Patterns Of Gene Flow Research Articles

Phylotranscriptomics reveals the reticulate evolutionary history of a widespread diatom species complex.

In contrast to surveys based on a few genes that often provide limited taxonomic resolution, transcriptomes provide a wealth of genomic loci that can resolve relationships among taxonomically challenging lineages. Diatoms are a diverse group of aquatic microalgae that includes important bioindicator species and many such lineages. One example is Nitzschia palea, a widespread species complex with several morphologically defined taxonomic varieties, some of which are critical pollution indicators. Morphological differences among the varieties are subtle and phylogenetic studies based on a few genes fail to resolve their evolutionary relationships. We conducted morphometric and transcriptome analyses of 10 Nitzschia palea strains to resolve the relationships among strains and taxonomic varieties. Nitzschia palea was resolved into three clades, one of which corresponds to a group of strains with narrow linear-lanceolate valves. The other morphological group recovered in the shape outline analysis was not monophyletic and consisted of two clades. Gene-tree concordance analyses and phylogenetic network estimations revealed patterns of incomplete lineage sorting and gene flow between intraspecific lineages. We detected reticulated evolutionary patterns among lineages with different morphologies, resulting in a putative recent hybrid. Our study shows that phylogenomic analyses of unlinked nuclear loci, complemented with morphometrics, can resolve complex evolutionary histories of recently diverged species complexes.

Phylogeographic Structuring of the Kuroshio-Type Prawn Macrobrachium japonicum (Decapoda: Palaemonidae) in Taiwan and Ryukyu Islands

Oceanic currents, biological traits, and geological evidence from historical climate change have shaped the distribution of genetic diversity and demographic history in Macrobrachium japonicum. In this study, we investigated the phylogeographic structures and demographic history of M. japonicum in Taiwan and the Ryukyu Islands by the partial mitochondrial COI gene. The topology of the haplotype minimum-spanning network revealed a star-like structure, which suggested a recent range expansion. With the apparent lack of strong dispersal barriers to gene flow between ocean basins, amphidromous prawns, as marine organisms with larvae of high dispersal abilities, are generally expected to show genetic homogeneity. Divergence data suggested that M. japonicum populations diverged 0.462 ± 0.164 myr. Complex patterns of asymmetrical gene flow indicate that variation in dispersal ability is affected by the dominant Kuroshio Current systems of the Pacific Ocean. Analysis of its demographic history revealed that M. japonicum underwent a decline in size following a recent population expansion based on ABC analysis. Bayesian skyline plot analyses of all populations indicated that the expansion of M. japonicum was estimated to have occurred in 175 Kya and that the effective population size rapidly increased by approximately 50 Kya. The results of this study may offer both practical and theoretical value for the further study of conservation genetics, management, and sustainable resource utilization.

Demography and evolutionary history of grey wolf populations around the Bering Strait.

Glacial and interglacial periods throughout the Pleistocene have been substantial drivers of change in species distributions. Earlier analyses suggested that modern grey wolves (Canis lupus) trace their origin to a single Late Pleistocene Beringian population that expanded east and westwards, starting c. 25,000 years ago (ya). Here, we examined the demographic and phylogeographic histories of extant populations around the Bering Strait with wolves from two inland regions of the Russian Far East (RFE) and one coastal and two inland regions of North‐western North America (NNA), genotyped for 91,327 single nucleotide polymorphisms. Our results indicated that RFE and NNA wolves had a common ancestry until c. 34,400 ya, suggesting that these populations started to diverge before the previously proposed expansion out of Beringia. Coastal and inland NNA populations diverged c. 16,000 ya, concordant with the minimum proposed date for the ecological viability of the migration route along the Pacific Northwest coast. Demographic reconstructions for inland RFE and NNA populations reveal spatial and temporal synchrony, with large historical effective population sizes that declined throughout the Pleistocene, possibly reflecting the influence of broadscale climatic changes across continents. In contrast, coastal NNA wolves displayed a consistently lower effective population size than the inland populations. Differences between the demographic history of inland and coastal wolves may have been driven by multiple ecological factors, including historical gene flow patterns, natural landscape fragmentation, and more recent anthropogenic disturbance.

