THE CHANGING PACE OF INSULAR LIFE: 5000 YEARS OF MICROEVOLUTION IN THE ORKNEY VOLE (MICROTUS ARVALIS ORCADENSIS)

Island evolution may be expected to involve fast initial morphological divergence followed by stasis. We tested this model using the dental phenotype of modern and ancient common voles (Microtus arvalis), introduced onto the Orkney archipelago (Scotland) from continental Europe some 5000 years ago. First, we investigated phenotypic divergence of Orkney and continental European populations and assessed climatic influences. Second, phenotypic differentiation among Orkney populations was tested against geography, time, and neutral genetic patterns. Finally, we examined evolutionary change along a time series for the Orkney Mainland. Molar gigantism and anterior‐lobe hypertrophy evolved rapidly in Orkney voles following introduction, without any transitional forms detected. Founder events and adaptation appear to explain this initial rapid evolution. Idiosyncrasy in dental features among different island populations of Orkney voles is also likely the result of local founder events following Neolithic translocation around the archipelago. However, against our initial expectations, a second marked phenotypic shift occurred between the 4th and 12th centuries AD, associated with increased pastoral farming and introduction of competitors (mice and rats) and terrestrial predators (foxes and cats). These results indicate that human agency can generate a more complex pattern of morphological evolution than might be expected in island rodents.     

岛屿植物舟山新木姜子居群遗传多样性的RAPD分析

基于随机扩增多态 DNA(RAPD)方法分析了舟山群岛濒危植物舟山新木姜子 (N eolitsea sericea) 6个居群的遗传多样性及分化程度。 10条随机引物扩增出 84个可分析位点 ,多态位点百分比 (PPL)为 3 8.10 %。经 POPOGENE分析发现 ,舟山新木姜子居群平均水平的多态位点百分比 (PPL )为 2 3 .18% ,Nei' s基因多样度 (HE)为 0 .0 793 ,Shannon信息指数 (H )为 0 .12 0 1,与其它岛屿植物比较具有中等偏低水平的遗传多样性 ;岛屿各居群间遗传分化程度较高 (Gst=0 .3 646) ;地理距离与遗传距离之间具有显著相关性 (r=0 .7697,P=96.62 % ) ,岛屿隔离效应是导致居群间遗传分化的重要因素。结合居群遗传多样性及UPGMA聚类分析 ,推测普陀山岛舟山新木姜子部分个体可能为大猫岛迁入的后裔 ,而朱家尖岛舟山新木姜子则由人为移植自普陀山岛。基于舟山新木姜子的物种保护及资源利用 ,建议加强现有自然居群的就地保护 ,促进居群自然更新 ;建立种质资源库 ,收集不同岛屿的种源进行混合繁殖 ,促进基因交流 ;选育优良品系用于海岛植被恢复及园林观赏     

Genome architecture enables local adaptation of Atlantic cod despite high connectivity

Adaptation to local conditions is a fundamental process in evolution; however, mechanisms maintaining local adaptation despite high gene flow are still poorly understood. Marine ecosystems provide a wide array of diverse habitats that frequently promote ecological adaptation even in species characterized by strong levels of gene flow. As one example, populations of the marine fish Atlantic cod (Gadus morhua) are highly connected due to immense dispersal capabilities but nevertheless show local adaptation in several key traits. By combining population genomic analyses based on 12K single nucleotide polymorphisms with larval dispersal patterns inferred using a biophysical ocean model, we show that Atlantic cod individuals residing in sheltered estuarine habitats of Scandinavian fjords mainly belong to offshore oceanic populations with considerable connectivity between these diverse ecosystems. Nevertheless, we also find evidence for discrete fjord populations that are genetically differentiated from offshore populations, indicative of local adaptation, the degree of which appears to be influenced by connectivity. Analyses of the genomic architecture reveal a significant overrepresentation of a large ~5 Mb chromosomal rearrangement in fjord cod, previously proposed to comprise genes critical for the survival at low salinities. This suggests that despite considerable connectivity with offshore populations, local adaptation to fjord environments may be enabled by suppression of recombination in the rearranged region. Our study provides new insights into the potential of local adaptation in high gene flow species within fine geographical scales and highlights the importance of genome architecture in analyses of ecological adaptation.     

