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402 results for “hybrid zone”
Data from: Climate-mediated movement of an avian hybrid zone
The interaction between sibling species that share a zone of contact is a multifaceted relationship affected by climate change. Between sibling species, interactions may occur at whole-organism (direct or indirect competition) or genomic (hybridization and introgression) levels. Tracking hybrid zone movements can provide insights about influences of environmental change on species interactions. Here, we explore the extent and mechanism of movement of the contact zone between black-capped chickadees (Poecile atricapillus) and Carolina chickadees (Poecile carolinensis) at whole-organism and genomic levels. We find strong evidence that winter temperatures limit the northern extent of P. carolinensis by demonstrating a current-day association between the range limit of this species and minimum winter temperatures. We further show that this temperature limitation has been consistent over time because we are able to accurately hindcast the previous northern range limit under earlier climate conditions. Using genomic data, we confirm northward movement of this contact zone over the past decade and highlight temporally consistent differential—but limited—geographic introgression of alleles. Our results provide an informative example of the influence of climate change on a contact zone between sibling species.
Data from: Fitness dynamics within a poplar hybrid zone: II. Impact of exotic sex on native poplars in an urban jungle.
Trees bearing novel or exotic gene components are poised to contribute to the bioeconomy for a variety of purposes such as bioenergy production, phytoremediation, and carbon sequestration within the forestry sector, but sustainable release of trees with novel traits in large-scale plantations requires the quantification of risks posed to native tree populations. Over the last century, exotic hybrid poplars produced through artificial crosses were planted throughout eastern Canada as ornamentals or windbreaks and these exotics provide a proxy by which to examine the fitness of exotic poplar traits within the natural environment to assess risk of exotic gene escape, establishment, and spread into native gene pools. We assessed postzygotic fitness traits of native and exotic poplars within a naturally regenerated stand in eastern Canada (Quebec City, QC). Pure natives (P. balsamifera and P. deltoides spp. deltoides), native hybrids (P. deltoides × P. balsamifera), and exotic hybrids (trees bearing Populus nigra and P. maximowiczii genetic components) were screened for reproductive biomass, yield, seed germination, and fungal disease susceptibility. Exotic hybrids expressed fitness traits intermediate to pure species and were not significantly different from native hybrids. They formed fully viable seed and backcrossed predominantly with P. balsamifera. These data show that exotic hybrids were not unfit and were capable of establishing and competing within the native stand. Future research will seek to examine the impact of exotic gene regions on associated biotic communities to fully quantify the risk exotic poplars pose to native poplar forests.
Data from: Genomic and phenotypic architecture of a spruce hybrid zone (Picea sitchensis x P. glauca)
Interspecific hybridization may enhance the capacity of populations to adapt to changing environments, and has practical implications for reforestation. We use genomewide estimates of admixture and phenotypic traits for trees in a common garden to examine the extent and direction of gene flow across a Picea hybrid zone, testing assumptions of the bounded hybrid superiority and tension zone models of hybrid zone maintenance. Seeds were collected from the ecological transition zone spanning from maritime to continental climates across the Picea sitchensis-P. glauca contact zone, and 721 trees were planted in a common garden experiment within the hybrid zone. Individuals were genotyped using a panel of 384 candidate-gene single nucleotide polymorphisms (SNPs) putatively associated with adaptive traits in Picea, and phenotyped at age ten for height and autumn cold hardiness. Low interspecific heterozygosity in hybrids indicated intrinsic reproductive barriers were too weak to prevent widespread recombination, although introgression appeared asymmetric with P. sitchensis dominating the zone. While marker-based hybrid index was strongly correlated with climate and geography, phenotypic traits exhibited weak or no significant clines. Our results indicated that exogenous selection appeared to play a strong role in the distribution and structure of this hybrid zone, indicative of an environmentally determined bounded hybrid superiority model of hybrid zone maintenance, although endogenous mechanisms could not be ruled out. This study provides insight into the mechanisms underlying adaptation across ecologically transitional hybrid zones that will ultimately provide an additional tool in managing these economically important tree species.