New Insight into Genetic Structure and Diversity of Scots Pine (Pinus sylvestris L.) Populations in Lithuania Based on Nuclear, Chloroplast and Mitochondrial DNA Markers

We studied the genetic differentiation, structure, and diversity of Scots pine populations in Lithuania based on nuclear, chloroplast microsatellite, and mitochondrial DNA markers. We focused on revealing evolutionary history, country-wide geneflow patterns, and structuring among the Scots pine populations. We genotyped 439 Scots pine individuals of mature age from 23 natural Scots pine stands in Lithuania and used the AMOVA and a set of genetic-clustering methods. The among-population differentiation was weak for nuclear microsatellite loci (nSSRs) (FST = 0.005) but much stronger for cpSSRs (PhiST = 0.240). The populations were structured into highland and lowland populations based on cpSSRs and eastern highland versus the rest for nSSRs. We detected two mtDNA mitotypes—the universal type A and northeastern type B, and the latter occurred at a markedly higher frequency in eastern Lithuania. Within-population genetic diversity was higher in large pine-dominated forest tracts in the eastern highlands than in fragmented forests in the western highlands. We concluded that phenology-based genetic networks following the temperature climate gradients have a strong effect on shaping the genetic structure of otherwise rather homogeneous gene pools of Scots pine populations in Lithuania. The possible effects of human interference with forests on genetic diversity of Scots pine populations in Lithuania are discussed.

Sex-biased admixture and assortative mating shape genetic variation and influence demographic inference in admixed Cabo Verdeans.

Genetic data can provide insights into population history, but first, we must understand the patterns that complex histories leave in genomes. Here, we consider the admixed human population of Cabo Verde to understand the patterns of genetic variation left by social and demographic processes. First settled in the late 1400s, Cabo Verdeans are admixed descendants of Portuguese colonizers and enslaved West African people. We consider Cabo Verde’s well-studied historical record alongside genome-wide SNP data from 563 individuals from 4 regions within the archipelago. We use genetic ancestry to test for patterns of nonrandom mating and sex-specific gene flow, and we examine the consequences of these processes for common demographic inference methods and genetic patterns. Notably, multiple population genetic tools that assume random mating underestimate the timing of admixture, but incorporating nonrandom mating produces estimates more consistent with historical records. We consider how admixture interrupts common summaries of genomic variation such as runs of homozygosity. While summaries of runs of homozygosity may be difficult to interpret in admixed populations, differentiating runs of homozygosity by length class shows that runs of homozygosity reflect historical differences between the islands in their contributions from the source populations and postadmixture population dynamics. Finally, we find higher African ancestry on the X chromosome than on the autosomes, consistent with an excess of European males and African females contributing to the gene pool. Considering these genomic insights into population history in the context of Cabo Verde’s historical record, we can identify how assumptions in genetic models impact inference of population history more broadly.

Alternative Modes of Introgression-Mediated Selection Shaped Crop Adaptation to Novel Climates.

Recent plant genomic studies provide fine-grained details on the evolutionary consequences of adaptive introgression during crop domestication. Modern genomic approaches and analytical methods now make it possible to better separate the introgression signal from the demographic signal thus providing a more comprehensive and complex picture of the role of introgression in local adaptation. Adaptive introgression has been fundamental for crop expansion and has involved complex patterns of gene flow. In addition to providing new and more favorable alleles of large effect, introgression during the early stages of domestication also increased allelic diversity at adaptive loci. Previous studies have largely underestimated the effect of such increased diversity following introgression. Recent genomic studies in wheat, potato, maize, grapevine, and ryegrass show that introgression of multiple genes, of as yet unknown effect, increased the effectiveness of purifying selection, and promoted disruptive or fluctuating selection in early cultivars and landraces. Historical selection processes associated with introgression from crop wild relatives provide an instructive analog for adaptation to current climate change and offer new avenues for crop breeding research that are expected to be instrumental for strengthening food security in the coming years.

The status and role of genetic diversity of trees for the conservation and management of riparian ecosystems: A European experts' perspective

