetic pool, including a unique fixed allele. We also provide evidence of the recent divergence of P. atlantica from Northern African date palm populations, suggesting a relatively recent colonization of Cape Verde by palm trees. Additionally, we characterized the genetic composition of palm tree populations across three Cape Verde islands, concluding that wild samples from certain populations in Boavista and Sal are best suited for establishing a seed and/or germplasm bank for replantation efforts, representing a crucial step for the conservation of Cape Verde's natural heritage. Overall, our results enhance the understanding of the historical trajectories and genetic characterization of palm trees in Africa, offering valuable insights for conservation strategies.

Preliminary insights of the genetic diversity and invasion pathways of Cedrela odorata in the Galapagos Islands, Ecuador

Cedrela odorata is considered the second most invasive tree species of the Galapagos Islands. Although it is listed in CITES Appendix II and there are population losses in mainland Ecuador, in Galapagos it is paradoxically a species of concern due to its invasive potential. Genetic studies can shed light on the invasion history of introduced species causing effects on unique ecosystems like the Galapagos. We analyzed nine microsatellite markers in C. odorata individuals from Galapagos and mainland Ecuador to describe the genetic diversity and population structure of C. odorata in the Galapagos and to explore the origin and invasion history of this species. The genetic diversity found for C. odorata in Galapagos (H e = 0.55) was lower than reported in the mainland (H e = 0.81), but higher than other invasive insular plant species, which could indicate multiple introductions. Our results suggest that Ecuador's northern Coastal region is the most likely origin of the Galapagos C. odorata, although further genomic studies, like Whole Genome Sequencing, Rad-Seq, and/or Whole Genome SNP analyses, are needed to confirm this finding. Moreover, according to our proposed pathway scenarios, C. odorata was first introduced to San Cristobal and/or Santa Cruz from mainland Ecuador. After these initial introductions, C. odorata appears to have arrived to Isabela and Floreana from either San Cristobal or Santa Cruz. Here, we report the first genetic study of C. odorata in the Galapagos and the first attempt to unravel the invasion history of this species. The information obtained in this research could support management and control strategies to lessen the impact that C. odorata has on the islands' local flora and fauna.

Genetic diversity and shallow genetic differentiation of the endangered scaly-sided merganser Mergus squamatus

Examining patterns of genetic diversity are crucial for conservation planning on endangered species, while inferring the underlying process of recent anthropogenic habitat modifications in the context potential long-term demographic changes remains challenging. The globally endangered scaly-sided merganser (SSME), Mergus squamatus, is endemic to a narrow range in Northeast Asia, and its population has recently been contracted into two main breeding areas. Although low genetic diversity has been suggested in the Russian population, the genetic status and demographic history of these individuals have not been fully elucidated. We therefore examined the genetic diversity and structure of the breeding populations of the SSME and investigated the relative importance of historical and recent demographic changes to the present-day pattern of genetic diversity. Using 10 nuclear microsatellite (SSR) markers and mitochondrial DNA (mtDNA) control region sequences, we found limited female-inherited genetic diversity and a high level of nuclear genetic diversity. In addition, analysis of both markers consistently revealed significant but weak divergence between the breeding populations. Inconsistent demographic history parameters calculated from mtDNA and bottleneck analysis results based on SSR suggested a stable historical effective population size. By applying approximate Bayesian computation, it was estimated that populations started to genetically diverge from each other due to recent fragmentation events caused by anthropogenic effects rather than isolation during Last Glacial Maximum (LGM) and post-LGM recolonization. These results suggest that limited historical population size and shallow evolutionary history may be potential factors contributing to the contemporary genetic diversity pattern of breeding SSME populations. Conservation efforts should focus on protecting the current breeding habitats from further destruction, with priority given to both the Russian and Chinese population, as well as restoring the connected suitable breeding grounds.

Population structure and diversification of Gymnospermium kiangnanense, a plant species with extremely small populations endemic to eastern China

Background

Gymnospermium kiangnanense is the only species distributed in the subtropical region within the spring ephemeral genus Gymnospermium. Extensive human exploitation and habitat destruction have resulted in a rapid shrink of G. kiangnanense populations. This study utilizes microsatellite markers to analyze the genetic diversity and structure and to deduce historical population events of extant populations of G. kiangnanense.

Methods

A total of 143 individuals from eight extant populations of G. kiangnanense, including two populations from Anhui Province and six populations from Zhejiang Province, were analyzed with using 21 pairs of microsatellite markers. Genetic diversity indices were calculated using Cervus, GENEPOP, GenALEX. Population structure was assessed using genetic distance (UPGMA), principal coordinate analysis (PCoA), Bayesian clustering method (STRUCTURE), and molecular variation analysis of variance (AMOVA). Population history events were inferred using DIYABC.

Results

The studied populations of G. kiangnanense exhibited a low level of genetic diversity (He = 0.179, I = 0.286), but a high degree of genetic differentiation (FST = 0.521). The mean value of gene flow (Nm ) among populations was 1.082, indicating prevalent gene exchange via pollen dispersal. Phylogeographic analyses suggested that the populations of G. kiangnanense were divided into two lineages, Zhejiang (ZJ) and Anhui (AH). These two lineages were separated by the Huangshan-Tianmu Mountain Range. AMOVA analysis revealed that 36.59% of total genetic variation occurred between the two groups. The ZJ lineage was further divided into the Hangzhou (ZJH) and Zhuji (ZJZ) lineages, separated by the Longmen Mountain and Fuchun River. DIYABC analyses suggested that the ZJ and AH lineages were separated at 5.592 ka, likely due to the impact of Holocene climate change and human activities. Subsequently, the ZJZ lineage diverged from the ZJH lineage around 2.112 ka. Given the limited distribution of G. kiangnanense and the significant genetic differentiation among its lineages, both in-situ and ex-situ conservation strategies should be implemented to protect the germplasm resources of G. kiangnanense.

