Hybrid Ancestry Research Articles

"Let Them Sink Into Oblivion": Genealogical Form and Familial Forgetting in Susanna Rowson's Reuben and Rachel

This essay examines thematic and structural "forgetting" in Susanna Rowson's 1798 Reuben and Rachel . As the novel moves closer to the postrevolutionary era of its publication, its second volume shifts abruptly from genealogy to sentimental romance, and its eponymous characters actively forget the transatlantic, hemispheric, and hybrid ancestry that the novel heretofore existed to construct and that would otherwise destabilize their emergent national identity. I locate Reuben and Rachel's sibling intimacy at the heart of the contradiction between the second volume's forgetfulness and both the first volume's and Rowson's stated authorial commitments to the transmission of historical memory.

Morphological variation of genetically confirmedAlouatta Pigra×A. palliatahybrids from a natural hybrid zone in Tabasco, Mexico

While hybridization has been reported for a large number of primate taxa, there is a general lack of data on hybrid morphology for wild individuals with known genetic ancestry. A confirmed hybrid zone for the closely related Neotropical primates Alouatta palliata and A. pigra has provided a unique opportunity to study primate hybrid morphological variation. Here we used molecular evidence based on mitochondrial, Y-chromosome, and autosomal data to assess hybrid ancestry. We conducted univariate and multivariate statistical comparisons of morphometric data collected from individuals both outside and within the hybrid zone in Tabasco, Mexico. Our results show that of all the hybrids detected (N = 128), only 12% of them were approximately genetically intermediate, and none of them were first generation hybrids. Univariate pairwise comparisons among parental individuals, multigenerational backcrossed hybrids, and intermediate hybrids showed that overall, multigenerational backcrossed hybrids resemble the parental species with which they share most of their alleles. Conversely, intermediates were highly variable. Similarly, principal component analysis depicts an overlap between the parental species and their backcrosses when considering overall morphological differences. Finally, discriminant function analysis of the morphological variables was overall unreliable for classifying individuals into their assigned genotypic classes. Taken together, our results suggest that primate natural hybridization studies should incorporate molecular methods for determining ancestry, because morphology may not always be a reliable indicator of hybrid status. Hybrid zones could comprise a large number of multigenerational backcrossed hybrids that are indistinguishable from the parental species. The implications for studying hybridization in the primate fossil record are discussed.

Recent nonhybrid origin of sunflower ecotypes in a novel habitat

The genomics of local adaptation is an increasingly active field, providing insights into the forces driving ecological speciation and the repeatability of evolution. Demography and gene flow play an important role in determining the paths by which parallel evolution occurs and the genomic signatures of adaptation. In the annual sunflowers, hybridization between species has repeatedly led to the colonization of extreme habitats, such as sand dunes. In a new case of adaptation to sand dunes that occurs in populations of H. petiolaris growing at Great Sand Dunes National Park and Preserve (Colorado), we wished to determine the age and long-term migration patterns of the system, as well as its ancestry. We addressed these questions with restriction-associated DNA (RAD) sequence data, aligned to a reference transcriptome. In an isolation with migration model using RAD sequences, coalescent analysis showed that the dune ecotype originated since the last ice age, which is very recent compared with the hybrid dune species, H. anomalus. Large effective population sizes and substantial numbers of gene migrants per generation between dune and nondune ecotypes explained the highly heterogeneous divergence observed among loci. Analysis of RAD-derived SNPs identified heterogeneous divergence between the dune and nondune ecotypes, as well as identifying its nearest relative. Our results did not support the hypothesis that the dune ecotype has hybrid ancestry, suggesting that adaptation of sunflowers to dunes has occurred by multiple mechanisms. The ancestry and long-term history of gene flow between incipient sunflower species provides valuable context for our understanding of ecological speciation and parallel adaptation.

