Phylogeny, species delimitation, and biogeographical history of Bredia

Species delimitation in plants is sometimes challenging due to morphological convergence, interspecific gene flow, and historically limited sampling. Bredia Blume as currently defined comprises 27 species and has been resolved as monophyletic in previous phylogenomic studies. However, relationships among several major lineages in the genus remain elusive, and the species boundaries of some problematic taxa have not been tested. In this study, we employed comprehensive taxon sampling and reconstructed the phylogeny of Bredia using single-copy orthologs (SCOs), genomic single nucleotide polymorphisms (SNPs), and whole plastomes. The species tree derived from SCOs provided the highest resolution, strongly supporting all interspecific relationships. We identified instances of morphological convergence and potential hybridization/introgression within groups of interest and discussed species limits based on monophyly, genetic divergence, and morphological diagnosability. Using this robust phylogeny, we inferred divergence times and biogeographical history for Bredia. The genus originated in the Yunnan-Myanmar-Thailand Border region and the Beibu Gulf region during the middle Miocene, initially adapting to karst habitats. Over time, certain lineages shifted to non-karst environments. One such lineage migrated to the southeastern part of the Eastern Asiatic Kingdom in the late Miocene, where it rapidly diversified forming several major lineages. Subsequently, a mainland lineage reached Taiwan via a land bridge between the late Pliocene and the early Pleistocene and diversified in the region, eventually spreading to the Ryukyu Islands in the middle Pleistocene.

Cryptic divergence in and evolutionary dynamics of endangered hybrid Picea brachytyla sensu stricto in the Qinghai-Tibet Plateau

BACKGROUND

The visual similarities observed across various plant groups often conceal underlying genetic distinctions. This occurrence, known as cryptic diversity, underscores the key importance of identifying and understanding cryptic intraspecific evolutionary lineages in evolutionary ecology and conservation biology.

RESULTS

In this study, we conducted transcriptome analysis of 81 individuals from 18 natural populations of a northern lineage of Picea brachytyla sensu stricto that is endemic to the Qinghai-Tibet Plateau. Our analysis revealed the presence of two distinct local lineages, emerging approximately 444.8 thousand years ago (kya), within this endangered species. The divergence event aligns well with the geographic and climatic oscillations that occurred across the distributional range during the Mid-Pleistocene epoch. Additionally, we identified numerous environmentally correlated gene variants, as well as many other genes showing signals of positive selection across the genome. These factors likely contributed to the persistence and adaptation of the two distinct local lineages.

CONCLUSIONS

Our findings shed light on the highly dynamic evolutionary processes underlying the remarkably similar phenotypes of the two lineages of this endangered species. Importantly, these results enhance our understanding of the evolutionary past for this and for other endangered species with similar histories, and also provide guidance for the development of conservation plans.

Hybridization, polyploidization, and morphological convergence make dozens of taxa into one chaotic genetic pool: a phylogenomic case of the Ficus erecta species complex (Moraceae)

The Ficus erecta complex, characterized by its morphological diversity and frequent interspecific overlap, shares pollinating fig wasps among several species. This attribute, coupled with its intricate phylogenetic relationships, establishes it as an exemplary model for studying speciation and evolutionary patterns. Extensive researches involving RADseq (Restriction-site associated DNA sequencing), complete chloroplast genome data, and flow cytometry methods were conducted, focusing on phylogenomic analysis, genetic structure, and ploidy detection within the complex. Significantly, the findings exposed a pronounced nuclear-cytoplasmic conflict. This evidence, together with genetic structure analysis, confirmed that hybridization within the complex is a frequent occurrence. The ploidy detection revealed widespread polyploidy, with certain species exhibiting multiple ploidy levels, including 2×, 3×, and 4×. Of particular note, only five species (F. abelii, F. erecta, F. formosana, F. tannoensis and F. vaccinioides) in the complex were proved to be monophyletic. Species such as F. gasparriniana, F. pandurata, and F. stenophylla were found to encompass multiple phylogenetically distinct lineages. This discovery, along with morphological comparisons, suggests a significant underestimation of species diversity within the complex. This study also identified F. tannoensis as an allopolyploid species originating from F. vaccinioide and F. erecta. Considering the integration of morphological, molecular systematics, and cytological evidences, it is proposed that the scope of the F. erecta complex should be expanded to the entire subsect. Frutescentiae. This would redefine the complex as a continuously evolving group comprising at least 33 taxa, characterized by blurred species boundaries, frequent hybridization and polyploidization, and ambiguous genetic differentiation.