Biogeography and genetic consequences of anagenetic speciation of Rhaphithamnus venustus (Verbenaceae) in the Juan Fernández archipelago,Chile: insights from AFLP and SSR markers

The genus R haphithamnus (Verbenaceae) consists of two species, one in South America and another endemic to the Juan Fernández archipelago, Chile. The genus represents an example of anagenetic speciation in which the island populations have diverged from their colonizing ancestors to the point where they are recognized as a distinct species. The island species R haphithamnus venustus differs from the continental R . spinosus primarily by floral traits associated with adaptation to hummingbird pollination. Two molecular markers, amplified fragment length polymorphisms (AFLPs) and microsatellites, were used to estimate divergence between the continental and insular species, and to compare diversity in the two species. The comparable or greater diversity in the insular species observed in some diversity indices of AFLPs would support the hypothesis that during the course of anagenetic speciation it has recovered from any reduction of genetic diversity associated with colonization of the archipelago. This pattern of comparable or higher diversity in insular species is seen with other instances of anagenetic speciation in the Juan Fernández archipelago. By contrast, the lower genetic diversity in the insular R . venustus found in microsatellites is likely to be the result of a founder effect from the original colonization of the archipelago; prior molecular studies suggest recent colonization of the Juan Fernández archipelago by R haphithamnus . The seeming non‐concordance between the present results and the widely accepted biogeography of R haphithamnus inferred from other data is discussed and an explanation is presented.     

Genetic structure of house mouse (Mus musculus Linnaeus 1758) populations in the Atlantic archipelago of the Azores: colonization and dispersal

We analyzed the genetic structure and relationships of house mouse (Mus musculus) populations in the remote Atlantic archipelago of the Azores using nuclear sequences and microsatellites. We typed Btk and Zfy2 to confirm that the subspecies Mus musculus domesticus was the predominant genome in the archipelago. Nineteen microsatellite loci (one per autosome) were typed in a total of 380 individuals from all nine Azorean islands, the neighbouring Madeiran archipelago (Madeira and Porto Santo islands), and mainland Portugal. Levels of heterozygosity were high on the islands, arguing against population bottlenecking. The Azorean house mouse populations were differentiated from the Portuguese and Madeiran populations and no evidence of recent migration between the three was obtained. Within the Azores, the Eastern, Western, and Central island groups tended to act as separate genetic units for house mice, with some exceptions. In particular, there was evidence of recent migration events among islands of the Central island group, whose populations were relatively undifferentiated. Santa Maria had genetically distinctive mice, which may relate to its colonization history. © 2013 The Linnean Society of London     

Evolution of an invasive rodent on an archipelago as revealed by molar shape analysis: the house mouse in the Canary Islands

