Facilitate Gene Flow Research Articles

Permeability of postzygotic barriers: embryology of a partially fertile Epidendrum (Orchidaceae) hybrid.

Hybrid zones offer unique insight into reproductive barriers and plant speciation mechanisms. This study investigated postzygotic reproductive isolation in the natural hybrid Epidendrum × purpureum, which occurs in sympatry with its parent species, Epidendrum denticulatum and E. orchidiflorum. We examined the development of male and female gametophytes and the events leading to seed formation in this hybrid zone. Floral buds and flowers from E. × purpureum individuals were collected at various stages of development. Both self-pollination and backcrosses between hybrids and parental species were performed to follow ovule and seed development up to 60 days after pollination. The material was analysed using optical and confocal microscopy. In most hybrids, microsporogenesis and microgametogenesis occur regularly, forming viable male gametophytes. Non-viable male gametophytes were also observed and are the result of symmetrical mitotic division. The development of the female gametophyte occurs after self-pollination, and proceeds regularly, resulting in a reduced female gametophyte. Embryo development in the parental species occurs without abnormalities, while in backcrosses between hybrids and parental species, most embryos degenerate. Embryo degeneration in the crosses between hybrids can be explained by genetic incompatibilities. The co-occurrence of viable embryos and degenerating embryos in backcrosses between hybrids and parental species point to incomplete postzygotic reproductive barriers between the hybrid and the progenitors. Our findings suggest that E. × purpureum could facilitate gene flow between parental species, as much of its embryological development occurs without abnormalities.

Contrasting the role of historic factors in phylogeograpic patterns in the native Johnny darter (Etheostoma nigrum) and invasive round goby (Neogobius melanostomus) in lower michigan.

Round goby (Neogobius melanostomus) is an invasive fish present in all five Great Lakes and is becoming increasingly common in their tributaries. Johnny darter (Etheostoma nigrum) is a native species that often coexists with N. melanostomus. In this work, historic factors are addressed as a source of genomic variation in study populations of these species. To do this, patterns of variation in the mitochondrial gene NADH dehydrogenase subunit 2 (ND2) were characterized for both species throughout Lower Michigan. Populations of N. melanostomus and E. nigrum were sampled from 17 localities representing both eastern and western basins of Lower Michigan to test the hypothesis that populations differ between the eastern and western basins of the Great Lakes. Neogobius melanostomus populations were largely homogenous with no significant differences detected among populations or between the eastern and western basins. Additionally, N. melanostomus exhibited no evidence of overarching historical genetic structure, consistent with the recent invasion and rapid expansion of this species. Etheostoma nigrum exhibited significant differentiation among local populations; however, similarity among mtDNA haplotypes indicated that differences among populations are recent, suggesting that local forces are a more important factor in shaping patterns of variation than historical factors. Contrary to predictions, there were no significant differences detected between the eastern and western basins of the Great Lakes; however, construction of a neighbor-joining tree with F ST estimates revealed clustering of populations by basin with some anomalies. These anomalies may be the result of recent stream capture events facilitating gene flow between the two basins.

Impact of silvicultural practices on the genetic variations between sugar maple (Acer saccharum Marsh.) stands in the Northern Forest, U.S.A

Tree harvesting practices that enhance genetic diversity are essential for the long-term sustainability of our forests. Using eSSRs, which are markers within expressed genes and thus, potentially subjected to natural selection and reveal adaptive potential, this study examines the effects of selection (SE) and shelterwood (SW) management systems using unmanaged (UM) stands as reference on the genetic diversity of sugar maples in the Northern Forest, USA. Comparison between management types shows no difference between SE and SW, but compared to UM, both have lower allelic richness (AR) while only SE has lower expected heterozygosity (HE). Size class comparison shows that seedlings have higher AR and HE than poles and mature trees. Two-way interactions between management types, size classes, and study stands from each of the four states that comprise the Northern Forest region (Maine, New Hampshire, Vermont and New York) were also examined. Results show that seedlings in UM and SW have higher AR compared to all size classes in SE and poles and mature trees in SW, while only seedlings from SW have higher HE compared to poles and mature trees in SE and SW. Only in Maine was there a difference in AR between SW and SE stands per state. Seedlings in New Hampshire and Maine have higher HE, as well as seedlings and mature trees in New York compared to the poles in New Hampshire and mature trees in Maine. Overall, the results indicate genetic erosion in sugar maple stands in the Northern Forest region. This genetic impact may be due to several factors including the intensity of cutting associated with SE and SW systems and size of the canopy gaps created. Higher seedling genetic diversity in SW compared to SE may be due to their more open stand structure that facilitates gene flow and seedling recruitment. When using SE, longer cutting cycle paired with lower level of residual basal area is recommended. This approach allows for a more open stand structure that could facilitate pollen and seed exchanges from the stands, improving their genetic diversity. In both SE and SW systems, leaving high-quality growing stocks will enhance their genetic diversity and ensure their sustainability. This study increases our awareness of the potential genetic impacts of forest harvesting practices and guides the development of recommendations to alleviate genetic erosion in sugar maple stands.

