Genetic Clines Research Articles

Genetic history and biological adaptive landscape of the Tujia people inferred from shared haplotypes and alleles

BackgroundHigh-quality genomic datasets from under-representative populations are essential for population genetic analysis and medical relevance. Although the Tujia are the most populous ethnic minority in southwestern China, previous genetic studies have been fragmented and only partially reveal their genetic diversity landscape. The understanding of their fine-scale genetic structure and potentially differentiated biological adaptive features remains nascent.ObjectivesThis study aims to explore the demographic history and genetic architecture related to the natural selection of the Tujia people, focusing on a meta-Tujia population from the central regions of the Yangtze River Basin.ResultsPopulation genetic analyses conducted on the meta-Tujia people indicate that they occupy an intermediate position in the East Asian North-South genetic cline. A close genetic affinity was identified between the Tujia people and neighboring Sinitic-speaking populations. Admixture models suggest that the Tujia can be modeled as a mixture of northern and southern ancestries. Estimates of f3/f4 statistics confirmed the presence of ancestral links to ancient Yellow River Basin millet farmers and the BaBanQinCen-related groups. Furthermore, population-specific natural selection signatures were explored, revealing highly differentiated functional variants between the Tujia and southern indigenous populations, including genes associated with hair morphology (e.g., EDAR) and skin pigmentation (e.g., SLC24A5). Additionally, both shared and unique selection signatures were identified among ethnically diverse but geographically adjacent populations, highlighting their extensive admixture and the biological adaptations introduced by this admixture.ConclusionsThe study unveils significant population movements and genetic admixture among the Tujia and other ethno-linguistically diverse East Asian groups, elucidating the differentiated adaptation processes across geographically diverse populations from the current genetic landscape.

Geographical and genetic clines in Dracocephalum kotschyi X Dracocephalum oligadenium hybrids: landscape genetics and genocline analyses

Conservation and management of medicinally important plants are among the necessary tasks all over the world. The genus Dracocephalum (Lamiaceae) contains about 186 perennials, or annual herb species that have been used for their medicinal values in different parts of the world as an antihyperlipidemic, analgesic, antimicrobial, antioxidant, as well as anticancer medicine. Producing detailed data on the genetic structure of these species and their response against climate change and human landscape manipulation can be very important for conservation purposes. Therefore, the present study was performed on six geographical populations of two species in the Dracocephalum genus, namely, Dracocephalum kotschyi, and Dracocephalum oligadenium, as well as their inter-specific hybrid population. We carried out, population genetic study, landscape genetics, species modeling, and genetic cline analyses on these plants. We present here, new findings on the genetic structure of these populations, and provide data on both geographical and genetic clines, as well as morphological clines. We also identified genetic loci that are potentially adaptive to the geographical spatial features and genocide conditions. Different species distribution modeling (SDM) methods, used in this work revealed that bioclimatic variables related to the temperature and moisture, play an important role in Dracocephalum population’s geographical distribution within IRAN and that due to the presence of some potentially adaptive genetic loci in the studied plants, they can survive well enough by the year 2050 and under climate change. The findings can be used for the protection of these medicinally important plant.

Genetic variation in phenology of wild Arabidopsis thaliana plants.

Phenology and the timing of development are often under selection, but at the same time influence selection on other traits by controlling how traits are expressed across seasons. Plants often exhibit high natural genetic variation in phenology when grown in controlled environments, and many genetic and molecular mechanisms underlying phenology have been dissected. There remains considerable diversity of germination and flowering time within populations in the wild and the contribution of genetics to phenological variation of wild plants is largely unknown. We obtained collection dates of naturally inbred Arabidopsis thaliana accessions from nature and compared them to experimental data on the descendant inbred lines that we synthesized from two new and 155 published controlled experiments. We tested whether the genetic variation in flowering and germination timing from experiments predicted the phenology of the same inbred lines in nature. We found that genetic variation in phenology from controlled experiments significantly, but weakly, predicts day of collection from the wild, even when measuring collection date with accumulated photothermal units. We found that experimental flowering time breeding values were correlated to wild flowering time at location of origin estimated from herbarium collections. However, local variation in collection dates within a region was not explained by genetic variation in experiments, suggesting high plasticity across small-scale environmental gradients. This apparent low heritability in natural populations may suggest strong selection or many generations are required for phenological adaptation and the emergence of genetic clines in phenology.

