Reduced Gene Flow Research Articles

Complex genetic patterns and distribution limits mediated by native congeners of the worldwide invasive red-eared slider turtle.

Non-native (invasive) species offer a unique opportunity to study the geographical distribution and range limits of species, wherein the evolutionary change driven by interspecific interactions between native and non-native closely related species is a key component. The red-eared slider turtle, Trachemys scripta elegans (TSE), has been introduced and successfully established worldwide. It can coexist with its native congeners T.cataspila, T.venusta and T.taylori in Mexico. We performed comprehensive fieldwork, executed a battery of genetic analyses and applied a novel species distribution modelling approach to evaluate their historical lineage relationships and contemporary population genetic patterns. Our findings support the historical common ancestry between native TSE and non-native (TSEalien ), while also highlighting the genetic differentiation of the exotic lineage. Genetic patterns are associated with their range size/endemism gradient; the microendemic T.taylori showed significant reduced genetic diversity and high differentiation, whereas TSEalien showed the highest diversity and signals of population size expansion. Counter to our expectations, lower naturally occurring distribution overlap and little admixture patterns were found between TSE and its congeners, exhibiting reduced gene flow and clear genetic separation across neighbouring species despite having zones of contact. We demonstrate that these native Trachemys species have distinct climatic niche suitability, probably preventing establishment of and displacement by the TSEalien . Moreover, we found major niche overlap between TSEalien and native species worldwide, supporting our prediction that sites with closer ecological optima to the invasive species have higher establishment risk than those that are closer to the niche-centre of the native species.

The role of mitonuclear incompatibilities in allopatric speciation.

Aerobic metabolism in eukaryotic cells requires extensive interactions between products of the nuclear and mitochondrial genomes. Rapid evolution of the mitochondrial genome, including fixation of both adaptive and deleterious mutations, creates intrinsic selection pressures favoring nuclear gene mutations that maintain mitochondrial function. As this process occurs independently in allopatry, the resulting divergence between conspecific populations can subsequently be manifest in mitonuclear incompatibilities in inter-population hybrids. Such incompatibilities, mitonuclear versions of Bateson-Dobzhansky-Muller incompatibilities that form the standard model for allopatric speciation, can potentially restrict gene flow between populations, ultimately resulting in varying degrees of reproductive isolation. The potential role of mitonuclear incompatibilities in speciation is further enhanced where mtDNA substitution rates are elevated compared to the nuclear genome and where population structure maintains allopatry for adequate time to evolve multiple mitonuclear incompatibilities. However, the fact that mitochondrial introgression occurs across species boundaries has raised questions regarding the efficacy of mitonuclear incompatibilities in reducing gene flow. Several scenarios now appear to satisfactorily explain this phenomenon, including cases where differences in mtDNA genetic load may drive introgression or where co-introgression of coadapted nuclear genes may support the function of introgressed mtDNA. Although asymmetries in reproductive isolation between taxa are consistent with mitonuclear incompatibilities, interactions between autosomes and sex chromosomes yield similar predictions that are difficult to disentangle. With regard to establishing reproductive isolation while in allopatry, existing studies clearly suggest that mitonuclear incompatibilities can contribute to the evolution of barriers to gene flow. However, there is to date relatively little definitive evidence supporting a primary role for mitonuclear incompatibilities in the speciation process.

Evolutionary neuroecology of olfactory‐mediated sexual communication and host specialization in Drosophila – a review

AbstractIn humans, finding a partner is quite a difficult task because there are many criteria that one needs to consider. However, in comparison to many animals, when choosing a partner, we easily discriminate between ourselves and members of other species through various communication systems. On the contrary, many fly species (Diptera) are morphologically similar and overlap in their geographical distributions and ecological habitats. Sexual interactions of most drosophilid flies occur on their hosts. Therefore, flies rely on olfactory sex pheromones, as well as on non‐pheromonal chemicals such as host volatiles – which guide and restrict the search for conspecifics within limited locations – as honest signals for pre‐mating reproductive isolation. A subtle divergence in the perception of these signals can lead to accumulated changes among populations of the same species, and ultimately to a reduction in gene flow and reproductive isolation. In recent years, we have seen an increased interest in how olfactory systems diverge to drive host adaptation and speciation. In this review, we discuss the evolutionary changes of the neural circuits that underlie mate recognition. We shed light onto sex pheromone communication systems, the construction of olfactory nervous systems, and the role of host specialization in reproductive isolation. Finally, leveraging the incipient speciation of Drosophila mojavensis Patterson populations, we highlight the underlying sensory mechanisms of the reproductive isolation barriers. In the end, we propose future research topics of the evolutionary neuroecology field of sexual communication.

