Evidence Of Introgression Research Articles

Genome‐Wide Population Structure in a Marine Keystone Species, the European Flat Oyster (Ostrea edulis)

ABSTRACTOstrea edulis, the European flat oyster, was once a widespread economically and ecologically important marine species, but has suffered dramatic declines over the past two centuries. Consequently, there has been a surge in European restoration efforts, many of which focus on restocking as a conservation measure. In this study, we used whole‐genome sequencing (WGS) data to investigate the population structure, demographic history, and patterns of local adaptation of O. edulis across its natural distribution with increased sampling densities at Scandinavian localities. Results revealed seven distinct genetic clusters, including previously undescribed complex population structure in Norway, and evidence for introgression between genetic clusters in Scandinavia. We detected large structural variants (SVs) on three pseudo‐chromosomes. These megabase long regions were characterised by strong linkage disequilibrium and clear geographical differentiation, suggestive of chromosomal inversions potentially associated with local adaptation. The results indicated that genomic traces of past translocations of non‐native O. edulis were still present in some individuals, but overall, we found limited evidence of major impacts of translocations on the scale of contemporary population structure. Our findings highlight the importance of considering population structure and signatures of selection in the design of effective conservation strategies to preserve and restore wild native European flat oyster populations, and we provide direct knowledge safeguarding sustainable mitigation actions in this important species.

Towards the conservation of the crucian carp in Europe: Prolific hybridization but no evidence for introgression between native and non-native taxa.

Hybridization plays a pivotal role in evolution, influencing local adaptation and speciation. However, it can also reduce biodiversity, which is especially damaging when native and non-native species meet. Hybridization can threaten native species via competition (with vigorous hybrids), reproductive resource wastage and gene introgression. The latter, in particular, could result in increased fitness in invasive species, decreased fitness of natives and compromise reintroduction or recovery conservation practices. In this study, we use a combination of RAD sequencing and microsatellites for a range-wide sample set of 1366 fish to evaluate the potential for hybridization and introgression between native crucian carp (Carassius carassius) and three non-native taxa (Carassius auratus auratus, Carassius auratus gibelio and Cyprinus carpio) in European water bodies. We found hybridization between native and non-native taxa in 82% of populations with non-natives present, highlighting the potential for substantial ecological impacts from hybrids on crucian carp populations. However, despite such high rates of hybridization, we could find no evidence of introgression between these taxa. The presence of triploid backcrosses in at least two populations suggests that the lack of introgression among these taxa is likely due to meiotic dysfunction in hybrids, leading to the production of polyploid offspring which are unable to reproduce sexually. This result is promising for crucian reintroduction programs, as it implies limited risk to the genetic integrity of source populations. Future research should investigate the reproductive potential of triploid hybrids and the ecological pressures hybrids impose on C. carassius.

Genetic diversity of Pyrus pyraster (L.) Burgsd. and P. spinosa Forssk.: evidence of introgression from cultivated into wild pear populations

Genetic diversity of Pyrus pyraster (L.) Burgsd. and P. spinosa Forssk.: evidence of introgression from cultivated into wild pear populations

Speciation across biomes: Rapid diversification with reproductive isolation in the Australian delicate mice.

Phylogeographic studies of continental clades, especially when combined with palaeoclimate modelling, provide powerful insight into how environment drives speciation across climatic contexts. Australia, a continent characterized by disparate modern biomes and dynamic climate change, provides diverse opportunity to reconstruct the impact of past and present environments on diversification. Here, we use genomic-scale data (1310 exons and whole mitogenomes from 111 samples) to investigate Pleistocene diversification, cryptic diversity, and secondary contact in the Australian delicate mice (Hydromyini: Pseudomys), a recent radiation spanning almost all Australian environments. Across northern Australia, we find no evidence for introgression between cryptic lineages within Pseudomys delicatulus sensu lato, with palaeoclimate models supporting contraction and expansion of suitable habitat since the last glacial maximum. Despite multiple contact zones, we also find little evidence of introgression at a continental scale, with the exception of a potential hybrid zone in the mesic biome. In the arid zone, combined insights from genetic data and palaeomodels support a recent expansion in the arid specialist P. hermannsburgensis and contraction in the semi-arid P. bolami. In the face of repeated secondary contact, differences in sperm morphology and chromosomal rearrangements are potential mechanisms that maintain species boundaries in these recently diverged species. Additionally, we describe the western delicate mouse as a new species and recommend taxonomic reinstatement of the eastern delicate mouse. Overall, we show that speciation in an evolutionarily young and widespread clade has been driven by environmental change, and potentially maintained by divergence in reproductive morphology and chromosome rearrangements.