Genomic divergence and introgression between cryptic species of a widespread North American songbird

Analysis of genomic variation among related populations can sometimes reveal distinct species that were previously undescribed due to similar morphological appearances, and close examination of such cases can provide much insight regarding speciation. Genomic data can also reveal the role of reticulate evolution in differentiation and speciation. White-breasted nuthatches (Sitta carolinensis) are widely distributed North American songbirds that are currently classified as a single species but have been suspected to represent a case of cryptic speciation. Previous genetic analyses suggested four divergent groups, but it was unclear whether these represented multiple reproductively isolated species. Using extensive genomic sampling of over 350 white-breasted nuthatches from across North America and a new chromosome-level reference genome, we asked if white-breasted nuthatches are comprised of multiple species and whether introgression has occurred between divergent populations. Genomic variation of over 300,000 loci revealed four highly differentiated populations (Pacific, n = 45; Eastern, n = 23; Rocky Mountains North, n = 138; and Rocky Mountains South, n = 150) with geographic ranges that are adjacent. We observed a moderate degree of admixture between Rocky Mountain populations but only a small number of hybrids between the Rockies and the Eastern population. The rarity of hybrids together with high levels of differentiation between populations is supportive of populations having some level of reproductive isolation. Between populations, we show evidence for introgression from a divergent ghost lineage of white-breasted nuthatches into the Rocky Mountains South population, which is otherwise closely related to Rocky Mountains North. We conclude that white-breasted nuthatches are best considered at least three species and that ghost lineage introgression has contributed to differentiation between the two Rocky Mountain populations. White-breasted nuthatches provide a dramatic case of morphological similarity despite high genomic differentiation, and the varying levels of reproductive isolation among the four groups provide an example of the speciation continuum.

Integrative taxonomy in a rapid speciation group associated with mating system transition: A case study in the Primula cicutariifolia complex

Accurate species delimitation is the key to biodiversity conservation and is fundamental to most branches of biology. However, species delimitation remains challenging in those evolutionary radiations associated with mating system transition from outcrossing to self-fertilization, which have frequently occurred in angiosperms and are usually accompanied by rapid speciation. Here, using the Primula cicutariifolia complex as a case, we integrated molecular, morphological and reproductive isolation evidence to test and verify whether its outcrossing (distylous) and selfing (homostylous) populations have developed into independent evolutionary lineages. Phylogenetic trees based on whole plastomes and SNPs of the nuclear genome both indicated that the distylous and homostylous populations grouped into two different clades. Multispecies coalescent, gene flow and genetic structure analyses all supported such two clades as two different genetic entities. In morphology, as expected changes in selfing syndrome, homostylous populations have significantly fewer umbel layers and smaller flower and leaf sizes compared to distylous populations, and the variation range of some floral traits, such as corolla diameter and umbel layers, show obvious discontinuity. Furthermore, hand-pollinated hybridization between the two clades produced almost no seeds, indicating that well post-pollination reproductive isolation has been established between them. Therefore, the distylous and homostylous populations in this studied complex are two independent evolutionary lineages, and thus these distylous populations should be treated as a distinct species, here named Primula qiandaoensis W. Zhang & J.W. Shao sp. nov.. Our empirical study of the P. cicutariifolia complex highlights the importance of applying multiple lines of evidence, in particular genomic data, to delimit species in pervasive evolutionary plant radiations associated with mating system transition.

Genome-wide data reveal cryptic diversity and hybridization in a group of tree ferns