More than multiple introductions: Multiple taxa contribute to the genesis of the invasive California's wild artichoke thistle

AbstractThe history of some invasive species is so complex that their origins can be difficult to determine. One example of such invasive species is the California invasive known as “wild artichoke thistle” (Cynara cardunculus var. sylvestris), found in natural and disturbed ecosystems. Wild artichoke thistle is a Mediterranean native and the progenitor of two domesticated horticultural taxa, artichoke and cardoon. Different hypotheses regarding the origins of California plants have included introductions by 19th century Italian immigrants and the de‐domestication (evolutionary reversion to wild‐type morphology) of feral (escaped, free‐living) cultivars. Using microsatellite markers, we compared the genetic constitutions of 12 artichoke thistle populations in California with possible progenitor populations: 17 Spanish and Italian wild populations and eight different artichoke and cardoon cultivars. Each California population was compared with its putative progenitors using STRUCTURE analysis. Our results suggest that California's artichoke thistle populations are polyphyletic. Surprisingly, two‐thirds of California's populations closely matched populations from the Iberian Peninsula. Three populations matched domesticated artichoke. One population appears to have wild and cultivar hybrid ancestry. Alleles specific to Italian populations were found at low frequencies in some California plants, suggesting that Italian wild plants may have been in California, but have left a trivial genetic legacy. Given that the de‐domesticated plants in this study appear to be as invasive as the wild taxon, we conclude with a discussion of the role that ferality and de‐domestication may have in plant invasions.

Characterizing the physical and genetic structure of the lodgepole pine × jack pine hybrid zone: mosaic structure and differential introgression

Understanding the physical and genetic structure of hybrid zones can illuminate factors affecting their formation and stability. In north-central Alberta, lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia) and jack pine (Pinus banksiana Lamb) form a complex and poorly defined hybrid zone. Better knowledge of this zone is relevant, given the recent host expansion of mountain pine beetle into jack pine. We characterized the zone by genotyping 1998 lodgepole, jack pine, and hybrids from British Columbia, Alberta, Saskatchewan, Ontario, and Minnesota at 11 microsatellites. Using Bayesian algorithms, we calculated genetic ancestry and used this to model the relationship between species occurrence and environment. In addition, we analyzed the ancestry of hybrids to calculate the genetic contribution of lodgepole and jack pine. Finally, we measured the amount of gene flow between the pure species. We found the distribution of the pine classes is explained by environmental variables, and these distributions differ from classic distribution maps. Hybrid ancestry was biased toward lodgepole pine; however, gene flow between the two species was equal. The results of this study suggest that the hybrid zone is complex and influenced by environmental constraints. As a result of this analysis, range limits should be redefined.

Hybridization between an invasive and a native species of the crayfish genus Orconectes in north-central Ohio

Hybridization between native and invasive species is an important but little-studied factor in crayfish invasions, with few documented natural cases. Here, we report genetic evidence of hybridization between invasive O. rusticus (Girard, 1852) and native O. sanbornii (Girard, 1852) in the Huron River in north-central Ohio based on a combination of molecular markers: nuclear DNA, mitochondrial DNA, and allozymes. Although we found no fixed differences between the species at nuclear DNA loci, fixed differences in mtDNA and allozyme loci confirmed the presence of individuals of hybrid ancestry. We also found preliminary evidence of possible mitochondrial recombination and biparental inheritance (though the existence of rare haplotypes cannot be excluded at the present time). We examined morphological features of both species in sympatry and allopatry and confirmed species-diagnostic morphological features including gonopod traits and shape of the annulus ventralis. This study is the second to detect hybridization between O. rusticus and a congener, which suggests that this may be an important mechanism of invasion by O. rusticus when closely related species are present. Further study of this system, including more extensive sampling and additional molecular markers, is necessary to understand the extent and implications of hybridization for the native species.