Introgression and persistence of cultivar alleles in wild carrot (Daucus carota) populations in the United States.

Cultivated species and their wild relatives often hybridize in the wild, and the hybrids can survive and reproduce in some environments. However, it is unclear whether cultivar alleles are permanently incorporated into the wild genomes or whether they are purged by natural selection. This question is key to accurately assessing the risk of escape and spread of cultivar genes into wild populations. We used genomic data and population genomic methods to study hybridization and introgression between cultivated and wild carrot (Daucus carota) in the United States. We used single nucleotide polymorphisms (SNPs) obtained via genotyping by sequencing for 450 wild individuals from 29 wild georeferenced populations in seven states and 144 cultivars from the United States, Europe, and Asia. Cultivated and wild carrot formed two genetically differentiated groups, and evidence of crop-wild admixture was detected in several but not all wild carrot populations in the United States. Two regions were identified where cultivar alleles were present in wild carrots: California and Nantucket Island (Massachusetts). Surprisingly, there was no evidence of introgression in some populations with a long-known history of sympatry with the crop, suggesting that post-hybridization barriers might prevent introgression in some areas. Our results provide support for the introgression and long-term persistence of cultivar alleles in wild carrots populations. We thus anticipate that the release of genetically engineered (GE) cultivars would lead to the introduction and spread of GE alleles in wild carrot populations.

Evidence of introgression, ecological divergence and adaptation in Asterias sea stars.

Hybrid zones are important windows into the evolutionary dynamics of populations, revealing how processes like introgression and adaptation structure population genomic variation. Importantly, they are useful for understanding speciation and how species respond to their environments. Here, we investigate two closely related sea star species, Asterias rubens and A. forbesi, distributed along rocky European and North American coastlines of the North Atlantic, and use genome-wide molecular markers to infer the distribution of genomic variation within and between species in this group. Using genomic data and environmental niche modelling, we document hybridization occurring between northern New England and the southern Canadian Maritimes. We investigate the factors that maintain this hybrid zone, as well as the environmental variables that putatively drive selection within and between species. We find that the two species differ in their environmental niche breadth; Asterias forbesi displays a relatively narrow environmental niche while conversely, A. rubens has a wider niche breadth. Species distribution models accurately predict hybrids to occur within environmental niche overlap, thereby suggesting environmental selection plays an important role in the maintenance of the hybrid zone. Our results imply that the distribution of genomic variation in North Atlantic sea stars is influenced by the environment, which will be crucial to consider as the climate changes.

Traditional Management of Maize in the Sierra Sur, Oaxaca, Maintains Moderate Levels of Genetic Diversity and Low Population Differentiation Among Landraces

Oaxaca is one of the areas of early maize diversification, with 28 to 35 recognized agronomic races. Campesinos (farmers) cultivate at least ten different races in the Los Loxicha region. There is evidence of introgression between them; however, some traditional practices have promoted further differentiation evidenced by the presence of different landraces, clearly recognized by various morphological and phenological characteristics. Therefore, moderate levels of genetic diversity and low levels of population differentiation are expected. Seven communities belonging to two municipalities were selected in 2005. In total, 140 semistructured interviews were administered, inquiring about cultural practices, which included questions about maize seed, ear, and cob management and selection and maize cultivation. Based on interviews and permissions, 30 maize plants from each of 28 fields (milpas) with maize crop belonging to five landraces (Conejo, Hueso, Tablita, Tepecente, and Pinto) were sampled. From the 82 ISSR loci amplified, Hueso and Conejo exhibited the highest and lowest number of loci (70 and 56 loci, respectively); 72% of loci analyzed in the five populations were polymorphic. The Hueso landrace presented the highest percentage of polymorphism (73%) and Conejo the lowest (54%). The expected heterozygosity (HeT) for the five landraces was 0.225 ± 0.032, and the genetic diversity of Nei (HST) was 0.225 ± 0.034. The population differentiation values obtained with GST indicated that Tablita and Hueso were the least differentiated, while the most differentiated were Pinto and Tepecente. STRUCTURE analysis identified two genetically differentiated groups (k = 2), consistent with the length of their agricultural cycle (number of days until flowering). UPGMA analysis showed that milpas belonging to the same landrace and with a specific agricultural cycle length were grouped, regardless of their geographic distribution. These results indicate that traditional management of maize in the Los Loxicha region, particularly as it relates to the selection of ears and seeds and control of the agricultural cycle, maintains a balance between morphological differentiation, moderate levels of genetic diversity and gene flow, and low levels of population differentiation. This has contributed to the high richness and low evenness of agronomic races reported for the mountainous regions of the Sierra Madre del Sur and for Oaxaca.