Whole Genomes Inform Genetic Rescue Strategy for Montane Red Foxes in North America.

A few iconic examples have proven the value of facilitated gene flow for counteracting inbreeding depression and staving off extinction; yet, the practice is often not implemented for fear of causing outbreeding depression. Using genomic sequencing, climatic niche modeling, and demographic reconstruction, we sought to assess the risks and benefits of using translocations as a tool for recovery of endangered montane red fox (Vulpes vulpes) populations in the western United States. We demonstrated elevated inbreeding and homozygosity of deleterious alleles across all populations, but especially those isolated in the Cascade and Sierra Nevada ranges. Consequently, translocations would be expected to increase population growth by masking deleterious recessive alleles. Demographic reconstructions further indicated shallow divergences of less than a few thousand years among montane populations, suggesting low risk of outbreeding depression. These genomic-guided findings set the stage for future management, the documentation of which will provide a roadmap for recovery of other data-deficient taxa.

Hydrographic basins dictate the genetic structure of the paradoxical frog Pseudis bolbodactyla (Anura: Hylidae) in the rivers of Central Brazil

Abstract Rivers are prominent landscape features, acting as key promoters of diversification among freshwater organisms. Albeit generally considered potential barriers to species movement, they may also facilitate gene flow and structure populations of semiaquatic species (Riverine Thruway Hypothesis, RTH). We evaluated the role of rivers on the processes responsible for current genetic variation in the semiaquatic frog Pseudis bolbodactyla, testing whether each hydrographic basin harbours distinct genetic lineages. We sequenced three markers on 166 samples from 13 localities along the Paraná (PR), Araguaia–Tocantins (AT), and São Francisco (SF) River basins in Brazil. We recovered three populations geographically matching each hydrographic basin. Our results indicate migration among basins, with the best model selected using approximate Bayesian computation, including migration between AT and SF and ancient gene flow from PR to the AT–SF ancestor. Our findings are likely related to the orogenic events in Central Brazil dating to the Late Miocene (5 Mya), when hydrographic basins and the geomorphological features of the Brazilian Shield were formed. This suggests that P. bolbodactyla probably represents a species complex, with each lineage occurring in a distinct hydrographic basin, matching the predictions of the RTH.

Moving to mate? Migration strategy does not predict genetic structure or diversity in bats (Chiroptera)

Abstract How, when, and where animals move during mating periods directs gene-flow patterns across landscapes. Traits associated with movement, such as movement ability and migratory behaviour, are sometimes correlated with population genetic structure, but this relationship depends on where and when mating occurs relative to annual movements. With their wide diversity in behaviours and life-history strategies, bats provide a testing ground for hypotheses about population structure related to migration and mating. We used a global sample of microsatellite data (N = 233 sampling locations from 17 bat species) associated with published studies to examine links between genetic variation and short-distance, long-distance, or non-migratory strategies that also relate to varied mating strategies. The genetic measures we tested were population-specific differentiation, gene diversity, and allelic richness. Using Bayesian models that accounted for phylogenetic distances among species and spatial autocorrelation, we identified no correlations between migration strategy and genetic variation. Our results suggest that hypotheses about genetic structure being mediated by migration might not hold, in general, for bat species. We discuss the need for continued research into the complex association of ecological, biogeographical, and behavioural factors that facilitate gene flow among populations, especially in species with diverse movement patterns.