Simultaneous delimitation of species and quantification of interspecific hybridization in Amazonian peacock cichlids (genus cichla) using multi-locus data

BackgroundIntrogression likely plays a significant role in evolution, but understanding the extent and consequences of this process requires a clear identification of species boundaries in each focal group. The delimitation of species, however, is a contentious endeavor. This is true not only because of the inadequacy of current tools to identify species lineages, but also because of the inherent ambiguity between natural populations and species paradigms. The result has been a debate about the supremacy of various species concepts and criteria. Here, we utilized multiple separate sources of molecular data, mtDNA, nuclear sequences, and microsatellites, to delimit species under a polytypic species concept (PTSC) and estimate the frequency and genomic extent of introgression in a Neotropical genus of cichlid fishes (Cichla). We compared our inferences of species boundaries and introgression under this paradigm to those when species are identified under a diagnostic species concept (DSC).ResultsWe find that, based on extensive molecular data and an inclusive species concept, 8 separate biological entities should be recognized rather than the 15 described species of Cichla. Under the PTSC, fewer individuals are expected to exhibit hybrid ancestry than under the DSC (~2% vs. ~12%), but a similar number of the species exhibit introgression from at least one other species (75% vs. 60%). Under either species concept, the phylogenetic breadth of introgression in this group is notable, with both sister species and species from different major mtDNA clades exhibiting introgression.ConclusionsIntrogression was observed to be a widespread phenomenon for delimited species in this group. While several instances of introgressive hybridization were observed in anthropogenically altered habitats, most were found in undisturbed natural habitats, suggesting that introgression is a natural but ephemeral part of the evolution of many tropical species. Nevertheless, even transient introgression may facilitate an increase in genetic diversity or transfer of adaptive mutations that have important consequences in the evolution of tropical biodiversity.

Genetic distinctness of parthenogenetic forms of European Polydrusus weevils of the subgenus Scythodrusus

Abstract Among eight species of Polydrusus weevils which belong to subgenus Scythodrusus, at least two possess parthenogenetic forms: P. (S.) inustus and P. (S.) pilifer. Both of these species consist of dioecious populations in the Caspian area and of parthenogenetic populations in Eastern Europe (P. (S.) inustus), the Caucasus region (both species) and Middle Asia (P. (S.) pilifer). The origin of parthenogenesis in this subgenus is unresolved; however some data suggest that the parthenogenetic forms are of hybrid ancestry. The genetic distinctness of parthenogenetic Scythodrusus was assessed on the basis of COII, ITS2, EF1‐α and Wolbachiawsp, 16S ribosomal DNA, ftsZ and hcpA sequence comparisons. Both taxa turned out to be monophyletic for all markers, which is an evidence against hybridization of their dioecious ancestors. On the other hand, a high frequency of heterozygous P. (S.) inustus females suggests an origin resulting from hybridization between genetically distinct dioecious representatives of this species. Very similar strains of Wolbachia supergroup A were found in both species, indicating that they have been either inherited from a common ancestor or were transmitted between parthenogenetic Scythodrusus weevils and probably spread randomly across their ranges.

Genetic monitoring of two decades of hybridization between allis shad (Alosa alosa) and twaite shad (Alosa fallax)

Habitat alteration has been implicated in driving hybridization between the sympatric migratory shads Alosa alosa and Alosa fallax. Morphological and molecular evidence is consistent with hybridization across the overlapping range of these species, but the temporal extent of hybrid occurrence and genetic consequences for populations have not been explored. Using eight nuclear microsatellite loci and samples collected between 1989 and 2008 in the Solway Firth (UK), we genetically identified hybrids, studied temporal changes in their frequency, and explored changes in allele frequencies of parental populations. These molecular data confirmed the hybrid status of individuals identified using morphology (number of rakers on the outer gill arch), and enabled separation of hybrids from purebred individuals. Mitochondrial cytochrome-b sequencing revealed the presence of two haplogroups, each predominantly occurring in one species. Heterospecific haplotypes were found in 22.3 and 12.8% of A. alosa and A. fallax individuals, respectively, consistent with backcrossing and suggesting that hybrids are fertile. On average, microsatellite-identified hybrids comprised 12.7% of all samples, but when individuals with cytonuclear discordance were also considered introgressed on average 25.4% of individuals were of hybrid ancestry. Overall, allelic richness remained largely unchanged within species, but there were declines in the inbreeding coefficient (FIS) of both species and episodes of significant temporal allelic frequency change. Hybrids sampled between 2004 and 2008 showed no evidence of lower fecundity relative to purebred individuals. Together, results suggest that hybridization between shad species in northern Europe is prevalent, and has been ongoing over at least two decades. The challenge is now to understand the extent to which observed patterns are linked to immigration from other populations, and the mechanisms that have prevented species collapse despite apparent hybrid fertility and longstanding introgression of neutral markers.