Genomes of the extinct Bachman's warbler show high divergence and no evidence of admixture with other extant Vermivora warblers.

Bachman's warbler1 (Vermivora bachmanii)-last sighted in 1988-is one of the only North American passerines to recently go extinct.2,3,4 Given extensive ongoing hybridization of its two extant congeners-the blue-winged warbler (V.cyanoptera) and golden-winged warbler (V.chrysoptera)5,6,7,8-and shared patterns of plumage variation between Bachman's warbler and hybrids between those extant species, it has been suggested that Bachman's warbler might have also had a component of hybrid ancestry. Here, we use historic DNA (hDNA) and whole genomes of Bachman's warblers collected at the turn of the 20th century to address this. We combine these data with the two extant Vermivora species to examine patterns of population differentiation, inbreeding, and gene flow. In contrast to the admixture hypothesis, the genomic evidence is consistent with V.bachmanii having been a highly divergent, reproductively isolated species, with no evidence of introgression. We show that these three species have similar levels of runs of homozygosity (ROH), consistent with effects of a small long-term effective population size or population bottlenecks, with one V.bachmanii outlier showing numerous long ROH and a FROH greater than 5%. We also found-using population branch statistic estimates-previously undocumented evidence of lineage-specific evolution in V.chrysoptera near a pigmentation gene candidate, CORIN, which is a known modifier of ASIP, which is in turn involved in melanic throat and mask coloration in this family of birds. Together, these genomic results also highlight how natural history collections are such invaluable repositories of information about extant and extinct species.

Genetic diversity and population structure of the Saharan honey bee Apis mellifera sahariensis from southeastern Morocco: introgression assessment and implications for conservation

This study assessed the conservation status of the Saharan honey bee (Apis mellifera sahariensis) from southeastern Morocco using 12 microsatellite loci to examine genetic diversity and hybridization with other subspecies. Samples from 148 colonies were clustered into seven populations representing the expected distribution of A. m. intermissa and A. m. sahariensis, and reference samples from two European subspecies, A. m. carnica and A. m. mellifera, were included. Moroccan honey bees showed higher genetic diversity than European reference samples, and genetic structure analysis revealed two distinct clusters in Morocco separated by the High Atlas Mountains (FST = 0.05). Although high rates of hybridization with A. m. intermissa jeopardize the genetic integrity of the Saharan honey bee, no evidence of introgression was detected from the European reference subspecies. Additionally, we found that the probability of assignment to Saharan subspecies decreased with increasing human management intensity and precipitation. These findings are important for developing a conservation strategy for the Saharan honey bee in Morocco.

Gene flow assessment helps to distinguish strong genomic structure from speciation in an Iberian ant-eating spider

Although genomic data is boosting our understanding of evolution, we still lack a solid framework to perform reliable genome-based species delineation. This problem is especially critical in the case of phylogeographically structured organisms, with allopatric populations showing similar divergence patterns as species. Here, we assess the species limits and phylogeography of Zodarion alacre, an ant-eating spider widely distributed across the Iberian Peninsula. We first performed species delimitation based on genome-wide data and then validated these results using additional evidence. A commonly employed species delimitation strategy detected four distinct lineages with almost no admixture, which present allopatric distributions. These lineages showed ecological differentiation but no clear morphological differentiation, and evidence of introgression in a mitochondrial barcode. Phylogenomic networks found evidence of substantial gene flow between lineages. Finally, phylogeographic methods highlighted remarkable isolation by distance and detected evidence of range expansion from south-central Portugal to central-north Spain. We conclude that despite their deep genomic differentiation, the lineages of Z. alacre do not show evidence of complete speciation. Our results likely shed light on why Zodarion is among the most diversified spider genera despite its limited distribution and support the use of gene flow evidence to inform species boundaries.