Discovery of cryptic diversity is essential to understanding both the process of speciation and the conservation of species. Determining species boundaries in fern lineages represents a major challenge due to lack of morphologically diagnostic characters and frequent hybridization. Genomic data has substantially enhanced our understanding of the speciation process, increased the resolution of species delimitation studies, and led to the discovery of cryptic diversity. Here, we employed restriction-site-associated DNA sequencing (RAD-seq) and integrated phylogenomic and population genomic analyses to investigate phylogenetic relationships and evolutionary history of 16 tree ferns with marginate scales (Cyatheaceae) from China and Vietnam. We conducted multiple species delimitation analyses using the multispecies coalescent (MSC) model and novel approaches based on genealogical divergence index (gdi) and isolation by distance (IBD). In addition, we inferred species trees using concatenation and several coalescent-based methods, and assessed hybridization patterns and rate of gene flow across the phylogeny. We obtained highly supported and generally congruent phylogenies inferred from concatenated and summary-coalescent methods, and the monophyly of all currently recognized species were strongly supported. Our results revealed substantial evidence of cryptic diversity in three widely distributed Gymnosphaera species, each of which was composite of two highly structure lineages that may correspond to cryptic species. We found that hybridization was fairly common between not only closely related species, but also distantly related species. Collectively, it appears that scaly tree ferns may contain cryptic diversity and hybridization has played an important role throughout the evolutionary history of this group.

A set of SSR markers to characterize genetic diversity in all Viburnum species

About 160 species are classified within the Viburnum genus and many of these are cultivated for horticultural purposes. The vast dispersal of Viburnum makes the genus a useful model for studying evolutionary history and inferring how species expanded into their current distributions. Simple sequence repeat (SSR) markers were previously developed for five Viburnum species that were classified within the four major clades (Laminotinus, Crenotinus, Valvatotinus, and Porphyrotinus). The ability of some of these markers to cross-amplify in Viburnum species has been scantly evaluated, but there has not been any genus-wide assessment for the markers. We evaluated a collection of 49 SSR markers for the ability to cross-amplify in 224 samples, including 46 Viburnum species, representing all 16 subclades, and five additional species in the Viburnaceae and Caprifoliaceae. A subset of 14 potentially comprehensive markers for Viburnum species was identified and evaluated for the ability to detect polymorphisms in species outside of their respective clades. The 49 markers had overall amplification success in 52% of the samples, including a 60% success rate within the Viburnum genus and 14% in other genera. The comprehensive marker set amplified alleles in 74% of all samples tested, including 85% of Viburnum samples and 19% of outgroup samples. To the best of our knowledge, this is the first comprehensive set of markers able to characterize species across an entire genus. This set of markers can be used to assess the genetic diversity and population structure of most Viburnum species and closely allied species.

Gene flow assessment helps to distinguish strong genomic structure from speciation in an Iberian ant-eating spider

Although genomic data is boosting our understanding of evolution, we still lack a solid framework to perform reliable genome-based species delineation. This problem is especially critical in the case of phylogeographically structured organisms, with allopatric populations showing similar divergence patterns as species. Here, we assess the species limits and phylogeography of Zodarion alacre, an ant-eating spider widely distributed across the Iberian Peninsula. We first performed species delimitation based on genome-wide data and then validated these results using additional evidence. A commonly employed species delimitation strategy detected four distinct lineages with almost no admixture, which present allopatric distributions. These lineages showed ecological differentiation but no clear morphological differentiation, and evidence of introgression in a mitochondrial barcode. Phylogenomic networks found evidence of substantial gene flow between lineages. Finally, phylogeographic methods highlighted remarkable isolation by distance and detected evidence of range expansion from south-central Portugal to central-north Spain. We conclude that despite their deep genomic differentiation, the lineages of Z. alacre do not show evidence of complete speciation. Our results likely shed light on why Zodarion is among the most diversified spider genera despite its limited distribution and support the use of gene flow evidence to inform species boundaries.

Incompatibility Phylogenetic Signals between Double-Digest Restriction Site-Associated DNA Sequencing and Plastid Genomes in Chinese Curcuma (Zingiberaceae)—A Recent Qinghai–Tibetan Plateau Diversification Genera

Curcuma is of high economic value, credited to its medicinal, edible, and ornamental properties, which possess all signatures of adaptability, and rapid radiation, especially species of Curcuma (Chinese Curcuma, a recent Qinghai–Tibetan Plateau diversification genera) scattered in China. However, little is known about the incongruent phylogenetic signals within this genera from different inheritance patterns that will militate against the further development of this genera. In this research, we applied complete chloroplast genome data together with double-digest restriction site-associated DNA sequencing data (ddRAD-seq) strategy to investigate phylogenetic signals of Chinese Curcuma species, clustering using two RAD analysis pipelines (STACKS and pyRAD). Phylogenetic trees were obtained from each locus based on the maximum likelihood (ML) and multispecies coalescent (BEAST) methods. For visual comparison, multi-method and different datasets were used to infer the phylogeny. We discovered inconsistent relationships for the Chinese Curcuma with varying degrees of support using different methods and datasets.

