Long-distance gene flow and adaptation of forest trees to rapid climate change

Local adaptation of Pinus leiophylla under climate and land use change models in the Avocado Belt of Michoacán

Climate change and land use change are two main drivers of global biodiversity decline, decreasing the genetic diversity that populations harbour and altering patterns of local adaptation. Landscape genomics allows measuring the effect of these anthropogenic disturbances on the adaptation of populations. However, both factors have rarely been considered simultaneously. Based on a set of 3660 SNPs from which 130 were identified as outliers by a genome-environment association analysis (LFMM), we modelled the spatial turnover of allele frequencies in 19 localities of Pinus leiophylla across the Avocado Belt in Michoacán state, Mexico. Then, we evaluated the effect of climate change and land use change scenarios, in addition to evaluating assisted gene flow strategies and connectivity metrics across the landscape to identify priority conservation areas for the species. We found that localities in the centre-east of the Avocado Belt would be more vulnerable to climate change, while localities in the western area are more threatened by land conversion to avocado orchards. Assisted gene flow actions could aid in mitigating both threats. Connectivity patterns among forest patches will also be modified by future habitat loss, with central and eastern parts of the Avocado Belt maintaining the highest connectivity. These results suggest that areas with the highest priority for conservation are in the eastern part of the Avocado Belt, including the Monarch Butterfly Biosphere Reserve. This work is useful as a framework that incorporates distinct layers of information to provide a more robust representation of the response of tree populations to anthropogenic disturbances.

Highly clustered mating networks in naturally fragmented riparian tree populations

Understanding how spatial patterns of mating and gene flow respond to habitat loss and geographical isolation is a crucial aspect of forest fragmentation genetics. Naturally fragmented riparian tree populations exhibit unique characteristics that significantly influence these patterns. In this study, we investigate mating patterns, pollen-mediated gene flow, and genetic diversity in relict populations of Frangula alnus in southern Spain by testing specific hypotheses related to the riparian habitat. We employ a novel approach that combines paternity analysis, particularly suited for small and isolated populations, with complex network theory and Bayesian models to predict mating likelihood among tree pairs. Our findings reveal a prevalence of short-distance pollination, resulting in spatially driven local mating clusters with a distinct subset of trees being highly connected in the mating network. Additionally, we observe numerous pollination events over distances of hundreds of metres and considerable pollen immigration. Local neighbourhood density is the primary factor influencing within-population mating patterns and pollen dispersal; moreover, mating network properties reflect the population's size and spatial configuration. Conversely, among-population pollen dispersal is mainly determined by tree size, which influences floral display. Our results do not support a major role of directional pollen dispersal in longitudinal trends of genetic diversity. We provide evidence that long-term fragmented tree populations persist in unique environments that shape mating patterns and impose constraints to pollen-mediated gene flow. Nevertheless, even seemingly strongly isolated populations can maintain functional connectivity over extended periods, especially when animal-mediated mating networks promote genetic diversity, as in this riparian tree species.

Weak local adaptation to drought in seedlings of a widespread conifer

Tree seedlings from populations native to drier regions are often assumed to be more drought tolerant than those from wetter provenances. However, intraspecific variation in drought tolerance has not been well-characterized despite being critical for developing climate change mitigation and adaptation strategies, and for predicting the effects of drought on forests. We used a large-scale common garden drought-to-death experiment to assess range-wide variation in drought tolerance, measured by decline of photosynthetic efficiency, growth, and plastic responses to extreme summer drought in seedlings of 73 natural populations of the two main varieties of Douglas-fir (Pseudotsuga menziesii var. menziesii and var. glauca). Local adaptation to drought was weak in var. glauca and nearly absent in menziesii. Var. glauca showed higher tolerance to drought but slower growth than var. menziesii. Clinal variation in drought tolerance and growth species-wide was mainly associated with temperature rather than precipitation. A higher degree of plasticity for growth was observed in var. menziesii in response to extreme drought. Genetic variation for drought tolerance in seedlings within varieties is maintained primarily within populations. Selective breeding within populations may facilitate adaptation to drought more than assisted gene flow.

Discerning structure versus speciation in phylogeographic analysis of Seepage Salamanders (Desmognathus aeneus) using demography, environment, geography, and phenotype

Numerous mechanisms can drive speciation, including isolation by adaptation, distance, and environment. These forces can promote genetic and phenotypic differentiation of local populations, the formation of phylogeographic lineages, and ultimately, completed speciation. However, conceptually similar mechanisms may also result in stabilizing rather than diversifying selection, leading to lineage integration and the long-term persistence of population structure within genetically cohesive species. Processes that drive the formation and maintenance of geographic genetic diversity while facilitating high rates of migration and limiting phenotypic differentiation may thereby result in population genetic structure that is not accompanied by reproductive isolation. We suggest that this framework can be applied more broadly to address the classic dilemma of "structure" versus "species" when evaluating phylogeographic diversity, unifying population genetics, species delimitation, and the underlying study of speciation. We demonstrate one such instance in the Seepage Salamander (Desmognathus aeneus) from the southeastern United States. Recent studies estimated up to 6.3% mitochondrial divergence and four phylogenomic lineages with broad admixture across geographic hybrid zones, which could potentially represent distinct species supported by our species-delimitation analyses. However, while limited dispersal promotes substantial isolation by distance, microhabitat specificity appears to yield stabilizing selection on a single, uniform, ecologically mediated phenotype. As a result, climatic cycles promote recurrent contact between lineages and repeated instances of high migration through time. Subsequent hybridization is apparently not counteracted by adaptive differentiation limiting introgression, leaving a single unified species with deeply divergent phylogeographic lineages that nonetheless do not appear to represent incipient species.

Nuclear and chloroplast DNA phylogeography reveals high genetic diversity and postglacial range expansion in Quercus mexicana

PREMISE

Phylogeographical studies are fundamental for understanding factors that influence the spatial distribution of genetic lineages within species. Population expansions and contractions, distribution shifts, and climate changes are among the most important factors shaping the genetic compositions of populations.

METHODS

We investigated the phylogeography of an endemic oak, Quercus mexicana (Fagaceae), which has a restricted distribution in northeastern Mexico along the Sierra Madre Oriental and adjacent areas. Nuclear and chloroplast DNA microsatellite markers were used to describe the genetic diversity and structure of 39 populations of Q. mexicana along its entire distribution area. We tested whether population expansion or contraction events influenced the genetic diversity and structure of the species. We also modeled the historical distributional range of Q. mexicana (for the Mid Holocene, the Last Glacial Maximum, and the Last Interglacial) to estimate the extent to which climate fluctuations have impacted the distribution of this oak species.

RESULTS

Our results revealed high genetic diversity and low genetic structure in Q. mexicana populations. Ecological niche models suggested historical fluctuations in the distributional range of Q. mexicana. Historical range changes, gene flow, and physical barriers seem to have played an important role in shaping the phylogeographic structure of Q. mexicana.

CONCLUSIONS

Our study indicates that the genetic structure of Q. mexicana may have been the result of responses of oak trees not only to heterogeneous environments present in the Sierra Madre Oriental and adjacent areas, but also to elevational and latitudinal shifts in response to climate changes in the past.

Adaptive divergence and genetic vulnerability of relict species under climate change: a case study of Pterocarya macroptera

BACKGROUND AND AIMS

Understanding adaptive genetic variation and whether it can keep pace with predicted future climate change is critical in assessing the genetic vulnerability of species and developing conservation management strategies. The lack of information on adaptive genetic variation in relict species carrying abundant genetic resources hinders the assessment of genetic vulnerability. Using a landscape genomics approach, this study aimed to determine how adaptive genetic variation shapes population divergence and to predict the adaptive potential of Pterocarya macroptera (a vulnerable relict species in China) under future climate scenarios.

METHODS

We applied restriction site-associated DNA sequencing (RAD-seq) to obtain 8244 single-nucleotide polymorphisms (SNPs) from 160 individuals across 28 populations. We examined the pattern of genetic diversity and divergence, and then identified outliers by genetic differentiation (FST) and genotype-environment association (GEA) methods. We further dissected the effect of geographical/environmental gradients on genetic variation. Finally, we predicted genetic vulnerability and adaptive risk under future climate scenarios.