Data from: Differential introgression in a mosaic hybrid zone reveals candidate barrier genes
Hybrid zones act as genomic sieves; although globally advantageous alleles will spread throughout the zone and neutral alleles can be freely exchanged between species, introgression will be restricted for genes that contribute to reproductive barriers or local adaptation. Seminal fluid proteins (SFPs) are known to contribute to reproductive barriers in insects and have been proposed as candidate barrier genes in the hybridizing field crickets G. pennsylvanicus and G. firmus. Here, we have used 125 SNPs to characterize patterns of differential introgression and to identify genes that may contribute to prezygotic barriers between these species. Using a transcriptome scan of the male cricket accessory gland (the site of SFP synthesis), we identified genes with major allele frequency differences between the species. We then compared patterns of introgression for genes encoding seminal fluid proteins with patterns for genes expressed in the same tissue that do not encode SFPs. We find no evidence that seminal fluid proteins have reduced gene exchange across the cricket hybrid zone. However, a number of genes exhibit dramatically reduced introgression, and many of these genes encode proteins with functional roles consistent with known barriers.
Data from: Movement of a Heliconius hybrid zone over 30 years: a Bayesian approach
Hybrid zones have long been of interest to biologists as natural laboratories where we can gain insight into the processes of adaptation and speciation. Repeated sampling of individual hybrid zones has been particularly useful in elucidating the dynamic balance between selection and dispersal that maintains most hybrid zones. Here, we revisit a hybrid zone between Heliconius erato butterflies in Panamá for a third time over more than 30 years. We combine a novel Bayesian extension of stepped‐cline hybrid zone models with environmental data to understand the genetic and environmental causes of cline dynamics in this species. The cline has continued to move west, likely due to dominance drive, but has slowed and broadened. Environmental analyses suggest that widespread deforestation in Panamá could be leading to decreased avian predation and relaxed selection, causing the observed changes in cline dynamics.
Data from: Spatial genetic and morphologic structure of wolves and coyotes in relation to environmental heterogeneity in a Canis hybrid zone
Eastern wolves have hybridized extensively with coyotes and gray wolves and are listed as a 'species of special concern' in Canada. However, a distinct population of eastern wolves has been identified in Algonquin Provincial Park (APP) in Ontario. Previous Canis studies have not linked genetic analysis with field data to investigate genotype-specific morphology or determine how resident animals of different ancestry are distributed across the landscape in relation to heterogeneous environmental conditions. Accordingly, we studied resident wolves and coyotes in and adjacent to APP to identify distinct Canis types, clarify the occurrence of eastern wolves adjacent to APP, and investigate spatial genetic structure and landscape-genotype associations in the hybrid zone. We documented 3 genetically distinct Canis types that also differed morphologically, corresponding to putative gray wolves, eastern wolves, and coyotes. We also documented a substantial number of hybrid individuals (36%). Breeding eastern wolves were less common outside of APP, but occurred in some unprotected areas. We identified a steep cline extending west from APP where the dominant genotype shifted abruptly from eastern wolves to coyotes and hybrids. The genotypic pattern to the south and northwest was a more complex mosaic of alternating genotypes. We modeled genetic ancestry in response to prey availability and human disturbance and found positive and negative associations between wolf ancestry and 1) moose density and 2) road densities, respectively. Our results clarify the structure of the Canis hybrid zone adjacent to APP and provide unique insight into environmental conditions influencing hybridization dynamics between wolves and coyotes.
Data from: Unexpected ancestry of Populus seedlings from a hybrid zone implies a large role for postzygotic selection in the maintenance of species
In the context of potential interspecific gene flow, the integrity of species will be maintained by reproductive barriers that reduce genetic exchange, including traits associated with prezygotic isolation or poor performance of hybrids. Hybrid zones can be used to study the importance of different reproductive barriers, particularly when both parental species and hybrids occur in close spatial proximity. We investigated the importance of barriers to gene flow that act early versus late in the life cycle of European Populus by quantifying the prevalence of homospecific and hybrid matings within a mosaic hybrid zone. We obtained genotypic data for 11,976 loci from progeny and their maternal parents and constructed a Bayesian model to estimate individual admixture proportions and hybrid classes for sampled trees, and for the unsampled pollen parent. Matings that included one or two hybrid parents were common, resulting in admixture proportions of progeny that spanned the whole range of potential ancestries between the two parental species. This result contrasts strongly with the distribution of admixture proportions in adult trees, where intermediate hybrids and each of the parental species are separated into three discrete ancestry clusters. The existence of the full range of hybrids in seedlings is consistent with weak reproductive isolation early in the life cycle of Populus. Instead, a considerable amount of selection must take place between the seedling stage and maturity to remove many hybrid seedlings. Our results highlight that high hybridization rates and appreciable hybrid fitness do not necessarily conflict with the maintenance of species integrity.