DNA barcodes reveal different speciation scenarios in the four North American Anthocharis Boisduval, Rambur, [Duménil] & Graslin, [1833] (Lepidoptera: Pieridae: Pierinae: Anthocharidini) species groups.

The mitochondrial DNA COI barcode segment sequenced from American Anthocharis specimens across their distribution ranges partitions them into four well-separated species groups and reveals different levels of differentiation within these groups. The lanceolata group experienced the deepest divergence. About 2.7% barcode difference separates the two species: A. lanceolata Lucas, 1852 including A. lanceolata australis (F. Grinnell, 1908), from A. desertolimbus J. Emmel, T. Emmel & Mattoon, 1998. The sara group consists of three species distinctly defined by more than 2% sequence divergence: A. sara Lucas, 1852, A. julia W. H. Edwards, 1872, and A. thoosa (Scudder, 1878). Our treatment is fully consistent with morphological evidence largely based on the characters of fifth instar larvae and pupal cone curvature (Stout, 2005, 2018). In barcodes, it is not possible to see evidence of introgression or hybridization between the three species, and identification by morphology of immature stages always agrees with DNA barcode identification. Interestingly, A. thoosa exhibited the largest intraspecific divergence in DNA barcodes, and several of its metapopulations are identifiable by haplotypes. The cethura group is characterized by the smallest divergence and is best considered as a single species variable in expression of yellow coloration: A cethura C. Felder & R. Felder, 1865. Notably, the most sexually dimorphic subspecies A. cethura morrisoni W. H. Edwards, 1881 is the most distinct by the barcodes. Finally, the midea group barcodes do not always separate A. midea (Hübner, [1809]) and A. limonea (A. Butler, 1871) and we observe gradual accumulation of differences from north (northeastern USA) to south (Hidalgo, Mexico). This barcode gradient suggests a recent origin of the two midea group species and provides another example of vicariant sister species well defined by morphology, ecology and geography, but not necessarily by DNA barcodes.

Whole-genome phylogeography of the blue-faced honeyeater (Entomyzon cyanotis) and discovery and characterization of a neo-Z chromosome.

Whole-genome surveys of genetic diversity and geographic variation often yield unexpected discoveries of novel structural variation, which long-read DNA sequencing can help clarify. Here, we report on whole-genome phylogeography of a bird exhibiting classic vicariant geographies across Australia and New Guinea, the blue-faced honeyeater (Entomyzon cyanotis), and the discovery and characterization of a novel neo-Z chromosome by long-read sequencing. Using short-read genome-wide SNPs, we inferred population divergence events within E. cyanotis across the Carpentarian and other biogeographic barriers during the Pleistocene (~0.3-1.7Ma). Evidence for introgression between nonsister populations supports a hypothesis of reticulate evolution around a triad of dynamic barriers around Pleistocene Lake Carpentaria between Australia and New Guinea. During this phylogeographic survey, we discovered a large (134 Mbp) neo-Z chromosome and we explored its diversity, divergence and introgression landscape. We show that, as in some sylvioid passerine birds, a fusion occurred between chromosome 5 and the Z chromosome to form a neo-Z chromosome; and in E. cyanotis, the ancestral pseudoautosomal region (PAR) appears nonrecombinant between Z and W, along with most of the fused chromosome 5. The added recombination-suppressed portion of the neo-Z (~37.2Mbp) displays reduced diversity and faster population genetic differentiation compared with the ancestral-Z. Yet, the new PAR (~17.4Mbp) shows elevated diversity and reduced differentiation compared to autosomes, potentially resulting from introgression. In our case, long-read sequencing helped clarify the genomic landscape of population divergence on autosomes and sex chromosomes in a species where prior knowledge of genome structure was still incomplete.