Climatic fluctuations, geographic features, and evolutionary forces: Shaping high genomic diversity and local adaptation in Muntiacus reevesi

AbstractAimGenetic diversity is crucial for species adaptability. Understanding the mechanisms behind its formation and maintenance is essential for effective conservation. Recent studies have demonstrated that despite experiencing severe population bottlenecks, Muntiacus reevesi retains high genetic diversity and continues its northward migration, indicative of ongoing adaptive evolution. However, our comprehension of this phenomenon remains incomplete. The objective of this study is to explore the mechanisms underlying the formation of high genetic diversity and the genomic characteristics associated with local adaptation, using M. reevesi as a case study.LocationSouthern China.MethodsWe analysed resequencing data from 62 genomes and identified 29,124,081 high‐quality single‐nucleotide polymorphisms (SNPs). We used population genetics, demographic history, population differentiation, gene flow analysis software, and genotype‐environment association (GEA) models to assess the factors that have contributed to high genetic diversity and environmental adaptability in the historical climate and geographical context.ResultsThe study identified that during Pleistocene climatic fluctuations, M. reevesi diverged into eastern (DB and WJW populations) and western lineages (WL, BA, and QL populations), all displayed high genetic diversity. Historically, M. reevesi maintained large effective populations, but contemporary human‐induced threats have led to a significant decline. Population differentiation models suggest distinct expansion pathways for eastern and western lineages, resulting in population admixture, with mountain corridors facilitating gene flow and maintaining high genetic diversity. Additionally, environmental‐genotype analysis revealed local adaptation in the QL‐BA population, highlighting candidate adaptive genes (ME3 and PRKG1) potentially linked to cold adaptation and foraging behaviour.ConclusionThis study enhances our understanding of the mechanisms behind the high genetic diversity and environmental adaptability of M. reevesi, offering insights into how bottleneck populations maintain diversity, crucial for biogeographic research and conservation strategies for similar species.

Genetic divergence and one-way gene flow influence contemporary evolution and ecology of a partially migratory fish.

Recent work has revealed the importance of contemporary evolution in shaping ecological outcomes. In particular, rapid evolutionary divergence between populations has been shown to impact the ecology of populations, communities, and ecosystems. While studies have focused largely on the role of adaptive divergence in generating ecologically important variation among populations, much less is known about the role of gene flow in shaping ecological outcomes. After divergence, populations may continue to interact through gene flow, which may influence evolutionary and ecological processes. Here, we investigate the role of gene flow in shaping the contemporary evolution and ecology of recently diverged populations of anadromous steelhead and resident rainbow trout (Oncorhynchus mykiss). Results show that resident rainbow trout introduced above waterfalls have diverged evolutionarily from downstream anadromous steelhead, which were the source of introductions. However, the movement of fish from above to below the waterfalls has facilitated gene flow, which has reshaped genetic and phenotypic variation in the anadromous source population. In particular, gene flow has led to an increased frequency of residency, which in turn has altered population density, size structure, and sex ratio. This result establishes gene flow as a contemporary evolutionary process that can have important ecological outcomes. From a management perspective, anadromous steelhead are generally regarded as a higher conservation priority than resident rainbow trout, even when found within the same watershed. Our results show that anadromous and resident O. mykiss populations may be connected via gene flow, with important ecological consequences. Such eco-evolutionary processes should be considered when managing recently diverged populations connected by gene flow.

Phylogenomics, Lineage Diversification Rates, and the Evolution of Diadromy in Clupeiformes (Anchovies, Herrings, Sardines, and Relatives).