Aim The aim of this paper is to identify the patterns in the morphological differentiation in Canary Island mice, based on fossil and modern samples. In order to achieve this, the mouse species present on the archipelago were first compared with a set of continental mice. The differences between the continental and Canary Island samples, and among the Canary Island samples, provide insights into the processes of colonization and the subsequent insular evolution. Location Canary archipelago. Methods An outline analysis based on Fourier transformation was used to quantify shape differences between lower molars. Together with the fossil and modern Canary Island samples, a reference set of genotyped continental populations of the commensal Mus musculus and the wild Mus spretus was used for comparison. Results The morphometric analysis showed that all the mouse specimens from the Canary Islands and Cape Verde belonged to Mus musculus domesticus. Lower molars of extant mice from La Gomera, El Hierro, Gran Canaria, Tenerife, and to a lesser degree from Lanzarote, were similar to those of genotyped M. m. domesticus from the continent, while teeth of extant mice from Fuerteventura were more divergent. Fossil mice from Fuerteventura were very similar to the extant representatives on this island, and similar to the fossil mice on the nearby islands of Lobos and La Graciosa. Main conclusions The mouse present on the Canary archipelago has been identified as the house mouse M. m. domesticus. Based on the shape of the lower molar, the Canary Island mice are divergent from the continental ones, but the degree of divergence varies with the geography of the archipelago. Overall, populations from eastern islands are more divergent from the continental mice than populations from western ones. Fossil populations indicate that this situation was established several centuries ago. Two main factors may have contributed to this pattern: the appearance of different types of environment on the islands since the successful settlement of the mouse, and/or the number of subsequent introductions of continental individuals via shipping.     

Population genetic structure of the winter moth,Operophtera brumata Linnaeus,in the Orkney Isles suggests long‐distance dispersal

1. The application of population genetic analysis and molecular ecological approaches allows us to examine the invasion of species in the wild. In particular, we can gain an insight into the role of dispersal, a key determinant of the invasion and population dynamics of important pest species. Since the 1980s, severe outbreaks of the winter moth, Operophtera brumata (Linnaeus), have caused extensive damage to heather moorlands in the Orkney Isles. The population genetic structure of O. brumata in Orkney was examined in order to establish whether the widely dispersed outbreaking populations are connected. 2. Amplified fragment length polymorphism (AFLP) analysis showed a high level of genetic diversity within subpopulations. This is consistent with an initial mass colonisation event and/or continuing dispersal between populations of O. brumata in Orkney. 3. Genetic differentiation among populations is low, and although some weak isolation by distance is detectable, no effect of isolation as a result of a sea barrier was found. High gene flow between populations is consistent with the low genetic differentiation observed, although there is evidence to suggest that the populations are not panmictic. 4. Given the limited dispersal of adults, the present results suggest that larvae may disperse over considerable distances by ballooning on strong winds across the Orkney Isles.     

Isolation and biodiversity in Cytisus villosus Pourret (Fabaceae,Genisteae): enzyme polymorphism in disjunct populations

ABSTRACT

The genetic diversity of isolated populations of Cytisus villosus has been studied by means of enzyme polymorphism analysis. Two types of isolated populations were studied: “terrestrial islands” in Sicily, and “true islands” in the Aeolian archipelago. In the populations of “true islands” the number of alleles and the heterozygosity are lower than in “terrestrial islands”. Isolation amongst Sicilian populations seems to be more recent than isolation of the Aeolian populations, and may be attributed to climatic changes which occurred during the Holocene and/or to human activities. The disjunction of the Aeolian populations seems much more recent than the origin of the isles themselves; the colonization of the archipelago is attributed to a single, recent dispersal event not followed by local evolution. In view of the biological structure of the Aeolian populations, C. villosus must be regarded as a locally endangered species.     

Evidence of connectivity between continental and differentiated insular populations in a highly mobile species

Aim Genetically differentiated insular populations are candidates for independent units for conservation. However, occasional immigration to reduced island populations may occur and potentially have important consequences in their future viability and evolutionary potential. In this study, we investigate the conservation implications of population structure and connectivity of insular and continental populations of a migratory raptor as determined using genetic tools and satellite tracking. Location Western European populations in the Iberian Peninsula and two insular populations in the Mediterranean Sea (Balearic Islands) and Atlantic Ocean (Canary Islands). Methods We genotyped 22 microsatellite loci in 96 Egyptian vultures (Neophron percnopterus) from the Iberian Peninsula, 36 from Menorca (Balearic archipelago) and 242 (85% of the current population) from Fuerteventura (Canary Islands). We analysed genetic variation to estimate structure, gene flow, genetic diversity, effective size and recent demographic history of the populations. Additionally, 19 vultures were marked with satellite transmitters to track their migration routes. Results Insular populations were genetically differentiated from those of the mainland. We detected immigration in the insular populations and within the continental counterpart. We found similar levels of genetic variability between the continent and the islands, and a bottleneck analysis indicated recent sharp population declines in both archipelagos but not on the continent. Main conclusions Our study provides evidence that, in spite of significant differentiation, insular populations of highly mobile species may remain connected with the mainland. Conservation programmes should take into account population connectivity and integrate differentiated units of management within complex units of conservation that can best maintain processes and potential for evolutionary change.     