KEY RESULTS

We identified three genetic lineages within P. macroptera: the Qinling-Daba-Tianmu Mountains (QDT), Western Sichuan (WS) and Northwest Yunnan (NWY) lineages, which showed significant signals of isolation by distance (IBD) and isolation by environment (IBE). IBD and IBE explained 3.7-5.7 and 8.6-12.8 % of the genetic structure, respectively. The identified GEA SNP-related genes were involved in chemical defence and gene regulation and may exhibit higher genetic variation to adapt to the environment. Gradient forest analysis revealed that the genetic variation was mainly shaped by temperature-related variables, indicating its adaptation to local thermal environments. A limited adaptive potential was suggested by the high levels of genetic vulnerability in marginal populations.

CONCLUSIONS

Environmental gradient mainly shaped the population differentiation of P. macroptera. Marginal populations may be at high risk of extinction, and thus proactive management measures, such as assisted gene flow, are required to ensure the survival of these populations.

Seed predation-induced Allee effects, seed dispersal and masting jointly drive the diversity of seed sources during population expansion

The environmental factors affecting plant reproduction and effective dispersal, in particular biotic interactions, have a strong influence on plant expansion dynamics, but their demographic and genetic consequences remain an understudied body of theory. Here, we use a mathematical model in a one-dimensional space and on a single reproductive period to describe the joint effects of predispersal seed insect predators foraging strategy and plant reproduction strategy (masting) on the spatio-temporal dynamics of seed sources diversity in the colonisation front of expanding plant populations. We show that certain foraging strategies can result in a higher seed predation rate at the colonisation front compared to the core of the population, leading to an Allee effect. This effect promotes the contribution of seed sources from the core to the colonisation front, with long-distance dispersal further increasing this contribution. As a consequence, our study reveals a novel impact of the predispersal seed predation-induced Allee effect, which mitigates the erosion of diversity in expanding populations. We use rearrangement inequalities to show that masting has a buffering role: it mitigates this seed predation-induced Allee effect. This study shows that predispersal seed predation, plant reproductive strategies and seed dispersal patterns can be intermingled drivers of the diversity of seed sources in expanding plant populations, and opens new perspectives concerning the analysis of more complex models such as integro-difference or reaction-diffusion equations.

Recruitment and migration patterns reveal a key role for seed banks in the meta-population dynamics of an aquatic plant

Progressive habitat fragmentation threatens plant species with narrow habitat requirements. While local environmental conditions define population growth rates and recruitment success at the patch level, dispersal is critical for population viability at the landscape scale. Identifying the dynamics of plant meta-populations is often confounded by the uncertainty about soil-stored population compartments. We combined a landscape-scale assessment of an amphibious plant's population structure with measurements of dispersal complexity in time to track dispersal and putative shifts in functional connectivity. Using 13 microsatellite markers, we analyzed the genetic structure of extant Oenanthe aquatica populations and their soil seed banks in a kettle hole system to uncover hidden connectivity among populations in time and space. Considerable spatial genetic structure and isolation-by-distance suggest limited gene flow between sites. Spatial isolation and patch size showed minor effects on genetic diversity. Genetic similarity found among extant populations and their seed banks suggests increased local recruitment, despite some evidence of migration and recent colonization. Results indicate stepping-stone dispersal across adjacent populations. Among permanent and ephemeral demes the resulting meta-population demography could be determined by source-sink dynamics. Overall, these spatiotemporal connectivity patterns support mainland-island dynamics in our system, highlighting the importance of persistent seed banks as enduring sources of genetic diversity.

Long-distance gene flow in Acacia senegal: Hope for disturbed and fragmented populations

Even though pollen and seed dispersals are some of the important factors that determine tree species survival across landscapes, gene dispersal data of important tropical dryland tree species such as Acacia senegal that are undergoing various population disturbances remain scarce. Understanding patterns of gene dispersal in these ecosystems is important for conservation, landscape restoration and tree improvement. We investigated pollen and seed mediated gene flow in two A. senegal populations of contrasting state (less disturbed and heavily undisturbed) using nine microsatellites and 128 genotyping-by-sequencing single nucleotide polymorphism (SNPs) multilocus genotypes of two growth stages (juvenile and adult trees) and their spatial locations. We performed parentage assignments using likelihood approach and undertook spatial genetic structure (SGS) analyses for the two growth stages through correlation among kinship coefficients and geographical distances between pair of individuals. The SNPs showed higher resolving power and assignment rates than microsatellites; however, a combination of the two marker-types improved the assignment rate and provided robust parentage assessments. We found evidence of long-distance (up to 210 m) pollination events for both populations; however, the majority of seed dispersal was found closer to the putative maternal parent. On average, parentage analysis showed high amounts of pollen (40%) and seed (20%) immigration in both populations. Significant positive SGS was found only for the adult cohorts in the less disturbed population for distance classes 20 and 40 m, indicating historical short-distance seed dispersals. Our results suggest long-distance gene flow within the species and we recommend conservation of remnant and isolated populations or individual trees to promote genetic connectivity.

Antagonistic Effects of Assortative Mating on the Evolution of Phenotypic Plasticity along Environmental Gradients

AbstractPrevious theory has shown that assortative mating for plastic traits can maintain genetic divergence across environmental gradients despite high gene flow. Yet these models did not examine how assortative mating affects the evolution of plasticity. We here describe patterns of genetic variation across elevation for plasticity in a trait under assortative mating, using multiple-year observations of budburst date in a common garden of sessile oaks. Despite high gene flow, we found significant spatial genetic divergence for the intercept, but not for the slope, of reaction norms to temperature. We then used individual-based simulations, where both the slope and the intercept of the reaction norm evolve, to examine how assortative mating affects the evolution of plasticity, varying the intensity and distance of gene flow. Our model predicts the evolution of either suboptimal plasticity (reaction norms with a slope shallower than optimal) or hyperplasticity (slopes steeper than optimal) in the presence of assortative mating when optimal plasticity would evolve under random mating. Furthermore, a cogradient pattern of genetic divergence for the intercept of the reaction norm (where plastic and genetic effects are in the same direction) always evolves in simulations with assortative mating, consistent with our observations in the studied oak populations.

Response of Fragaria vesca to projected change in temperature, water availability and concentration of CO2 in the atmosphere

The high rate of climate change may soon expose plants to conditions beyond their adaptation limits. Clonal plants might be particularly affected due to limited genotypic diversity of their populations, potentially decreasing their adaptability. We therefore tested the ability of a widely distributed predominantly clonally reproducing herb (Fragaria vesca) to cope with periods of drought and flooding in climatic conditions predicted to occur at the end of the twenty-first century, i.e. on average 4 °C warmer and with twice the concentration of CO2 in the air (800 ppm) than the current state. We found that F. vesca can phenotypically adjust to future climatic conditions, although its drought resistance may be reduced. Increased temperature and CO2 levels in the air had a far greater effect on growth, phenology, reproduction, and gene expression than the temperature increase itself, and promoted resistance of F. vesca to repeated flooding periods. Higher temperature promoted clonal over sexual reproduction, and increased temperature and CO2 concentration in the air triggered change in expression of genes controlling the level of self-pollination. We conclude that F. vesca can acclimatise to predicted climate change, but the increased ratio of clonal to sexual reproduction and the alteration of genes involved in the self-(in)compatibility system may be associated with reduced genotypic diversity of its populations, which may negatively impact its ability to genetically adapt to novel climate in the long-term.