Data from: The last bastion? X chromosome genotyping of Anopheles gambiae species pair males from a hybrid zone reveals complex recombination within the major candidate 'genomic island of speciation'
Speciation with gene flow may be aided by reduced recombination helping to build linkage between genes involved in the early stages of reproductive isolation. Reduced recombination on chromosome X has been implicated in speciation within the Anopheles gambiae complex, species of which represent the major Afrotropical malaria vectors. The most recently diverged, morphologically indistinguishable, species pair, A. gambiae and Anopheles coluzzii, ubiquitously displays a 'genomic island of divergence' spanning over 4 Mb from chromosome X centromere, which represents a particularly promising candidate region for reproductive isolation genes, in addition to containing the diagnostic markers used to distinguish the species. Very low recombination makes the island intractable for experimental recombination studies, but an extreme hybrid zone in Guinea Bissau offers the opportunity for natural investigation of X-island recombination. SNP analysis of chromosome X hemizygous males revealed: (i) strong divergence in the X-island despite a lack of autosomal divergence; (ii) individuals with multiple-recombinant genotypes, including likely double crossovers and localized gene conversion; (iii) recombination-driven discontinuity both within and between the molecular species markers, suggesting that the utility of the diagnostics is undermined under high hybridization. The largely, but incompletely protected nature of the X centromeric genomic island is consistent with a primary candidate area for accumulation of adaptive variants driving speciation with gene flow, while permitting some selective shuffling and removal of genetic variation.
Data from: Genetic analysis of an ephemeral intraspecific hybrid zone in the hypervariable tree, Metrosideros polymorpha, on Hawai'i Island
Intraspecific hybrid zones involving long-lived woody species are rare and can provide insights into the genetic basis of early-diverging traits in speciation. Within the landscape-dominant Hawaiian tree, Metrosideros polymorpha, are morphologically distinct successional varieties, incana and glaberrima, that dominate new and old lava flows, respectively, below 1200 me on volcanically active Hawai'i Island, with var. glaberrima also extending to higher elevations and bogs. Here, we use morphological measurements on 86 adult trees to document the presence of an incana-glaberrima hybrid zone on the 1855 Mauna Loa lava flow on east Hawai'i Island and parent-offspring analysis of 1311 greenhouse seedlings from 71 crosses involving 72 adults to estimate heritabilities and genetic correlations among vegetative traits. Both the variation in adult leaf pubescence at the site and the consistency between adult and offspring phenotypes suggest the presence of two hybrid classes, F1s and var. incana backcrosses, as would be expected on a relatively young lava flow. Nine nuclear microsatellite loci failed to distinguish parental and hybrid genotypes. All four leaf traits examined showed an additive genetic basis with moderate to strong heritabilities, and genetic correlations were stronger for the more range-restricted var. incana. The differences between varieties in trait values, heritabilities and genetic correlations, coupled with high genetic variation within but low genetic variation between varieties, are consistent with a multi-million-year history of alternating periods of disruptive selection in contrasting environments and admixture in ephemeral hybrid zones. Finally, the contrasting genetic architectures suggest different evolutionary trajectories of leaf traits in these forms.