Europe as a secondary distribution hub in the worldwide invasion of the potato cyst nematode Globodera rostochiensis

The potato cyst nematode Globodera rostochiensis originates from the Andean Mountain region in South America and has unintentionally been introduced to all inhabited continents. Several studies have examined the population genetic structure of this pest in various countries by using microsatellite markers. However, merging microsatellite data produced from different laboratories is challenging and can introduce uncertainty when interpreting the results. To overcome this challenge and to explore invasion routes of this pest, we have genotyped 22 G. rostochiensis populations from all continents. Within populations, the highest genetic diversity was observed in the South American populations, the European populations showed an intermediate level of genetic diversity and the remaining populations were the less diverse. This confirmed pre-existing knowledge such as a first introduction event from South America to Europe, but the less diverse populations could originate either from South America or from Europe. At the continental scale, STRUCTURE genetic clustering output indicated that North America and Asia have experienced at least two introduction events. Comparing different evolutionary scenarios, the Approximate Bayesian Computation analysis showed that Europe served as a secondary distribution centre for the invasion of G. rostochiensis into all other continents (North America, Africa, Asia and Oceania).

Intraspecific divergence in a coastal plant, Euphorbia jolkinii, at a major biogeographic boundary in East Asia

PREMISE

Quaternary climatic fluctuations and long-distance seed dispersal across the sea are critical factors affecting the distribution of coastal plants, but the spatiotemporal nature of population expansion and distribution change of East Asian coastal plants during this period are rarely examined. To explore this process, we investigated the genome-wide phylogenetic patterns of Euphorbia jolkinii Boiss. (Euphorbiaceae), which grows widely on littoral areas of Japan, Korea, and Taiwan.

METHODS

We used plastome sequences and genome-wide single nucleotide polymorphisms in samples across the species range to reveal phylogeographic patterns and spatiotemporal distributional changes. We conducted ecological niche modeling for the present and the last glacial maximum (LGM).

RESULTS

Genetic differentiation was observed between the northern and southern populations of E. jolkinii, separated by the major biogeographic boundary, the Tokara Gap. These two groups of populations differentiated during the glacial period and subsequently intermingled in the intermorainic areas of the central Ryukyu Islands after the LGM. Ecological niche models suggested that the potential range of E. jolkinii was restricted to southern Kyushu; however, it was widespread in the southern Ryukyu Islands and Taiwan during the LGM.

CONCLUSIONS

This study provides evidence of genetic differentiation among coastal plant populations separated by the prominent biogeographical boundary. Although coastal plants are typically expected to maintain population connectivity through sea-drifted seed dispersal, our findings suggest that genetic differences may arise because of a combination of limited gene flow and changes in climate during the glacial period.

The direction, timing and demography of Popillia japonica (Coleoptera) invasion reconstructed using complete mitochondrial genomes

The Japanese beetle Popillia japonica is a pest insect that feeds on hundreds of species of wild and cultivated plants including important fruit, vegetable, and field crops. Native to Japan, the pest has invaded large areas of the USA, Canada, the Azores (Portugal), Italy, and Ticino (Switzerland), and it is considered a priority for control in the European Union. We determined the complete mitochondrial genome sequence in 86 individuals covering the entire distribution of the species. Phylogenetic analysis supports a major division between South Japan and Central/North Japan, with invasive samples coming from the latter. The origin of invasive USA samples is incompatible, in terms of the timing of the event, with a single introduction, with multiple Japanese lineages having been introduced and one accounting for most of the population expansion locally. The origin of the two invasive European populations is compatible with two different invasions followed by minimal differentiation locally. Population analyses provide the possibility to estimate the rate of sequence change from the data and to date major invasion events. Demographic analysis identifies a population expansion followed by a period of contraction prior to the invasion. The present study adds a time and demographic dimension to available reconstructions.

Approximate Bayesian computational methods to estimate the strength of divergent selection in population genomics models

Statistical estimation of parameters in large models of evolutionary processes is often too computationally inefficient to pursue using exact model likelihoods, even with single-nucleotide polymorphism (SNP) data, which offers a way to reduce the size of genetic data while retaining relevant information. Approximate Bayesian Computation (ABC) to perform statistical inference about parameters of large models takes the advantage of simulations to bypass direct evaluation of model likelihoods. We develop a mechanistic model to simulate forward-in-time divergent selection with variable migration rates, modes of reproduction (sexual, asexual), length and number of migration-selection cycles. We investigate the computational feasibility of ABC to perform statistical inference and study the quality of estimates on the position of loci under selection and the strength of selection. To expand the parameter space of positions under selection, we enhance the model by implementing an outlier scan on summarized observed data. We evaluate the usefulness of summary statistics well-known to capture the strength of selection, and assess their informativeness under divergent selection. We also evaluate the effect of genetic drift with respect to an idealized deterministic model with single-locus selection. We discuss the role of the recombination rate as a confounding factor in estimating the strength of divergent selection, and emphasize its importance in break down of linkage disequilibrium (LD). We answer the question for which part of the parameter space of the model we recover strong signal for estimating the selection, and determine whether population differentiation-based summary statistics or LD-based summary statistics perform well in estimating selection.