Exploiting genetic and genomic resources to enhance productivity and abiotic stress adaptation of underutilized pulses

Underutilized pulses and their wild relatives are typically stress tolerant and their seeds are packed with protein, fibers, minerals, vitamins, and phytochemicals. The consumption of such nutritionally dense legumes together with cereal-based food may promote global food and nutritional security. However, such species are deficient in a few or several desirable domestication traits thereby reducing their agronomic value, requiring further genetic enhancement for developing productive, nutritionally dense, and climate resilient cultivars. This review article considers 13 underutilized pulses and focuses on their germplasm holdings, diversity, crop-wild-crop gene flow, genome sequencing, syntenic relationships, the potential for breeding and transgenic manipulation, and the genetics of agronomic and stress tolerance traits. Recent progress has shown the potential for crop improvement and food security, for example, the genetic basis of stem determinacy and fragrance in moth bean and rice bean, multiple abiotic stress tolerant traits in horse gram and tepary bean, bruchid resistance in lima bean, low neurotoxin in grass pea, and photoperiod induced flowering and anthocyanin accumulation in adzuki bean have been investigated. Advances in introgression breeding to develop elite genetic stocks of grass pea with low β-ODAP (neurotoxin compound), resistance to Mungbean yellow mosaic India virus in black gram using rice bean, and abiotic stress adaptation in common bean, using genes from tepary bean have been carried out. This highlights their potential in wider breeding programs to introduce such traits in locally adapted cultivars. The potential of de-domestication or feralization in the evolution of new variants in these crops are also highlighted.

Reduced within-population quantitative genetic variation is associated with climate harshness in maritime pine

How evolutionary forces interact to maintain genetic variation within populations has been a matter of extensive theoretical debates. While mutation and exogenous gene flow increase genetic variation, stabilizing selection and genetic drift are expected to deplete it. To date, levels of genetic variation observed in natural populations are hard to predict without accounting for other processes, such as balancing selection in heterogeneous environments. We aimed to empirically test three hypotheses: (i) admixed populations have higher quantitative genetic variation due to introgression from other gene pools, (ii) quantitative genetic variation is lower in populations from harsher environments (i.e., experiencing stronger selection), and (iii) quantitative genetic variation is higher in populations from heterogeneous environments. Using growth, phenological and functional trait data from three clonal common gardens and 33 populations (522 clones) of maritime pine (Pinus pinaster Aiton), we estimated the association between the population-specific total genetic variances (i.e., among-clone variances) for these traits and ten population-specific indices related to admixture levels (estimated based on 5165 SNPs), environmental temporal and spatial heterogeneity and climate harshness. Populations experiencing colder winters showed consistently lower genetic variation for early height growth (a fitness-related trait in forest trees) in the three common gardens. Within-population quantitative genetic variation was not associated with environmental heterogeneity or population admixture for any trait. Our results provide empirical support for the potential role of natural selection in reducing genetic variation for early height growth within populations, which indirectly gives insight into the adaptive potential of populations to changing environments.

The role of oceanic currents in the dispersal and connectivity of the mangrove Rhizophora mangle on the Southwest Atlantic region

Dispersal is a crucial mechanism to living beings, allowing them to reach new resources such that populations and species can occupy new environments. However, directly observing the dispersal mechanisms of widespread species can be costly or even impractical, which is the case for mangrove trees. The influence of ocean currents on mangrove dispersal is increasingly evident; however, few studies mechanistically relate the patterns of population distribution with the dispersal by oceanic currents under an integrated framework. Here, we evaluate the role of oceanic currents on connectivity of Rhizophora mangle along the Southwest Atlantic. We inferred population genetic structure and migration rates, simulated the displacement of propagules and tested our hypotheses with Mantel tests and redundancy analysis. We observed populations structured in two major groups, north and south, which is corroborated by other studies with Rhizophora and other coastal plants. Inferred recent migration rates do not indicate ongoing gene flow between sites. Conversely, long-term migration rates were low across groups and contrasting dispersal patterns within each one, which is consistent with long-distance dispersal events. Our hypothesis tests suggest that both isolation by distance and isolation by oceanography (derived from the oceanic currents) can explain the neutral genetic variation of R. mangle in the region. Our findings expand current knowledge of mangrove connectivity and highlight how the association of molecular methods with oceanographic simulations improve the interpretation of the dispersal process. This integrative approach is a cost- and time-efficient strategy to include dispersal and connectivity data into marine protected areas planning and management.

Plant Species' Capacity for Range Shifts at the Habitat and Geographic Scales: A Trade-Off-Based Framework

Climate change is causing rapid shifts in the abiotic and biotic environmental conditions experienced by plant populations, but we lack generalizable frameworks for predicting the consequences for species. These changes may cause individuals to become poorly matched to their environments, potentially inducing shifts in the distributions of populations and altering species' habitat and geographic ranges. We present a trade-off-based framework for understanding and predicting whether plant species may undergo range shifts, based on ecological strategies defined by functional trait variation. We define a species' capacity for undergoing range shifts as the product of its colonization ability and the ability to express a phenotype well-suited to the environment across life stages (phenotype-environment matching), which are both strongly influenced by a species' ecological strategy and unavoidable trade-offs in function. While numerous strategies may be successful in an environment, severe phenotype-environment mismatches result in habitat filtering: propagules reach a site but cannot establish there. Operating within individuals and populations, these processes will affect species' habitat ranges at small scales, and aggregated across populations, will determine whether species track climatic changes and undergo geographic range shifts. This trade-off-based framework can provide a conceptual basis for species distribution models that are generalizable across plant species, aiding in the prediction of shifts in plant species' ranges in response to climate change.

Mechanisms driving interspecific variation in regional synchrony of trees reproduction

Seed production in many plants is characterized by large interannual variation, which is synchronized at subcontinental scales in some species but local in others. The reproductive synchrony affects animal migrations, trophic responses to resource pulses and the planning of management and conservation. Spatial synchrony of reproduction is typically attributed to the Moran effect, but this alone is unable to explain interspecific differences in synchrony. We show that interspecific differences in the conservation of seed production-weather relationships combine with the Moran effect to explain variation in reproductive synchrony. Conservative timing of weather cues that trigger masting allows populations to be synchronized at distances >1000 km. Conversely, if populations respond to variable weather signals, synchrony cannot be achieved. Our study shows that species vary in the extent to which their weather cueing is spatiotemporally conserved, with important consequences, including an interspecific variation of masting vulnerability to climate change.

Oak stands along an elevation gradient have different molecular strategies for regulating bud phenology

BACKGROUND

Global warming raises serious concerns about the persistence of species and populations locally adapted to their environment, simply because of the shift it produces in their adaptive landscape. For instance, the phenological cycle of tree species may be strongly affected by higher winter temperatures and late frost in spring. Given the variety of ecosystem services they provide, the question of forest tree adaptation has received increasing attention in the scientific community and catalyzed research efforts in ecology, evolutionary biology and functional genomics to study their adaptive capacity to respond to such perturbations.

RESULTS

In the present study, we used an elevation gradient in the Pyrenees Mountains to explore the gene expression network underlying dormancy regulation in natural populations of sessile oak stands sampled along an elevation cline and potentially adapted to different climatic conditions mainly driven by temperature. By performing analyses of gene expression in terminal buds we identified genes displaying significant dormancy, elevation or dormancy-by-elevation interaction effects. Our Results highlighted that low- and high-altitude populations have evolved different molecular strategies for minimizing late frost damage and maximizing the growth period, thereby increasing potentially their respective fitness in these contrasting environmental conditions. More particularly, population from high elevation overexpressed genes involved in the inhibition of cell elongation and delaying flowering time while genes involved in cell division and flowering, enabling buds to flush earlier were identified in population from low elevation.

CONCLUSION

Our study made it possible to identify key dormancy-by-elevation responsive genes revealing that the stands analyzed in this study have evolved distinct molecular strategies to adapt their bud phenology in response to temperature.