Data from: Growth gains from selective breeding in a spruce hybrid zone do not compromise local adaptation to climate
Hybrid zones contain extensive standing genetic variation that facilitates rapid responses to selection. The Picea glauca x P. engelmannii hybrid zone in western Canada is the focus of tree breeding programs that annually produce ~90 million reforestation seedlings. Understanding the direct and indirect effects of selective breeding on adaptive variation is necessary to implement assisted gene flow polices in Alberta and British Columbia that match these seedlings with future climates. We decomposed relationships among hybrid ancestry, adaptive traits and climate to understand the implications of selective breeding for climate adaptations and assisted gene flow strategies. The effects of selection on associations among hybrid index estimated from ~6500 SNPs, adaptive traits, and provenance climates were assessed for ~2400 common garden seedlings. Hybrid index differences between natural and selected seedlings within breeding zones were small in Alberta (average +2%), but larger and more variable in BC (average -7 %, range -24% to +1%), slightly favoring P. glauca ancestry. The average height growth gain of selected seedlings over natural seedlings within breeding zones was 36% (range 12% to 86%). Clines in growth with temperature-related variables were strong, but differed little between selected and natural populations. Seedling hybrid index and growth trait associations with evapotranspiration-related climate variables were stronger in selected than in natural seedlings, indicating possible pre-adaptation to drier future climates. Associations among cold hardiness, hybrid ancestry and cold-related climate variables dominated signals of local adaptation that were preserved in breeding populations. Strong hybrid ancestry-phenotype-climate associations suggest that assisted gene flow will be necessary to match interior spruce breeding populations with shifting future climates. The absence of antagonistic selection responses among traits and maintenance of cold adaptation in selected seedlings suggests breeding populations can be safely redeployed using assisted gene flow prescriptions similar to those of natural populations.
Data from: Rise and fall of a hybrid zone: implications for the roles of aggression, mate choice, and secondary succession
Hybridization can be an important evolutionary force by generating new species and influencing evolution of parental species in multiple ways, including introgression and the consequences of hybrid vigor. Determining the ecological processes underlying evolution in hybrid zones is difficult however because it requires examining changes in both genotypic frequencies over time and corresponding ecological information, data that are rarely collected together. Here, we describe genetic and ecological aspects of a hybrid zone between the Eastern Fence Lizard, Sceloporus undulatus, and the Florida Scrub Lizard, Sceloporus woodi, occurring over at least 23 generations. The hybrid zone, discovered greater than 35 years ago using morphological characters, originally consisted of nearly even proportions of parental species and hybrids. Now, using genetic markers (species-diagnostic mtDNA sites and 6 nDNA microsatellite loci across a total of n = 117 individuals), we confirm not only that hybridization occurred but also that subsequent backcrossing has resulted in highly introgressed hybrids, with many hybrids containing mitochondrial DNA from one species on a nuclear DNA background of the other. Ecological aspects explaining these shifts in genetic composition include female mate choice, changes in habitat associated with secondary succession, and, most strongly, a hierarchy of male territorial advantage—ecological mechanisms likely to be involved in the emergence and disappearance of many animal hybrid zones. Our results suggest that genetic assimilation is not a significant threat to either species and that rather transient hybrid zones such as this may serve to increase genetic diversity and are candidates for causing genetic discordance in phylogeographic analyses.
Data from: Development of diagnostic microsatellite markers from whole-genome sequences of Ammodramus sparrows for assessing admixture in a hybrid zone
Studies of hybridization and introgression and, in particular, the identification of admixed individuals in natural populations benefit from the use of diagnostic genetic markers that reliably differentiate pure species from each other and their hybrid forms. Such diagnostic markers are often infrequent in the genomes of closely related species, and genomewide data facilitate their discovery. We used whole-genome data from Illumina HiSeqS2000 sequencing of two recently diverged (600,000 years) and hybridizing, avian, sister species, the Saltmarsh (Ammodramus caudacutus) and Nelson's (A. nelsoni) Sparrow, to develop a suite of diagnostic markers for high-resolution identification of pure and admixed individuals. We compared the microsatellite repeat regions identified in the genomes of the two species and selected a subset of 37 loci that differed between the species in repeat number. We screened these loci on 12 pure individuals of each species and report on the 34 that successfully amplified. From these, we developed a panel of the 12 most diagnostic loci, which we evaluated on 96 individuals, including individuals from both allopatric populations and sympatric individuals from the hybrid zone. Using simulations, we evaluated the power of the marker panel for accurate assignments of individuals to their appropriate pure species and hybrid genotypic classes (F1, F2, and backcrosses). The markers proved highly informative for species discrimination and had high accuracy for classifying admixed individuals into their genotypic classes. These markers will aid future investigations of introgressive hybridization in this system and aid conservation efforts aimed at monitoring and preserving pure species. Our approach is transferable to other study systems consisting of closely related and incipient species.