The first steps toward a global pandemic: Reconstructing the demographic history of parasite host switches in its native range.

Host switching allows parasites to expand their niches. However, successful switching may require suites of adaptations and also may decrease performance on the old host. As a result, reductions in gene flow accompany many host switches, driving speciation. Because host switches tend to be rapid, it is difficult to study them in real-time, and their demographic parameters remain poorly understood. As a result, fundamental factors that control subsequent parasite evolution, such as the size of the switching population or the extent of immigration from the original host, remain largely unknown. To shed light on the host switching process, we explored how host switches occur in independent host shifts by two ectoparasitic honey bee mites (Varroa destructor and V. jacobsoni). Both switched to the western honey bee (Apis mellifera) after being brought into contact with their ancestral host (Apis cerana), ~70 and ~12years ago, respectively. Varroa destructor subsequently caused worldwide collapses of honey bee populations. Using whole-genome sequencing on 63mites collected in their native ranges from both the ancestral and novel hosts, we were able to reconstruct the known temporal dynamics of the switch. We further found multiple previously undiscovered mitochondrial lineages on the novel host, along with the genetic equivalent of tens of individuals that were involved in the initial host switch. Despite being greatly reduced, some gene flow remains between mites adapted to different hosts. Our findings suggest that while reproductive isolation may facilitate the fixation of traits beneficial for exploiting the new host, ongoing genetic exchange may allow genetic amelioration of inbreeding effects.

Editorial 2022

Editorial 2022

Fine‐scale population structure within an Eastern Nearctic snake complex (Pituophis melanoleucus)

AbstractUnderstanding the processes and mechanisms that promote lineage divergence is a central goal in evolutionary biology. For instance, studies investigating the spatial distribution of genomic variation often highlight biogeographic barriers underpinning geographic isolation or patterns of isolation by environment and isolation by distance that can also lead to lineage divergence. However, the patterns and processes that shape genomic variation and drive lineage divergence may be taxon‐specific, even across closely related taxa co‐occurring within the same biogeographic region. Here, we use molecular data in the form of ultraconserved elements (UCEs) to infer the evolutionary relationships and population genomic structure of the Eastern Pinesnake complex (Pituophis melanoleucus)—a polytypic wide‐ranging species that occupies much of the Eastern Nearctic. In addition to inferring evolutionary relationships, population genomic structure and gene flow, we also test relationships between genomic diversity and putative barriers to dispersal, environmental variation, and geographic distance. We present results that reveal shallow population genomic structure and ongoing gene flow, despite an extensive geographic range that transcends geographic features found to reduce gene flow among many taxa, including other squamate reptiles within the Eastern Nearctic. Further, our results indicate that the observed genomic diversity is spatially distributed as a pattern of isolation by distance and suggest that the current subspecific taxonomy do not adhere to independent lineages, but, rather, show a significant amount of admixture across the entire P. melanoleucus range.

Ecological Divergence and the History of Gene Flow in the Nearctic Milksnakes (Lampropeltis triangulum Complex).

Many phylogeographic studies on species with large ranges have found genetic-geographic structure associated with changes in habitat and physical barriers preventing or reducing gene flow. These interactions with geographic space, contemporary and historical climate, and biogeographic barriers have complex effects on contemporary population genetic structure and processes of speciation. While allopatric speciation at biogeographic barriers is considered the primary mechanism for generating species, more recently it has been shown that parapatric modes of divergence may be equally or even more common. With genomic data and better modeling capabilities, we can more clearly define causes of speciation in relation to biogeography and migration between lineages, the location of hybrid zones with respect to the ecology of parental lineages, and differential introgression of genes between taxa. Here, we examine the origins of three Nearctic milksnakes (Lampropeltis elapsoides, Lampropeltis triangulum and Lampropeltis gentilis) using genome-scale data to better understand species diversification. Results from artificial neural networks show that a mix of a strong biogeographic barrier, environmental changes, and physical space has affected genetic structure in these taxa. These results underscore conspicuous environmental changes that occur as the sister taxa L. triangulum and L. gentilis diverged near the Great Plains into the forested regions of the Eastern Nearctic. This area has been recognized as a region for turnover for many vertebrate species, but as we show here the contemporary boundary does not isolate these sister species. These two species likely formed in the mid-Pleistocene and have remained partially reproductively isolated over much of this time, showing differential introgression of loci. We also demonstrate that when L. triangulum and L. gentilis are each in contact with the much older L. elapsoides, some limited gene flow has occurred. Given the strong agreement between nuclear and mtDNA genomes, along with estimates of ecological niche, we suggest that all three lineages should continue to be recognized as unique species. Furthermore, this work emphasizes the importance of considering complex modes of divergence and differential allelic introgression over a complex landscape when testing mechanisms of speciation. [Cline; delimitation; Eastern Nearctic; Great Plains; hybrids; introgression; speciation.].