Molecular insights into the dynamics of species invasion by hybridisation in Tasmanian eucalypts

In plants where seed dispersal is limited compared with pollen dispersal, hybridisation may enhance gene exchange and species dispersal. We provide genetic evidence of hybridisation contributing to the expansion of the rare Eucalyptus risdonii into the range of the widespread Eucalyptus amygdalina. These closely related tree species are morphologically distinct, and observations suggest that natural hybrids occur along their distribution boundaries and as isolated trees or in small patches within the range of E. amygdalina. Hybrid phenotypes occur outside the range of normal dispersal for E. risdonii seed, yet in some hybrid patches small individuals resembling E. risdonii occur and are hypothesised to be a result of backcrossing. Using 3362 genome-wide SNPs assessed from 97 individuals of E. risdonii and E. amygdalina and 171 hybrid trees, we show that (i) isolated hybrids match the genotypes expected of F₁ /F₂ hybrids, (ii) there is a continuum in the genetic composition among the isolated hybrid patches from patches dominated by F₁ /F₂ -like genotypes to those dominated by E. risdonii-backcross genotypes, and (iii) the E. risdonii-like phenotypes in the isolated hybrid patches are most-closely related to proximal larger hybrids. These results suggest that the E. risdonii phenotype has been resurrected in isolated hybrid patches established from pollen dispersal, providing the first steps in its invasion of suitable habitat by long-distance pollen dispersal and complete introgressive displacement of E. amygdalina. Such expansion accords with the population demographics, common garden performance data, and climate modelling which favours E. risdonii and highlights a role of interspecific hybridisation in climate change adaptation and species expansion.

Genetic diversity and gene expression diversity shape the adaptive pattern of the aquatic plant Batrachium bungei along an altitudinal gradient on the Qinghai-Tibet plateau

It is an intriguing issue of evolutionary biology how genetic diversity and gene expression diversity shape the adaptive patterns. Comparative transcriptomic studies of wild populations in extreme environments provide critical insights into the relative contribution of genetic and expressive components. In this study, we analyzed the genetic diversity and gene expression diversity of 20 populations of the aquatic plant Batrachium bungei along elevations ranging from 2690 to 4896 m on the Qinghai-Tibet plateau (QTP). Based on single nucleotide polymorphisms (SNPs) and gene expression data from 100 individuals of B. bungei, we found that variation in genetic sequence was more sensitive to detect weak differentiation than gene expression. Using 292,613 high-quality SNPs, we documented a significant phylogeographical structure, a low within-population genetic diversity, and a high inter-population genetic differentiation in B. bungei populations. Analysis of relationship between geographic distance, genetic distance, and gene expression similarity showed that geographic isolation shaped gene flow patterns but not gene expression patterns. We observed a negative relationship between genetic diversity and gene expression diversity within and among B. bungei populations, and we demonstrated that as environmental conditions worsen with increasing altitude, genetic diversity played an increased role in maintaining the stability of populations, while the corresponding role of gene expression diversity decreased. These results suggested that genetic diversity and gene expression diversity might act as a complementary mechanism contributing to the long-term survival of B. bungei in extreme environments.

Genetics and epigenetics of Pinus nigra populations with differential exposure to air pollution

Forest species in the course of their evolution have experienced several environmental challenges, which since historic times include anthropogenic pollution. The effects of pollution on the genetic and epigenetic diversity in black pine (Pinus nigra) forests were investigated in the Amyntaio - Ptolemais - Kozani Basin, which has been for decades the largest lignite mining and burning center of Greece, with a total installed generating capacity of about 4.5 GW, operating for more than 70 years and resulting in large amounts of primary air pollutant emissions, mainly SO₂, NOx and PM10. P. nigra, a biomarker for air pollution and a keystone species of affected natural ecosystems, was examined in terms of phenology (cone and seed parameters), genetics (283 AFLP loci) and epigenetics (606 MSAP epiloci), using two populations (exposed to pollution and control) of the current (mature trees) and future (embryos) stand. It was found that cone, seed, as well as genetic diversity parameters, did not show statistically significant differences between the exposed population and the control. Nevertheless, statistically significant differences were detected at the population epigenetic level. Moreover, there was a further differentiation regarding the intergenerational comparison: while the epigenetic diversity does not substantially change in the two generations assessed in the control population, epigenetic diversity is significantly higher in the embryo population compared to the parental stand in the exposed population. This study sheds a light to genome dynamics in a forest tree population exposed to long term atmospheric pollution burden and stresses the importance of assessing both genetics and epigenetics in biomonitoring applications.

Divergent selection predating the Last Glacial Maximum mainly acted on macro-phenotypes in Norway spruce

The current distribution and population structure of many species were, to a large extent, shaped by cycles of isolation in glacial refugia and subsequent population expansions. Isolation in and postglacial expansion through heterogeneous environments led to either neutral or adaptive divergence. Norway spruce is no exception, and its current distribution is the consequence of a constant interplay between evolutionary and demographic processes. We investigated population differentiation and adaptation of Norway spruce for juvenile growth, diameter of the stem, wood density, and tracheid traits at breast height. Data from 4461 phenotyped and genotyped Norway spruce from 396 half-sib families in two progeny tests were used to test for divergent selection in the framework of Q _ST vs. F _ST. We show that the macroscopic resultant trait (stem diameter), unlike its microscopic components (tracheid dimensions) and juvenile growth, was under divergent selection that predated the Last Glacial Maximum. Altogether, the current variation in these phenotypic traits in Norway spruce is better explained by local adaptation to ancestral environments than to current ones, where populations were partly preadapted, mainly through growth-related traits.

Local seed sourcing for sustainable forestry

Seed sourcing strategies are the basis for identifying genetic material meeting the requirements of future climatic conditions and social demands. Specifically, local seed sourcing has been extensively promoted, based on the expected adaptation of the populations to local conditions, but there are some limitations for the application. We analyzed Strict-sense local and Wide-sense local (based on climatic similarity) seed sourcing strategies. We determined species and genetic pools based on these strategies for 40 species and deployment zones in Spain. We also obtained the total number of seed sources and stands for these species in the EU countries. We analyzed the richness of the pools, the relationship with variables related to the use of the species in afforestation, and the availability of seed production areas approved for the production of reproductive material destined to be marketed. This study confirms the existence of extensive species and genetic local pools. Also, that the importance of these pools differs for different species, limitations being derived from the use of forest reproductive material and the existence of approved basic materials. Strategies derived from local seed sourcing approaches are the basis for the use of forest reproductive material because a large number of the species in the area considered in the study are under regulation. However, despite the extensive work done to approve basic materials, limitations based on the availability of seed production areas to provide local material for sustainable forestry are found in those species. Considering a Wide-sense local seed sourcing strategy we provide alternative pools in order to meet social demands under the actual regulations on marketing of reproductive materials.

Population structure and genetic variation of fragmented mountain birch forests in Iceland

Betula pubescens Ehrh. (mountain birch) is the only forest-forming tree in Iceland. Since human settlement (874 AD), the continuous 25,000-30,000 km 2 forest has shrunk to 1.200 km 2 of fragmented patches, making it a good object to study population genetic consequences of habitat fragmentation and disturbance. Further, genetic studies have also shown that hybridization between the tetraploid (2n=56) B. pubescens and the diploid (2n=28) Betula nana L. (dwarf birch) occurs among Iceland's natural populations. This study assessed the genetic variation within and among eleven birch forests remaining across Iceland. Genotype-by-sequencing methodology (GBS) provided a total of 24,585 SNPs, with a minor allele frequency > 5% for genetic analyses. The analysis showed similar diversity within forests, suggesting that fragmentation and hybridization have had a limited effect on the genetic variation within sites. A clear genetic divergence is found among forests from the different regions of Iceland that may reflect historical isolation; the differentiation between forests increased with geographic distances reflecting isolation by distance. Information on the distribution of genetic variation of birch in Iceland is essential for its conservation and to establish genotype-phenotype associations to predict responses to new environmental conditions imposed by climate change and novel biotic/abiotic stressors.