Genetic consequences of Last Glacial-Holocene changes in snowfall regime in Arnica mallotopus populations: A plant confined to heavy-snow areas of Japan

PREMISE

Snow is an important environmental factor affecting plant distribution. Past changes in snowfall regimes may have controlled the demographies of snow-dependent plants. However, our knowledge of changes in the distribution and demographies of such plants is limited because of the lack of fossil records.

METHODS

Population genetic and landscape genetic analyses were used to investigate the response of population dynamics of Arnica mallotopus (Asteraceae)-a plant confined to heavy-snow areas of Japan-to changes in snowfall regimes from the Last Glacial Period to the Holocene.

RESULTS

The population genetic analysis suggested that the four geographic lineages diverged during the Last Glacial Period. The interaction between reduced snowfall and lower temperatures during this period likely triggered population isolation in separate refugia. Subpopulation differentiation in the northern group was lower than in the southern group. Our ecological niche model predicted that the current distribution was patchy in the southern region; that is, the populations were isolated by topologically flat and climatically unsuitable lowlands. The landscape genetic analysis suggested that areas with little snowfall acted as barriers to the Holocene expansion of species distribution and continued limiting gene flow between local populations.

CONCLUSIONS

These findings indicate that postglacial population responses vary among regions and are controlled by environmental and geographic factors. Thus, changes in snowfall regime played a major role in shaping the distribution and genetic structure of the snow-dependent plant.

Mass-Rearing Conditions Do Not Always Reduce Genetic Diversity: The Case of the Mexican Fruit Fly, Anastrepha ludens (Diptera: Tephritidae)

The application of the sterile insect technique (SIT) requires the adaptation of insects to mass-rearing conditions. It is generally accepted that this adaptation may include a reduction in genetic diversity and an associated loss of desirable characteristics for the effective performance of sterile insects in the field. Here, we compare the genetic diversity of two mass-reared strains of the Mexican fruit fly, Anastrepha ludens, and a wild (WIL) population collected near Tapachula, Mexico, using seven DNA microsatellites as molecular genetic markers. The mass-reared strains were a bisexual laboratory strain (LAB) with approximately 130 generations under mass-rearing and a genetic sexing strain, Tapachula-7 (TA7), also under mass-rearing for 100 generations. Our results revealed an overall low level of genetic differentiation (approximately 15%) among the three strains, with the LAB and WIL populations being genetically most similar and TA7 most genetically differentiated. Although there were some differences in allele frequencies between strains, our results show that overall, the adaptation to mass-rearing conditions did not reduce genetic variability compared to the wild sample in terms of heterozygosity or allelic richness, nor did it appear to alter the level of inbreeding with respect to the wild populations. These results are contrary to the general idea that mass-rearing always results in a reduction in genetic diversity. Overall, our findings can contribute to a better understanding of the impact that adaptation to mass-rearing conditions may have on the genetic make-up of strains.

Origin and spatial population structure of Malagasy native chickens based on mitochondrial DNA

Since Malagasy human culture became established in a multi-layered way by genetic admixture of Austronesian (Indonesia), Bantu (East Africa) and West Asian populations, the Malagasy native livestock should also have originated from these regions. While recent genetic studies revealed that Malagasy native dogs and goats were propagated from Africa, the origin of Malagasy native chickens is still controversial. Here, we conducted a phylogeographic analysis of the native chickens, focusing on the historical relationships among the Indian Ocean rim countries and based on mitochondrial D-loop sequences. Although previous work suggested that the rare Haplogroup D occurs with high frequencies in Island Southeast Asia-Pacific, East Africa and Madagascar, the major mitochondrial lineage in Malagasy populations is actually not Haplogroup D but the Sub-haplogroup C2, which is also observed in East Africa, North Africa, India and West Asia. We demonstrate that the Malagasy native chickens were propagated directly from West Asia (including India and North Africa), and not via East Africa. Furthermore, they display clear genetic differentiation within Madagascar, separated into the Highland and Lowland regions as seen in the human genomic landscape on this island. Our findings provide new insights for better understanding the intercommunion of material/non-material cultures within and around Madagascar.

Conservation genetics and potential geographic distribution modeling of Corybas taliensis, a small 'sky Island' orchid species in China

BACKGROUND

Corybas taliensis is an endemic species of sky islands in China. Its habitat is fragile and unstable, and it is likely that the species is threatened. However, it is difficult to determine the conservation priority or unit without knowing the genetic background and the overall distribution of this species. In this study, we used double digest restriction-site associated DNA-sequencing (ddRAD-seq) to investigate the conservation genomics of C. taliensis. At the same time, we modeled the extent of suitable habitat for C. taliensis in present and future (2030 and 2090) habitat using the maximum-entropy (MaxEnt) model.

RESULTS

The results suggested that the related C. fanjingshanensis belongs to C. taliensis and should not be considered a separate species. All the sampling locations were divided into three genetic groups: the Sichuan & Guizhou population (SG population), the Hengduan Mountains population (HD population) and Himalayan population (HM population), and we found that there was complex gene flow between the sampling locations of HD population. MT was distinct genetically from the other sampling locations due to the unique environment in Motuo. The genetic diversity (π, He) of C. taliensis was relatively high, but its contemporary effective population size (Ne) was small. C. taliensis might be currently affected by inbreeding depression, although its large population density may be able to reduce the effect of this. The predicted areas of suitable habitat currently found in higher mountains will not change significantly in the future, and these suitable habitats are predicted to spread to other higher mountains under future climate change. However, suitable habitat in relatively low altitude areas may disappear in the future. This suggests that C. taliensis will be caught in a 'summit trap' in low altitude areas, however, in contrast, the high altitude of the Himalaya and the Hengduan Mountains are predicted to act as 'biological refuges' for C. taliensis in the future.