Investigating the footprint of post-domestication dispersal on the diversity of modern European, African and Asian goats

BackgroundGoats were domesticated in the Fertile Crescent about 10,000 years before present (YBP) and subsequently spread across Eurasia and Africa. This dispersal is expected to generate a gradient of declining genetic diversity with increasing distance from the areas of early livestock management. Previous studies have reported the existence of such genetic cline in European goat populations, but they were based on a limited number of microsatellite markers. Here, we have analyzed data generated by the AdaptMap project and other studies. More specifically, we have used the geographic coordinates and estimates of the observed (Ho) and expected (He) heterozygosities of 1077 European, 1187 African and 617 Asian goats belonging to 38, 43 and 22 different breeds, respectively, to find out whether genetic diversity and distance to Ganj Dareh, a Neolithic settlement in western Iran for which evidence of an early management of domestic goats has been obtained, are significantly correlated.ResultsPrincipal component and ADMIXTURE analyses revealed an incomplete regional differentiation of European breeds, but two genetic clusters representing Northern Europe and the British-Irish Isles were remarkably differentiated from the remaining European populations. In African breeds, we observed five main clusters: (1) North Africa, (2) West Africa, (3) East Africa, (4) South Africa, and (5) Madagascar. Regarding Asian breeds, three well differentiated West Asian, South Asian and East Asian groups were observed. For European and Asian goats, no strong evidence of significant correlations between Ho and He and distance to Ganj Dareh was found. In contrast, in African breeds we detected a significant gradient of diversity, which decreased with distance to Ganj Dareh.ConclusionsThe detection of a genetic cline associated with distance to the Ganj Dareh in African but not in European or Asian goat breeds might reflect differences in the post-domestication dispersal process and subsequent migratory movements associated with the management of caprine populations from these three continents.

High dispersal ability versus migratory traditions: Fine-scale population structure and post-glacial colonisation in bar-tailed godwits.

In migratory animals, high mobility may reduce population structure through increased dispersal and enable adaptive responses to environmental change, whereas rigid migratory routines predict low dispersal, increased structure, and limited flexibility to respond to change. We explore the global population structure and phylogeographic history of the bar-tailed godwit, Limosa lapponica, a migratory shorebird known for making the longest non-stop flights of any landbird. Using nextRAD sequencing of 14,318 single-nucleotide polymorphisms and scenario-testing in an Approximate Bayesian Computation framework, we infer that bar-tailed godwits existed in two main lineages at the last glacial maximum, when much of their present-day breeding range persisted in a vast, unglaciated Siberian-Beringian refugium, followed by admixture of these lineages in the eastern Palearctic. Subsequently, population structure developed at both longitudinal extremes: in the east, a genetic cline exists across latitude in the Alaska breeding range of subspecies L. l. baueri; in the west, one lineage diversified into three extant subspecies L. l. lapponica, taymyrensis, and yamalensis, the former two of which migrate through previously glaciated western Europe. In the global range of this long-distance migrant, we found evidence of both (1) fidelity to rigid behavioural routines promoting fine-scale geographic population structure (in the east) and (2) flexibility to colonise recently available migratory flyways and non-breeding areas (in the west). Our results suggest that cultural traditions in highly mobile vertebrates can override the expected effects of high dispersal ability on population structure, and provide insights for the evolution and flexibility of some of the world's longest migrations.