Exploring Species Limits in Two Closely Related Chinese Oaks

BackgroundThe species status of two closely related Chinese oaks, Quercus liaotungensis and Q. mongolica, has been called into question. The objective of this study was to investigate the species status and to estimate the degree of introgression between the two taxa using different approaches.Methodology/Principal FindingsUsing SSR (simple sequence repeat) and AFLP (amplified fragment length polymorphism) markers, we found that interspecific genetic differentiation is significant and higher than the differentiation among populations within taxa. Bayesian clusters, principal coordinate analysis and population genetic distance trees all classified the oaks into two main groups consistent with the morphological differentiation of the two taxa rather than with geographic locations using both types of markers. Nevertheless, a few individuals in Northeast China and many individuals in North China have hybrid ancestry according to Bayesian assignment. One SSR locus and five AFLPs are significant outliers against neutral expectations in the interspecific F ST simulation analysis, suggesting a role for divergent selection in differentiating species.Main Conclusions/SignificanceAll results based on SSRs and AFLPs reached the same conclusion: Q. liaotungensis and Q. mongolica maintain distinct gene pools in most areas of sympatry. They should therefore be considered as discrete taxonomic units. Yet, the degree of introgression varies between the two species in different contact zones, which might be caused by different population history or by local environmental factors.

Detecting hybridization between willow grouse (Lagopus lagopus) and rock ptarmigan (L. muta) in Central Sweden through Bayesian admixture analyses and mtDNA screening

Willow grouse (L. lagopus) and rock ptarmigan (L. muta) are sibling species with similar phenotypic and life histories that coexist sympatrically in wide areas of their distribution range. These grouse are amongst the most popular game birds in Scandinavia but contrary to other quarry species, no restocking with captive-bred animals has ever been performed. The discovery of two individuals with intermediate plumage features evoked the question of possible hybridization events between both species, an idea that did not seem too unlikely on the basis of habitat overlap. Thus, to assess whether any genetic exchange is occurring, we used different Bayesian-based admixture analyses of multilocus genotypes determined at twelve microsatellite loci. We also obtained mitochondrial COI-sequences from a selected number of individuals to infer the maternal geneflow and potential introgression. The capacity of our panel of microsatellite markers to detect hybridization was verified using assignments of simulated genotypes. We then evaluated the extent of hybridization in an actual sample of 111 individuals collected in a 100-km2 area in the Scandinavian mountain range. An admixed condition was verified in one of the suspected hybrids, that seemed to carry a L. muta genotype with partial L. lagopus introgression. In addition, more than 4% of L. lagopus showed signs of hybridization under the most conservative scenario with respect to discrepancies between population assignment methods. This was unexpected, given that no L. lagopus displayed any apparent intermediate plumage features. Furthermore, interspecific geneflow of mtDNA haplotypes was lower than expected; which suggests that Haldane’s rule might apply for these two grouse species. Hence, plumage identification of hybrid ancestry is not always reliable and might lead to biases in the estimation of hybridization rates. Hybridisation may be expected to increase if the climate gets warmer as the habitat overlap between the species will become more extensive. We discuss whether hybridisation is a threat to the long-term survival of any of the two species.