Seed sourcing strategies for ecological restoration under climate change: A review of the current literature

Climate change continues to alter the seasonal timing and extremes of global temperature and precipitation patterns. These departures from historic conditions along with the predicted variability of future climates present a challenge to seed sourcing, or provenance strategy decisions, within the practice of ecological restoration. The “local is best” for seed sourcing paradigm is predicated upon the assumption that ecotypes are genetically adapted to their local environment. However, local adaptations are potentially being outpaced by climate change, and the ability of plant populations to naturally migrate or shift their distribution accordingly may be limited by habitat fragmentation. Restoration practitioners and natural area managers have a general understanding of the importance of matching the inherent adaptations of source populations with the current and/or future site conditions where those seeds or propagules are planted. However, for many species used in seed-based restoration, there is a lack of empirical evidence to guide seed sourcing decisions, which are critical for the longevity and ecological function of restored natural communities. With the goal of characterizing, synthesizing, and applying experimental research to guide restoration practice, we conducted a systematic review of the literature on provenance testing of taxa undertaken to inform seed sourcing strategies for climate resiliency. We found a strong bias in the choice of study organism: most studies have been conducted on tree species. We also found a strong bias regarding where this research has been conducted, with North America (52%) and Europe (31%) overrepresented. Experiments were designed to assess how propagule origin influences performance across both climatic (26%) and geographic (15%) distance, with some studies focused on determining how climate normal conditions (39%) impacted performance related to survivorship, growth and other parameters. We describe the patterns and gaps our review identified, highlight specific topics which require further research, and provide practical suggestions of immediate and longer-term tools that restoration practitioners can use to guide and build resilient natural communities under future climate scenarios.

Genetic basis of growth reaction to drought stress differs in contrasting high-latitude treeline ecotones of a widespread conifer

Climate change is increasing the frequency and intensity of drought events in many boreal forests. Trees are sessile organisms with a long generation time, which makes them vulnerable to fast climate change and hinders fast adaptations. Therefore, it is important to know how forests cope with drought stress and to explore the genetic basis of these reactions. We investigated three natural populations of white spruce (Picea glauca) in Alaska, located at one drought-limited and two cold-limited treelines with a paired plot design of one forest and one treeline plot. We obtained individual increment cores from 458 trees and climate data to assess dendrophenotypes, in particular the growth reaction to drought stress. To explore the genetic basis of these dendrophenotypes, we genotyped the individual trees at 3000 single nucleotide polymorphisms in candidate genes and performed genotype-phenotype association analysis using linear mixed models and Bayesian sparse linear mixed models. Growth reaction to drought stress differed in contrasting treeline populations. Therefore, the populations are likely to be unevenly affected by climate change. We identified 40 genes associated with dendrophenotypic traits that differed among the treeline populations. Most genes were identified in the drought-limited site, indicating comparatively strong selection pressure of drought-tolerant phenotypes. Contrasting patterns of drought-associated genes among sampled sites and in comparison to Canadian populations in a previous study suggest that drought adaptation acts on a local scale. Our results highlight genes that are associated with wood traits which in turn are critical for the establishment and persistence of future forests under climate change.

Climate Change in the Provenance Regions of Romania over the Last 70 Years: Implications for Forest Management

The recent climate change scenarios show significant increases in temperature and extreme drought events in Southern and Eastern Europe by the end of the 21st century, which will have a serious impact on forest growth and adaptation, and important consequences for forest management. The system of provenance regions, according to the OECD Scheme and EU Directive, was thought to encourage the use of the local seed sources, under the concept ‘local is the best’. However, climate is changing faster than some species or populations can adapt or migrate, which raises some uncertainties with respect to the future performance of local populations. In Romania, as in other countries, the delimitation of provenance regions is based on geographical, ecological and vegetation criteria. The aim of this study is to evaluate: (1) the climate change that has occurred at the level of the provenance regions; (2) which regions will be most vulnerable to climate change; (3) which forest types will be the most vulnerable in a certain region; and (4) changes in the climatic envelope of forest species. Several climatic parameters and an ecoclimatic indices have been calculated and analyzed at the level of provenance regions, subregions and ecological sectors (forest types) in Romania, during the period 1951–2020. The results highlight a general shift towards warmer and drier conditions in the last 30 years, the mean annual temperature increasing with 0.3–1.1 °C across the provenance subregions. The De Martonne aridity index for the vegetation season shows that 86% of the ecological sectors fell into the arid and semiarid categories, which indicates a very high degree of vulnerability for forest species. On the Lang rainfall index, forest steppe climatic conditions occurred in all pure or mixed pedunculate oak forests, thermophile oak species, meadow forests, poplar and willow, Turkey oak and Hungarian oak forests. The Ellenberg coefficient highlights that the warming process is more evident along the altitude and the degree of vulnerability increase at lower altitude or at the edge of species distribution. The climate envelopes of many forest species have already shifted to another ecosystem’s climate. This paper presents the importance of re-delineation the provenance regions for the production and deployment of forest reproductive materials according to the climate change occurred in the last decades, as a fundamental tool for an adaptive forest management.

Genetic Diversity and Population Structure of Jubaea chilensis, an Endemic and Monotype Gender from Chile, Based on SNP Markers

Jubaea chilensis (Molina) Baill., also named Chilean palm, is an endemic species found in the coastal area of Mediterranean sclerophyllous forest in Chile. It has a highly restricted and fragmented distribution along the coast, being under intense exploitation and anthropogenic impact. Based on 1038 SNP markers, we evaluated the genetic diversity and population structure among six J. chilensis natural groups encompassing 96% of the species distribution. We observed low levels of genetic diversity, a deficit of heterozygotes (mean HE = 0.024; HO = 0.014), and high levels of inbreeding (mean FIS = 0.424). The fixation index (FST) and Nei’s genetic distance pairwise comparisons indicated low to moderate structuring among populations. There was no evidence of isolation by distance (r = −0.214, p = 0.799). In the cluster analysis, we observed a closer relationship among Culimo, Cocalán, and Candelaria populations. Migration rates among populations were low, except for some populations with moderate values. The K value that best represented the spatial distribution of genetic diversity was ∆K = 3. Habitat fragmentation, deterioration of the sclerophyllous forest, lack of long-distance dispersers, and a natural regeneration deficit may have driven inbreeding and low levels of genetic diversity in the palm groves of J. chilensis. Although extant populations are not at imminent risk of extinction, the rate of inbreeding could increase and migration could decrease if the effects of climate change and human impact become more acute.

Long-Distance Pollen Dispersal in Urban Green Roof and Ground-Level Habitats

Long-distance pollen dispersal is critical for gene flow in plant populations, yet pollen dispersal patterns in urban habitats such as green roofs have not been extensively studied. Pollen dispersal patterns typically are assessed either by fitting non-linear models to the relationship between the degree of pollen dispersal and distance to the pollen source (i.e., curve fitting), or by fitting probability density functions (PDFs) to pollen dispersal probability histograms (i.e., PDF fitting). Studies using curve fitting typically report exponential decay patterns in pollen dispersal. However, PDF fitting typically produces more fat-tailed distributions, suggesting the exponential decay may not be the best fitting model. Because the two approaches may yield conflicting results, we used both approaches to examine pollen dispersal patterns in the wind-pollinated Amaranthus tuberculatus and the insect-pollinated Solanum lycopersicum at two green roof and two ground-level sites in the New York (NY, United States) metropolitan area. For the curve fitting analyses, the exponential decay and inverse power curves provided good fits to pollen dispersal patterns across both green roof and ground-level sites for both species. Similar patterns were observed with the PDF fitting analyses, where the exponential or inverse Gaussian were the top PDF at most sites for both species. While the curve fitting results are consistent with other studies, the results differ from most studies using PDF fitting, where long-distance pollen dispersal is more common than we observed. These results highlight the need for further research to compare curve and PDF fitting for predicting pollen dispersal patterns. And, critically, while long-distance pollen dispersal may be an important component of overall pollen dispersal for A. tuberculatus and S. lycopersicum in both urban green roof and ground-level sites, our results suggest it potentially may occur to a lesser extent compared with plants in less-urban areas.