Adaptive divergence in bill morphology and other thermoregulatory traits is facilitated by restricted gene flow in song sparrows on the California Channel Islands.

Disentangling the effects of neutral and adaptive processes in maintaining phenotypic variation across environmental gradients is challenging in natural populations. Song sparrows (Melospiza melodia) on the California Channel Islands occupy a pronounced east-west climate gradient within a small spatial scale, providing a unique opportunity to examine the interaction of genetic isolation (reduced gene flow) and the environment (selection) in driving variation. We used reduced representation genomic libraries to infer the role of neutral processes (drift and restricted gene flow) and divergent selection in driving variation in thermoregulatory traits with an emphasis on the mechanisms that maintain bill divergence among islands. Analyses of 22,029 neutral SNPs confirm distinct population structure by island with restricted gene flow and relatively large effective population sizes, suggesting bill differences are probably not a product of genetic drift. Instead, we found strong support for local adaptation using 3294 SNPs in differentiation-based and environmental association analyses coupled with genome-wide association tests. Specifically, we identified several putatively adaptive and candidate loci in or near genes involved in bill development pathways (e.g., BMP, CaM, Wnt), confirming the highly complex and polygenic architecture underlying bill morphology. Furthermore, we found divergence in genes associated with other thermoregulatory traits (i.e., feather structure, plumage colour, and physiology). Collectively, these results suggest strong divergent selection across an island archipelago results in genomic changes in a suite of traits associated with climate adaptation over small spatial scales. Future research should move beyond studying univariate traits to better understand multidimensional responses to complex environmental conditions.

Functional connectivity in sympatric spiny rats reflects different dimensions of Amazonian forest‐association

AbstractAimUnderstanding how the landscape influences gene flow is important in explaining biodiversity, especially when co‐distributed taxa across heterogeneous landscapes exhibit species‐specific habitat associations. Here, we test predictions about the effects of forest‐type on population connectivity in two sympatric species of spiny rats that differ in their forest associations. Specifically, we evaluate the hypothesis that seasonal floodplain forests (várzea) provide linear connectivity, facilitating gene flow among individuals, while non‐flooded forests (terra‐firme) may diminish the functional connectivity.LocationWestern Amazon, South America.TaxonProechimys simonsi (non‐flooded forests, terra‐firme) and Proechimys steerei (seasonal floodplain forests, várzea).MethodsWe analyse about 13,000 single nucleotide polymorphisms along with characterizations of landscape heterogeneity for two forest types to test for differences in the functional connectivity. Influence of the landscape and environmental variables are quantified using maximum‐likelihood population effect models to identify the relative importance of variables in explaining the gene flow.ResultsThere are significant differences in functional connectivity between species. However, the genomic data does not support the conventional hypotheses of higher connectivity for inhabitants of várzea than those of terra‐firme. Stronger genetic structure in P. steerei than P. simonsi based on isolation by distance models suggests reduced gene flow in species associated with várzea forests. Isolation by resistance reinforces that wetland habitats inhibit and promote the functional connectivity in P. simonsi and P. steerei, respectively, although large distances along the rivers can prevent gene flow in P. steerei.Main conclusionInterpreting differences between connectivity in taxa apparent from genetic analyses through the lens of a single dimension of Amazonian heterogeneity—that is, forest type—may be an oversimplification. Our statistical modelling and fit of the data to different models points to specific environmental and habitat differences between the ecological divergent spiny rat species that may contribute to differences in the genetic structure of these sympatric taxa.