Patterns of co‐existence and hybridisation between narrowly endemic (Fundulus euryzonus) and broadly distributed (F. olivaceus) topminnows in a riverine contact zone

Abstract – Two ecologically similar topminnow species (Fundulus olivaceus and F. euryzonus) were studied in a contact zone in the West Fork of the Amite River of the Lake Pontchartrain drainage. We assessed whether relative abundance and measures of fitness of each species, and their hybrids, were correlated with predictable abiotic or biotic factors. We sampled the full fish assemblage and measured a suite of local and landscape level environmental characteristics at ten sites. Topminnows were genotyped to identify individuals of hybrid ancestry. We compared the abundance and distribution of parental species in the context of overall fish assemblage structure and environmental variables. Hybridisation was generally rare with only nine of 244 genotyped topminnows exhibiting evidence of hybrid ancestry. The relative abundance of the two topminnows was related to site assemblage structure, species diversity and a number of local but not landscape level environmental variables. Both species were in better condition and females were more fecund at sites with greater abundance of F. olivaceus. Hybrid individuals were not morphological or ecological intermediates.

The Rutilus alburnoides complex (Cyprinidae): evidence for a hybrid origin

A genetic survey of 18 presumptive enzyme loci was conducted on members of the diploid-triploid R. alburnoides complex in order to test the hypothesis of hybrid origin. Most specimens examined were heterozygous at a high proportion of loci, with seven loci showing virtually fixed heterozygosity in some or all populations. This observation strongly supports the hypothesized hybrid ancestry. Involvement in the origin of the R. alburnoides complex was examined by comparison of allels with those observed in the other diploid cyprinids that inhabit the same Portuguese drainages. Allelic composition at the homozygous loci IDDH* and LDH-B* seems to rule out the genus Chondrostoma and other members of the genus Rutilus as one of the ancestors, and supports Leuciscus sp. as one parental species involved in the putative hybrid origin of the R. alburnoides complex. Moreover, with few exceptions, all specimens exhibited at every locus one or two alleles also present in extant populations of Leuciscus. The indentity of the other parental taxon remains unclear. Five diploid males exhibited multilocus genotypes that fit to the hypothetical genotype(s) of the ‘missing’ ancestor. However, the possibility exists that a hybrid female could produce or re-create a genotype of a parental species.

Evolution of enhanced reproduction in the hybrid-derived invasive, California wild radish (Raphanus sativus)

Evolution is receiving increased attention as a potentially important factor in invasions. For example, hybridization may have stimulated the evolution of invasiveness in several well-known plant pests. However, the mechanism for success of such hybrid-derived lineages remains unknown in the majority of the cases studied. Here we ask whether increased reproductive success (in terms of maternal fitness) has evolved in an invasive lineage with confirmed hybrid ancestry. We compare the relative fitness of the non-native, hybrid-derived California wild radish (Raphanus sativus) to that of its two progenitor species in field experiments at different sites and in different years. We found that California wild radish has high survivorship and produces more fruits per plant and more seeds per plant than either of its progenitors in several environments. Furthermore, populations of California wild radish display a strong genotype-by-environment interaction, indicating that maintenance of genetic and phenotypic diversity between populations may be responsible for the weed’s ability to invade a wide breadth of California habitats. Our results suggest that hybridization may contribute the evolution of enhanced invasiveness and, also, that by limiting the introduction and subsequent hybridization of congeners, we may be able to prevent the evolution of new invasive lineages.