Evolution of Castanea in North America: restriction-site-associated DNA sequencing and ecological modeling reveal a history of radiation, range shifts, and disease

PREMISE

Although chestnuts and chinquapins are some of the best known and most widely loved of any plants in North America, relatively little genomic sequencing has been done, and much is still unknown about their evolution.

METHODS

We used double-digest restriction-site-associated DNA (ddRAD) sequencing data to infer the species-level phylogeny for Castanea and assess the phylogeography of the North American species using samples collected from populations that span the full extent of the species' ranges. We also constructed species distribution models using digitized herbarium specimens and observational data from field surveys.

RESULTS

We identified strong population structure within Castanea dentata (American chestnut) that reflects a stepwise northern migration since the last glacial maximum. Our species distribution models further confirmed this scenario and matched closely with the Castanea fossil pollen record. We also found significant structure within the Castanea pumila lineage, most notably a genetic cluster that corresponds to the frequently recognized Castanea pumila var. ozarkensis.

CONCLUSIONS

The two North American Castanea species have contrasting patterns of population structure, but each is typical of plant phylogeography in North America. Within the C. pumila complex, we found novel genetic structure that provides new insights about C. pumila taxonomy. Our results also identified a series of distinctive populations that will be valuable in ongoing efforts to conserve and restore chestnuts and chinquapins in North America.

Phylogenomic species delimitation dramatically reduces species diversity in an Antarctic adaptive radiation

Application of genetic data to species delimitation often builds confidence in delimitations previously hypothesized using morphological, ecological, and geographic data and frequently yields recognition of previously-undescribed cryptic diversity. However, a recent critique of genomic data-based species delimitation approaches is that they have the potential to conflate population structure with species diversity, resulting in taxonomic oversplitting. The need for an integrative approach to species delimitation, in which molecular, morphological, ecological, and geographic lines of evidence are evaluated together, is becoming increasingly apparent. Here, we integrate phylogenetic, population genetic, and coalescent analyses of genome-wide sequence data with investigation of variation in multiple morphological traits to delimit species within the Antarctic barbeled plunderfishes (Artedidraconidae: Pogonophryne). Pogonophryne currently comprises 29 valid species, most of which are distinguished solely by variation in ornamentation of the mental barbel that projects from the lower jaw, a structure previously shown to vary widely within a single species. However, our genomic and phenotypic analyses result in a dramatic reduction in the number of distinct species recognized within the clade, providing evidence to support the recognition of no more than six species. We propose to synonymize 24 of the currently recognized species with five species of Pogonophryne. We find genomic and phenotypic evidence for a new species of Pogonophryne from specimens collected in the Ross Sea. Our findings represent a rare example in which application of molecular data provides evidence of taxonomic oversplitting on the basis of morphology, clearly demonstrating the utility of an integrative species delimitation framework.

Genomic analyses overturn two long-standing homoploid hybrid speciation hypotheses

The importance of hybridization in generating biological diversity has been historically controversial. Previously, inference about hybridization was limited by dependence on morphological data; with the advent of the next-generation sequencing tools for nonmodel organisms, the evolutionary significance of hybridization is more evident. Here, we test classic hypotheses of hybrid origins of two species in the Phlox pilosa complex. Morphological intermediacy motivated the hypotheses that Phlox amoena lighthipei and Phlox pilosa deamii were independent homoploid hybrid lineages derived from P. amoena amoena and P. pilosa pilosa. We use double-digest restriction site-associated DNA sequencing of individuals from throughout the range of these taxa to conduct the most thorough analysis of evolutionary history in this system to date. Surprisingly, we find no support for the hybrid origin of P. pilosa deamii or P. amoena lighthipei. Our data do identify a history of admixture in individuals collected at a contemporary hybrid zone between the putative parent lineages. We show that three very different evolutionary histories, only one of which involves hybrid origin, have produced intermediate or recombinant morphological traits between P. amoena amoena and P. pilosa pilosa. Although morphological data are still an efficient means of generating hypotheses about past gene flow, genomic data are now the standard of evidence for elucidating evolutionary history.