Genomics facilitates evaluation and monitoring of McCloud River Redband Trout (Oncorhynchus mykiss stonei)

The McCloud River Redband Trout (MRRT; Oncorhynchus mykiss stonei) is a unique subspecies of rainbow trout that inhabits the isolated Upper McCloud River of Northern California. A major threat to MRRT is introgressive hybridization with non-native rainbow trout from historical stocking and contemporary unauthorized introductions. To help address this concern, we collected RAD-sequencing data on 308 total individuals from MRRT and other California O. mykiss populations and examined population structure using Principal Component and admixture analyses. Our results are consistent with previous studies; we found that populations of MRRT in Sheepheaven, Swamp, Edson, and Moosehead creeks are nonintrogressed. Additionally, we saw no evidence of introgression in Dry Creek, and suggest further investigation to determine if it can be considered a core MRRT conservation population. Sheepheaven Creek was previously thought to be the sole historical lineage of MRRT, but our analysis identified three: Sheepheaven, Edson, and Dry creeks, all of which should be preserved. Finally, we discovered diagnostic and polymorphic SNP markers for monitoring introgression and genetic diversity in MRRT. Collectively, our results provide a valuable resource for the conservation and management of MRRT.

Response to Hill and Powers: It is irrelevant that the mode and tempo of Cassia crossbill speciation is not typical for birds

Species delineation has a long and contentious history, yet most agree that sympatric populations exhibiting high levels of reproductive isolation and evolving independently are species. In an opinion piece, Hill and Powers (2021; hereafter H&P) claim that several recognized species of crossbills (Loxia spp.) do not represent species because by no measure are they discrete, the vocalizations used to categorize crossbills are learned, modified and can switch to that of a different species, and reproductive isolation is incomplete and weak. We argue that the behavioral and genetic evidence indicate that Cassia crossbills L. sinesciuris, which we focus on because the data relevant to species status are more diverse and extensive, are genetically discrete; call modification rarely leads to crossbill misclassification and overwhelmingly results in call divergence and enhanced discrimination; and are nearly completely reproductively isolated with little evidence of introgression from sympatric red crossbills. The differences in our conclusions result in part from H&P mischaracterizing and misconstruing the ecology of Cassia crossbills, geographic context of their divergence, and evidence for reproductive isolation. H&P seemingly require that crossbills must adhere to the typical model of bird speciation–protracted divergence in allopatry, followed by a gradual increase in sympatry if reproductive isolation and ecological divergence allow–and require evidence such as initial long periods of allopatry, FST values > 0.2, divergent mtDNA and intrinsic postzygotic isolation. Although such evidence commonly distinguishes bird species, an increasing number of studies show that such criteria are not necessary to indicate sympatric, evolutionarily independent lineages.

Limited Introgression between Rock-Wallabies with Extensive Chromosomal Rearrangements.

Chromosome rearrangements can result in the rapid evolution of hybrid incompatibilities. Robertsonian fusions, particularly those with monobrachial homology, can drive reproductive isolation amongst recently diverged taxa. The recent radiation of rock-wallabies (genus Petrogale) is an important model to explore the role of Robertsonian fusions in speciation. Here, we pursue that goal using an extensive sampling of populations and genomes of Petrogale from north-eastern Australia. In contrast to previous assessments using mitochondrial DNA or nuclear microsatellite loci, genomic data are able to separate the most closely related species and to resolve their divergence histories. Both phylogenetic and population genetic analyses indicate introgression between two species that differ by a single Robertsonian fusion. Based on the available data, there is also evidence for introgression between two species which share complex chromosomal rearrangements. However, the remaining results show no consistent signature of introgression amongst species pairs and where evident, indicate generally low introgression overall. X-linked loci have elevated divergence compared with autosomal loci indicating a potential role for genic evolution to produce reproductive isolation in concert with chromosome change. Our results highlight the value of genome scale data in evaluating the role of Robertsonian fusions and structural variation in divergence, speciation, and patterns of molecular evolution.