Population structure in Quercus suber L. revealed by nuclear microsatellite markers

Quercus suber L. is a sclerophyllous tree species native to the western Mediterranean, a region that is considered highly vulnerable to increased temperatures and severe dry conditions due to environmental changes. Understanding the population structure and demographics of Q. suber is essential in order to anticipate whether populations at greater risk and the species as a whole have the genetic background and reproductive dynamics to enable rapid adaptation. The genetic diversity of Q. suber has been subject to different studies using both chloroplast and nuclear data, but population structure patterns remain unclear. Here, we perform genetic analyses on Q. suber using 13 nuclear microsatellite markers, and analysed 17 distinct locations across the entire range of the species. Structure analyses revealed that Q. suber may contain three major genetic clusters that likely result from isolation in refugia combined with posterior admixture and putative introgression from other Quercus species. Our results show a more complex structure scenario than previously inferred for Q. suber using nuclear markers and suggest that different southern populations contain high levels of genetic variation that may contribute to the resilience of Q. suber in a context of environmental change and adaptive pressure.

Chasing genetic correlation breakers to stimulate population resilience to climate change

Global climate change introduces new combinations of environmental conditions, which is expected to increase stress on plants. This could affect many traits in multiple ways that are as yet unknown but will likely require the modification of existing genetic relationships among functional traits potentially involved in local adaptation. Theoretical evolutionary studies have determined that it is an advantage to have an excess of recombination events under heterogeneous environmental conditions. Our study, conducted on a population of radiata pine (Pinus radiata D. Don), was able to identify individuals that show high genetic recombination at genomic regions, which potentially include pleiotropic or collocating QTLs responsible for the studied traits, reaching a prediction accuracy of 0.80 in random cross-validation and 0.72 when whole family was removed from the training population and predicted. To identify these highly recombined individuals, a training population was constructed from correlation breakers, created through tandem selection of parents in the previous generation and their consequent mating. Although the correlation breakers showed lower observed heterogeneity possibly due to direct selection in both studied traits, the genomic regions with statistically significant differences in the linkage disequilibrium pattern showed higher level of heretozygosity, which has the effect of decomposing unfavourable genetic correlation. We propose undertaking selection of correlation breakers under current environmental conditions and using genomic predictions to increase the frequency of these ’recombined’ individuals in future plantations, ensuring the resilience of planted forests to changing climates. The increased frequency of such individuals will decrease the strength of the population-level genetic correlations among traits, increasing the opportunity for new trait combinations to be developed in the future.

The costs and benefits of dispersal in small populations

Dispersal has three major effects on adaptation. First, gene flow mixes alleles adapted to different environments, potentially hindering (swamping) adaptation. Second, it brings in other variants and inflates genetic variance: this aids adaptation to spatially (and temporally) varying environments but if selection is hard, it lowers the mean fitness of the population. Third, neighbourhood size, which determines how weak genetic drift is, increases with dispersal-when genetic drift is strong, increase of the neighbourhood size with dispersal aids adaptation. In this note, I focus on the role of dispersal in environments that change gradually across space, and when local populations are quite small such that genetic drift has a significant effect. Using individual-based simulations, I show that in small populations, even leptokurtic dispersal benefits adaptation by reducing the power of genetic drift. This has implications for management of fragmented or marginal populations: the beneficial effect of increased dispersal into small populations is stronger than swamping of adaption under a broad range of conditions, including a mixture of local and long-distance dispersal. However, when environmental gradient is steep, heavily fat-tailed dispersal will swamp continuous adaptation so that only patches of locally adapted subpopulations remain. This article is part of the theme issue 'Species' ranges in the face of changing environments (Part II)'.

One hundred years into the study of ecotypes, new advances are being made through large-scale field experiments in perennial plant systems

A hundred years after Turesson first clearly described how locally adaptive variation is distributed within species, plant biologists are making major breakthroughs in our understanding of mechanisms underlying adaptation from local populations to the scale of continents. Although the genetics of local adaptation has typically been studied in smaller reciprocal transplant experiments, it is now being evaluated with whole genomes in large-scale networks of common garden experiments with perennial switchgrass and poplar trees. These studies support the hypothesis that a complex combination of loci, both with and without adaptive trade-offs, underlies local adaptation and that hybridization and adaptive introgression play a key role in the evolution of these species. Future studies incorporating high-throughput phenotyping, gene expression, and modeling will be used to predict responses of these species to climate change.

Frugivory and Seed Dispersal by Carnivorans

Seed dispersal is critical to the ecological performance of sexually reproducing plant species and the communities that they form. The Mammalian order Carnivora provide valuable and effective seed dispersal services but tend to be overlooked in much of the seed dispersal literature. Here we review the literature on the role of Carnivorans in seed dispersal, with a literature search in the Scopus reference database. Overall, we found that Carnivorans are prolific seed dispersers. Carnivorans’ diverse and plastic diets allow them to consume large volumes of over a hundred families of fruit and disperse large quantities of seeds across landscapes. Gut passage by these taxa generally has a neutral effect on seed viability. While the overall effect of Carnivorans on seed dispersal quality is complex, Carnivorans likely increase long-distance dispersal services that may aid the ability of some plant species to persist in the face of climate change.

The important role of animal social status in vertebrate seed dispersal

Seed dispersal directly affects plant establishment, gene flow and fitness. Understanding patterns in seed dispersal is, therefore, fundamental to understanding plant ecology and evolution, as well as addressing challenges of extinction and global change. Our ability to understand dispersal is limited because seeds may be dispersed by multiple agents, and the effectiveness of these agents can be highly variable both among and within species. We provide a novel framework that links seed dispersal to animal social status, a key component of behaviour. Because social status affects individual resource access and movement, it provides a critical link to two factors that determine seed dispersal: the quantity of seeds dispersed and the spatial patterns of dispersal. Social status may have unappreciated effects on post-dispersal seed survival and recruitment when social status affects individual habitat use. Hence, environmental changes, such as selective harvesting and urbanisation, that affect animal social structure may have unappreciated consequences for seed dispersal. This framework highlights these exciting new hypotheses linking environmental change, social structure and seed dispersal. By outlining experimental approaches to test these hypotheses, we hope to facilitate studies across a wide diversity of plant-animal networks, which may uncover emerging hotspots or significant declines in seed dispersal.

Signatures of natural selection in a foundation tree along Mediterranean climatic gradients

Temperature and precipitation regimes are rapidly changing, resulting in forest dieback and extinction events, particularly in Mediterranean‐type climates (MTC). Forest management that enhance forests’ resilience is urgently required, however adaptation to climates in heterogeneous landscapes with multiple selection pressures is complex. For widespread trees in MTC we hypothesized that: patterns of local adaptation are associated with climate; precipitation is a stronger factor of adaptation than temperature; functionally related genes show similar signatures of adaptation; and adaptive variants are independently sorting across the landscape. We sampled 28 populations across the geographic distribution of Eucalyptus marginata (jarrah), in South‐west Western Australia, and obtained 13,534 independent single nucleotide polymorphic (SNP) markers across the genome. Three genotype‐association analyses that employ different ways of correcting population structure were used to identify putatively adapted SNPs associated with independent climate variables. While overall levels of population differentiation were low (F_ST = 0.04), environmental association analyses found a total of 2336 unique SNPs associated with temperature and precipitation variables, with 1440 SNPs annotated to genic regions. Considerable allelic turnover was identified for SNPs associated with temperature seasonality and mean precipitation of the warmest quarter, suggesting that both temperature and precipitation are important factors in adaptation. SNPs with similar gene functions had analogous allelic turnover along climate gradients, while SNPs among temperature and precipitation variables had uncorrelated patterns of adaptation. These contrasting patterns provide evidence that there may be standing genomic variation adapted to current climate gradients, providing the basis for adaptive management strategies to bolster forest resilience in the future.

Evolution of flowering time in a selfing annual plant: Roles of adaptation and genetic drift

Resurrection studies are a useful tool to measure how phenotypic traits have changed in populations through time. If these trait modifications correlate with the environmental changes that occurred during the time period, it suggests that the phenotypic changes could be a response to selection. Selfing, through its reduction of effective size, could challenge the ability of a population to adapt to environmental changes. Here, we used a resurrection study to test for adaptation in a selfing population of Medicago truncatula, by comparing the genetic composition and flowering times across 22 generations. We found evidence for evolution toward earlier flowering times by about two days and a peculiar genetic structure, typical of highly selfing populations, where some multilocus genotypes (MLGs) are persistent through time. We used the change in frequency of the MLGs through time as a multilocus fitness measure and built a selection gradient that suggests evolution toward earlier flowering times. Yet, a simulation model revealed that the observed change in flowering time could be explained by drift alone, provided the effective size of the population is small enough (<150). These analyses suffer from the difficulty to estimate the effective size in a highly selfing population, where effective recombination is severely reduced.