CONCLUSIONS

These results not only provide a new understanding of the genetic background and potential resource distribution of C. taliensis, but also lay the foundation for its conservation and management.

Genomic insights into differentiation and adaptation of Amorphophallus yunnanensis in the mountainous region of Southwest China

The role of geographical isolation and environmental adaptation in driving the differentiation and radiation of species has been a hotspot in evolutionary biology. The extremely complicated and fragmented geography of the mountainous region of Southwest China provides an excellent system for investigating the process of species divergence in heterogeneous habitats. Amorphophallus yunnanensis is a species of extreme habitat preference that resides mainly in the mountainous region of Southwest China. Here, we used restriction site-associated DNA sequencing (RAD-seq) to characterize the geographic pattern of genetic variation among 19 populations of A. yunnanensis as well as the genomic basis of environmental adaptation. A pattern of low population genetic diversity and high level of genetic differentiation was observed. The genomic data revealed a clear east-west genetic differentiation, with two distinct genetic lineages corresponding to the Guizhou plateau and Yunnan plateau, respectively. However, we discovered demographic expansion of the Guizhou Plateau lineage and recent hybridization in populations at the contact region. Significant levels of isolation by distance along with isolation by environment were detected. Outlier tests and genome-environment association analyses identified 89 putatively adaptive loci that might play a role in environmental adaptation. Our results suggest that the genetic divergence of A. yunnanensis is attributed to geographical isolation together with divergent selection in the mountainous region of Southwest China.

Peripatric speciation within Torreya fargesii (Taxaceae) in the Hengduan Mountains inferred from multi-loci phylogeography

BACKGROUND

The Hengduan Mountains (HDM) are one of the major global biodiversity hotspots in the world. Several evolutionary scenarios, especially in-situ diversification, have been proposed to account for the high species richness of temperate plants. However, peripatric speciation, an important mode of allopatric speciation, has seldom been reported in this region.

RESULTS

Here, two chloroplast DNA regions and 14 nuclear loci were sequenced for 112 individuals from 10 populations of Torreya fargesii var. fargesii and 63 individuals from 6 populations of T. fargesii var. yunnanensis. Population genetic analyses revealed that the two varieties are well differentiated genetically (FST, 0.5765) and have uneven genetic diversity (π, 0.00221 vs. 0.00073 on an average of nuclear loci). The gene genealogical relationship showed that T. fargesii var. yunnanensis is inferred as derived from T. fargesii var. fargesii, which was further supported by the coalescent simulations (DIYABC, fastsimcoal2 and IMa2). By the coalescent simulations, the divergence time (~ 2.50-3.65 Ma) and the weak gene flow between the two varieties were detected. The gene flow was asymmetrical and only occurred in later stages of divergence, which is caused by second contact due to the population expansion (~ 0.61 Ma) in T. fargesii var. fargesii. In addition, niche modeling indicated that the two varieties are differentiated geographically and ecologically and have unbalanced distribution range.

CONCLUSIONS

Overall, T. fargesii var. fargesii is always parapatric with respect to T. fargesii var. yunnanensis, and the latter derived from the former in peripatry of the HDM following a colonization from central China during the late Pliocene. Our findings demonstrate that peripatric speciation following dispersal events may be an important evolutionary scenario for the formation of biodiversity hotspot of the HDM.

Approximate Bayesian computation and ecological niche models elucidate the demographic history and current fragmented population distribution of a Korean endemic shrub

Climatic fluctuations and geological events since the LGM are believed to have significantly impacted the population size, distribution, and mobility of many species that we observe today. In this paper, we determined the processes driving the phylogeographic structure of the Korean endemic white forsythia by combining the use of genome-wide SNPs and predicting paleoclimatic habitats during the LGM (21 kya), Early Holocene (10 kya), Mid-Holocene (6 kya), and Late Holocene (3 kya). Using a maximum of 1897 SNPs retrieved from 124 samples across nine wild populations, five environmental predictors, and the species' natural occurrence records, we aimed to infer the species' demographic history and reconstruct its possible paleodistributions with the use of approximate Bayesian computation and ecological niche models, respectively. Under this integrated framework, we found strong evidence for patterns of range shift and expansion, and population divergence events from the onset of the Holocene, resulting in the formation of its five distinct genetic units. The most highly supported model inferred that after the split of an ancestral population into the southern group and a larger central metapopulation lineage, the latter gave rise to the eastern and northern clusters, before finally dividing into two sub-central groups. While the use of molecular data allowed us to identify and refine the (phylo)genetic relationships of the species' lineages and populations, the use of ecological data helped us infer a past LGM refugium and the directions of post-glacial range dynamics. The time frames of these demographic events were shown to be congruent with climatic and geological events that affected the central Korean Peninsula during these periods. These findings gave us a better understanding of the consequences of past spatiotemporal factors that may have resulted in the current fragmented population distribution of this endangered plant.