Contrasting environmental drivers of genetic and phenotypic divergence in an Andean poison frog (Epipedobates anthonyi).

Phenotypic and genetic divergence are shaped by the homogenizing effects of gene flow and the differentiating processes of genetic drift and local adaptation. Herein, we examined the mechanisms that underlie phenotypic (size and color) and genetic divergence in 35 populations (535 individuals) of the poison frog Epipedobates anthonyi along four elevational gradients (0-1800 m asl) in the Ecuadorian Andes. We found phenotypic divergence in size and color despite relatively low genetic divergence at neutral microsatellite loci. Genetic and phenotypic divergence were both explained by landscape resistance between sites (isolation-by-resistance, IBR), likely due to a cold and dry mountain ridge between the northern and southern elevational transects that limits dispersal and separates two color morphs. Moreover, environmental differences among sites also explained genetic and phenotypic divergence, suggesting isolation-by-environment (IBE). When northern and southern transects were analyzed separately, genetic divergence was predicted either by distance (isolation-by-distance, IBD; northern) or environmental resistance between sites (IBR; southern). In contrast, phenotypic divergence was primarily explained by environmental differences among sites, supporting the IBE hypothesis. These results indicate that although distance and geographic barriers are important drivers of population divergence, environmental variation has a two-fold effect on population divergence. On the one hand, landscape resistance between sites reduces gene flow (IBR), while on the other hand, environmental differences among sites exert divergent selective pressures on phenotypic traits (IBE). Our work highlights the importance of studying both genetic and phenotypic divergence to better understand the processes of population divergence and speciation along ecological gradients.

Overlooked Species Diversity and Distribution in the Antarctic Mite Genus Stereotydeus

In the harsh Antarctic terrestrial ecosystems, invertebrates are currently confined to sparse and restricted ice free areas, where they have survived on multi-million-year timescales in refugia. The limited dispersal abilities of these invertebrate species, their specific habitat requirements, and the presence of geographical barriers can drastically reduce gene flow between populations, resulting in high genetic differentiation. On continental Antarctica, mites are one of the most diverse invertebrate groups. Recently, two new species of the free living prostigmatid mite genus Stereotydeus Berlese, 1901 were discovered, bringing the number of Antarctic and sub-Antarctic species of this genus up to 15, of which 7 occur along the coast of Victoria Land and in the Transantarctic Mountains. To examine the biodiversity of Stereotydeus spp., the present study combines phylogenetic, morphological and population genetic data of specimens collected from nine localities in Victoria Land. Genetically distinct intraspecific groups are spatially isolated in northern Victoria Land, while, for other species, the genetic haplogroups more often occur sympatrically in southern Victoria Land. We provide a new distribution map for the Stereotydeus species of Victoria Land, which will assist future decisions in matters of the protection and conservation of the unique Antarctic terrestrial fauna.

High genetic diversity and low structure in an endemic long-lived tree, Yucca capensis (Asparagaceae).

Endemic species distributed in fragmented habitats are highly vulnerable to extinction because they may have low genetic diversity. However, some life-history traits can mitigate the effect of genetic drift on populations. We analysed the level and distribution of genetic variation and ancestral population size of Yucca capensis, a long-lived endemic plant of the Baja California Peninsula, Mexico. Its populations are scattered across a habitat that is suffering accelerated transformation. We used six nuclear microsatellites to genotype 224 individuals from 17 locations across the entire species' geographic range. We estimated polymorphisms, heterozygosity and genetic structure. We also evaluated the ancestral and recent effective size and time since the population started to change. We found high heterozygosity, high polymorphism and low differentiation among locations, suggesting a panmictic population across the range. We also detected a large ancestral effective population size, which suffered a strong reduction in the Mid-Holocene. Despite changes in environmental conditions caused by habitat modification, the high diversity and low differentiation in Y. capensis may result from its large ancestral effective size and life-history traits, such as plant longevity, clonal growth and mating system, which reduce the rate of loss of genetic variation. However, the dependence on a specialist pollinator that displays short flight range can reduce gene flow among the plant populations and could, shortly, lead them into an extinction vortex.