Introgressive hybridization of human and rodent schistosome parasites in western Kenya

Hybridization and introgression can have important consequences for the evolution, ecology and epidemiology of pathogenic organisms. We examined the dynamics of hybridization between a trematode parasite of humans, Schistosoma mansoni, and its sister species, S. rodhaini, a rodent parasite, in a natural hybrid zone in western Kenya. Using microsatellite markers, rDNA and mtDNA, we showed that hybrids between the two species occur in nature, are fertile and produce viable offspring through backcrosses with S. mansoni. Averaged across collection sites, individuals of hybrid ancestry comprised 7.2% of all schistosomes collected, which is a large proportion given that one of the parental species, S. rodhaini, comprised only 9.1% of the specimens. No F1 individuals were collected and all hybrids represented backcrosses with S. mansoni that were of the first or successive generations. The direction of introgression appears highly asymmetric, causing unidirectional gene flow from the rodent parasite, S. rodhaini, to the human parasite, S. mansoni. Hybrid occurrence was seasonal and most hybrids were collected during the month of September over a 2-year period, a time when S. rodhaini was also abundant. We also examined the sex ratios and phenotypic differences between the hybrids and parental species, including the number of infective stages produced in the snail host and the time of day the infective stages emerge. No statistical differences were found in any of these characteristics, and most of the hybrids showed an emergence pattern similar to that of S. mansoni. One individual, however, showed a bimodal emergence pattern that was characteristic of both parental species. In conclusion, these species maintain their identity despite hybridization, although introgression may cause important alterations of the biology and epidemiology of schistosomiasis in this region.

Molecular phylogeny and adaptive radiation of the endemic Hawaiian Plantago species (Plantaginaceae)

Insular oceanic islands provide excellent opportunities for the study of evolutionary processes and adaptive radiation. The Hawaiian Plantago radiation comprises six endemic taxa showing considerable inter- and intraspecific morphological and ecological diversity. The rDNA internal (ITS) and external (ETS) transcribed spacers and two recently described chloroplast spacers, ndhF-rpl32 and rpl32-trnL, were sequenced to study phylogenetic relationships within this morphologically complex group. Phylogenetic analysis provided strong evidence for the monophyly of Hawaiian Plantago, suggesting that the lineage arose from a single long-distance dispersal event. Inconsistencies between nuclear and chloroplast phylogenies suggest a history of hybridization. The basal, unresolved dichotomy of the combined phylogeny is consistent with rapid phenotypic diversification of the major lineages early in the history of this group. Speciation has largely occurred allopatrically, with divergence a result of intraisland ecological shifts between bog and woodland habitats and interisland dispersal events. Most interisland colonizations were from older to younger islands with initial colonization of Kaua'i. In our analysis, P. pachyphylla is paraphyletic and taxonomic separation of the distinct morphotypes of this species appears justified. Furthermore, the apparent hybrid ancestry and unique morphology and habitat of the endangered P. princeps var. longibracteata support its recognition at the specific rank.

Factors related to the occurrence of hybrids between brown haresLepus europaeusand mountain haresL. timidusin Sweden

Hybridization occurs among many species, and may have implications for conservation as well as for evolution. Interspecific gene flow between brown haresLepus europaeusand mountain haresL. timidushas been documented in Sweden and in continental Europe, and has probably to some extent occurred throughout history in sympatric areas. What local factors or ecological relationships that correlate with or trigger hybridization between these species has however been unclear. We studied spatial distribution of hybrids between brown hares and mountain hares in Sweden in relation to characteristics of the sampled localities (hunting grounds). In a sample of 70 brown hares collected from 39 populations in south‐central Sweden during 2003–2005, 11 (16%) showed introgressed mtDNA from mountain hares. Among the brown hares from their northern range, i.e. in general the most recent establishments, the corresponding figure was 75% (9/12). The frequency of samples with hybrid ancestry increased significantly with latitude, altitude and hilliness, and were higher (p<0.1) in recently established populations and/or where the proportion of arable land was low. Several site‐specific parameters were correlated, e.g. latitude as expected to hilliness, and no parameter explained the occurrence of hybrids exclusively. Instead, the appearance of mountain hare mtDNA among brown hares was associated with a conglomerate of parameters reflecting landscapes atypical for the brown hare, e.g. forest dominated and steep areas where the species quite recently was established. We suggest that these abiotic factors mirror the main aspect influencing hybridization frequency, namely the density or relative frequency of the two species. In atypical brown hare landscapes with recent establishment, mountain hares are probably relatively more common. When one species dominate in numbers, or when both species display low densities, increased frequency of hybridization is expected due to low availability of conspecific partners, a phenomenon referred to as Hubbs’ principle.