Bronze age Northern Eurasian genetics in the context of development of metallurgy and Siberian ancestry

The Eurasian Bronze Age (BA) has been described as a period of substantial human migrations, the emergence of pastoralism, horse domestication, and development of metallurgy. This study focuses on two north Eurasian sites sharing Siberian genetic ancestry. One of the sites, Rostovka, is associated with the Seima-Turbino (ST) phenomenon (~2200-1900 BCE) that is characterized by elaborate metallurgical objects found throughout Northern Eurasia. The genetic profiles of Rostovka individuals vary widely along the forest-tundra Siberian genetic cline represented by many modern Uralic-speaking populations, and the genetic heterogeneity observed is consistent with the current understanding of the ST being a transcultural phenomenon. Individuals from the second site, Bolshoy Oleni Ostrov in Kola, in comparison form a tighter cluster on the Siberian ancestry cline. We further explore this Siberian ancestry profile and assess the role of the ST phenomenon and other contemporaneous BA cultures in the spread of Uralic languages and Siberian ancestry.

A new look at genetic variability in pomegranate: Landscape genetics and structural equation modeling (SEM)

Pomegranate (Punica granatum L.) is an important horticultural plant in Iran and has been a food source since ancient times. Despite several genetic diversity studies conducted on these taxa, there are no reports on the landscape genetics of these important plants in Iran, nor is there any information on the effects of environmental, spatial, and climatic variables on the genetic structure of pomegranate. Therefore, this study used genetics, structural equation modeling (SEM), and species distribution modeling (SDM) approaches to explore the above-mentioned objectives. We used both cytogenetic and molecular analyses (SSR and SCoT markers) of several pomegranate samples along with environmental, spatial, and climatic variables. The redundancy analysis (RDA) analysis showed a significant positive association between terminal chiasmata with the longitudinal distribution of the pomegranate accession, while total chiasma number and interstitial chiasmata have an association with the altitude. The spatial PCA analysis indicated the role played by both global and local spatial variables in the cytogenetic variability like the univalent and terminal chiasmata formation. The Mantel test indicates that the cytogenetic difference in pomegranate plants is not related to their geographical distance, while the Moran I test result shows that geographical regions with similar spatial conditions affect the cytogenetic structuring of pomegranate plants in a similar way. SEM methods showed a strong negative association between bivalent formation and the environmental variables, while they showed both positive and negative associations between some of the environmental variables and different kinds of chiasmata. The sPCA analysis of molecular data showed a significant global, and local, spatial structuring of the molecular data and the genetic cline formation within the pomegranate accessions studied. Similarly, the spatial PCA analysis of climate variables, precipitation, and temperature revealed a significant structuring of genetic diversity and the formation of genetic clines by these factors. RDA analysis identified some of the loci that are significantly associated with temperature and precipitation. Therefore, both geographical/ or spatial variables and climate factors contribute to the genetic structure of the pomegranate accessions studied. SEM models based on genetic data revealed a positive association between environmental and climate variables with genetic diversity parameters and SSR-SCoT molecular loci studied. Climate change is unlikely to hurt pomegranate growing areas due to the high genetic diversity of pomegranate plants and the diverse genetic lineages present in the country.

Correction to: A genetic cline shapes population structure of the round sardinella along its West African distribution

Correction to: A genetic cline shapes population structure of the round sardinella along its West African distribution

Genomic formation of Tibeto-Burman speaking populations in Guizhou, Southwest China

Sino-Tibetan is the most prominent language family in East Asia. Previous genetic studies mainly focused on the Tibetan and Han Chinese populations. However, due to the sparse sampling, the genetic structure and admixture history of Tibeto-Burman-speaking populations in the low-altitude region of Southwest China still need to be clarified. We collected DNA from 157 individuals from four Tibeto-Burman-speaking groups from the Guizhou province in Southwest China. We genotyped the samples at about 700,000 genome-wide single nucleotide polymorphisms. Our results indicate that the genetic variation of the four Tibeto-Burman-speaking groups in Guizhou is at the intermediate position in the modern Tibetan-Tai-Kadai/Austronesian genetic cline. This suggests that the formation of Tibetan-Burman groups involved a large-scale gene flow from lowland southern Chinese. The southern ancestry could be further modelled as deriving from Vietnam’s Late Neolithic-related inland Southeast Asia agricultural populations and Taiwan’s Iron Age-related coastal rice-farming populations. Compared to the Tibeto-Burman speakers in the Tibetan-Yi Corridor reported previously, the Tibeto-Burman groups in the Guizhou region received additional gene flow from the southeast coastal area of China. We show a difference between the genetic profiles of the Tibeto-Burman speakers of the Tibetan-Yi Corridor and the Guizhou province. Vast mountain ranges and rivers in Southwest China may have decelerated the westward expansion of the southeast coastal East Asians. Our results demonstrate the complex genetic profile in the Guizhou region in Southwest China and support the multiple waves of human migration in the southern area of East Asia.