A multiscale analysis of landscape resistance reveals genetic isolates in an endangered forest-specialist species the Barbary macaque (Macaca sylvanus)

In forest-specialist mammals, forest loss may induce resistance to animal movement and reduce gene flow between populations, and thereby increase genetic erosion and extinction risks for populations. Understanding how landscape features affect gene flow is of critical importance for conservation. Using landscape genetic tools at multiple spatial scales, we assessed the effects of landscape heterogeneity (in particular the presence of wide open or rural habitats) on gene flow in an endangered forest-specialist species – the Barbary macaque (Macaca sylvanus) –, in its major forest site in Morocco. We genotyped 248 individuals from 23 macaque groups using 11 microsatellite loci. We modelled different scenarios of isolation by landscape resistance. We further tested the relationships between genetic distance and isolation by resistance, after controlling for the effect of isolation by distance. Our results revealed a significant genetic structure and a disruption of gene flow even in geographic proximity. Whatever the spatial scale, remoteness from the forest edge beyond 1 km acted as a barrier to macaque movements. In addition, at a fine scale, human-dominated areas were also detected as a barrier. The detection of private alleles in each population suggests an ongoing process of isolation. The preservation of the Barbary macaque implies 1) strictly avoiding all silvicultural practices (in particular clear-cutting of holm oak forests) that could contribute to increase distances between forest patches, 2) restoring corridors between forests, 3) and preserving key small forest patches as potential stepping stones facilitating macaque dispersal.

High population density of bee pollinators increasing Camelina sativa (L.) Crantz seed yield: Implications on the potential risk for insect-mediated gene flow

New Camelina sativa genotypes have been genetically engineered (GE) to produce unique high-value chemical compounds and biofuel products. However, baseline information on predictive environmental risk assessment on this plant is urgently needed to establish guidelines for commercial large-scale production. Pollinating insects such as bees could facilitate the spread of transgenes into the ecosystem and raises ecological concerns on insect-mediated gene flow. Thus determination of the potential impact of pollinating insects on C. sativa pollination and gene flow becomes important. A 4-year experiment conducted in Connecticut, USA (2017) and Yangzhou, China (2019–2021) was carried out to determine the pollination effect of different densities of honey bees (Apis mellifera L.) populations on C. sativa seed yield and assess their involvement on C. sativa pollen dispersal. Insect cages experiments with presence or absence of honey bees showed that C. sativa seed yield was not affected by a relatively low population density of honey bees (20 honey bees m−2). However, at a higher density of honey bee population, Camelina sativa seed yield (0.23 g plant-1 and 73.3 g m−2) was statistically greater than those of the uncaged control (0.21 g plant-1 and 68.9 g m−2), caged C. sativa plants without honey bees (0.20 g plant-1 and 66.3 g m−2) or with 20 honey bees m−2 (0.21 g plant-1 and 66.9 g m−2), although C. sativa is commonly assumed to be self-pollinated. Principle coordinate analysis (PCoA) made from SSR markers revealed that honey bee and bumble bee are able to transfer C. sativa pollen from pollen source to adjacent flowers of other species (e.g., Brassica juncea, Brassica napus) up to 10−15 m beyond the field edge, raising ecological concerns on insect-mediated gene flow between adjacent C. sativa fields particularly if GE C. sativa cultivars are involved. The new information in this study will help to better understand C. sativa pollination biology, environmental risks associated with insect-mediated gene flow, and develop management strategies to reduce gene flow and facilitate coexistence between GE and non-GE C. sativa under natural agroecosystem.