Abstract Riparian vegetation supports high biodiversity providing many services and is, therefore, an important landscape element. Riparian ecosystems are subject to numerous pressures leading to population decline and genetic erosion of riparian plants. This may have cascading effects at various ecosystem levels, including decreasing ecosystem services, so identifying the current status of genetic diversity of riparian tree species is vital to improve the effectiveness of restoration efforts. We aimed to elicit expert views on the status and importance of genetic diversity of tree species, and conservation needs across European riparian ecosystems. Sharing of such information among researchers, managers and policymakers has the potential to enhance ecological restoration and management of riparian ecosystems. We identified experts in riparian genetic resources conservation and management across Europe. These included stakeholders with different perspectives, ranging from researchers to practitioners. We designed a set of questionnaires where our identified experts were asked to answer questions related to the status and conservation of genetic diversity of riparian tree species in their respective countries. Specifically, we asked about societal awareness, legislative tools, good practices and conservation or restoration projects accounting for intraspecific genetic diversity and differentiation of tree species in riparian ecosystems. Questionnaire responses were analysed and discussed in light of the scientific literature to define needs and priorities related to the management and conservation of genetic diversity of riparian tree species. The experts recognized that a combination of in situ and ex situ measures and/or integrative conservation of riparian ecosystems is the most appropriate option for conserving the genetic diversity of riparian tree species. Simultaneous application of conservation measures at the level of priority species, identified by experts, and protection of riparian areas are required. Synthesis and applications. This study revealed the importance of recognizing the ecological processes that shape the genetic diversity of riparian tree species in hydrographic networks (dendritic spatial configuration, specific patterns of gene flow among riparian populations, fragmentation of river by dams) but also the need to overcome socio‐economic barriers, such as lack of policy priority, deficiency in funding and weak legislation framework.

The central Alps comprise a major dispersal barrier between western and eastern populations of two butterfly species

AbstractAimGenetic connectivity and diversity are key components of species' resilience to environmental change. However, the specific factors shaping species' resilience are poorly understood. We here aim to strengthen our understanding of resilience in two butterfly species, by identifying regions of high genetic diversity and barriers to dispersal.LocationEuropean Alps.TaxonCopper butterflies (Lycaena spp.).MethodsWe sampled 21 Lycaena hippothoe and 14 L. virgaureae populations with 18 individuals each in the European Alps. Using 14 and 9 microsatellite markers, respectively, we analysed genetic diversity and population structure (using arlequin, genalex, structure and snmf). We analysed spatial patterns of gene flow and genetic diversity (using an estimated effective migration surface), population demographic history and effective population size (diyabc), habitat suitability (maxent), and isolation by distance, and with resistance (genalex, circuitscape).ResultsWe found higher genetic diversity and a more pronounced genetic structure in L. hippothoe than in L. virgaureae. Both species displayed a major genetic barrier in the central Alps. Western and eastern populations showed the highest genetic diversity in L. hippothoe, but central ones in L. virgaureae. Populations of both species were structured by geodetic distance, and minimum and maximum altitude.Main ConclusionsThe population genetic structure of both Copper butterflies seemed to be strongly affected by population history, demography and geographic features. Valleys and high mountain ridges seem to comprise major dispersal barriers. The high genetic diversity and pronounced population structure found in L. hippothoe seems to be related to a low dispersal ability and closed populations with high local abundances as opposed to L. virgaureae. We suggest that different conservation strategies are needed for these closely related species, focussing on connecting suitable habitats in L. hippothoe and increasing local population sizes in L. virgaureae.

Patterns of gene flow across multiple anthropogenic infrastructures: Insights from a multi-species approach

Large-scale Transportation Infrastructures (LTIs) are among the main determinants of landscape fragmentation, with strong impacts on animal dispersal movements and metapopulation functioning. Although the detection of LTIs impacts is now facilitated by landscape genetic tools, studies are often conducted on a single species, although different species might react differently to the same obstacle. We surveyed four species (a snake, an amphibian, a butterfly and a ground-beetle) in a landscape fragmented by six LTIs: a motorway, a railway, a country road, a gas pipeline, a power line and a secondary road network. We hypothesized that LTIs carrying vehicles would mostly impact ground-dwelling species, possibly in a cumulative way. We showed that half of the overall explained genetic variability across all species was due to LTIs. While the butterfly was seemingly not impacted by any LTI, the genetic structure of the three other species was mostly influenced by roads and motorway. The power line did not affect any species and the gas pipeline only impacted gene flow in the ground-beetle through forest fragmentation, but roads systematically affected at least two species. Interestingly, we also showed that some LTIs could somehow promote gene flow, embankments probably providing favourable habitats for vertebrate species. Considering the high variability in species response to LTIs, we argue that drawing general conclusions on landscape connectivity from the study of a single species may lead to counterproductive mitigation measures and that multi-species approaches should be more systematically considered in conservation planning.

Development of 27 new microsatellite markers for the shanny Lipophrys pholis.

The shanny Lipophrys pholis is an intertidal fish that is widely distributed throughout the Northeast Atlantic. Characterized by limited adult mobility and a long pelagic larval duration, the shanny stands as an ideal model to better understand larval dispersal and connectivity dynamics, which are critical parameters with implications for marine conservation and management. To this aim, we developed 27 highly polymorphic microsatellite markers and characterized a population of 42 individuals, presenting an average allelic diversity of 20.1 alleles per locus and heterozygosity ranging from 0.619 to 1. This set of newly developed microsatellite markers will be useful in providing critical insights into the processes which shape L. pholis gene flow and connectivity patterns and can be used to investigate local parentage lineages.