Gene Flow and Genetic Structure Reveal Reduced Diversity between Generations of a Tropical Tree, Manilkara multifida Penn., in Atlantic Forest Fragments

The Atlantic Forest remnants in southern Bahia, Brazil, contain large tree species that have suffered disturbances in recent decades. Anthropogenic activities have led to a decrease in the population of many tree species and a loss of alleles that can maintain the evolutionary fitness of their populations. This study assessed patterns of genetic diversity, spatial genetic structure, and genetic structure among Manilkara multifida Penn. populations, comparing the genetic parameters of adult and juvenile trees. In particular, we collected leaves from adults and juveniles of M. multifida in two protected areas, the Veracel Station (EVC) and the Una Biological Reserve (UBR), located in threatened Atlantic Forest fragments. We observed a substantial decay in genetic variability between generations in both areas i.e., adults’ H_O values were higher (EVC = 0.720, UBR = 0.736) than juveniles’ (EVC = 0.463 and UBR = 0.560). Both juveniles and adults showed genetic structure between the two areas (θ = 0.017 for adults and θ = 0.109 for juveniles). Additionally, forest fragments indicated an unexpectedly short gene flow. Our results, therefore, highlight the pervasive effects of historical deforestation and other human disturbances on the genetic diversity of M. multifida populations within a key conservation region of the Atlantic Forest biodiversity hotspot.

Modes of climate variability bridge proximate and evolutionary mechanisms of masting

There is evidence that variable and synchronous reproduction in seed plants (masting) correlates to modes of climate variability, e.g. El Niño Southern Oscillation and North Atlantic Oscillation. In this perspective, we explore the breadth of knowledge on how climate modes control reproduction in major masting species throughout Earth's biomes. We posit that intrinsic properties of climate modes (periodicity, persistence and trends) drive interannual and decadal variability of plant reproduction, as well as the spatial extent of its synchrony, aligning multiple proximate causes of masting through space and time. Moreover, climate modes force lagged but in-phase ecological processes that interact synergistically with multiple stages of plant reproductive cycles. This sets up adaptive benefits by increasing offspring fitness through either economies of scale or environmental prediction. Community-wide links between climate modes and masting across plant taxa suggest an evolutionary role of climate variability. We argue that climate modes may 'bridge' proximate and ultimate causes of masting selecting for variable and synchronous reproduction. The future of such interaction is uncertain: processes that improve reproductive fitness may remain coupled with climate modes even under changing climates, but chances are that abrupt global warming will affect Earth's climate modes so rapidly as to alter ecological and evolutionary links. This article is part of the theme issue 'The ecology and evolution of synchronized seed production in plants'.

Macroevolutionary consequences of mast seeding

Masting characterizes large, intermittent and highly synchronous seeding events among individual plants and is found throughout the plant Tree of Life (ToL). Although masting can increase plant fitness, little is known about whether it results in evolutionary changes across entire clades, such as by promoting speciation or enhanced trait selection. Here, we tested if masting has macroevolutionary consequences by combining the largest existing dataset of population-level reproductive time series and time-calibrated phylogenetic tree of vascular plants. We found that the coefficient of variation (CVp) of reproductive output for 307 species covaried with evolutionary history, and more so within clades than expected by random. Speciation rates estimated at the species level were highest at intermediate values of CVp and regional-scale synchrony (Sr) in seed production, that is, there were unimodal correlations. There was no support for monotonic correlations between either CVp or Sr and rates of speciation or seed size evolution. These results were robust to different sampling decisions, and we found little bias in our dataset compared with the wider plant ToL. While masting is often adaptive and encompasses a rich diversity of reproductive behaviours, we suggest it may have few consequences beyond the species level. This article is part of the theme issue 'The ecology and evolution of synchronized seed production in plants'.

Provenance Variation in Early Survival, Growth, and Carbon Isotope Discrimination of Southwestern Ponderosa Pine Growing in Three Common Gardens across an Elevational Gradient

We investigated early survival, growth, and carbon isotope discrimination of ponderosa pine (Pinus ponderosa Lawson & C. Lawson var. scopulorum Engelm.) seedlings from different provenances using common gardens across an elevational gradient in order to examine the potential for adaptation to extreme environments and constraints to artificial regeneration. Twenty-one provenances from a range of elevations across Arizona and New Mexico were planted in three common gardens: a high-elevation meadow in aspen-mixed conifer forest, a mid-elevation ponderosa pine forest, and a low-elevation pinyon juniper woodland. Two years after planting in 2018, survival was highest at the mid-elevation site (54%), low at the high-elevation site (1.5%), and 0% at the low-elevation site. At the hot and dry low-elevation site, provenances from low-elevations survived longer than provenances from mid- and high-elevations, which suggests greater drought tolerance of low-elevation provenances. Mortality agents changed from abiotic (drought) to biotic (herbivory) with an increase in elevation across sites. High mortality of seedlings planted at high-elevation sites from biotic agents, such as rodents, may challenge efforts to establish ponderosa pine in assisted migration projects. Seedlings had significantly higher growth rate and carbon isotope discrimination (∆13C) at the mid-elevation site than the high-elevation site. Provenances differed significantly in diameter, and ∆13C, but not in height growth rate for the first year after planting. Provenance variation in ∆13C suggests genetic variation in water use efficiency that may be useful for future evaluation of southwestern ponderosa pine seed sources for reforestation.

The Effects of Climate Change on Landscape Connectivity and Genetic Clusters in a Small Subtropical and Warm-Temperate Tree

Climate change is a great threat to global biodiversity and has resulted in serious ecological consequences. Although the potential effects of climate change on genetic diversity have recently received much research attention, little research has focused on the impacts of climate change on genetic connectivity and the relationship between climate stability and genetic divergence. Here, we combined population connectivity with genetic data to predict the impacts of future climate change on genetic connectivity. Coupled with climatic variables and genetic data, we used POPS software to create spatially explicit simulations and predict the dynamics in genetic clusters in response to climate changes. A generalized additive model was employed to test the correlation between climatic stability and genetic diversification. Our findings indicated that a reduction in species distribution due to severe climate change would lead to a substantial loss of genetic connectivity. More severe future climatic scenarios would likely cause greater loss of variability or more distinct homogenization in genetic variation of species. Relatively low interpolated genetic distances are generally associated with areas of greater losses in climatic suitability from the present to the future. The displacement of climatic genetic clusters will challenge species adaptation to future climate change because of the loss of fundamental evolutionary potential. The persistence capacity of plant species may be weakened in the face of future climate change.

Congruence between ocean-dispersal modelling and phylogeography explains recent evolutionary history of Cycas species with buoyant seeds

Ocean currents play a significant role in driving the long-distance dispersal (LDD), spatial distribution and phylogeographic patterns of many organisms. Integrating phylogeographic analyses and mechanistic ocean current modelling can provide novel insights into the evolutionary history of terrestrial littoral species but has been rarely applied in this context. We focused on a group of Cycas that have buoyant seeds and occupy coastal habitats. By integrating evidence from mechanistic simulations and whole plastomic data, we examined the role of ocean circulation in shaping the phylogeography of these Cycas species. Plastomes of the studied Cycas species showed extreme conservatism, following a post-Pleistocene divergence. Phylogenies revealed three subclades, corresponding to the Pacific Ocean, Sunda Shelf and Indian Ocean. The ocean modelling results indicate that hotspots of seed stranding coincide well with the contemporary distribution of the Cycas species and that drifting trajectories from the three subclades are largely confined to separate regions. These findings suggest that ocean current systems, by driving long-distance dispersal, have shaped the distribution and phylogeography for Cycas with buoyant seeds. This study highlights how the combination of genomic data and ocean drift modelling can help explain phylogeographic patterns and diversity in terrestrial littoral ecosystems.