Biogeographic Drivers of Evolutionary Radiations

Some lineages radiate spectacularly when colonizing a region, but others do not. Large radiations are often attributed to species’ adaptation into niches, or to other drivers, such as biogeography including dispersal ability and spatial structure of the landscape. Here we aim to disentangle the factors determining radiation size, by modeling simplified scenarios without the complexity of explicit niches. We build a spatially structured neutral model free from niches and incorporating a form of protracted speciation that accounts for gene flow between populations. We find that a wide range of radiation sizes are possible in this model depending on the combination of geographic isolation and species’ dispersal ability. At extremely low rates of dispersal between patches, each patch maintains its own endemic species. Intermediate dispersal rates foster larger radiations as they allow occasional movement between patches whilst sufficiently restricting gene flow to support further speciation in allopatry. As dispersal rates increase further, a critical point is reached at which demographically identical lineages may vary greatly in radiation size due to rare and stochastic dispersal events. At the critical point in dispersal frequency, some lineages remain a single species for a comparatively long time, whilst others with identical characteristics produce the largest radiations of all via a new mechanism for rapid radiation that we term a ‘radiation cascade’. Given a single species covering many patches connected with gene flow, a radiation cascade is triggered when stochastic dispersal is unusually low for a period, leading to an initial speciation event. This speciation means there are fewer individuals per species and thus further reduced gene flow between conspecifics. Reduced gene flow in turn makes it easier for further speciation to occur. During a radiation cascade, dispersal of individuals between patches continues at the same rate as before, but due to the increasing diversity it primarily introduces novel species that will later speciate, rather than adding to gene flow of existing species. Once a radiation cascade begins, it continues rapidly until it is arrested by a new equilibrium between speciation and extinction. We speculate that such radiation cascades may occur more generally and are not only present in neutral models. This process may help to explain rapid radiation, and the extreme radiation sizes of certain lineages with dispersing ancestors. Whilst niches no doubt play a role in community assembly, our findings lead us to question whether diversification and adaptation into niches is sometimes an effect of speciation and rapid radiation, rather than its cause.

The role of anthropogenic dispersal in shaping the distribution and genetic composition of a widespread North American tree species.

Dispersal and colonization are among the most important ecological processes for species persistence as they allow species to track changing environmental conditions. During the last glacial maximum (LGM), many cold‐intolerant Northern Hemisphere plants retreated to southern glacial refugia. During subsequent warming periods, these species expanded their ranges northward. Interestingly, some tree species with limited seed dispersal migrated considerable distances after the LGM ~19,000 years before present (YBP). It has been hypothesized that indigenous peoples may have dispersed valued species, in some cases beyond the southern limits of the Laurentide Ice Sheet. To investigate this question, we employed a molecular genetics approach on a widespread North American understory tree species whose fruit was valued by indigenous peoples. Twenty putative anthropogenic (near pre‐Columbian habitations) and 62 wild populations of Asimina triloba (pawpaw), which produces the largest edible fruit of any North American tree, were genetically assayed with nine microsatellite loci. Putative anthropogenic populations were characterized by reduced genetic diversity and greater excess heterozygosity relative to wild populations. Anthropogenic populations in regions that were glaciated during the LGM had profiles consistent with founder effects and reduced gene flow, and shared rare alleles with wild populations hundreds of kilometers away (mean = 723 km). Some of the most compelling evidence for human‐mediated dispersal is that putative anthropogenic and wild populations sharing rare alleles were separated by significantly greater distances (mean = 695 km) than wild populations sharing rare alleles (mean = 607 km; p = .014). Collectively, the genetic data suggest that long‐distance dispersal played an important role in the distribution of pawpaw and is consistent with the hypothesized role of indigenous peoples.

Population structure and the influence of microenvironment and genetic similarity on individual growth at Alaskan white spruce treelines

Knowledge on the adaptation of trees to rapid environmental changes is essential to preserve forests and their ecosystem services under climate change. Treeline populations are particularly suitable for studying adaptation processes in trees, as environmental stress together with reduced gene flow can enhance local adaptation. We investigated white spruce (Picea glauca) populations in Alaska on one moisture-limited and two cold-limited treeline sites with a paired plot design of one forest and one treeline population each, resulting in six plots. Additionally, one forest plot in the middle of the distribution range complements the study design. We combined spatial, climatic and dendrochronological data with neutral genetic marker of 2203 trees to investigate population genetic structure and drivers of tree growth. We used several individual-based approaches including random slope mixed-effects models to test the influence of genetic similarity and microenvironment on growth performance. A high degree of genetic diversity was found within each of the seven plots associated with high rates of gene flow. We discovered a low genetic differentiation between the three sites which was better explained by geographic distances than by environmental differences, indicating genetic drift as the main driver of population differentiation. Our findings indicated that microenvironmental features had an overall larger influence on growth performances than genetic similarity among individuals. The effects of climate on growth differed between sites but were smaller than the effect of tree size. Overall, our results suggest that the high genetic diversity of white spruce may result in a wider range of phenotypes which enhances the efficiency of selection when the species is facing rapid climatic changes. In addition, the large intra-individual variability in growth responses may indicate the high phenotypic plasticity of white spruce which can buffer short-term environmental changes and, thus, allow enduring the present changing climate conditions.