Intra- and interspecific morphological variation in the field mouse species Apodemus argenteus and A. speciosus in the Japanese archipelago: the role of insular isolation and biogeographic gradients

Two species of field mice, Apodemus argenteus and A. speciosus, occur in sympatry across the Japanese archipelago. The inter- and intraspecific patterns of morphological differentiation have been evaluated, using a Fourier analysis of the mandible outline. The relative importance of the effect of insular isolation and latitudinal climatic gradient on the size and shape of the two species was assessed by a comparison of the populations from the large island of Honshu and the surrounding small-island populations. The size variation in A. argenteus is correlated with the climatic gradient whilst the shape variation corresponds mainly to a random differentiation of the small-island populations from a Honshu-like basic morphological pattern. A. speciosus displays increased size on small islands, and its shape variation is related to both the climatic gradient and insularity. Finally, the two species are differentiated by both the size and shape of the mandible across the Japanese archipelago, suggesting that interspecific competition between both species is reduced via niche partitioning. Our results emphasize the importance of insular isolation on shape differentiation, but a part of the morphological differentiation is also related to the latitudinal climatic gradient. Isolation on small islands could have favoured such a response to environmental factors by lowering the gene flow that prevents almost any significant differentiation within Honshu populations.     

Riverscape genomics of a threatened fish across a hydroclimatically heterogeneous river basin

Understanding how natural selection generates and maintains adaptive genetic diversity in heterogeneous environments is key to predicting the evolutionary response of populations to rapid environmental change. Detecting selection in complex spatial environments remains challenging, especially for threatened species where the effects of strong genetic drift may overwhelm signatures of selection. We carried out a basinwide riverscape genomic analysis in the threatened southern pygmy perch (Nannoperca australis), an ecological specialist with low dispersal potential. High‐resolution environmental data and 5162 high‐quality filtered SNPs were used to clarify spatial population structure and to assess footprints of selection associated with a steep hydroclimatic gradient and with human disturbance across the naturally and anthropogenically fragmented Murray–Darling Basin (Australia). Our approach included F_ST outlier tests to define neutral loci, and a combination of spatially explicit genotype–environment association analyses to identify candidate adaptive loci while controlling for the effects of landscape structure and shared population history. We found low levels of genetic diversity and strong neutral population structure consistent with expectations based on spatial stream hierarchy and life history. In contrast, variables related to precipitation and temperature appeared as the most important environmental surrogates for putatively adaptive genetic variation at both regional and local scales. Human disturbance also influenced the variation in candidate loci for adaptation, but only at a local scale. Our study contributes to understanding of adaptive evolution along naturally and anthropogenically fragmented ecosystems. It also offers a tangible example of the potential contributions of landscape genomics for informing in situ and ex situ conservation management of biodiversity.     