Introgression and Species Delimitation in the Longear Sunfish Lepomis megalotis (Teleostei: Percomorpha: Centrarchidae)

Introgression and hybridization are major impediments to genomic-based species delimitation because many implementations of the multispecies coalescent framework assume no gene flow among species. The sunfish genus Lepomis, one of the world's most popular groups of freshwater sport fish, has a complicated taxonomic history. The results of ddRAD phylogenomic analyses do not provide support for the current taxonomy that recognizes two species, L. megalotis and L. peltastes, in the L. megalotis complex. Instead, evidence from phylogenomics and phenotype warrants recognizing six relatively ancient evolutionary lineages in the complex. The introgressed and hybridizing populations in the L. megalotis complex are localized and appear to be the result of secondary contact or rare hybridization events between non-sister species. Segregating admixed populations from our multispecies coalescent analyses identifies six species with moderate to high genealogical divergence, whereas including admixed populations drives all but one lineage below the species threshold of genealogical divergence. Segregation of admixed individuals also helps reveal phenotypic distinctiveness among the six species in morphological traits used by ichthyologists to discover and delimit species over the last two centuries. Our protocols allow for the identification and accommodation of hybridization and introgression in species delimitation. Genomic-based species delimitation validated with multiple lines of evidence provides a path towards the discovery of new biodiversity and resolving long-standing taxonomic problems.

The natural hybridization between species Ligularia nelumbifolia and Cremanthodium stenoglossum (Senecioneae, Asteraceae) suggests underdeveloped reproductive isolation and ambiguous intergeneric boundary

Natural hybridization is frequent in plants and is considered an important factor facilitating speciation. The natural intergeneric hybridization between Ligularia and Cremanthodium was previously confirmed using a couple of DNA markers. However, the mechanism of this intergeneric hybridization and the role of reproductive isolation in the process of hybridization remain unclear. Here we used double-digest restriction site-associated DNA sequencing (ddRAD-seq) to further quantify the occurrence of hybridization, the genetic structure of the hybrid population and the role of reproductive isolation between Ligularia nelumbifolia and Cremanthodium stenoglossum. The results based on the ddRAD-seq SNP data sets indicated that hybridization between L. nelumbifolia and C. stenoglossum was restricted to F₁s, and no gene introgression was identified between these two species. STRUCTURE analysis and maximum likelihood (ML) tree results showed a slightly larger genetic contribution of L. nelumbifolia to putative hybrid F₁s. We deduced that the reproductive isolation between these two parent species is not well-developed but still strong enough to maintain the genetic integrity of the species, and that their F₁s are sterile or with low fertility. Given the poorly resolved phylogenetic relationship between Ligularia and Cremanthodium, the occurrence of natural hybridization between L. nelumbifolia and C. stenoglossum may provide new insights into the re-circumscription and re-delimitation of these two genera.

Development and Characterization of 15 Novel Genomic SSRs for Viburnum farreri

The Viburnum genus is of particular interest to horticulturalists, phylogeneticists, and biogeographers. Despite its popularity, there are few existing molecular markers to investigate genetic diversity in this large genus, which includes over 160 species. There are also few polymorphic molecular tools that can delineate closely related species within the genus. Viburnum farreri, a member of the Solenotinus subclade and one of the centers of diversity for Viburnum, was selected for DNA sequencing and development of genomic simple sequence repeats (gSSRs). In this study, 15 polymorphic gSSRs were developed and characterized for a collection of 19 V. farreri samples. Number of alleles per locus ranged from two- to- eight and nine loci had four or more alleles. Observed heterozygosity ranged from 0 to 0.84 and expected heterozygosity ranged from 0.10 to 0.80 for the 15 loci. Shannon diversity index values across these loci ranged from 0.21 to 1.62. The markers developed in this study add to the existing molecular toolkit for the genus and will be used in future studies investigating cross-transferability, genetic variation, and species and cultivar delimitation in the Viburnum genus and closely allied genera in the Adoxaceae and Caprifoliaceae.