A role of asynchrony of seasons in explaining genetic differentiation in a Neotropical toad.

The process of diversification can be studied at the phylogeographic level by attempting to identify the environmental features that promote and maintain population divergence. Here we investigate diversification in Rhinella granulosa, a Neotropical toad from northeastern Brazil, by testing a range of hypotheses that encompass different putative mechanisms reducing gene flow among populations. We sequenced single nucleotide polymorphisms and examined individual predictions related to the role of geographic barriers (rivers), ecological gradients, historical habitat stability, and spatial variation in climate seasonality, also known as the asynchrony of seasons hypothesis. This hypothesis postulates that temporal asynchrony of wet and dry seasons over short distances causes parapatric populations to become isolated by time. After determining genetic structure, inferring past distributions, ranking demographic models, and estimating the power of monthly climatic variables, our results identified two populations that are not associated with geographic barriers, biome gradients, or historical refugia. Instead, they are predicted by spatial variation in monthly rainfall and minimum temperature, consistent with the asynchrony of seasons hypothesis, supported also by our comparative framework using multiple matrix regression and linear mixed effects modeling. Due to the toad's life history, climate likely mediates gene flow directly, with genetic differentiation being provoked by neutral mechanisms related to climate driven population isolation, and/or by natural selection against migrants from populations with different breeding times. The asynchrony of seasons hypothesis is seldom considered in phylogeographic studies, but our results indicate that it should be tested in systems where breeding is tightly coupled with climate.

Local climate adaptation and gene flow in the native range of two co-occurring fruit moths with contrasting invasiveness.

Invasive species pose increasing threats to global biodiversity and ecosystems. While previous studies have characterized successful invaders based on ecological traits, characteristics related to evolutionary processes have rarely been investigated. Here we compared gene flow and local adaptation using demographic analyses and outlier tests in two co-occurring moth pests across their common native range of China, one of which (the peach fruit moth, Carposina sasakii) has maintained its native distribution, while the other (the oriental fruit moth, Grapholita molesta) has expanded its range globally during the past century. We found that both species showed a pattern of genetic differentiation and an evolutionary history consistent with a common southwestern origin and northward expansion in their native range. However, for the noninvasive species, genetic differentiation was closely aligned with the environment, and there was a relatively low level of gene flow, whereas in the invasive species, genetic differentiation was associated with geography. Genome scans indicated stronger patterns of climate-associated loci in the noninvasive species. While strong local adaptation and reduced gene flow across its native range may have decreased the invasiveness of C. sasakii, this requires further validation with additional comparisons of invasive and noninvasive species across their native range.

Functional connectivity in a continuously distributed, migratory species as revealed by landscape genomics

Maintaining functional connectivity is critical for the long‐term conservation of wildlife populations. Landscape genomics provides an opportunity to assess long‐term functional connectivity by relating environmental variables to spatial patterns of genomic variation resulting from generations of movement, dispersal and mating behaviors. Identifying landscape features associated with gene flow at large geographic scales for highly mobile species is becoming increasingly possible due to more accessible genomic approaches, improved analytical methods and enhanced computational power. We characterized the genetic structure and diversity of migratory mule deer Odocoileus hemionus using 4051 single nucleotide polymorphisms in 406 individuals sampled across multiple habitats throughout Wyoming, USA. We then identified environmental variables associated with genomic variation within genetic groups and statewide using a stepwise approach to first evaluate nonlinear relationships of landscape resistance with genetic distances and then use mixed‐effects modeling to choose top landscape genomic models. We identified three admixed genetic groups of mule deer and found that environmental variables associated with gene flow varied among genetic groups, revealing scale‐dependent and regional variation in functional connectivity. At the statewide scale, more gene flow occurred in areas with low elevation and mixed habitat. In the southern genetic group, more gene flow occurred in areas with low elevation. In the northern genetic group, more gene flow occurred in grassland and forest habitats, while highways and energy infrastructure reduced gene flow. In the western genetic group, the null model of isolation by distance best represented genetic patterns. Overall, our findings highlight the role of different seasonal ranges on mule deer genetic connectivity, and show that anthropogenic features hinder connectivity. This study demonstrates the value of combining a large, genome‐wide marker set with recent advances in landscape genomics to evaluate functional connectivity in a wide‐ranging migratory species.