Migration independently evolved numerous times in animals, with a myriad of ecological and evolutionary implications. In fishes, perhaps the most extreme form of migration is diadromy, the migration between marine and freshwater environments. Key and long-standing questions are: how many times has diadromy evolved in fishes, how frequently do diadromous clades give rise to non-diadromous species, and does diadromy influence lineage diversification rates? Many diadromous fishes have large geographic ranges with constituent populations that use isolated freshwater habitats. This may limit gene flow between some populations, increasing the likelihood of speciation in diadromous lineages relative to nondiadromous lineages. Alternatively, diadromy may reduce lineage diversification rates if migration is associated with enhanced dispersal capacity that facilitates gene flow within and between populations. Clupeiformes (herrings, sardines, shads, and anchovies) is a model clade for testing hypotheses about the evolution of diadromy because it includes an exceptionally high proportion of diadromous species and several independent evolutionary origins of diadromy. However, relationships among major clupeiform lineages remain unresolved, and existing phylogenies sparsely sampled diadromous species, limiting the resolution of phylogenetically informed statistical analyses. We assembled a phylogenomic dataset and used multi-species coalescent and concatenation-based approaches to generate the most comprehensive, highly resolved clupeiform phylogeny to date, clarifying associations among several major clades and identifying recalcitrant relationships needing further examination. We determined that variation in rates of sequence evolution (heterotachy) and base-composition (nonstationarity) had little impact on our results. Using this phylogeny, we characterized evolutionary patterns of diadromy and tested for differences in lineage diversification rates between diadromous, marine, and freshwater lineages. We identified 13 transitions to diadromy, all during the Cenozoic Era (10 origins of anadromy, 2 origins of catadromy, and 1 origin of amphidromy), and 7 losses of diadromy. Two diadromous lineages rapidly generated nondiadromous species, demonstrating that diadromy is not an evolutionary dead end. We discovered considerably faster transition rates out of diadromy than to diadromy. The largest lineage diversification rate increase in Clupeiformes was associated with a transition to diadromy, but we uncovered little statistical support for categorically faster lineage diversification rates in diadromous versus nondiadromous fishes. We propose that diadromy may increase the potential for accelerated lineage diversification, particularly in species that migrate long distances. However, this potential may only be realized in certain biogeographic contexts, such as when diadromy allows access to ecosystems in which there is limited competition from incumbent species.

Seasonal migration directs and facilitates gene flow in the Broad-tailed and Lucifer Sheartail Hummingbirds

Gene flow, the movement of genes between populations, profoundly influences genetic and phenotypic homogeneity among populations. This study investigates gene flow patterns in two migratory hummingbird species, Selasphorus platycercus and Calothorax lucifer, shedding light on the intricate interplay between migration, resource availability, and genetic diversity. Using previously published information on microsatellites, we examine the genetic makeup and the movement of genes within populations. Selasphorus platycercus displays distinct genetic groups which can be associated with its migratory behaviour. Gene flow analysis suggests a higher level of connectivity among populations sharing winter ranges. In contrast, Calothorax lucifer populations exhibit genetic divergence despite overlapping winter ranges, possibly due to environmental niche adaptation and limited reproductive opportunities for dispersing individuals. While geographical distance does not explain genetic differentiation in these species, environmental niche similarities appear to facilitate gene flow. This study underscores the significance of migratory routes, resource availability, and niche adaptation in shaping gene flow dynamics in hummingbirds. Understanding these dynamics is crucial for the conservation and management of these unique avian populations.

How Important Is Variation in Extrinsic Reproductive Isolation to the Process of Speciation?

The strength of reproductive isolation (RI) between two or more lineages during the process of speciation can vary by the ecological conditions. However, most speciation research has been limited to studying how ecologically dependent RI varies among a handful of broadly categorized environments. Very few studies consider the variability of RI and its effects on speciation at finer scales-that is, within each environment due to spatial or temporal environmental heterogeneity. Such variation in RI across time and/or space may inhibit speciation through leaky reproductive barriers or promote speciation by facilitating reinforcement. To investigate this overlooked aspect of speciation research, we conducted a literature review of existing studies of variation in RI in the field and then conducted individual-based simulations to examine how variation in hybrid fitness across time and space affects the degree of gene flow. Our simulations indicate that the presence of variation in hybrid fitness across space and time often leads to an increase in gene flow compared to scenarios where hybrid fitness remains static. This observation can be attributed to the convex relationship between the degree of gene flow and the strength of selection on hybrids. Our simulations also show that the effect of variation in RI on facilitating gene flow is most pronounced when RI, on average, is relatively low. This finding suggests that it could serve as an important mechanism to explain why the completion of speciation is often challenging. While direct empirical evidence documenting variation in extrinsic RI is limited, we contend that it is a prevalent yet underexplored phenomenon. We support this argument by proposing common scenarios in which RI is likely to exhibit variability and thus influence the process of speciation.