Gene flow and species delimitation in fishes of Western North America: Flannelmouth (Catostomus latipinnis) and Bluehead sucker (C. Pantosteus discobolus)

The delimitation of species boundaries, particularly those obscured by reticulation, is a critical step in contemporary biodiversity assessment. It is especially relevant for conservation and management of indigenous fishes in western North America, represented herein by two species with dissimilar life histories codistributed in the highly modified Colorado River (i.e., flannelmouth sucker, Catostomus latipinnis; bluehead sucker, C. (Pantosteus) discobolus). To quantify phylogenomic patterns and examine proposed taxonomic revisions, we first employed double-digest restriction site-associated DNA sequencing (ddRAD), yielding 39,755 unlinked SNPs across 139 samples. These were subsequently evaluated with multiple analytical approaches and by contrasting life history data. Three phylogenetic methods and a Bayesian assignment test highlighted similar phylogenomic patterns in each, but with considerable difference in presumed times of divergence. Three lineages were detected in bluehead sucker, supporting elevation of C. (P.) virescens to species status and recognizing C. (P.) discobolus yarrowi (Zuni bluehead sucker) as a discrete entity. Admixture in the latter necessitated a reevaluation of its contemporary and historic distributions, underscoring how biodiversity identification can be confounded by complex evolutionary histories. In addition, we defined three separate flannelmouth sucker lineages as ESUs (evolutionarily significant units), given limited phenotypic and genetic differentiation, contemporary isolation, and lack of concordance (per the genealogical concordance component of the phylogenetic species concept). Introgression was diagnosed in both species, with the Little Colorado and Virgin rivers in particular. Our diagnostic methods, and the agreement of our SNPs with previous morphological, enzymatic, and mitochondrial work, allowed us to partition complex evolutionary histories into requisite components, such as isolation versus secondary contact.

Phylogenomics and molecular species delimitation reveals great cryptic diversity of leaf-toed geckos (Phyllodactylidae: Phyllodactylus), ancient origins, and diversification in Mexico

We utilize the efficient GBS technique to obtain thousands of nuclear loci and SNPs to reconstruct the evolutionary history of Mexican leaf-toed geckos (Phyllodactylus). Through the incorporation of unprecedented sampling for this group of geckos, in combination with genomic data analysis, we generate mostly consistent phylogenetic hypotheses using two approaches: supermatrix and coalescent-based inference. All topologies depict three, mutually exclusive major clades. Clade I comprises P. bordai and all species closer to P. bordai than to any other Phyllodactylus. Clade II comprises P. nocticolus and all species closer to P. nocticolus than to any other Phyllodactylus. Clade III comprises P. tuberculosus and all species closer to P. tuberculosus than to any other Phyllodactylus. Analyses estimate the age for the most recent common ancestor of Phyllodactylus in the Eocene (~43 mya), and the ancestors of each major clade date to the Eocene-Oligocene transition (32-36 mya). This group includes one late-Eocene lineage (P. bordai), Oligocene lineages (P. paucituberculatus, P. delcampi), but also topological patterns that indicate a recent radiation occurred during the Pleistocene on islands in the Gulf of California. The wide spatial and temporal scale indicates a complex and unique biogeographic history for each major clade. The 33 species delimited by BPP and stepping-stone BFD*coalescent based genomic approaches reflect this history. This diversity delimited for Mexican leaf-toed geckos demonstrates a vast underestimation in the number of species based on morphological data alone.

Joint Phylogenetic Estimation of Geographic Movements and Biome Shifts during the Global Diversification of Viburnum

Phylogeny, molecular sequences, fossils, biogeography, and biome occupancy are all lines of evidence that reflect the singular evolutionary history of a clade, but they are most often studied separately, by first inferring a fossil-dated molecular phylogeny, then mapping on ancestral ranges and biomes inferred from extant species. Here we jointly model the evolution of biogeographic ranges, biome affinities, and molecular sequences, while incorporating fossils to estimate a dated phylogeny for all of the 163 extant species of the woody plant clade Viburnum (Adoxaceae) that we currently recognize in our ongoing worldwide monographic treatment of the group. Our analyses indicate that while the major Viburnum lineages evolved in the Eocene, the majority of extant species originated since the Miocene. Viburnum radiated first in Asia, in warm, broad-leaved evergreen (lucidophyllous) forests. Within Asia, we infer several early shifts into more tropical forests, and multiple shifts into forests that experience prolonged freezing. From Asia, we infer two early movements into the New World. These two lineages probably first occupied warm temperate forests and adapted later to spreading cold climates. One of these lineages (Porphyrotinus) occupied cloud forests and moved south through the mountains of the Neotropics. Several other movements into North America took place more recently, facilitated by prior adaptations to freezing in the Old World. We also infer four disjunctions between Asia and Europe: the Tinus lineage is the oldest and probably occupied warm forests when it spread, whereas the other three were more recent and in cold-adapted lineages. These results variously contradict published accounts, especially the view that Viburnum radiated initially in cold forests and, accordingly, maintained vessel elements with scalariform perforations. We explored how the location and biome assignments of fossils affected our inference of ancestral areas and biome states. Our results are sensitive to, but not entirely dependent upon, the inclusion of fossil biome data. It will be critical to take advantage of all available lines of evidence to decipher events in the distant past. The joint estimation approach developed here provides cautious hope even when fossil evidence is limited. [Biogeography; biome; combined evidence; fossil pollen; phylogeny; Viburnum.].