The spatio-temporal diversification of SRK alleles in an Arabidopsis polyploid hybrid and introgression zone

Reproductive barriers and directional geneflow may play a key role in maintaining genetic gradients, thereby allowing ecological differentiation along ecological clines. In Brassicaceae, a sporophytic incompatibility system (SI) contributes to such barriers to geneflow, with the maternal component represented by a large diversity of SRK (stigma-specific S locus receptor kinase) alleles at varying frequencies and levels of dominance. Such clinal genetic gradient along an ecological gradient following a shift towards much drier and warmer conditions and also the bedrock type shifts from calcareous to silicious has been found earlier in an Arabidopsis introgression system involving A. lyrata and A. arenosa. The metapopulation system spans from the northeastern Austrian forealps northward towards the Danube river and the Bohemian massif. Here we explore diversification of population-level SRK gene pools across these hybrid Arabidopsis tetraploid metapopulation system and its putative parental source populations. Since it has been demonstrated that A. lyrata served as the maternal parent and A. arenosa introgressed via pollen constituting a genetic cline with decreasing contribution of A. arenosa genetic background, we test the hypothesis that this cline can be also explained by SRK allelic differentiation. A total of 603 individuals from 45 populations of introgressed and non-introgressed A. lyrata and A. arenosa across a 80 km transect were analysed for SRK allele variation. In total, 22 alleles from all four previously described dominance classes have been documented. Although there is clinal morphological and genetic variation following the introgression zone, SRK alleles do not follow this signature of the paternal taxa. Furthermore, the functional SI system is fully maintained across the transect, and crossing experiments show that there is no decrease in fitness depending on varying distances between populations along the transect studied herein. We conclude that transmission and structure of the SRK allelic gene pool contributes to the postglacial colonization success along such a pronounced ecological gradient maintaining a functional SI system and counteracting genetic depletion.

Demographic history of Ryukyu islanders at the southern part of the Japanese Archipelago inferred from whole-genome resequencing data

The Ryukyu Islands are located in the southernmost part of the Japanese Archipelago and consist of several island groups. Each island group has its own history and culture, which differ from those of mainland Japan. People of the Ryukyu Islands are genetically subdivided; however, their detailed demographic history remains unclear. We report the results of a whole-genome sequencing analysis of a total of 50 Ryukyu islanders, focusing on genetic differentiation between Miyako and Okinawa islanders. We confirmed that Miyako and Okinawa islanders cluster differently in principal component analysis and ADMIXTURE analysis and that there is a population structure among Miyako islanders. The present study supports the hypothesis that population differentiation is primarily caused by genetic drift rather than by differences in the rate of migration from surrounding regions, such as the Japanese main islands or Taiwan. In addition, the genetic cline observed among Miyako and Okinawa islanders can be explained by recurrent migration beyond the bounds of these islands. Our analysis also suggested that the presence of multiple subpopulations during the Neolithic Ryukyu Jomon period is not crucial to explain the modern Ryukyu populations. However, the assumption of multiple subpopulations during the time of admixture with mainland Japanese is necessary to explain the modern Ryukyu populations. Our findings add insights that could help clarify the complex history of populations in the Ryukyu Islands.