Impact of reproduction on roost selection of the Indian flying fox, Pteropus medius (Temminck, 1825)

A thorough knowledge of ecology and behaviour is a clear requirement for proper conservation and management of a species. The Indian flying fox, Pteropus medius (formerly P. giganteus Brünnich, 1782), lives gregariously in large trees and spends a considerable time at day roosts. The roost sites play vital roles in survival, reproduction and population persistence. This study describes changes in roost selection, colony size and behaviours of P. medius during reproductive and non-reproductive seasons in a large colony at Mohanlal Ganj, Lucknow (India). The colony size was significantly lower during the summer non-reproductive season (486.5 ± 121.1 SD) than during the spring (1942 ± 488.8 SD) and monsoon (2367.7 ± 277 SD) reproductive seasons. The number of roost trees utilised and roost site selection differed across the reproductive and non-reproductive seasons. The bats occupied the southern periphery of the sampled garden during the non-reproductive period (summer), whereas they shifted to the central and northern parts of the garden during the reproductive seasons and winter periods. The reproductively active individuals secluded themselves from the reproductively inactive colony members. The selection of secluded roost sites during the reproductive period demonstrates the need for social exclusion, less disturbance, and reduced mate competition. The higher population size during the reproductive period might be due to the immigration of bats, most probably male individuals, facilitating gene flow from nearby populations and thus increasing genetic diversity and species resilience.

Beyond color and pattern: elucidating the factors associated with intraspecific aggression in the mimic poison frog (Ranitomeya imitator)

Assortative or disassortative aggression – when individuals display more aggression towards conspecifics with similar or different phenotypic characteristics – can either maintain polymorphisms or facilitate gene flow between populations depending on which direction the aggression is aimed. Deciphering which factors elicit or prevent aggression is crucial to improving our knowledge of the origin and maintenance of reproductive barriers and subsequent speciation. The Peruvian mimic poison frog, Ranitomeya imitator, is a monogamous and territorial species that has evolved into four distinct color-pattern morphs in a mimetic radiation. Here we use historical landscape genetic data and competition trials between male individuals sourced from different populations and color-pattern morphs to show that the level of aggression between individuals is not associated with color morph or body size but rather with source population. Individuals spent more time in combat with individuals from their own deme (genetically homogeneous population), irrespective of color morph or size. These findings indicate that genotypic similarity is correlated with increased aggression in R. imitator, though the mechanism by which R. imitator males identify conspecifics as territorial threats remains unclear. As body size and color morph were not significantly associated with aggression levels, this study emphasizes the necessity of further research to identify whether other phenotypic traits are influencing territorial behavior between male frogs, and if these factors play a role in increasing gene flow, or conversely, the formation of reproductive barriers between populations.

First successful artificial insemination of the endangered Louisiana pinesnake, Pituophis ruthveni.

The Louisiana pinesnake (Pituophis ruthveni) is considered one of the rarest snakes in North America and was federally listed under the Endangered Species Act in 2018. Captive breeding and reintroduction of zoo-bred hatchlings has been successful, however, limited founders in the captive population and the inability to bring new, wild genes into the captive colony presents a major concern for the conservation of this species. The use of artificial insemination (AI) was first applied to snakes in the 1980s but further development of the technique has since received little attention. Our goal was to develop a method of AI for use in breeding Louisiana pinesnakes to facilitate gene flow from wild to captive populations. We inseminated two captive Louisiana pinesnakes with semen collected from one donor male, novel to both females. Timing of AI occurred following the emergence of females from brumation, and when large, distinct follicles were detected using digital palpation. Females were inseminated four and five times over a period of 14 and 19 days, respectively, using fresh and 2-day refrigerator stored semen. One female laid seven eggs, which resulted in four fertile eggs and two viable hatchlings, while the second female produced three fertile of seven eggs laid but no viable hatchlings. Genetic analyses confirmed the donor male was the sire of hatchlings. This is the first successful AI of an endangered snake species and provides a framework for the use and optimization of assisted reproductive technologies for use in conservation breeding programs.

River Drainage Reorganization and Reticulate Evolution in the Two-Lined Salamander (Eurycea bislineata) Species Complex.