Broadening Predictive Understanding of Species’ Range Responses to Climate Change: The Case of Aloidendron dichotomum

Concerns have been raised about attribution of species range shifts to anthropogenic climate change. Species paleo-range projections are emerging as a means to broaden understanding of range shifts and could be applied to assist in attribution. Apparent recent range contraction in the Quiver Tree (Aloidendron dichotomum (Masson) Klopper and Gideon F.Sm) has been attributed to anthropogenic climate change, but this has been challenged. We simulated the paleo- and future geographic range of A. dichotomum under changing climate using species distribution models (SDMs) to provide a broader perspective on its range dynamics. Ensemble modelling of the Last Glacial Maximum (LGM), mid-Holocene, current, and projected 2070 time periods simulates a paleo-historical poleward expansion of suitable bioclimatic space for this species under natural climate change post-LGM, and projects an eastward shift towards 2070. During the LGM, suitable bioclimatic space for A. dichotomum was simulated to be restricted to the equatorward part of its current range. During the Pleistocene/mid-Holocene climate transition period, the species’ range is predicted to have expanded significantly polewards at an average rate of 0.4 km per decade, assuming constant tracking of its optimal climatic niche. By 2070, suitable bioclimatic space is projected to expand further eastward into the summer rainfall region of South Africa, and contract in its equatorward reaches. Simulated post-LGM shifts roughly match expectations based on preliminary phylogenetic information, further supporting the attribution of current population declines to anthropogenic climate change drivers. Equatorward populations are required to migrate south-eastwards at a rate roughly 15 times faster than that calculated for the LGM/mid-Holocene climate transition period to avoid local extirpation. A preliminary analysis of range-wide genetic variation reveals a cline of variation, with generally higher levels in the central and more northerly part of the species distribution, as expected from the proposed paleo-range of the species. A more detailed analysis of the species’ phylogeographic history could be used to test the proposed paleo-range dynamics presented here, and if confirmed, would provide strong support for the use of this species as an indicator of anthropogenic climate change and a powerful case study for testing the implementation of conservation actions.

European oak chemical diversity - from ecotypes to herbivore resistance

Climate change is increasing insect pressure and forcing plants to adapt. Although chemotypic differentiation and phenotypic plasticity in spatially separated tree populations are known for decades, understanding their importance in herbivory resistance across forests remains challenging. We studied four oak forest stands in Germany using nontarget metabolomics, elemental analysis, and chemometrics and mapped the leaf metabolome of herbivore-resistant (T-) and herbivore-susceptible (S-) European oaks (Quercus robur) to Tortrix viridana, an oak pest that causes severe forest defoliation. Among the detected metabolites, we identified reliable metabolic biomarkers to distinguish S- and T-oak trees. Chemotypic differentiation resulted in metabolic shifts of primary and secondary leaf metabolism. Across forests, T-oaks allocate resources towards constitutive chemical defense enriched of polyphenolic compounds, e.g. the flavonoids kaempferol, kaempferol and quercetin glucosides, while S-oaks towards growth-promoting substances such as carbohydrates and amino-acid derivatives. This extensive work across natural forests shows that oaks' resistance and susceptibility to herbivory are linked to growth-defense trade-offs of leaf metabolism. The discovery of biomarkers and the developed predictive model pave the way to understand Quercus robur's susceptibility to herbivore attack and to support forest management, contributing to the preservation of oak forests in Europe.

The Role of Aging and Wind in Inducing Death and/or Growth Reduction in Korean Fir (Abies Koreana Wilson) on Mt. Halla, Korea

The purpose of this study was to investigate the role of strong winds and aging in the death and/or decline in the growth of Korean fir on Mt. Halla in Korea. Bangeoreum (BA-S), Jindalrebat (JD-E), and Youngsil (YS-W) on the southern, eastern, and western slopes of Mt. Halla (ca. 1600 and 1700 m a.s.l.) were selected for the study. The site chronologies were established using more than 10 living Korean firs at each site. Additionally, to date the years and seasons of death of standing/fallen dead Korean firs, 15/15, 14/15, and 10/10 trees were selected at BA-S, JD-E, and YS-W, respectively. After adjusting the age with the period of growth up to the sampling point, the oldest Korean fir found among the living trees was 114 years old at JD-E and the oldest fir among the dead trees was 131 years old at JD-E. Besides this, most of the trees at BA-S and JD-E were found to have died between 2008 and 2015, and at irregular intervals between 1976 and 2013 at YS-W. Also, the maximum number of trees, that is, 62.7% died between spring and summer, followed by 20.9% between summer and autumn, and 16.4% between autumn of the current year and spring of the following year. Abrupt growth reductions occurred at BA-S and JD-E, and have become more significant in recent years, whereas at YS-W, the abrupt growth reduction and recovery occur in a cyclic order. The intensity and frequency of the typhoons increased from 2012, and this trend was in-line with the increased number of abrupt growth reductions at BA-S and JD-E. Therefore, the typhoons of 2012 are considered as the most likely influencing factor in death and/or growth reduction in Korean firs. In contrast, the decline in the growth of the Korean firs located on the windward slope (YS-W) showed a relationship with winds stronger than 25–33 m/s.

Measuring recent effective gene flow among large populations in Pinus sylvestris: Local pollen shedding does not preclude substantial long-distance pollen immigration

The estimation of recent gene flow rates among vast and often weakly genetically differentiated tree populations remains a great challenge. Yet, empirical information would help understanding the interaction between gene flow and local adaptation in present-day non-equilibrium forests. We investigate here recent gene flow rates between two large native Scots pine (Pinus sylvestris L.) populations in central Iberian Peninsula (Spain), which grow on contrasting edaphic conditions six kilometers apart from each other and show substantial quantitative trait divergence in common garden experiments. Using a sample of 1,200 adult and offspring chloroplast-microsatellite haplotypes and a Bayesian inference model, we estimated substantial male gametic gene flow rates (8 and 21%) between the two natural populations, and even greater estimated immigration rates (42 and 64%) from nearby plantations into the two natural populations. Our results suggest that local pollen shedding within large tree populations does not preclude long-distance pollen immigration from large external sources, supporting the role of gene flow as a homogenizing evolutionary force contributing to low molecular genetic differentiation among populations of widely distributed wind-pollinated species. Our results also indicate the high potential for reproductive connectivity in large fragmented populations of wind-pollinated trees, and draw attention to a potential scenario of adaptive genetic divergence in quantitative traits under high gene flow.

Fine-scale spatial genetic structure across the species range reflects recent colonization of high elevation habitats in silver fir (Abies alba Mill.)

Variation in genetic diversity across species ranges has long been recognized as highly informative for assessing populations’ resilience and adaptive potential. The spatial distribution of genetic diversity within populations, referred to as fine‐scale spatial genetic structure (FSGS), also carries information about recent demographic changes, yet it has rarely been connected to range scale processes. We studied eight silver fir (Abies alba Mill.) population pairs (sites), growing at high and low elevations, representative of the main genetic lineages of the species. A total of 1,368 adult trees and 540 seedlings were genotyped using 137 and 116 single nucleotide polymorphisms (SNPs), respectively. Sites revealed a clear east‐west isolation‐by‐distance pattern consistent with the post‐glacial colonization history of the species. Genetic differentiation among sites (F_CT = 0.148) was an order of magnitude greater than between elevations within sites (F_SC = 0.031), nevertheless high elevation populations consistently exhibited a stronger FSGS. Structural equation modelling revealed that elevation and, to a lesser extent, post‐glacial colonization history, but not climatic and habitat variables, were the best predictors of FSGS across populations. These results suggest that high elevation habitats have been colonized more recently across the species range. Additionally, paternity analysis revealed a high reproductive skew among adults and a stronger FSGS in seedlings than in adults, suggesting that FSGS may conserve the signature of demographic changes for several generations. Our results emphasize that spatial patterns of genetic diversity within populations provide information about demographic history complementary to non‐spatial statistics, and could be used for genetic diversity monitoring, especially in forest trees.