Shared and distinct patterns of genetic structure in two sympatric large decapods

AbstractAimComparing genetic structure in species with shared spatial ranges and ecological niches can help identify how dissimilar aspects of biology can shape differences in population connectivity. Similarly, where species are widely distributed across heterogeneous environments and major topographic barriers, knowledge of the structuring of populations can help reveal the impacts of factors which limit dispersal and/or drive divergence, aiding conservation management.LocationEuropean seas of the northeast Atlantic and Mediterranean.TaxaEuropean clawed lobster (Homarus gammarus) and European crawfish (Palinurus elephas), two sympatric, heavily fished decapods with extensive dispersal potential.MethodsBy RAD‐sequencing 214 H. gammarus from 32 locations and 349 P. elephas from 15 locations, we isolated 6340 and 7681 SNP loci, respectively. Using these data to characterise contemporary population structuring, we investigate potential spatial and environmental drivers of genomic heterogeneity.ResultsWe found higher levels of differentiation among clawed lobsters than crawfish, both globally and within basins, and demonstrate where known hydrographic and topographic barriers generate shared patterns of divergence, such as a genetic break between the Atlantic and Mediterranean basins. Genetic structure not common to both species is principally apparent in the Atlantic portions of their range, where clawed lobster exhibits a genetic cline and increased differentiation towards range margins, while crawfish appear effectively panmictic throughout this region.Main ConclusionsWe attribute the comparative lack of crawfish population structuring to their greater dispersal tendencies via a longer pelagic larval duration and sporadic adult movements. In contrast, genetic connectivity in clawed lobster is relatively restricted, with the correlation of site of origin and temperature to geographical heterogeneity at many divergent loci indicative of both neutral and adaptive processes. Our results help inform how contemporary management can account for likely demographic connectivity and marry the conservation of genomic variation with sustainable fisheries in these ecologically and economically important crustaceans.

Interactions between environmental factors drive selection on cyanogenesis in Trifolium repens

Phenotypic and genetic clines frequently evolve due to varying selection along environmental gradients. However, the specific environmental factors that impose differential selection are often multivariate and difficult to tease apart. We addressed this complexity using a factorial manipulation of watering, soil nutrients and (simulated) herbivory in controlled conditions to better understand the agents of selection driving the evolution of clines in a polymorphic chemical antiherbivore defence, hydrogen cyanide (HCN), of the plant white clover Trifolium repens. We found the presence or absence of the two metabolic components required for HCN production (cyanogenic glucosides and linamarase) to be more prominent determinants of vegetative growth and sexual reproduction in T. repens than HCN itself. We also found that the ability to produce one or both of cyanogenic glucosides or linamarase resulted in a growth advantage under drought and simulated herbivory that outweighs the metabolic cost of their production. These results support the view that the metabolic components underlying HCN play important roles beyond defence by increasing plant tolerance to stress. The growth advantage under drought, however, was diminished in the absence of nutrient addition, consistent with multivariate interactions as drivers of selection. This study provides novel insight into how a cosmopolitan plant has adapted to environmental gradients, and more generally, highlights the importance of considering interactions between multiple environmental factors when studying the evolution of phenotypic and genetic clines.

Range-wide population genomics of the spongy moth, Lymantria dispar (Erebidae): Implications for biosurveillance, subspecies classification and phylogeography of a destructive moth.

The spongy moth, Lymantria dispar, is an irruptive forest pest native to Eurasia where its range extends from coast to coast and overspills into northern Africa. Accidentally introduced from Europe in Massachusetts in 1868-1869, it is now established in North America where it is considered a highly destructive invasive pest. A fine-scale characterization of its population genetic structure would facilitate identification of source populations for specimens intercepted during ship inspections in North America and would enable mapping of introduction pathways to help prevent future incursions into novel environments. In addition, detailed knowledge of L.dispar's global population structure would provide new insight into the adequacy of its current subspecies classification system and its phylogeographic history. To address these issues, we generated >2000 genotyping-by-sequencing-derived SNPs from 1445 contemporary specimens sampled at 65 locations in 25 countries/3 continents. Using multiple analytical approaches, we identified eight subpopulations that could be further partitioned into 28 groups, achieving unprecedented resolution for this species' population structure. Although reconciliation between these groupings and the three currently recognized subspecies proved to be challenging, our genetic data confirmed circumscription of the japonica subspecies to Japan. However, the genetic cline observed across continental Eurasia, from L.dispar asiatica in East Asia to L.d.dispar in Western Europe, points to the absence of a sharp geographical boundary (e.g., the Ural Mountains) between these two subspecies, as suggested earlier. Importantly, moths from North America and the Caucasus/Middle East displayed high enough genetic distances from other populations to warrant their consideration as separate subspecies of L.dispar. Finally, in contrast with earlier mtDNA-based investigations that identified the Caucasus as L.dispar's place of origin, our analyses suggest continental East Asia as its evolutionary cradle, from where it spread to Central Asia and Europe, and to Japan through Korea.