Allopatric divergence and secondary contact of two weak fish species (Macrodon ancylodon and Macrodon atricauda) from the South Atlantic

The king weakfish Macrodon ancylodon (Scianidae) has been regarded as a widespread representative of Macrodon in the South Atlantic, managed as a single stock in Brazilian fisheries. Nonetheless, molecular and morphological data showed that populations from cold and subtropical waters in southeastern and southern Brazil actually corresponded to another taxon (Macrodon atricauda or Southern king weakfish). Apparently, the environmental and geomorphological heterogeneity in the South Atlantic would account for their allopatric differentiation with a putative but largely overlooked barrier in a narrow area between the northeastern and southeastern coast of Brazil. Therefore, we performed phylogenetic and phylogeographic analyses based on mitochondrial and nuclear markers in populations of M. ancylodon and M. atricauda with increased sampling efforts within and nearby their alleged range boundaries (Southern Bahia to Rio de Janeiro coast) to infer their biogeographic history and verify putative contact zones and/or introgression. Mitochondrial markers recovered both taxa as reciprocally monophyletic species that have diverged in Pleistocene (~1.5 million years ago), probably related to isolation of ancestor populations by the exposure of Abrolhos shelf (southern Bahia) and the Vitoria-Trindade chain during sea level retreats in glaciation periods. This vicariant effect combined with distinct ecological features between northeastern (warm waters) and southeastern coast (cold waters) should have favored their allopatric speciation. On the other hand, syntopic populations of M. atricauda and M. ancylodon were clearly recognized within a narrow contact zone (~60 km) between the estuaries of the Mucuri (northeastern Brazil) and Conceição da Barra (southeastern Brazil) without evidence of introgression, as a result of secondary contact. Thus, estuarine areas along this region represent a hotspot for conservation of fisheries resources, since it encompasses two differentiated stocks of king weakfish.

New Insight into the Phylogeny and Taxonomy of Cultivated and Related Species of Crataegus in China, Based on Complete Chloroplast Genome Sequencing

Hawthorns (Crataegus L.) are one of the most important processing and table fruits in China, due to their medicinal properties and health benefits. However, the interspecific relationships and evolution history of cultivated Crataegus in China remain unclear. Our previously published data showed C. bretschneideri may be derived from the hybridization of C. pinnatifida with C. maximowiczii, and that introgression occurs between C. hupehensis, C. pinnatifida, and C. pinnatifida var. major. In the present study, chloroplast sequences were used to further elucidate the phylogenetic relationships of cultivated Crataegus native to China. The chloroplast genomes of three cultivated species and one related species of Crataegus were sequenced for comparative and phylogenetic analyses. The four chloroplast genomes of Crataegus exhibited typical quadripartite structures and ranged from 159,607 bp (C. bretschneideri) to 159,875 bp (C. maximowiczii) in length. The plastomes of the four species contained 113 genes consisting of 79 protein-coding genes, 30 tRNA genes, and 4 rRNA genes. Six hypervariable regions (ndhC-trnV(UAC)-trnM(CAU), ndhA, atpH-atpI, ndhF, trnR(UCU)-atpA, and ndhF-rpl32), 196 repeats, and a total of 386 simple sequence repeats were detected as potential variability makers for species identification and population genetic studies. In the phylogenomic analyses, we also compared the entire chloroplast genomes of three published Crataegus species: C. hupehensis (MW201730.1), C. pinnatifida (MN102356.1), and C. marshallii (MK920293.1). Our phylogenetic analyses grouped the seven Crataegus taxa into two main clusters. One cluster included C. bretschneideri, C. maximowiczii, and C. marshallii, whereas the other included C. hupehensis, C. pinnatifida, and C. pinnatifida var. major. Taken together, our findings indicate that C. maximowiczii is the maternal origin of C. bretschneideri. This work provides further evidence of introgression between C. hupehensis, C. pinnatifida, and C. pinnatifida var. major, and suggests that C. pinnatifida var. major might have been artificially selected and domesticated from hybrid populations, rather than evolved from C. pinnatifida.

Rampant Genome-Wide Admixture across the Heliconius Radiation.

