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Aim: We identified and evaluated general latitudinal trends in genetic diversity within populations of a widespread arctic–alpine plant, Dryas octopetala, to examine the applicability to this species of the dominant hypothesis that intraspecific genetic diversity is highest in the tropics and declines towards the poles. Location: The circumpolar Arctic and northern temperate alpine ranges, with a focus on high altitude mountains at the species lowest latitudinal margin in the Japanese archipelago. Methods: Within-population genetic diversity was assessed using genotypes determined at nine microsatellite loci (n = 489), chloroplast DNA sequences (atpB-rbcL and trnV-ndhC spacers, n = 181) and a nuclear gene sequence (LEAFY, n = 173) of 18 populations, as well as a previously published amplified fragment length polymorphism data-set for 26 populations, across the distributional range of the species. The latitudinal pattern of intra-population genetic diversity was modelled at hemispheric scale to discriminate linear latitudinal and quadratic central-marginal trends in genetic diversity. Population genetic structure was assessed by Bayesian clustering analyses. Results: At hemispheric scale, we identified two interacting effects: a general latitudinal decline in genetic diversity towards the equator and a central–marginal effect, whereby genetic diversity decreases towards the margins of a species' range. This decrease was more marked in low-latitude marginal populations than in high-latitude marginal populations. Populations at the lowest latitudes in the Japanese archipelago showed the lowest level of genetic diversity but exhibited distinctive genetic variation. Main conclusion: The latitudinal decline in genetic diversity within populations of this arctic–alpine plant across its range was opposite to the commonly observed trend. A significant part of the equator-ward latitudinal decline in genetic diversity in this arctic–alpine species may be attributable to a \"sky island\" effect, which played a greater role at low latitudes.

Marine heatwaves (MHWs) caused by anthropogenic climate change are becoming a key driver of change at the ecosystem level. Thermal conditions experienced by marine organisms across their distribution, particularly towards the equator, are likely to approach their physiological limits, resulting in extensive mortality and subsequent changes at the population level. Populations at the margins of their species’ distribution are thought to be more sensitive to climate-induced environmental pressures than central populations, but our understanding of variability in fitness-related physiological traits in trailing versus leading-edge populations is limited. In a laboratory simulation study, we tested whether two leading (Iceland) and two trailing (Spain) peripheral populations of the intertidal macroalga Corallina officinalis display different levels of maximum potential quantum efficiency (Fv/Fm) resilience to current and future winter MHWs scenarios. Our study revealed that ongoing and future local winter MHWs will not negatively affect leading-edge populations of C. officinalis , which exhibited stable photosynthetic efficiency throughout the study. Trailing edge populations showed apositive though non-significant trend in photosynthetic efficiency throughout winter MHWs exposure. Poleward and equatorward populations did not produce significantly different results, with winter MHWs having no negative affect on Fv/Fm of either population. Additionally, we found no long-term regional or population-level influence of a winter MHWs on this species’ photosynthetic efficiency. Thus, we found no statistically significant difference in thermal stress responses between leading and trailing populations. Nonetheless, C. officinalis showed a trend towards higher stress responses in southern than northern populations. Because responses rest on a variety of local population traits, they are difficult to predict based solely on thermal pressures.

We hypothesized that populations of ayu (Plecoglossus altivelis, an ecologically and commercially important fish) living in marginal habitats are under less favorable conditions, and are, thus, more vulnerable to extinction. To test this hypothesis, we analyzed the mitochondrial DNA control region of ayu collected from different localities, including central and marginal populations. The results showed that the ayu populations in southern marginal habitats (Tien Yen River in Vietnam; Yakugachi and Kawauchi Rivers in Amami-Oshima Island) displayed lower genetic diversity (haplotype diversity, h = 0.67; 0.54 and 0.80; nucleotide diversity, π = 0.006, 0.002, and 0.009, respectively) compared to the central populations. The genetic differences were highly significant between the southern marginal and the central populations (Fixation index (FST) values ranged from 0.412 to 0.543). However, ayu populations at the center of their distribution range (Shinano River in Honshu and Hamoji River in Sado Island) and the northern marginal habitats (Yoichi River in Hokkaido and Aonae River in Okushiri Island) exhibited high genetic diversity (h = 1 for all rivers; π = 0.024–0.029). The genetic differences between the populations in the central and northern marginal habitats were not significant (FST values ranged from 0.023 to 0.076). This study suggests that, in ayu, the central-marginal hypothesis is valid in the southern direction but invalid in the northern direction. Urgent conservation is needed for the genetically distinct populations in the degraded southern habitats with severely low genetic diversity.