Population connectivity and genetic offset in the spawning coral Acropora digitifera in Western Australia.

Anthropogenic climate change has caused widespread loss of species biodiversity and ecosystem productivity across the globe, particularly on tropical coral reefs. Predicting the future vulnerability of reef‐building corals, the foundation species of coral reef ecosystems, is crucial for cost‐effective conservation planning in the Anthropocene. In this study, we combine regional population genetic connectivity and seascape analyses to explore patterns of genetic offset (the mismatch of gene–environmental associations under future climate conditions) in Acropora digitifera across 12 degrees of latitude in Western Australia. Our data revealed a pattern of restricted gene flow and limited genetic connectivity among geographically distant reef systems. Environmental association analyses identified a suite of loci strongly associated with the regional temperature variation. These loci helped forecast future genetic offset in gradient forest and generalized dissimilarity models. These analyses predicted pronounced differences in the response of different reef systems in Western Australia to rising temperatures. Under the most optimistic future warming scenario (RCP 2.6), we predicted a general pattern of increasing genetic offset with latitude. Under the extreme climate scenario (RCP 8.5 in 2090–2100), coral populations at the Ningaloo World Heritage Area were predicted to experience a higher mismatch between current allele frequencies and those required to cope with local environmental change, compared to populations in the inshore Kimberley region. The study suggests complex and spatially heterogeneous patterns of climate‐change vulnerability in coral populations across Western Australia, reinforcing the notion that regionally tailored conservation efforts will be most effective at managing coral reef resilience into the future.

Genetic differentiation that is exceptionally high and unexpectedly sensitive to geographic distance in the absence of gene flow: Insights from the genus Eranthis in East Asian regions.

Genetic differentiation between populations is determined by various factors, including gene flow, selection, mutation, and genetic drift. Among these, gene flow is known to counter genetic differentiation. The genus Eranthis, an early flowering perennial herb, can serve as a good model to study genetic differentiation and gene flow due to its easily detectable population characteristics and known reproductive strategies, which can be associated with gene flow patterns. Eranthis populations are typically small and geographically separated from the others. Moreover, previous studies and our own observations suggest that seed and pollen dispersal between Eranthis populations is highly unlikely and therefore, currently, gene flow may not be probable in this genus. Based on these premises, we hypothesized that the genetic differentiation between the Eranthis populations would be significant, and that the genetic differentiation would not sensitively reflect geographic distance in the absence of gene flow. To test these hypotheses, genetic differentiation, genetic distance, isolation by distance, historical gene flow, and bottlenecks were analyzed in four species of this genus. Genetic differentiation was significantly high, and in many cases, extremely high. Moreover, genetic differentiation and geographic distance were positively correlated in most cases. We provide possible explanations for these observations. First, we suggest that the combination of the marker type used in our study (chloroplast microsatellites), genetic drift, and possibly selection might have resulted in the extremely high genetic differentiation observed herein. Additionally, we provide the possibility that genetic distance reflects geographic distance through historical gene flow, or adaptation in the absence of historical gene flow. Nevertheless, our explanations can be more rigorously examined and further refined through additional observations and various population genetic analyses. In particular, we suggest that other accessible populations of the genus Eranthis should be included in future studies to better characterize the intriguing population dynamics of this genus.

Evolution of Plasmid Mobility: Origin and Fate of Conjugative and Nonconjugative Plasmids.

Conjugation drives the horizontal transfer of adaptive traits across prokaryotes. One-fourth of the plasmids encode the functions necessary to conjugate autonomously, the others being eventually mobilizable by conjugation. To understand the evolution of plasmid mobility, we studied plasmid size, gene repertoires, and conjugation-related genes. Plasmid gene repertoires were found to vary rapidly in relation to the evolutionary rate of relaxases, for example, most pairs of plasmids with 95% identical relaxases have fewer than 50% of homologs. Among 249 recent transitions of mobility type, we observed a clear excess of plasmids losing the capacity to conjugate. These transitions are associated with even greater changes in gene repertoires, possibly mediated by transposable elements, including pseudogenization of the conjugation locus, exchange of replicases reducing the problem of incompatibility, and extensive loss of other genes. At the microevolutionary scale of plasmid taxonomy, transitions of mobility type sometimes result in the creation of novel taxonomic units. Interestingly, most transitions from conjugative to mobilizable plasmids seem to be lost in the long term. This suggests a source-sink dynamic, where conjugative plasmids generate nonconjugative plasmids that tend to be poorly adapted and are frequently lost. Still, in some cases, these relaxases seem to have evolved to become efficient at plasmid mobilization in trans, possibly by hijacking multiple conjugative systems. This resulted in specialized relaxases of mobilizable plasmids. In conclusion, the evolution of plasmid mobility is frequent, shapes the patterns of gene flow in bacteria, the dynamics of gene repertoires, and the ecology of plasmids.