Data from: Climate, demography, and zoogeography predict introgression thresholds in Salmonid hybrid zones in Rocky Mountain streams
Among the many threats posed by invasions of nonnative species is introgressive hybridization, which can lead to the genomic extinction of native taxa. This phenomenon is regarded as common and perhaps inevitable among native cutthroat trout and introduced rainbow trout in western North America, despite that these taxa naturally co-occur in some locations. We conducted a synthetic analysis of 13,315 genotyped fish from 558 sites by building logistic regression models using data from geospatial stream databases and from 12 published studies of hybridization to assess whether environmental covariates could explain levels of introgression between westslope cutthroat trout and rainbow trout in the U.S. northern Rocky Mountains. A consensus model performed well (AUC, 0.78–0.86; classification success, 72–82%; 10-fold cross validation, 70–82%) and predicted that rainbow trout introgression was significantly associated with warmer water temperatures, larger streams, proximity to warmer habitats and to recent sources of rainbow trout propagules, presence within the historical range of rainbow trout, and locations further east. Assuming that water temperatures will continue to rise in response to climate change and that levels of introgression outside the historical range of rainbow trout will equilibrate with those inside that range, we applied six scenarios across a 55,234-km stream network that forecast 9.5–74.7% declines in the amount of habitat occupied by westslope cutthroat trout populations of conservation value, but not the wholesale loss of such populations. We conclude that introgression between these taxa is predictably related to environmental conditions, many of which can be manipulated to foster largely genetically intact populations of westslope cutthroat trout and help managers prioritize conservation activities.
Data from: Metabolic traits of westslope cutthroat, introduced rainbow trout and their hybrids in an ecotonal hybrid zone along an elevation gradient
In the Upper Oldman River, Alberta, introduced non-native hatchery rainbow trout hybridize with native westslope cutthroat trout, resulting in a hybrid swarm. Rainbow trout dominate at low elevations (<1250 m) in the river mainstem, cutthroat in high elevation tributaries (>1400 m), and hybrids are numerically dominant in the mid-elevation range. We hypothesized that metabolism of rainbow trout would exceed that of cutthroat trout, and that the elevation gradient in genetic makeup would be mirrored by a gradient in metabolic traits, with intermediate traits in the hybrid dominated ecotone. Metabolic traits were measured and regressed against the genetic makeup of individuals and elevation. Rainbow trout had higher oxygen consumption rates (OCR), higher white muscle lactate dehydrogenase (LDH) and citrate synthase (CS) activity, and higher plasma acetylcholinesterase (AchE) than cutthroat trout. Hybrids had intermediate OCR and AchE, but LDH activity as high as rainbow trout. While hybrid zones are usually modeled as a balance between cross species mating and selection against hybrids, ecotonal hybrid zones, where hybrids proliferate in intermediate habitats and have traits that appear well suited to ecotonal conditions, have been proposed for some plants and animals, and may have important implications for resource management and conservation.