Aim Marginal tree populations, either those located at the edges of the species' range or in suboptimal environments, are often a valuable genetic resource for biological conservation. However, there is a lack of knowledge about the genetic consequences of population marginality, estimated across entire species' ranges. Our study addresses this gap by providing information about several genetic indicators and their variability in marginal and core populations identified using quantitative marginality indices. Location Southwestern Europe and North Africa. Methods Using 10,185 SNPs across 82 populations of maritime pine ( Pinus pinaster Ait.), a widespread conifer characterised by a fragmented range, we modelled the relationship of seven genetic indicators potentially related to population evolutionary resilience, namely genetic diversity (based on both all SNPs and outlier SNPs), inbreeding, genetic differentiation, recessive genetic load and genomic offset, with population geographical, demo‐historical and ecological marginality (as estimated by nine quantitative indices). Models were constructed for both regional (introducing gene pool as a random factor) and range‐wide spatial scales. Results We showed a trend towards decreasing overall genetic diversity and increasing differentiation with geographic marginality, supporting the centre‐periphery hypothesis (CPH). However, we found no correlation between population inbreeding and marginality, while geographically marginal populations had a lower recessive genetic load (only models without the gene pool effect). Ecologically marginal populations had a higher genomic offset, suggesting higher maladaptation to future climate, albeit some of these populations also had high genetic diversity for climate outliers. Main Conclusions Overall genetic diversity (but not outlier‐based estimates) and differentiation patterns support the CPH. Ecologically marginal populations and those at the southern edge could be more vulnerable to climate change due to higher climate maladaptation, as predicted by genomic offsets, and/or lower potentially adaptive genetic diversity. This risk is exacerbated by typically small effective population sizes and increasing human impact in marginal populations.

Populations occurring at species' range edges can be locally adapted to unique environmental conditions. From a species' perspective, range‐edge environments generally have higher severity and frequency of extreme climatic events relative to the range core. Under future climates, extreme climatic events are predicted to become increasingly important in defining species' distributions. Therefore, range‐edge genotypes that are better adapted to extreme climates relative to core populations may be essential to species' persistence during periods of rapid climate change. We use relatively simple conceptual models to highlight the importance of locally adapted range‐edge populations (leading and trailing edges) for determining the ability of species to persist under future climates. Using trees as an example, we show how locally adapted populations at species' range edges may expand under future climate change and become more common relative to range‐core populations. We also highlight how large‐scale habitat destruction occurring in some geographic areas where many species range edge converge, such as biome boundaries and ecotones (e.g., the arc of deforestation along the rainforest‐cerrado ecotone in the southern Amazonia), can have major implications for global biodiversity. As climate changes, range‐edge populations will play key roles in helping species to maintain or expand their geographic distributions. The loss of these locally adapted range‐edge populations through anthropogenic disturbance is therefore hypothesized to reduce the ability of species to persist in the face of rapid future climate change. We synthesize conservation, biogeographic, genetic, and climate change literature to provide a novel conceptual framework of the disproportionately important role that range‐edge populations will have in determining species' responses to climate change.

Subject-specific and marginal models have been developed for the analysis of longitudinal ordinal data. Subject-specific models often lack a population-average interpretation of the model parameters due to the conditional formulation of random intercepts and slopes. Marginal models frequently lack an underlying distribution for ordinal data, in particular when generalized estimating equations are applied. To overcome these issues, latent variable models underneath the ordinal outcomes with a multivariate logistic distribution can be applied. In this article, we extend the work of O'Brien and Dunson (2004), who studied the multivariate t-distribution with marginal logistic distributions. We use maximum likelihood, instead of a Bayesian approach, and incorporated covariates in the correlation structure, in addition to the mean model. We compared our method with GEE and demonstrated that it performs better than GEE with respect to the fixed effect parameter estimation when the latent variables have an approximately elliptical distribution, and at least as good as GEE for other types of latent variable distributions.

The maintenance of genetic variation is crucial at the margins of a species’ distribution range where plants grow in a suboptimal environment and often put less effort into sexual recruitment. The main focus of this study was on exploring the variation in genetic patterns and plant fitness of the long-lived clonal legume Trifolium alpestre in marginal populations in comparison to the distribution centre with the purpose to plan adequate conservation actions for this species. We used highly variable microsatellite loci to explore genetic patterns in 16 populations of varied size in Trifolium alpestre at the different parts of its range (marginal/central populations in Estonia, Poland and Czechia) of this species. We also studied overall genetic structure and population divergence, and historical and contemporary gene flow within each region. To estimate the potential for sexual reproduction at the marginal and central area, we measured the amount and weight of seeds produced in Estonian and Czech populations. Our study revealed high HE and AR in all studied populations that were unconnected with population size, and the occurrence of unique alleles both in central as well as in marginal northernmost (Estonian) populations. Overall genetic structure reflected the geographical location of populations. Very weak population structure together with high historical migration at the distribution margin imply a past, more continuous occurrence of T. alpestre in the northernmost region. Recent bottlenecks, lowered seed production and lighter seeds in marginal populations point to the local suboptimal conditions and indicate the need to pay more attention to management to prevent loss of genotypes and maintain diverse populations in this region.