Phylogeography of the veined squid, Loligo forbesii, in European waters

The veined squid, Loligo forbesii Steenstrup, 1856, occurs at the European Shelf areas including the Azores and represents a valuable resource for the European commercial fishery in the North East Atlantic. However, very little is known about its population structure and phylogeography. This lack of knowledge also impedes the development of sustainable fishery management for this species. The present study combined the use of two types of markers that retrieve patterns of gene flow in different time spans; the analysis of 16 nuclear microsatellites and sequencing of the mitochondrial cytochrome oxidase subunit I (COI). Whereas the high mutation rate of microsatellites allows the description of recent patterns of connectivity in species, the lower mutation rate of COI provides phylogeographic patterns on a longer timescale. A total of 347 individuals of L. forbesii were investigated from nearly the entire distribution range of the species, including the North East Atlantic Shelf, the Azores and the Mediterranean. Individuals from the Western and Eastern Mediterranean Sea have never been included in a genetic study before. We were able to analyse COI sequences from all 12 sampling areas and define three clades of L. forbesii. Due to our large sampling area, we are presenting 13 COI-haplotypes that were previously unknown. The microsatellite analysis does not include the Azores but three main clades could be identified at the remaining 11 sampling sites. Low FST values indicate gene flow over large geographical distances. However, the genetically significant differences and an additional slight grouping in the microsatellite structure reveal that geographical barriers seem to influence the population structure and reduce gene flow. Furthermore, both markers provide strong evidence that the observed phylogeographic pattern reflects the geographical history of the Azores and the Mediterranean Sea.

The impact of environment on genetic and epigenetic variation in Trifolium pratense populations from two contrasting semi-natural grasslands.

Central European grasslands, such as calcareous grasslands and oat-grass meadows, are characterized by diverse environmental conditions and management regimes. Therefore, we aimed to determine potential differences in genetic and epigenetic variation patterns between the contrasting habitats and to identify the drivers of genetic and epigenetic variation. We investigated the genetic and epigenetic variation of the ecologically variable plant species Trifolium pratense L. applying amplified fragment length polymorphism and methylation-sensitive amplification polymorphism analyses. We observed low levels of genetic and epigenetic differentiation among populations and between habitat types. Genetic and epigenetic variations were not interdependent. Thus, genetic variation was significantly isolated by habitat dissimilarity, whereas epigenetic variation was affected by environment. More specifically, we observed a significant correlation of epigenetic diversity with soil moisture and soil pH (the latter potentially resulting in phosphorus limitation). Genetic variation was, therefore, affected more strongly by habitat-specific environmental conditions induced by land use-related disturbance and gene flow patterns, while epigenetic variation was driven by challenging environmental conditions.

Disentangling the relative roles of geographical and ecological factors in driving genomic variations of a widely distributed bird across a longitudinal gradient

Unraveling geographical modes of speciation processes has been a longstanding topic in biogeography. Divergence can be driven by factors operating on multiple spatial scales, such as geographical distance (isolation by distance, IBD), landscape resistance (isolation by resistance, IBR) and environmental heterogeneity (isolation by environment, IBE). However, it is challenging to assess the relative contributions of such factors, which are usually autocorrelated with each other. On the basis of ~294 K nuclear single‐nucleotide polymorphisms from 53 samples, we integrated population genomics, geographical information and environmental variables to delineate genetic differentiation in the common pheasant Phasianus colchicus across a longitudinal gradient in northern China. Generalized dissimilarity modeling (GDM) was used to analyze the relative importance of IBD, IBR and IBE. We found that the common pheasant in northern China was grouped into six genetic clusters, which was consistent with the taxonomic affinities. Genetic diversity changed along the longitudinal gradient, reaching its lowest level at the eastern edge of the Qinghai–Tibetan Plateau (QTP). The spatial pattern of gene flow suggested that the mountains surrounding the QTP and the mountains in central China have acted as geographical barriers impeding common pheasant dispersal. GDM analysis indicated that environmental heterogeneity is the most important driver explaining the lineage divergence, which supports the IBE model. These results suggest that multiple isolation mechanisms shaped genetic diversity and genomic divergence in this wide‐ranging bird species. Together, our results underscore the importance of leveraging genome‐wide variations and ecological modeling to facilitate a deeper understanding of population divergence processes.