The genetic history of Scandinavia from the Roman Iron Age to the present

We investigate a 2,000-year genetic transect through Scandinavia spanning the Iron Age to the present, based on 48 new and 249 published ancient genomes and genotypes from 16,638 modern individuals. We find regional variation in the timing and magnitude of gene flow from three sources: the eastern Baltic, the British-Irish Isles, and southern Europe. British-Irish ancestry was widespread in Scandinavia from the Viking period, whereas eastern Baltic ancestry is more localized to Gotland and central Sweden. In some regions, a drop in current levels of external ancestry suggests that ancient immigrants contributed proportionately less to the modern Scandinavian gene pool than indicated by the ancestry of genomes from the Viking and Medieval periods. Finally, we show that a north-south genetic cline that characterizes modern Scandinavians is mainly due to the differential levels of Uralic ancestry and that this cline existed in the Viking Age and possibly earlier.

G-matrix stability in clinally diverging populations of an annual weed.

How phenotypic and genetic divergence among populations is influenced by the genetic architecture of those traits, and how microevolutionary changes in turn affect the within-population patterns of genetic variation, are of major interest to evolutionary biology. Work on Ipomoea hederacea, an annual vine, has found genetic clines in the means of a suite of ecologically important traits, including flowering time, growth rate, seed mass, and corolla width. Here we investigate the genetic (co)variances of these clinally varying traits in two northern range-edge and two central populations of I. hederacea to evaluate the influence of the genetic architecture on divergence across the range. We find (1) limited evidence for clear differentiation between Northern and Southern populations in the structure of G, suggesting overall stability of G across the range despite mean trait divergence and (2) that the axes of greatest variation (gmax) were unaligned with the axis of greatest multivariate divergence. Together these results indicate the role of the quantitative genetic architecture in constraining evolutionary response and divergence among populations across the geographic range.

Deep structured populations of geographically isolated nipa (Nypa fruticans Wurmb.) in the Indo-West Pacific revealed using microsatellite markers.

Nipa (Nypa fruticans Wurmb.) is an important mangrove palm species, but it is understudied due to lack of information on genetic patterns within its distribution range. In this study, we identified 18 informative microsatellite markers to assess genetic variations among local populations in the Indo-West Pacific (IWP). Results showed population stratification based on high genetic differentiation (FST = 0.22131) with the Mantel test indicating significance to isolation-by-distance. We found a pronounced differentiation between the west populations in Sri Lanka and east populations in Southeast Asia. The east populations around the South China Sea were more genetically similar than those along the Malacca Strait and Java Sea. These genetic clines were shaped by ocean circulations and seasonal monsoon reversals as plausible factors. The Malacca Strait was confirmed as both a genetic and a geographic barrier rather than a corridor according to the Monmonier plot. Simulations of directional migration indicated a statistically strong contemporary genetic connectivity from west to east where Sri Lankan immigrants were detected as far as central Philippines via long-distance dispersal. This is the first report on the recent migration patterns of nipa using microsatellites. Assignment of first-generation (F0) immigrants suggested Mainland Southeast Asia as a melting pot due to the admixture associated with excess of homozygosity. The western populations were recent expansions that emerged in rapid succession based on a phylogram as supported by footprints of genetic drift based on bottleneck tests.