The origin and eventual loss of biogeographic barriers can create alternating periods of allopatry and secondary contact, facilitating gene flow among distinct metapopulations and generating reticulate evolutionary histories that are not adequately described by a bifurcating evolutionary tree. One such example may exist in the two-lined salamander (Eurycea bislineata) species complex, where discordance among morphological and molecular datasets has created a "vexing taxonomic challenge." Previous phylogeographic analyses of mitochondrial DNA (mtDNA) suggested that the reorganization of Miocene paleodrainages drove vicariance and dispersal, but the inherent limitations of a single-locus dataset precluded the evaluation of subsequent gene flow. Here, we generate triple-enzyme restriction site-associated DNA sequencing (3RAD) data for > 100 individuals representing all major mtDNA lineages and use a suite of complementary methods to demonstrate that discordance among earlier datasets is best explained by a reticulate evolutionary history influenced by river drainage reorganization. Systematics of such groups should acknowledge these complex histories and relationships that are not strictly hierarchical. [Amphibian; hybridization; introgression; Plethodontidae; stream capture.].

Evolutionarily labile dispersal behavior and discontinuous habitats enhance population differentiation in island versus continentally distributed swallows.

The causes of population divergence in vagile groups remain a paradox in evolutionary biology: dispersive species should be able to colonize new areas, a prerequisite for allopatric speciation, but dispersal also facilitates gene flow, which erodes population differentiation. Strong dispersal ability has been suggested to enhance divergence in patchy habitats and inhibit divergence in continuous landscapes, but empirical support for this hypothesis is lacking. Here we compared patterns of population divergence in a dispersive clade of swallows distributed across both patchy and continuous habitats. The Pacific Swallow (Hirundo tahitica) has an insular distribution throughout Southeast Asia and the Pacific, while its sister species, the Welcome Swallow (H. neoxena), has a continental distribution in Australia. We used whole-genome data to demonstrate strong genetic structure and limited introgression among insular populations, but not among continental populations. Demographic models show that historic changes in habitat connectivity have contributed to population structure within the clade. Swallows appear to exhibit evolutionarily labile dispersal behavior in which they reduce dispersal propensity after island colonization despite retaining strong flight ability. Our data support the hypothesis that fragmented habitats enhance population differentiation in vagile groups, and suggest that labile dispersal behavior is a key mechanism underlying this pattern.

Multiscale landscape genetic analysis identifies major waterways as a barrier to dispersal of feral pigs in north Queensland, Australia.

Feral pigs (Sus scrofa) are a destructive and widespread invasive pest in Australia. An understanding of feral pig movement is required to develop management strategies to control feral pigs in Australia. Because landscape structure can have a strong influence on animal movement, it is important to determine how landscape features facilitate or impede the movement of feral pigs. Consequently, we conducted a landscape genetic analysis of feral pig populations in the Herbert region of far north Queensland, Australia, to determine management units and provide recommendations to better inform feral pig population control strategies. Using microsatellite data obtained from 256 feral pig samples from 44 sites, we examined feral pig population structure at multiple spatial scales for univariate and multivariate landscape resistance surfaces to determine the optimal spatial scale and to identify which of the nine landscape features tested impede or facilitate feral pig gene flow. Only weak genetic structure was found among the 44 sampling sites, but major waterways were identified as a minor barrier to gene flow, and an isolation by distance model was supported. We also found that highways facilitated gene flow across the study area, and this suggests that they may act as movement corridors or indicate translocation of feral pigs. Additionally, incorporating a second spatial scale enhanced the ability of our landscape genetics analysis to detect the influence of landscape structure on gene flow. We identified three management units based on natural barriers to gene flow and future targeted control should be undertaken in these management units to deliver sustained reduction of feral pig populations in the Herbert region. This study demonstrates how a landscape genetic approach can be used to gain insight into the ecology of an invasive pest species and be used to develop population control strategies which utilise natural barriers to movement.