Coping With Dynamism: Phylogenetics and Phylogeographic Analyses Reveal Cryptic Diversity in Heleobia Snails of Atacama Saltpan, Chile

The species that inhabit systems highly affected by anthropic activities usually exhibit this external influence in their gene pool. In this study, we investigated the genetic patterns of populations of Heleobia atacamensis, a freshwater microgastropod endemic to the Atacama Saltpan, a system historically exposed to environmental changes, and currently subjected to conditions associated with metallic and non-metallic mining and other anthropic activities. Molecular analyses based on nuclear and mitochondrial sequences indicate that the saltpan populations are highly fragmented and that the genetic structure is mainly explained by historical geographic isolation, with little influence of contemporary factors. The microsatellite results suggest a moderate genetic diversity and sharp differentiation mediated by isolation by distance. Additionally, despite the high environmental heterogeneity detected and the marked historical dynamism of the region, our data reveal no signs of demographic instability. The patterns of contemporary gene flow suggest a change in the current genetic structure, based on the geographic proximity and specific environmental conditions for each population. Our results, highlight the role of fragmentation as a modulator of genetic diversity, but also suggest that the historical persistence of isolated populations in naturally dynamic environments could explain the apparent demographic stability detected.

The influence of native populations’ genetic history on the reconstruction of invasion routes: the case of a highly invasive aquatic species

Insufficient data on the origins of the first introduced propagule and the initial stages of invasion complicate the reconstruction of a species’ invasion history. Phylogeography of the native area profoundly shapes the genomic patterns of the propagules on which subsequent demographic processes of the invasion are based. Thus, a better understanding of this aspect helps to disentangle native and invasive histories. Here, we used genomic data together with clustering methods, explicit admixture tests combined with ABC models and Machine Learning algorithms, to compare patterns of genetic structure and gene flow of native and introduced populations, and infer the most likely invasion pathways of the highly invasive freshwater fish Pseudorasbora parva. This species is the vector of a novel lethal fungal-like pathogen (Sphaerothecum destruens) that is responsible for the decline of several fish species in Europe. We found that the current genetic structuring in the native range of P. parva has been shaped by waves of gene flow from populations in southern and northern China. Furthermore, our results strongly suggest that the genetic diversity of invasive populations results from recurrent global invasion pathways of admixed native populations. Our study also illustrates how the combination of admixture tests, ABC and Machine Learning can be used to detect high-resolution demographic signatures and reconstruct an integrative biological invasion history.

Landscape genetics of the tropical willow Salix humboldtiana: influence of climate, salinity, and orography in an altitudinal gradient.

Gene flow in riparian ecosystems is influenced by landscape features such as orography, climate, and salinity. The downstream increase in genetic diversity (DIGD) hypothesis states that the unidirectionality of the watercourse causes an accumulation of genetic diversity toward downstream populations, while upstream populations are more structured and less diverse, especially in water-dispersed organisms. We used chloroplast and nuclear microsatellites to characterize genetic diversity, structure, and gene flow patterns among populations of Salix humboldtiana across an elevation and salinity gradient on three rivers (Actopan, Antigua, and Blanco) in Mexico. We used optimization of resistance surface methods to determine whether genetic distances between populations are correlated with landscape features. Positive FIS values evidenced biparental inbreeding in some populations, particularly at higher elevations where lower niche availability constrains colonization and persistence. Four genetic groups were distinguished, corresponding to populations on the Actopan and Antigua rivers and upstream and downstream on the Blanco, but with high admixture between populations on the Actopan and Antigua rivers. Higher gene flow rates were found among proximate populations on the same river than among different rivers. Genetic diversity increased toward the river mouths, in support of the DIGD hypothesis, probably due to greater niche availability and larger population size. Differences among rivers in precipitation patterns and salinity, as well as geographic distance, were significant predictors of gene flow. Our results depict that the DIGD and gene flow patterns in S. humboldtiana result from the complex interaction among physiography, climate, river salinity, and life-history traits of the species.

Highlighted articles for March 2022.

Highlighted articles for March 2022.