Lack of a genetic cline and temporal genetic stability in an introduced barnacle along the Pacific coast of Japan.

BackgroundLarge numbers of exotic marine species have been introduced worldwide. Monitoring of introduced species is important to reveal mechanisms underlying their establishment and expansion. Balanus glandula is a common intertidal barnacle native to the northeastern Pacific. However, this species has been introduced to Japan, South America, South Africa, and Europe. While a latitudinal genetic cline is well known in its native range, it is unclear whether such a genetic cline occurs in introduced areas. Twenty years have passed since it was first identified in Japan and its distribution now ranges from temperate to subarctic regions.MethodsIn the present study, we examined genotypes of cytochrome oxidase subunit I (COI) of mitochondrial (mt)-DNA and elongation factor 1a (EF1) across the distribution of B. glandula in Japan at high and mid intertidal zones.ResultsAt all sampling sites, native northern genotypes are abundant and I did not detect significant effects of latitude, tide levels, or their interaction on genotypic frequencies. Further, I did not detect any change of genotype composition between data collected during a study in 2004 and samples in the present study collected in 2019. Data from the present study offer an important baseline for future monitoring of this species and supply valuable insights into the mechanisms of establishment and expansion of introduced marine species generally.

Tension zone trapped by exogenous cline: Analysis of a narrow hybrid zone between two parapatric Oxytropis species (Fabaceae).

Hybrid zones have been widely highlighted for their interest in understanding evolutionary processes. It is generally accepted that hybrid zones can be maintained in a balance between dispersal and selection. However, the selective forces can either be endogenous (i.e., genetic incompatibilities between parental taxa) or exogenous (i.e., parental taxa are adapted to different environments). In this study, we evaluated these alternatives and determined the maintenance of a narrow hybrid zone between parapatric distributed Oxytropis diversifolia and O. leptophylla in Nei Mongol, China. For 507 individuals sampled from two populations in the hybrid zone, 12 O. diversifolia populations and five O. leptophylla populations, we measured leaf‐morphological characteristics, quantified genetic structure using 11 nuclear microsatellite loci and five chloroplast DNA intergenic regions, collected micro‐ and macrohabitat data, and conducted geographical cline analysis. We found that the two species differed in leaf morphology, and putative hybrids showed either intermediacy or a bias to O. diversifolia. Parental taxa formed two genetically distinct clusters, while populations in the hybrid zone consisted of both parental forms and various admixed individuals, exhibiting a bimodal pattern. The hybrid zone was coupled to ecological transitions of both microhabitat (i.e., the slope) and macroclimatic conditions. However, the genetic clines were significantly narrower than the environmental cline. Our results indicate that endogenous selection can be primarily responsible for maintaining the hybrid zone, while local adaptation accounts for the position of the zone. We further suggest the probable outcome of hybridization could be introgression.

Maintenance of local adaptation despite gene flow in a coastal songbird.

Adaptation to local environments is common in widespread species and the basis of ecological speciation. The song sparrow (Melospiza melodia) is a widespread, polytypic passerine that occurs in shrubland habitats throughout North America. We examined the population structure of two parapatric subspecies that inhabit different environments: the Atlantic song sparrow (M. m. atlantica), a coastal specialist, and the eastern song sparrow (M. m. melodia), a shrubland generalist. These populations lacked clear mitochondrial population structure, yet coastal birds formed a distinct nuclear genetic cluster. We found weak overall genomic differentiation between these subspecies, suggesting either recent divergence, extensive gene flow, or a combination thereof. There was a steep genetic cline at the transition to coastal habitats, consistent with isolation by environment, not isolation by distance. A phenotype under divergent selection, bill size, varied with the amount of coastal ancestry in transitional areas, but larger bill size was maintained in coastal habitats regardless of ancestry, further supporting a role for selection in the maintenance of these subspecies. Demographic modeling suggested a divergence history of limited gene flow followed by secondary contact, which has emerged as a common theme in adaptive divergence across taxa.