Data from: Sharp acoustic boundaries across an altitudinal avian hybrid zone despite asymmetric introgression
Birdsong is a sexually selected trait that could play an important evolutionary role when related taxa come into secondary contact. Many songbird species however learn their songs through copying one or more tutors, which complicates the evolutionary outcome of such contact. Two subspecies of a presumed vocal learner, the grey-breasted wood-wren (Henicorhina leucophrys), replace each other altitudinally across the western slope of the Ecuadorian Andes. These subspecies are morphologically very similar, but show striking differences in their song. We examined variation in acoustic traits and genetic composition across the altitudinal range covered by both subspecies and between two allopatric populations. The acoustic boundary between the subspecies was found to be highly abrupt across a narrow elevational range with virtually no evidence of song convergence. Mixed singing and use of hetero-subspecific song occurred in the contact zone and was biased towards the use of leucophrys song types. Hetero-subspecific song copying by hilaris and not by leucophrys reflected a previously found asymmetric pattern of response to song playback. Using AFLP markers, we detected hybridization in the contact zone and asymmetric introgression in parapatric populations, with more leucophrys alleles present in hilaris populations than vice versa. This pattern may be a trail of introgression due to upslope displacement of leucophrys by hilaris. Our data suggest that song learning may impact speciation and hybridization in contrasting ways at different spatial scales: while learning may speed up population divergence in songs, thereby enhancing assortative mating and reducing gene flow, it may at a local level also lead to the copying of heterospecific songs, therefore allowing some level of hybridization and introgression.
Data from: New evidence for hybrid zones of forest and savanna elephants in Central and West Africa
The African elephant consists of forest and savanna subspecies. Both subspecies are highly endangered due to severe poaching and habitat loss, and knowledge of their population structure is vital to their conservation. Previous studies have demonstrated marked genetic and morphological differences between forest and savanna elephants and despite extensive sampling, genetic evidence of hybridization between them has been restricted largely to a few hybrids in the Garamba region of northeastern Democratic Republic of Congo (DRC). Here we present new genetic data on hybridization from previously unsampled areas of Africa. Novel statistical methods applied to these data identify 46 hybrid samples - many more than have been previously identified - only two of which are from the Garamba region. The remaining 44 are from three other geographically-distinct locations: a major hybrid zone along the border of the DRC and Uganda, a second potential hybrid zone in Central African Republic, and a smaller fraction of hybrids in the Pendjari-Arli complex of West Africa. Most of the hybrids show evidence of interbreeding over more than one generation, demonstrating that hybrids are fertile. Mitochondrial and Y chromosome data demonstrate that the hybridization is bidirectional, involving males and females from both subspecies. We hypothesize that the hybrid zones may have been facilitated by poaching and habitat modification. The localized geography and rarity of hybrid zones, their possible facilitation from human pressures, and the high divergence and genetic distinctness of forest and savanna elephants throughout their ranges, are consistent with calls for separate species classification.
Data from: The hidden side of a major marine biogeographic boundary: a wide mosaic hybrid zone at the Atlantic–Mediterranean divide reveals the complex interaction between natural and genetic barriers in mussels
The Almeria-Oran Front (AOF) is a recognised hotspot of genetic differentiation in the sea. It is a barrier to dispersal and an ecological boundary, which explain the position of genetic breaks. However, the maintenance of genetic differentiation is likely reinforced by genetic barriers. A general drawback of previous studies is an insufficient density of sampling sites at the transition zone with a conspicuous lack of samples from the southern coastline. We analysed the genetic structure in the mussel Mytilus galloprovincialis with ancestry-informative loci. We discovered a 600 km wide mosaic hybrid zone eastward of the AOF along the Algerian coasts. This mosaic zone provides a new twist to our understanding of the Atlantic-Mediterranean transition because it demonstrates the two lineages can live in sympatry but hardly interbreed. This implies some form of reproductive isolation must exist to maintain the two genetic backgrounds locally cohesive. The zone ends with an abrupt genetic shift at a barrier to dispersal in the Gulf of Bejaia. Simulations in models that account for hydrodynamic features of the region support the hypothesis that sister hybrid zones could have been differentially trapped at two alternative barriers to dispersal or environmental boundaries. A preponderantly unidirectional north-south gene flow next to the AOF can also maintain a patch of an intrinsically maintained genetic background in the south and the mosaic structure. Our results concur with the coupling hypothesis that suggests natural barriers mostly explain the position of genetic breaks while their maintenance must additionally require genetic barriers.