Inferring landscape factors driving microgeographic genetic structure of large-sized mountain ungulates: A case of Alashan red deer (Cervus elaphus alxaicus)

Gene flow is crucial for maintaining population genetic diversity and increasing the adaptive potential of species. Therefore, identifying factors affecting gene flow is important for conservation planning, especially for threatened mammals in complex mountain system. In this study, we conducted a microgeographic-scale landscape genetic analysis for the endangered and ecologically isolated Alashan red deer (Cervus elaphus alxaicus) for the first time. Using data from 329 individuals for 11 microsatellite loci, we assessed how the environmental factors in the Chinese Helan Mountains affect the gene flow of this species. Three genetic clusters were identified by both Bayesian (STRUCTURE and GENELAND) and non-Bayesian (DAPC) methods, revealing clear spatial genetic structure within a limited geographic range. Landscape genetic analysis based on causal modelling and linear mixed-effect modelling revealed that gene flow was primarily restricted by topographic factors, including topographic complexity, aspect, altitude and slope, rather than geographical distance or anthropogenic barriers. Based on these results, we identified two important corridors that can potentially facilitate gene flow within the complex landscape of the Helan Mountains. Our results highlight the role of natural landscape features on Alashan red deer's population genetic structure and functional connectivity. This differs from findings regarding red deer populations in other regions, indicating that landscape genetic patterns are not homogenous across the range of a species, but rather differ among specific landscapes.

Long-term genetic monitoring of a reintroduced Eurasian lynx population does not indicate an ongoing loss of genetic diversity

Where reintroduced wildlife populations are considered as vulnerable this is generally due to limited founder size and isolation. While many of these populations show low levels of genetic diversity, little is known about the temporal patterns of genetic diversity loss and the role of initial founder effects vs. ongoing genetic drift. Here we analysed genotype data from 582 Eurasian lynx samples from the reintroduced Bohemian-Bavarian-Austrian population (BBA) over a time span of 35 years, representing approximately 13 generations. Two-wave reintroduction of lynx from at least two distinct West-Carpathian areas resulted in relatively high start-up of genetic diversity. After the initial decline when the population lost about a quarter of its genetic diversity compared to the Carpathian source population, the genetic diversity and effective population size remained almost unchanged over the next 20 years. Despite confirmed isolation of BBA and thus absence of gene flow, we detected relatively low inbreeding during the two recent decades within the slightly increasing population size, which may have prevented ongoing loss of genetic diversity. Given the current status of BBA, we do not support genetic reinforcement to maintain its long-term viability; but urge the importance of facilitating gene flow with neighbouring lynx populations through an improvement of landscape connectivity and by strengthening law enforcement as well as the prevention of illegal killings. A sound genetic monitoring alongside regular camera trap-based monitoring of population size, health status and reproduction is pivotal to decide on future conservation interventions. The genotype data are available within the supplementary material of this article.

Floral and genetic divergence across environmental gradients is moderated by inter-population gene flow in Platanthera dilatata (Orchidaceae)

Understanding how natural selection acts on intraspecific variation to bring about phenotypic divergence is critical to understanding processes of evolutionary diversification. The orchid family is well known for pollinator-mediated selection of floral phenotypes operating among species and along environmental or geographic gradients. Its effectiveness at small spatial scales is less understood, making the geographic scale at which intraspecific floral variation is examined important to evaluating causes of phenotypic divergence. In this study, we quantified phenotypic variation in the orchid Platanthera dilatata across 26 populations in coastal Southeast Alaska and compared this to edaphic and genetic variation at microsatellite loci. We sought to determine (1) if flower morphological variation is structured at smaller geographic scales, (2) the extent of genetic divergence in relation to phenotypic divergence, (3) the scale at which inter-population gene flow occurs, and (4) the relative importance of geographic distance and abiotic factors on population genetic structure. Two morphological groups were found to separate based on lip and spur length and are restricted to different habitats. Small-flowered forms occur in muskeg bogs, whereas large-flowered forms occur in fens and meadows, and rarely in sub-alpine habitat. Genetic analyses were concordant with the morphological clusters, except for four small-flowered populations that were genetically indistinguishable from large-flowered populations and considered to be introgressed. In fact, most populations exhibited some admixture, indicating incomplete reproductive isolation between the flower forms. Pollinators may partition phenotypes but also facilitate gene flow because short-tongued Noctuidae moths pollinate both phenotypes, but longer-tongued hawkmoths were only observed pollinating the large-flowered phenotype, which may strengthen phenotypic divergence. Nevertheless, pollinator movement between habitats could have lasting effects on neutral genetic variation. At this small spatial scale, population genetic structure is only associated with environmental distance, likely due to extensive seed and pollinator movement. While this study corroborates previous findings of cryptic genetic lineages and phenotypic divergence in P. dilatata, the small scale of examination provided greater understanding of the factors that may underlie divergence.