Pleistocene Landscape Dynamics Drives Lineage Divergence of a Temperate Freshwater Fish Gobio rivuloides in Coastal Drainages of Northern China

Understanding historical processes underlying lineage distribution patterns is a primary goal of phylogeography. We selected Gobio rivuloides (Cypriniformes: Gobionidae) as a model to improve our knowledge about how intraspecific genetic divergence of freshwater fishes arises in coastal drainages of northern China via statistical analysis using cytochrome b gene. The time-calibrated phylogeny of G. rivuloides showed the divergence of two major lineages (I and II) at ~0.98 Ma (million years ago). Lineage I can be divided into two sub-lineages (I-A and I-B) with a divergence time of ~0.83 Ma. Sub-lineage I-A inhabits the Amur River, and sub-lineage I-B lives in the Luan River and Liao River. Lineage II is distributed in the Yellow River and Hai River, with close genetic relationships between the two drainages, and can be split into two sub-lineages (II-C and II-D) with a divergence time of ~0.60 Ma. Our findings indicate that the splitting of lineages and sub-lineages could be attributed to geographic isolation caused by the formation of the Bohai Sea, river capture, and the episodic hydrologic closing of a paleolake during the late Lower-Middle Pleistocene. It is also the first report we know of displaying a clear phylogeographic break for freshwater fishes across coastal drainages in northern China.

Effective population size of Culex quinquefasciatus under insecticide-based vector management and following Hurricane Harvey in Harris County, Texas

Introduction: Culex quinquefasciatus is a mosquito species of significant public health importance due to its ability to transmit multiple pathogens that can cause mosquito-borne diseases, such as West Nile fever and St. Louis encephalitis. In Harris County, Texas, Cx. quinquefasciatus is a common vector species and is subjected to insecticide-based management by the Harris County Public Health Department. However, insecticide resistance in mosquitoes has increased rapidly worldwide and raises concerns about maintaining the effectiveness of vector control approaches. This concern is highly relevant in Texas, with its humid subtropical climate along the Gulf Coast that provides suitable habitat for Cx. quinquefasciatus and other mosquito species that are known disease vectors. Therefore, there is an urgent and ongoing need to monitor the effectiveness of current vector control programs. Methods: In this study, we evaluated the impact of vector control approaches by estimating the effective population size of Cx. quinquefasciatus in Harris County. We applied Approximate Bayesian Computation to microsatellite data to estimate effective population size. We collected Cx. quinquefasciatus samples from two mosquito control operation areas; 415 and 802, during routine vector monitoring in 2016 and 2017. No county mosquito control operations were applied at area 415 in 2016 and 2017, whereas extensive adulticide spraying operations were in effect at area 802 during the summer of 2016. We collected data for eighteen microsatellite markers for 713 and 723 mosquitoes at eight timepoints from 2016 to 2017 in areas 415 and 802, respectively. We also investigated the impact of Hurricane Harvey's landfall in the Houston area in August of 2017 on Cx. quinquefasciatus population fluctuation. Results: We found that the bottleneck scenario was the most probable historical scenario describing the impact of the winter season at area 415 and area 802, with the highest posterior probability of 0.9167 and 0.4966, respectively. We also detected an expansion event following Hurricane Harvey at area 802, showing a 3.03-fold increase in 2017. Discussion: Although we did not detect significant effects of vector control interventions, we found considerable influences of the winter season and a major hurricane on the effective population size of Cx. quinquefasciatus. The fluctuations in effective population size in both areas showed a significant seasonal pattern. Additionally, the significant population expansion following Hurricane Harvey in 2017 supports the necessity for post-hurricane vector-control interventions.

Nuclear genetic diversity of head lice sheds light on human dispersal around the world

The human louse, Pediculus humanus, is an obligate blood-sucking ectoparasite that has coevolved with humans for millennia. Given the intimate relationship between this parasite and the human host, the study of human lice has the potential to shed light on aspects of human evolution that are difficult to interpret using other biological evidence. In this study, we analyzed the genetic variation in 274 human lice from 25 geographic sites around the world by using nuclear microsatellite loci and female-inherited mitochondrial DNA sequences. Nuclear genetic diversity analysis revealed the presence of two distinct genetic clusters I and II, which are subdivided into subclusters: Ia-Ib and IIa-IIb, respectively. Among these samples, we observed the presence of the two most common louse mitochondrial haplogroups: A and B that were found in both nuclear Clusters I and II. Evidence of nuclear admixture was uncommon (12%) and was predominate in the New World potentially mirroring the history of colonization in the Americas. These findings were supported by novel DIYABC simulations that were built using both host and parasite data to define parameters and models suggesting that admixture between cI and cII was very recent. This pattern could also be the result of a reproductive barrier between these two nuclear genetic clusters. In addition to providing new evolutionary knowledge about this human parasite, our study could guide the development of new analyses in other host-parasite systems.