Genetic Influences on Mosquito Feeding Behavior and the Emergence of Zoonotic Pathogens

The feeding behavior of vectors influences the likelihood of pathogen invasion and the exposure of humans to vector-borne zoonotic pathogens. We used multilocus microsatellite genetic typing of an introduced mosquito vector and DNA sequencing of mosquito blood meals to determine the impact of hybrid ancestry on feeding behavior and the emergence of West Nile virus (WNV). The probability of ancestry of Culex pipiens mosquitoes from two bionomically divergent forms, form molestus and form pipiens, influenced the probability that they fed on humans but did not explain a late summer feeding shift from birds to humans. We used a simple model to show that the occurrence of pure form molestus mosquitoes would have decreased the likelihood of WNV invasion (R(0) in bird populations) 3- to 8-fold, whereas the occurrence of pure forms pipiens mosquitoes would have halved human exposure compared with the hybrids that are present. Data and modeling suggest that feeding preferences may be influenced by genetic ancestry and contribute to the emergence of vector-borne pathogens transmitted by introduced species, including malaria, and dengue, Chikungunya, yellow fever, and West Nile viruses.

A most distant intergeneric hybrid offspring (Larcon) of lesser apes, Nomascus leucogenys and Hylobates lar

Unlike humans, which are the sole remaining representatives of a once larger group of bipedal apes (hominins), the "lesser apes" (hylobatids) are a diverse radiation with numerous extant species. Consequently, the lesser apes can provide a valuable evolutionary window onto the possible interactions (e.g., interbreeding) of hominin lineages coexisting in the same time and place. In the present work, we employ chromosomal analyses to verify the hybrid ancestry of an individual (Larcon) produced by two of the most distant genera of lesser apes, Hylobates (lar-group gibbons) and Nomascus (concolor-group gibbons). In addition to a mixed pelage pattern, the hybrid animal carries a 48-chromosome karyotype that consists of the haploid complements of each parental species: Hylobates lar (n = 22) and Nomascus leucogenys leucogenys (n = 26). Studies of this animal's karyotype shed light onto the processes of speciation and genus-level divergence in the lesser apes and, by extension, across the Hominoidea.

An Assessment of Song Admixture as an Indicator of Hybridization in Black-Capped Chickadees (Poecile Atricapillus) and Carolina Chickadees (P. Carolinensis)

AbstractVocal admixture often occurs where differentiated populations or species of birds meet. This may entail song sympatry, bilingually singing birds, and songs with intermediate or atypical characteristics. Different levels of vocal admixture at the range interface between Black-capped Chickadees (Poecile atricapillus) and Carolina Chickadees (P. carolinensis) have been interpreted as indicating that hybridization is frequent at some locations but not others. However, song ontogeny in these birds has a strong nongenetic component, so that inferences regarding hybridization based on vocal admixture require confirmation. We used diagnostic genetic markers and quantitative analyses of song to characterize population samples along two transects of the chickadee contact zone in the Appalachian Mountains. More than 50% of individuals at the range interface were of hybrid ancestry, yet only 20% were observed to be bilingual or to sing atypical songs. Principal component analysis revealed minimal song intermediacy. This result contrasts with an earlier analysis of the hybrid zone in Missouri that found considerable song intermediacy. Re-analysis of the Missouri data confirmed this difference. Correlation between an individual’s genetic composition and its song type was weak in Appalachian hybrid populations, and genetic introgression in both forms extended far beyond the limits of vocal admixture. Therefore, song is not a reliable indicator of levels of hybridization or genetic introgression at this contact zone. Varying ecological factors may play a role in producing variable levels of song admixture in different regions of the range interface.Una Evaluación de la Mixtura de Cantos como Indicador de Hibridación en Poecile atricapillus y P. carolinensis