Demographic History,Population Structure,and Local Adaptation in Alpine Populations of Cardamine impatiens and Cardamine resedifolia

Species evolution depends on numerous and distinct forces, including demography and natural selection. For example, local adaptation and population structure affect the evolutionary history of species living along environmental clines. This is particularly relevant in plants, which are often characterized by limited dispersal ability and the need to respond to abiotic and biotic stress factors specific to the local environment. Here we study the demographic history and the possible existence of local adaptation in two related species of Brassicaceae, Cardamine impatiens and Cardamine resedifolia, which occupy separate habitats along the elevation gradient. Previous genome-wide analyses revealed the occurrence of distinct selective pressures in the two species, with genes involved in cold response evolving particularly fast in C. resedifolia. In this study we surveyed patterns of molecular evolution and genetic variability in a set of 19 genes, including neutral and candidate genes involved in cold response, across 10 populations each of C. resedifolia and C. impatiens from the Italian Alps (Trentino). We inferred the population structure and demographic history of the two species, and tested the occurrence of signatures of local adaptation in these genes. The results indicate that, despite a slightly higher population differentiation in C. resedifolia than in C. impatiens, both species are only weakly structured and that populations sampled at high altitude experience less gene flow than low-altitude ones. None of the genes showed signatures of positive selection, suggesting that they do not seem to play relevant roles in the current evolutionary processes of adaptation to alpine environments of these species.     

Adaptation and plasticity in insular evolution of the house mouse mandible

Morphometric methods allow the quantification of directions of phenotypic changes and their statistical comparison in a morphometric space. We applied this approach to investigate several candidate factors to explain changes in mandible shape occurring in house mice (Mus musculus domesticus, Mammalia, Rodentia) in Corsica and a nearby islet. The role of niche widening and of the concomitant change in diet was evaluated by comparing the micro‐evolutionary insular change to the macro‐evolutionary difference between omnivorous and herbivorous rodents. Phenotypic plasticity, which may contribute to rapid insular evolution, was assessed by breeding laboratory mice on hard versus soft food. The related change in mandible shape was compared with differences between continental and insular populations. The role of allometry was evaluated by assessing shape change related to size within the continental population and comparing this direction of change with differences on islands. Finally, evolution may be facilitated along the direction of the greatest phenotypic variance. This hypothesis was tested by computing in wild populations vectors corresponding to this direction and by comparing these vectors with those corresponding to estimates of shape changes related to plasticity, micro‐ and macro‐evolutionary processes. In Corsica, the congruence in directions of macro‐ and micro‐evolutionary phenotypic vectors (Corsican/continental mice versus omnivorous/herbivorous rodents) supports the hypothesis of adaptation in mandible shape evolution. By contrast, on the islet, phenotypic divergence follows directions of plastic response to food consistency as well as within‐population allometry. Thus, results suggest differences in the relative importance of processes which may influence rodent mandibular shape depending on the size of the islands they colonized. Faster evolution and plasticity may be more evident in small and often ephemeral populations living on small islands, whereas micro‐evolutionary processes may have enough time and genetic variability to progressively ‘align’ with macro‐evolutionary trends in large populations from big islands.     

Lack of adaptation from standing genetic variation despite the presence of putatively adaptive alleles in introduced sweet vernal grass (Anthoxanthum odoratum)

Population genetic theory predicts that the availability of appropriate standing genetic variation should facilitate rapid evolution when species are introduced to new environments. However, few tests of rapid evolution have been paired with empirical surveys for the presence of previously identified adaptive genetic variants in natural populations. In this study, we examined local adaptation to soil Al toxicity in the introduced range of sweet vernal grass (Anthoxanthum odoratum), and we genotyped populations for the presence of Al tolerance alleles previously identified at the long‐term ecological Park Grass Experiment (PGE, Harpenden, UK) in the species native range. We found that markers associated with Al tolerance at the PGE were present at appreciable frequency in introduced populations. Despite this, there was no strong evidence of local adaptation to soil Al toxicity among populations. Populations demonstrated significantly different intrinsic root growth rates in the absence of Al. This suggests that selection on correlated root growth traits may constrain the ability of populations to evolve significantly different root growth responses to Al. Our results demonstrate that genotype–phenotype associations may differ substantially between the native and introduced parts of a species range and that adaptive alleles from a native species range may not necessarily promote phenotypic differentiation in the introduced range.     