Speciation in Coastal Basins Driven by Staggered Headwater Captures: Dispersal of a Species Complex, Leporinus bahiensis, as Revealed by Genome-wide SNP Data

Past sea level changes and geological instability along watershed boundaries have largely influenced fish distribution across coastal basins, either by dispersal via palaeodrainages now submerged or by headwater captures, respectively. Accordingly, the South American Atlantic coast encompasses several small and isolated drainages that share a similar species composition, representing a suitable model to infer historical processes. Leporinus bahiensis is a freshwater fish species widespread along adjacent coastal basins over narrow continental shelf with no evidence of palaeodrainage connections at low sea level periods. Therefore, this study aimed to reconstruct its evolutionary history to infer the role of headwater captures in the dispersal process. To accomplish this, we employed molecular-level phylogenetic and population structure analyses based on Sanger sequences (5 genes) and genome-wide SNP data. Phylogenetic trees based on Sanger data were inconclusive, but SNPs data did support the monophyletic status of L. bahiensis. Both COI and SNP data revealed structured populations according to each hydrographic basin. Species delimitation analyses revealed from 3 (COI) to 5 (multilocus approach) MOTUs, corresponding to the sampled basins. An intricate biogeographic scenario was inferred and supported by Approximate Bayesian Computation (ABC) analysis. Specifically, a staggered pattern was revealed and characterized by sequential headwater captures from basins adjacent to upland drainages into small coastal basins at different periods. These headwater captures resulted in dispersal throughout contiguous coastal basins, followed by deep genetic divergence among lineages. To decipher such recent divergences, as herein represented by L. bahiensis populations, we used genome-wide SNPs data. Indeed, the combined use of genome-wide SNPs data and ABC method allowed us to reconstruct the evolutionary history and speciation of L. bahiensis. This framework might be useful in disentangling the diversification process in other neotropical fishes subject to a reticulate geological history.

Genetic signatures of lineage fusion closely resemble population decline

Accurate interpretation of the genetic signatures of past demographic events is crucial for reconstructing evolutionary history. Lineage fusion (complete merging, resulting in a single panmictic population) is a special case of secondary contact that is seldom considered. Here, the circumstances under which lineage fusion can be distinguished from population size constancy, growth, bottleneck, and decline were investigated. Multi-locus haplotype data were simulated under models of lineage fusion with different divergence versus sampling lag times (D:L ratios). These pseudo-observed datasets also differed in their allocation of a fixed amount of sequencing resources (number of sampled alleles, haplotype length, number of loci). Distinguishability of lineage fusion versus each of 10 untrue non-fusion scenarios was quantified based on six summary statistics (neutrality tests). Some datasets were also analyzed using extended Bayesian skyline plots. Results showed that signatures of lineage fusion very closely resemble those of decline-high distinguishability was generally limited to the most favorable scenario (D:L = 9), using the most sensitive summary statistics (F S and Z nS), coupled with the optimal sequencing resource allocation (maximizing number of loci). Also, extended Bayesian skyline plots often erroneously inferred population decline. Awareness of the potential for lineage fusion to carry the hallmarks of population decline is critical.

Disentangling the causes of high polymorphism sharing in sympatric Petunia species from subtropical highland grasslands: insights from nuclear diversity

Genetic polymorphism sharing between closely related and sympatric plant species could result from common ancestry, ancient or recent hybridization. Here we analyzed four Petunia species from the subtropical highland grasslands in southern South America based on nuclear diversity to disentangle the causes of high polymorphism sharing between them. We genotyped microsatellite loci, employed population genetic methods to estimate variability, species limits, and ancient and recent gene flow, and assigned individuals to genetic and taxonomic groups. Finally, we modeled evolutionary processes to determine the impact of Quaternary climate changes on species phylogenetic relationships. Our results indicated that genetic diversity was strongly influenced by expansion and habitat fragmentation during the Quaternary cycles. The extensive polymorphism sharing is mainly due to species' common ancestry, and we did not discard ancient hybridization. Nowadays, niche differentiation is the primary driver for maintaining genetic and morphological limits between the four analysed Petunia species and there is no recent gene flow between them.

Postglacial phylogeography, admixture, and evolution of red spruce (Picea rubens Sarg.) in Eastern North America

Climate change is a major evolutionary force that can affect the structure of forest ecosystems worldwide. Red spruce (Picea rubens Sarg.) has recently faced a considerable decline in the Southern Appalachians due to rapid environmental change, which includes historical land use, and atmospheric pollution. In the northern part of its range, red spruce is sympatric with closely related black spruce (Picea mariana (Mill.) B.S.P.), where introgressive hybridization commonly occurs. We investigated range-wide population genetic diversity and structure and inferred postglacial migration patterns and evolution of red spruce using nuclear microsatellites. Moderate genetic diversity and differentiation were observed in red spruce. Genetic distance, maximum likelihood and Bayesian analyses identified two distinct population clusters: southern glacial populations, and the evolutionarily younger northern populations. Approximate Bayesian computation suggests that patterns of admixture are the result of divergence of red spruce and black spruce from a common ancestor and then introgressive hybridization during post-glacial migration. Genetic diversity, effective population size (Ne) and genetic differentiation were higher in the northern than in the southern populations. Our results along with previously available fossil data suggest that Picea rubens and Picea mariana occupied separate southern refugia during the last glaciation. After initial expansion in the early Holocene, these two species faced a period of recession and formed a secondary coastal refugium, where introgressive hybridization occurred, and then both species migrated northward. As a result, various levels of black spruce alleles are present in the sympatric red spruce populations. Allopatric populations of P. rubens and P. mariana have many species-specific alleles and much fewer alleles from common ancestry. The pure southern red spruce populations may become critically endangered under projected climate change conditions as their ecological niche may disappear.