Phylogeography and the Evolutionary History of Sunflower (Helianthus annuus L.): Wild Diversity and the Dynamics of Domestication

Patterns of genetic variation in crops are the result of selection and demographic changes that occurred during their domestication and improvement. In many cases, we have an incomplete picture of the origin of crops in the context of their wild progenitors, particularly with regard to the processes producing observed levels of standing genetic variation. Here, we analyzed sequence diversity in cultivated sunflower (Helianthus annuus L.) and its wild progenitor (common sunflower, also H. annuus) to reconstruct phylogeographic relationships and population genetic/demographic patterns across sunflower. In common sunflower, south-north patterns in the distribution of nucleotide diversity and lineage splitting indicate a history of rapid postglacial range expansion from southern refugia. Cultivated sunflower accessions formed a clade, nested among wild populations from the Great Plains, confirming a single domestication event in central North America. Furthermore, cultivated accessions sorted by market type (i.e., oilseed vs. confectionery) rather than breeding pool, recapitulating the secondary development of oil-rich cultivars during its breeding history. Across sunflower, estimates of nucleotide diversity and effective population sizes suggest that cultivated sunflower underwent significant population bottlenecks following its establishment ~5000 years ago. The patterns inferred here corroborate those from previous studies of sunflower domestication, and provide a comprehensive overview of its evolutionary history.

Museomics Unveil the Phylogeny and Biogeography of the Neglected Juan Fernandez Archipelago Megalachne and Podophorus Endemic Grasses and Their Connection With Relict Pampean-Ventanian Fescues

Oceanic islands constitute natural laboratories to study plant speciation and biogeographic patterns of island endemics. Juan Fernandez is a southern Pacific archipelago consisting of three small oceanic islands located 600-700 km west of the Chilean coastline. Exposed to current cold seasonal oceanic climate, these 5.8-1 Ma old islands harbor a remarkable endemic flora. All known Fernandezian endemic grass species belong to two genera, Megalachne and Podophorus, of uncertain taxonomic adscription. Classical and modern classifications have placed them either in Bromeae (Bromus), Duthieinae, Aveneae/Poeae, or Loliinae (fine-leaved Festuca); however, none of them have clarified their evolutionary relationships with respect to their closest Festuca relatives. Megalachne includes four species, which are endemic to Masatierra (Robinson Crusoe island) (M. berteroniana and M. robinsoniana) and to Masafuera (Alejandro Selkirk island) (M. masafuerana and M. dantonii). The monotypic Podophorus bromoides is a rare endemic species to Masatierra which is only known from its type locality and is currently considered extinct. We have used museomic approaches to uncover the challenging evolutionary history of these endemic grasses and to infer the divergence and dispersal patterns from their ancestors. Genome skimming data were produced from herbarium samples of M. berteroniana and M. masafuerana, and the 164 years old type specimen of P. bromoides, as well as for a collection of 33 species representing the main broad- and fine-leaved Loliinae lineages. Paired-end reads were successfully mapped to plastomes and nuclear ribosomal cistrons of reference Festuca species and used to reconstruct phylogenetic trees. Filtered ITS and trnTLF sequences from these genomes were further combined with our large Loliinae data sets for accurate biogeographic reconstruction. Nuclear and plastome data recovered a strongly supported fine-leaved Fernandezian clade where Podophorus was resolved as sister to Megalachne. Bayesian divergence dating and dispersal-extinction-cladogenesis range evolution analyses estimated the split of the Fernandezian clade from its ancestral southern American Pampas-Ventanian Loliinae lineage in the Miocene-Pliocene transition, following a long distance dispersal from the continent to the uplifted volcanic palaeo-island of Santa Clara-Masatierra. Consecutive Pliocene-Pleistocene splits and a Masatierra-to-Masafuera dispersal paved the way for in situ speciation of Podophorus and Megalachne taxa.