Adaptive gradients and isolation-by-distance with postglacial migration in Picea sitchensis

Fossil pollen records suggest rapid migration of tree species in response to Quaternary climate warming. Long-distance dispersal and high gene flow would facilitate rapid migration, but would initially homogenize variation among populations. However, contemporary clinal variation in adaptive traits along environmental gradients shown in many tree species suggests that local adaptation can occur during rapid migration over just a few generations in interglacial periods. In this study, we compared growth performance and pollen genetic structure among populations to investigate how populations of Sitka spruce (Picea sitchensis) have responded to local selection along the historical migration route. The results suggest strong adaptive divergence among populations (average Q(ST)=0.61), corresponding to climatic gradients. The population genetic structure, determined by microsatellite markers (R(ST)=0.09; F(ST)=0.11), was higher than previous estimates from less polymorphic genetic markers. The significant correlation between geographic and pollen haplotype genetic (R(ST)) distances (r=0.73, P<0.01) indicates that the current genetic structure has been shaped by isolation-by-distance, and has developed in relatively few generations. This suggests relatively limited gene flow among populations on a recent timescale. Gene flow from neighboring populations may have provided genetic diversity to founder populations during rapid migration in the early stages of range expansion. Increased genetic diversity subsequently enhanced the efficiency of local selection, limiting gene flow primarily to among similar environments and facilitating the evolution of adaptive clinal variation along environmental gradients.     

Influence of learning on range expansion and adaptation to novel habitats

Learning has been postulated to ‘drive’ evolution, but its influence on adaptive evolution in heterogeneous environments has not been formally examined. We used a spatially explicit individual‐based model to study the effect of learning on the expansion and adaptation of a species to a novel habitat. Fitness was mediated by a behavioural trait (resource preference), which in turn was determined by both the genotype and learning. Our findings indicate that learning substantially increases the range of parameters under which the species expands and adapts to the novel habitat, particularly if the two habitats are separated by a sharp ecotone (rather than a gradient). However, for a broad range of parameters, learning reduces the degree of genetically‐based local adaptation following the expansion and facilitates maintenance of genetic variation within local populations. Thus, in heterogeneous environments learning may facilitate evolutionary range expansions and maintenance of the potential of local populations to respond to subsequent environmental changes.     

Incipient ecological speciation between successional varieties of a dominant tree involves intrinsic postzygotic isolating barriers

Whereas disruptive selection imposed by heterogeneous environments can lead to the evolution of extrinsic isolating barriers between diverging populations, the evolution of intrinsic postzygotic barriers through divergent selection is less certain. Long‐lived species such as trees may be especially slow to evolve intrinsic isolating barriers. We examined postpollination reproductive isolating barriers below the species boundary, in an ephemeral hybrid zone between two successional varieties of the landscape‐dominant Hawaiian tree, Metrosideros polymorpha, on volcanically active Hawai'i Island. These archipelago‐wide sympatric varieties show the weakest neutral genetic divergence of any taxon pair on Hawai'i Island but significant morphological and ecological differentiation consistent with adaptation to new and old lava flows. Cross‐fertility between varieties was high and included heterosis of F₁ hybrids at the seed germination stage, consistent with a substantial genetic load apparent within varieties through low self‐fertility and a lack of self‐pollen discrimination. However, a partial, but significant, barrier was observed in the form of reduced female and male fertility of hybrids, especially backcross hybrids, consistent with the accumulation of genetic incompatibilities between varieties. These results suggest that partial intrinsic postzygotic barriers can arise through disruptive selection acting on large, hybridizing populations of a long‐lived species.     