Integrating Pool-seq uncertainties into demographic inference

Next-generation sequencing of pooled samples (Pool-seq) is a popular method to assess genome-wide diversity patterns in natural and experimental populations. However, Pool-seq is associated with specific sources of noise, such as unequal individual contributions. Consequently, using Pool-seq for the reconstruction of evolutionary history has remained underexplored. Here we describe a novel Approximate Bayesian Computation (ABC) method to infer demographic history, explicitly modelling Pool-seq sources of error. By jointly modelling Pool-seq data, demographic history and the effects of selection due to barrier loci, we obtain estimates of demographic history parameters accounting for technical errors associated with Pool-seq. Our ABC approach is computationally efficient as it relies on simulating subsets of loci (rather than the whole-genome) and on using relative summary statistics and relative model parameters. Our simulation study results indicate Pool-seq data allows distinction between general scenarios of ecotype formation (single versus parallel origin) and to infer relevant demographic parameters (e.g. effective sizes and split times). We exemplify the application of our method to Pool-seq data from the rocky-shore gastropod Littorina saxatilis, sampled on a narrow geographical scale at two Swedish locations where two ecotypes (Wave and Crab) are found. Our model choice and parameter estimates show that ecotypes formed before colonization of the two locations (i.e. single origin) and are maintained despite gene flow. These results indicate that demographic modelling and inference can be successful based on pool-sequencing using ABC, contributing to the development of suitable null models that allow for a better understanding of the genetic basis of divergent adaptation.

Phylogeography of the true freshwater crab, Geothelphusa dehaani: Detected dual dispersal routes via land and sea

Dispersal is an important factor that determines the potential for colonization to pioneer sites. Although most decapods employ seaward migration for reproduction with a planktonic larval phase, true freshwater crabs spend their entire life cycle in freshwater. Therefore, it is expected that genetic regionality can be easily detected. In this study, we focused on true freshwater crabs, Geothelphusa Stimpson, 1858. Herein, we reveal the evolutionary history and dispersal patterns of freshwater crustaceans. We collected and genetically analyzed 283 specimens at 138 localities across the Japanese Islands. Phylogenetic analyses were conducted on the combined dataset (mtDNA COI, 16S, and nDNA ITS1, histone H3 regions) and the data set based on the mtDNA COI region. The phylogenetic relationships detected 10 clades that were highly monophyletic. The highlights of this study were the discovery of several cryptic species or undescribed species, and the completely different heterogeneous dual dispersal pathways within a single species; i.e., both land and ocean routes. Although it was concluded that Japanese crabs are basically genetically divided by straits, strong evidence for dispersion via ocean currents was also detected (i.e., a "sweepstake"). It was also confirmed that Geothelphusa dehaani (White, 1847) could survive in seawater.

Phylogeography of Populus koreana reveals an unexpected glacial refugium in Northeast Asia

The genetic structure of temperate plants in the northern hemisphere was significantly influenced by the Quaternary climate oscillations. A species' biological characteristics and ecological niche are significant elements that can affect its phylogeographic history. We adopted the cold-tolerant, anemophilous and anemochorous tree, Populus koreana, as a model species to examine the impact of historical climate changes and biological characteristics on the evolutionary history of vegetation in Northeast Asia throughout the Quaternary period. The results showed that there is moderate genetic differentiation and a lack of phylogeographic structure among populations of P. koreana based on nuclear microsatellite and plastid markers. Demographic analyses and ecological niche modeling suggested that P. koreana is likely to have experienced a bottleneck around the last glacial maximum (LGM), followed by a rapid and continued range expansion coupled with a northward migration from the LGM to the mid-holocene (MH), present, and 2050. Notably, there were several separate refugia present throughout the range of P. koreana in Northeast Asia during the LGM. These include two widely recognized refugia located in the Changbai Mountains and the southern Korean Peninsula. We also unexpectedly found a previously unknown one in the northern Greater Khingan Mountains. Our study contributes to the understanding of the phylogeographic history of plant species in Northeast Asia, providing novel insights into the Greater Khingan Mountains as glacial refugia for a cold-tolerant tree species. These findings provide valuable insights into the Quaternary historical patterns of temperate forests in East Asia.

Temporal matches between monarch butterfly and milkweed population changes over the past 25,000 years

In intimate ecological interactions, the interdependency of species may result in correlated demographic histories. For species of conservation concern, understanding the long-term dynamics of such interactions may shed light on the drivers of population decline. Here, we address the demographic history of the monarch butterfly, Danaus plexippus, and its dominant host plant, the common milkweed Asclepias syriaca (A. syriaca), using broad-scale sampling and genomic inference. Because genetic resources for milkweed have lagged behind those for monarchs, we first release a chromosome-level genome assembly and annotation for common milkweed. Next, we show that despite its enormous geographic range across eastern North America, A. syriaca is best characterized as a single, roughly panmictic population. Using approximate Bayesian computation with random forests (ABC-RF), a machine learning method for reconstructing demographic histories, we show that both monarchs and milkweed experienced population expansion during the most recent recession of North American glaciers 10,000-20,000 years ago. Our data also identify concurrent population expansions in both species during the large-scale clearing of eastern forests (∼200 years ago). Finally, we find no evidence that either species experienced a reduction in effective population size over the past 75 years. Thus, the well-documented decline of monarch abundance over the past 40 years is not visible in our genomic dataset, reflecting a possible mismatch of the overwintering census population to effective population size in this species.

Recurrent allopolyploidizations diversify ecophysiological traits in marsh orchids (Dactylorhiza majalis s.l.)