How frequent is gene flow between species? The pattern of evolution is typically portrayed as a phylogenetic tree, yet gene flow between good species may be an important mechanism in diversification, spreading adaptive traits and leading to a complex pattern of phylogenetic incongruence. This process has thus far been studied mainly among a few closely related species, or in geographically restricted areas such as islands, but not on the scale of a continental radiation. Using a genomic representation of 40 out of 47 species in the genus, we demonstrate that admixture has played a role throughout the evolution of the charismatic Neotropical butterflies Heliconius. Modeling of phylogenetic networks based on the exome uncovers up to 13 instances of interspecific gene flow. Admixture is detected among the relatives of Heliconius erato, as well as between the ancient lineages leading to modern clades. Interspecific gene flow played a role throughout the evolution of the genus, although the process has been most frequent in the clade of Heliconius melpomene and relatives. We identify Heliconius hecalesia and relatives as putative hybrids, including new evidence for introgression at the loci controlling the mimetic wing patterns. Models accounting for interspecific gene flow yield a more complete picture of the radiation as a network, which will improve our ability to study trait evolution in a realistic comparative framework.

Genomic and acoustic differences separate Lilian’s Meadowlark (Sturnella magna lilianae) from Eastern (S. magna) and Western (S. neglecta) meadowlarks

AbstractExamining differences among recently diverged populations can provide insight into the traits and evolutionary mechanisms that drive or maintain divergence. The genus Sturnella includes 2 recently diverged species, Sturnella magna (Eastern Meadowlark) and S. neglecta (Western Meadowlark), the former of which has a complex of subspecies distributed across the Americas. Of the S. magna subspecies that occur in the United States, S. m. lilianae is the only one with a disjunct range, occurring in the southwestern United States and central Mexico. It also has markedly different song patterns than all other S. magna subspecies. In order to assess population differentiation, we performed whole-genome sequencing of 35 birds and analyzed song characteristics from 85 birds. Songs from each species and S. m. lilianae were diagnosable using linear discriminant function analysis and support divergence in song between all taxa. Phylogenetic analysis and admixture proportions support 3 distinct clades within North American meadowlarks, and tests of introgression failed to detect a significant signal. Overall, our results indicate that S. m. lilianae exhibits high levels of genetic and vocal differentiation from both S. magna and S. neglecta, with no evidence of introgression between any group, and forms a distinct evolutionary lineage. We thus recommend the elevation of S. m. lilianae to species status.

Whole‐genome resequencing reveals persistence of forest‐associated mammals in Late Pleistocene refugia along North America’s North Pacific Coast

AbstractAimNumerous glacial refugia have been hypothesized along North America's North Pacific Coast that may have increased divergence of refugial taxa, leading to elevated endemism and subsequently clustered hybrid zones following deglaciation. The locations and community composition of these ice‐free areas remains controversial, but whole‐genome sequences now enable detailed analysis of the demographic and evolutionary histories of refugial taxa. Here, we use genomic data to test spatial and temporal processes of diversification among martens with respect to the Coastal Refugium Hypothesis, to understand the role of climate cycling in shaping diversity across complex landscapes.LocationNorth America and North Pacific Coast archipelagos.TaxonNorth American martens (Martes).MethodsShort‐read whole‐genome resequencing data were generated for 11 martens: four M. americana, four M. caurina, two hybrids, and one outgroup (Martes zibellina). Sampling was representative of known genetic clades within New World martens, including sampling within insular and continental hybrid zones and along the North Pacific Coast (five island populations). ADMIXTURE, F‐statistics, and D‐statistics (ABBA‐BABA) were used to identify introgression and infer directionality. Heterozygosity densities, estimated via PSMC, were used to characterize historical demography at and below the species level to infer refugial and colonization processes.ResultsForest‐associated Pacific martens (M. caurina) are divided into distinct insular and continental clades consistent with the Coastal Refugium Hypothesis. There was no evidence of introgression on islands that received historical translocations of American pine martens (M. americana), but introgression was detected in two active zones of secondary contact: one insular and one continental. Only early‐generational hybrids were identified across multiple hybrid zones, a pattern consistent with potential genetic swamping of M. caurina by M. americana.Main conclusionsDespite an incomplete fossil record, genomic evidence supports the persistence of forest‐associated martens, likely the insular Pacific marten lineage, along the western edges of the Alexander Archipelago during the Last Glacial Maximum. This discovery informs our understanding of refugial paleoenvironments, critical to interpreting refugial timing, duration, and community composition. Genomic reevaluations of other taxa along North America's North Pacific Coast may yield new and deeper perspectives on the history of refugial forest communities and the role of dynamic climate shifts in shaping high‐latitude diversity across complex insular landscapes.