MULTIPLE COLONIZATIONS OF ASPLENIUM ADIANTUM-NIGRUM ONTO THE HAWAIIAN ARCHIPELAGO

The extreme isolation and mid-Pacific origin of the Hawaiian archipelago has ensured that all indigenous organisms have arrived via long-distance dispersal or have evolved from successfully colonizing species. Although this isolation has also produced high rates of species endemism in angiosperms (89% or more), that rate in pteridophytes is considerably less (76%). The ratio of native species to the estimated number of original successful colonizing species in angiosperms (3.4) is more than double that for pteridophytes (1.6). One possible explanation for the lower speciation rate in pteridophytes is that populations of these species are more likely to experience interpopulational gene flow because of the great vagility of their wind-dispersed spores. We conducted isozymic surveys of populations from the island of Hawaii of the indigenous allotetraploid species Asplenium adiantum-nigrum, putatively derived from two strictly European diploid taxa. Our data support multiple hybrid origins for the populations surveyed, with a minimum of 3, and possibly as many as 17, discrete hybridization events having produced the genetic diversity observed. Since the parental taxa are not found in Hawaii, each hybrid lineage must have arrived in the archipelago independently of the others. Similar long-distance, repeated dispersal events may be occurring between insular and noninsular populations of other native pteridophytes in Hawaii and in other insular regions of the world, thus contributing to the relatively low rates of speciation and insular endemism in this ancient group of plants.     

Low genetic diversity and local adaptive divergence of Dracaena cambodiana (Liliaceae) populations associated with historical population bottlenecks and natural selection: an endangered long‐lived tree endemic to Hainan Island,China

Historical population bottlenecks and natural selection have important effects on the current genetic diversity and structure of long‐lived trees. Dracaena cambodiana is an endangered, long‐lived tree endemic to Hainan Island, China. Our field investigations showed that only 10 populations remain on Hainan Island and that almost all have been seriously isolated and grow in distinct habitats. A considerable amount of genetic variation at the species level, but little variation at the population level, and a high level of genetic differentiation among the populations with limited gene flow in D. cambodiana were detected using inter‐simple sequence repeat (ISSR) and random amplified polymorphic DNA (RAPD) analyses. No significant correlation was found between genetic diversity and actual population size, as the genetic diversities were similar regardless of population size. The Mantel test revealed that there was no correlation between genetic and geographic distances among the 10 populations. The UPGMA, PCoA and Bayesian analyses showed that local adaptive divergence has occurred among the D. cambodiana populations, which was further supported by habitat‐private fragments. We suggest that the current genetic diversity and population differentiation of D. cambodiana resulted from historical population bottlenecks and natural selection followed by historical isolation. However, the lack of natural regeneration of D. cambodiana indicates that former local adaptations with low genetic diversity may have been genetically weak and are unable to adapt to the current ecological environments.     

Landscape heterogeneity and local adaptation define the spatial genetic structure of Pacific salmon in a pristine environment

Identifying the spatial distribution of genetic variation across the landscape is an essential step in informing species conservation. Comparison of closely related and geographically overlapping species can be particularly useful in cases where landscape may similarly influence genetic structure. Congruent patterns among species highlight the importance that landscape heterogeneity plays in determining genetic structure whereas contrasting patterns emphasize differences in species-specific ecology and life-history or the importance of species-specific adaptation to local environments. We examined the interacting roles of demography and adaptation in determining spatial genetic structure in two closely related and geographically overlapping species in a pristine environment. Using single nucleotide polymorphism (SNP) loci exhibiting both neutral and putative adaptive variation, we evaluated the genetic structure of sockeye salmon in the Copper River, Alaska; these data were compared to existing data for Chinook salmon from the same region. Overall, both species exhibited patterns of isolation by distance; the spatial distribution of populations largely determined the distribution of genetic variation across the landscape. Further, both species exhibited largely congruent patterns of within- and among-population genetic diversity, highlighting the role that landscape heterogeneity and historical processes play in determining spatial genetic structure. Potential adaptive differences among geographically proximate sockeye salmon populations were observed when high F_ST outlier SNPs were evaluated in a landscape genetics context. Results were evaluated in the context of conservation efforts with an emphasis on reproductive isolation, historical processes, and local adaptation.