Taming the Red Bastards: Hybridisation and species delimitation in the Rhodanthemum arundanum-group (Compositae, Anthemideae)

Delineating species boundaries in a group of recently diverged lineages is challenging due to minor morphological differences, low genetic differentiation and the occurrence of gene flow among taxa. Here, we employ traditional Sanger sequencing and restriction-site associated DNA (RAD) sequencing, to investigate species delimitation in the close-knit Moroccan daisy group around Rhodanthemum arundanum B.H.Wilcox & al. that diverged recently during the Quaternary. After evaluation of genotyping errors and parameter optimisation in the course of de-novo assembly of RADseq reads in Ipyrad, we assess hybridisation patterns in the study group based on different data assemblies and methods (Neighbor-Net networks, FastStructure and ABBA-BABA tests). RADseq data and Sanger sequences are subsequently used for delimitation of species, using both, multi-species coalescent methods (Stacey and Snapp) and a novel approach based on consensus k-means clustering. In addition to the unveiling of two novel subspecies in the R. arundanum-group, our study provides insights into the performance of different species delimitation methods in the presence of hybridisation and varying quantities of data.

Differences in flowering time maintain species boundaries in a continental radiation of Viburnum

PREMISE

We take an integrative approach in assessing how introgression and Pleistocene climate fluctuations have shaped the diversification of the core Lentago clade of Viburnum, a group of five interfertile species with broad areas of sympatry. We specifically tested whether flowering time plays a role in maintaining species isolation.

METHODS

RAD-seq data for 103 individuals were used to infer the species relationships and the genetic structure within each species. Flowering times were compared among species on the basis of historical flowering dates documented by herbarium specimens.

RESULTS

Within each species, we found a strong relationship between flowering date and latitude, such that southern populations flower earlier than northern ones. In areas of sympatry, the species flower in sequence rather than simultaneously, with flowering dates offset by ≥9 d for all species pairs. In two cases it appears that the offset in flowering times is an incidental consequence of adaptation to differing climates, but in the recently diverged sister species V. prunifolium and V. rufidulum, we find evidence that reinforcement led to reproductive character displacement. Long-term trends suggest that the two northern-most species are flowering earlier in response to recent climate change.

CONCLUSIONS

We argue that speciation in the Lentago clade has primarily occurred through ecological divergence of allopatric populations, but differences in flowering time were essential to maintain separation of incipient species when they came into secondary contact. This combination of factors may underlie diversification in many other plant clades.

Phylogeography of a widespread eastern North American shrub, Viburnum lantanoides

PREMISE OF THE STUDY

There have been relatively few phylogeographic studies of eastern North American plants, especially of animal-dispersed shrubby species, and this leaves a significant gap in our understanding of how such species were affected by glacial events. Here, we analyzed the phylogeography of the widespread understory shrub Viburnum lantanoides.

METHODS

We generated RADseq data and paleoclimatic species distribution models (SDMs) to identify the locations of refugia where V. lantanoides may have survived the Last Glacial Maximum (LGM) and how its range expanded as glaciers receded.

KEY RESULTS

Genetic diversity falls off with increasing latitude and longitude, indicating that range expansion likely occurred via serial founder events from southern source populations. Samples from the southern Appalachians form a grade, while those from the north form a clade, suggesting that a single genetic lineage recolonized the north. SDMs indicate that V. lantanoides probably survived the LGM in refugia on the mid-Atlantic Coastal Plain and/or the interior Gulf Coastal Plain.

CONCLUSIONS

Our analyses indicate that V. lantanoides survived the LGM in refugia south of the glacier but north of the extensive refugium along the Gulf Coast. Following the LGM, a single population expanded northward along the Appalachian Mountains and eventually into eastern Canada. The patterns observed here suggest that range expansion occurred in a stepwise manner, similar to postglacial dynamics observed in a number of European plant species.