Plant's life history can evolve in response to variation in climate spatio‐temporally, but numerous multiple‐species studies overlook species‐specific (especially a foundation species) ecological effects and genetic underpinnings. For a species to successfully invade a region, likely to become a foundation species, life‐history variation of invasive plants exerts considerable ecological and evolutionary impacts on invaded ecosystems. We examined how an invasive foundation plant, Spartina alterniflora, varied in its life history along latitudinal gradient using a common gardens experiment. Two common gardens were located at range boundary in tropical zone and main distribution area of S. alterniflora in temperate zone in China. Within each population/garden, we measured the onset time of three successive phenological stages constituting the reproductive phase and a fitness trait. In the low‐latitude garden with higher temperature, we found that reproductive phase was advanced and its length prolonged compared to the high‐latitude garden. This could possibly due to lower plasticity of maturity time. Additionally, plasticity in the length of the reproductive phase positively related with fitness in the low‐latitude garden. Marginal population from tropic had the lowest plasticity and fitness, and the poor capacity to cope with changing environment may result in reduction of this population. These results reflected genetic divergence in life history of S. alterniflora in China. Our study provided a novel view to test the center–periphery hypothesis by integration across a plant's life history and highlighted the significance in considering evolution. Such insights can help us to understand long‐term ecological consequences of life‐history variation, with implications for plant fitness, species interaction, and ecosystem functions under climate change. The ecological effects of the variation in the plant life history of specific species (e.g., foundation species) and genetic underpinnings therein were rarely studied. We found that geographic populations of invasive Spartina alterniflora had different plasticity in the reproductive phase in response to warming, and the lowest plasticity and fitness of southernmost population may suggest the slowdown of rapid dispersion of S. alterniflora in China. Our study provided a novel view to test the center–periphery hypothesis by integration across a plant's life history.

Areas hosting hotspots of low-latitude marginal populations of cold-adapted plant species could be key areas for understanding geographical attributes that result in refugia during climatic shifts as well as the conservation of genetic diversity in the face of climate change. Low-latitude populations of cold-adapted plants are important because they may harbour the combination of alleles that foster persistence in a warmer climate. Consequently, identification of areas where arctic-alpine, circumpolar and circumboreal species reach the low-latitude ends of their distribution will present a unique opportunity to uncover processes that shaped current biogeographical patterns, as well as prepare for future scenarios. Here, we identify 35 main marginal population hotspots (19 and 16 areas in North America and Europe, respectively) of 183 plant taxa. These hotspots represent areas where southern marginal populations of cold-adapted species co-occur. The identification of hotspots was based on geographic overlap of southernmost locations of the target species, in a 50 × 50 km grid. With a threshold of two species in a single grid cell or in two contiguous cells, the analysis revealed that hotspots are in most cases located in the southern portion of major mountain chains. However, hotspots also occur in lowland areas at high latitudes (Fennoscandia, Alaska, Hudson Bay) which do not necessarily correspond to known cold- or warm-stage refugia (e.g. Alps). Rockies and Sierra Nevada both in California and Spain, Apennines, and the southern Scandes, maintain their hotspot status even with more stringent cut-off thresholds (>3 and >5 species per cell group). From a conservation point of view, our analysis reveals that only a small portion of the hotspots are currently included within protected areas. We discuss the importance of marginal population hotspots to future research on climate change and, finally, outline how conservation strategies can capitalize on the knowledge gained from studying climate change effects on cold-adapted plants.

Context Habitat fragmentation is expected to erode genetic diversity, which instead needs to be preserved for promoting species adaptation to a changing climate. As this expectation has found mixed support in forest trees, consistent results on the genetic consequences of fragmentation requires adequately replicated experimental designs, as well as an explicit assessment of which landscape features, if any, could mitigate its detrimental effects. Objective Evaluating the role of several landscape attributes in buffering the detrimental effects of fragmentation in two metapopulations of silver fir. Methods We genotyped 904 silver fir ( Abies alba Mill.) trees from 18 local populations forming two metapopulations comparable for size and extension in the Apennines, a Mediterranean mountain range. We identified the signatures left by the fragmentation process on the genetic features of silver fir local populations. After removing potentially confounding effects due to different evolutionary histories, we used a multivariate approach for testing the relative effect of demographic, geographic, environmental and topographic factors on genetic features of both metapopulations. Results We found comparable signals of the habitat fragmentation impact on the genetic diversity and structure of both investigated metapopulations. Fragmentation effects were less pronounced in the largest local populations (but not the least isolated), located on gentler slopes with higher soil water availability and lower heat exposure. Conclusions Our results suggest the existence of a set of demographic and environmental factors that could have coherently buffered the detrimental genetic effects of fragmentation in both metapopulations. These findings could be useful to plan landscape restoration for the evolutionary rescue of mixed forests that once characterized Mediterranean mountain ecosystems.