Whole-genome duplication has shaped the evolution of angiosperms and other organisms, and is important for many crops. Structural reorganization of chromosomes and repatterning of gene expression are frequently observed in allopolyploids, with physiological and ecological consequences. Recurrent origins from different parental populations are widespread among polyploids, resulting in an array of lineages that provide excellent models to uncover mechanisms of adaptation to divergent environments in early phases of polyploid evolution. We integrate here transcriptomic and ecophysiological comparative studies to show that sibling allopolyploid marsh orchid species (Dactylorhiza, Orchidaceae) occur in different habitats (low nutrient fens vs. meadows with mesic soils) and are characterized by a complex suite of intertwined, pronounced ecophysiological differences between them. We uncover distinct features in leaf elemental chemistry, light-harvesting, photoprotection, nutrient transport and stomata activity of the two sibling allopolyploids, which appear to match their specific ecologies, in particular soil chemistry differences at their native sites. We argue that the phenotypic divergence between the sibling allopolyploids has a clear genetic basis, generating ecological barriers that maintain distinct, independent lineages, despite pervasive interspecific gene flow. This suggests that recurrent origins of polyploids bring about a long-term potential to trigger and maintain functional and ecological diversity in marsh orchids and other groups.

Genetic differentiation and evolution of broad-leaved evergreen shrub and tree varieties of Daphniphyllum macropodum (Daphniphyllaceae)

Tree form evolution is an important ecological specialization for woody species, but its evolutionary process with adaptation is poorly understood, especially on the microevolutionary scale. Daphniphyllum macropodum comprises two varieties: a tree variety growing in a warm temperate climate with light snowfall and a shrub variety growing in a cool temperate climate with heavy snowfall in Japan. Chloroplast DNA variations and genome-wide single-nucleotide polymorphisms across D. macropodum populations and D. teijsmannii as an outgroup were used to reveal the evolutionary process of the shrub variety. Population genetic analysis indicated that the two varieties diverged but were weakly differentiated. Approximate Bayesian computation analysis supported a scenario that assumed migration between the tree variety and the southern populations of the shrub variety. We found migration between the two varieties where the distributions of the two varieties are in contact, and it is concordant with higher tree height in the southern populations of the shrub variety than the northern populations. The genetic divergence between the two varieties was associated with snowfall. The heavy snowfall climate is considered to have developed since the middle Quaternary in this region. The estimated divergence time between the two varieties suggests that the evolution of the two varieties may be concordant with such paleoclimatic change.

Geographic Variation in Genomic Signals of Admixture Between Two Closely Related European Sepsid Fly Species

The extent of interspecific gene flow and its consequences for the initiation, maintenance, and breakdown of species barriers in natural systems remain poorly understood. Interspecific gene flow by hybridization may weaken adaptive divergence, but can be overcome by selection against hybrids, which may ultimately promote reinforcement. An informative step towards understanding the role of gene flow during speciation is to describe patterns of past gene flow among extant species. We investigate signals of admixture between allopatric and sympatric populations of the two closely related European dung fly species Sepsis cynipsea and S. neocynipsea (Diptera: Sepsidae). Based on microsatellite genotypes, we first inferred a baseline demographic history using Approximate Bayesian Computation. We then used genomic data from pooled DNA of natural and laboratory populations to test for past interspecific gene flow based on allelic configurations discordant with the inferred population tree (ABBA-BABA test with D-statistic). Comparing the detected signals of gene flow with the contemporary geographic relationship among interspecific pairs of populations (sympatric vs. allopatric), we made two contrasting observations. At one site in the French Cevennes, we detected an excess of past interspecific gene flow, while at two sites in Switzerland we observed lower signals of past microsatellite genotypes gene flow among populations in sympatry compared to allopatric populations. These results suggest that the species boundaries between these two species depend on the past and/or present eco-geographic context in Europe, which indicates that there is no uniform link between contemporary geographic proximity and past interspecific gene flow in natural populations.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11692-023-09612-5.

East‒West genetic differentiation across the Indo-Burma hotspot: evidence from two closely related dioecious figs

BACKGROUND

Understanding biodiversity patterns and their underlying mechanisms is of interest to ecologists, biogeographers and conservationists and is critically important for conservation efforts. The Indo-Burma hotspot features high species diversity and endemism, yet it also faces significant threats and biodiversity losses; however, few studies have explored the genetic structure and underlying mechanisms of Indo-Burmese species. Here, we conducted a comparative phylogeographic analysis of two closely related dioecious Ficus species, F. hispida and F. heterostyla, based on wide and intensive population sampling across Indo-Burma ranges, using chloroplast (psbA-trnH, trnS-trnG) and nuclear microsatellite (nSSR) markers, as well as ecological niche modeling.

RESULTS

The results indicated large numbers of population-specific cpDNA haplotypes and nSSR alleles in the two species. F. hispida showed slightly higher chloroplast diversity but lower nuclear diversity than F. heterostyla. Low-altitude mountainous areas of northern Indo-Burma were revealed to have high genetic diversity and high habitat suitability, suggesting potential climate refugia and conservation priority areas. Strong phylogeographic structure and a marked east‒west differentiation pattern were observed in both species, due to the interactions between biotic and abiotic factors. Interspecific dissimilarities at fine-scale genetic structure and asynchronized historical dynamics of east‒west differentiation between species were also detected, which were attributed to different species-specific traits.

CONCLUSIONS

We confirm hypothesized predictions that interactions between biotic and abiotic factors largely determine the patterns of genetic diversity and phylogeographic structure of Indo-Burmese plants. The east‒west genetic differentiation pattern observed in two targeted figs can be generalized to some other Indo-Burmese plants. The results and findings of this work will contribute to the conservation of Indo-Burmese biodiversity and facilitate targeted conservation efforts for different species.