Data from: Integrating phylogeography and paleoecology to investigate the origin and dynamics of hybrid zones: insights from two widespread North American firs
Secondary contact between closely related taxa routinely occurs during postglacial migrations. After initial contact, the location of hybrid zones may shift geographically or remain spatially stable over time in response to various selective pressures or neutral processes. Studying the extent and direction of introgression using markers having contrasted levels of gene flow can help unravel the historical dynamics of hybrid zones. Thanks to their contrasted maternal and paternal inheritance, resulting in different levels of gene flow for mitochondrial and chloroplast DNA (mtDNA and cpDNA), the Pinaceae stand out as a relevant biological model for this purpose. The objective of the study was to assess whether the hybrid zone between Abies balsamea and Abies lasiocarpa (two largely distributed Pinaceae) has moved or remained stable over time by analysing the distribution of cytoplasmic DNA variation as well as published palaeobotanical data. Interspecific gene flow was higher for cpDNA than mtDNA markers; hence, the geographic distribution of mitotypes was more congruent with species distributions than chlorotypes. This genetic signature was contrary to expectations under a moving hybrid zone scenario, as well as empirical observations in other conifers. Genetic evidence for this rare instance of stable hybrid zone was corroborated by the colonization chronology derived from published fossil data, indicating that the two fir species initially came into contact in the area corresponding to the current sympatric zone 11 kyr ago. While an explanatory analysis suggested the putative influence of various environmental factors on the relative abundance of cytoplasmic genome combinations, further research appears necessary to assess the role of both demographic history and selective factors in driving the dynamics of hybrid zones.
Data from: Formation of a recent hybrid zone offers insight to the geographic puzzle and maintenance of species boundaries in musk turtles
Speciation is the result of an accumulation of reproductive barriers between populations, pinpointing these factors is often difficult. However, hybrid zones can form when these barriers are not complete, especially when lineages come into contact in intermediate or modified habitats. We examine a hybrid zone between two closely related riverine turtle species, Sternotherus depressus and S. peltifer, and use ddRAD sequencing to to understand how this hybrid zone formed and elucidate genomic patterns of reproductive isolation. First the geographic extent and timing of the hybrid zone formation is established to provide context for understanding the role of extrinsic and intrinsic reproductive isolating mechanisms in this system. Then, the strength of selection on taxon-specific contributions to maintenance of the hybrid zone is inferred using a Bayesian genomic cline model. These analyses find a role for selection inhibiting introgression in some genomic regions at one end of the hybrid zone and promoting introgression in many loci at the other. When selective pressures necessary to generate outliers to the genomic cline are considered with the geographic and temporal context of this hybrid zone we conclude that habitat-specific selection likely limits introgression from S. depressus to S. peltifer in the direction of river flow. However, selection is mediating rapid, unidirectional introgression from S. peltifer to S. depressus which is likely facilitated by anthropogenic habitat alteration. These findings indicate a potentially imminent threat of population-level genomic extinction for an already imperiled species due to ongoing human-caused habitat alteration.
Data from: Climate-driven build-up of temporal isolation within a recently formed avian hybrid zone
Divergence in the onset of reproduction can act as an important source of reproductive isolation (i.e. allochronic isolation) between co-occurring young species, but evidence for the evolutionary processes leading to such divergence is often indirect. While advancing spring seasons strongly affect the onset of reproduction in many taxa, it remains largely unexplored whether contemporary spring advancement directly affects allochronic isolation between young species. We examined how increasing spring temperatures affected onset of reproduction and thereby hybridization between pied and collared flycatchers (Ficedula spp.) across habitat types in a young secondary contact zone. We found that both species have advanced their timing of breeding in 14 years. However, selection on pied flycatchers to breed earlier was weaker, resulting in a slower response to advancing springs compared to collared flycatchers and thereby build-up of allochronic isolation between the species. We argue that a pre-adaptation to a broader niche use (diet) of pied flycatchers explains the slower response to raising spring temperature, but that reduced risk to hybridize may contribute to further divergence in the onset of breeding in the future. Our results show that minor differences in the response to environmental change of co-occurring closely related species can quickly cause allochronic isolation.
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Allen Brain Atlas
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Annotated Behaviour and Observability Dataset (ABODe)
ABODe is a University of Edinburgh DataShare dataset for behavior classification in group-housed mice using home-cage video, identities, bounding boxes, ground-plate positions, and annotator labels.
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