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Introgressive Hybridization (introgressive + hybridization)

Distribution by Scientific Domains

Life Sciences	100%

Selected Abstracts

MULTILOCUS ANALYSES OF ADMIXTURE AND INTROGRESSION AMONG HYBRIDIZING HELICONIUS BUTTERFLIES

EVOLUTION, Issue 6 2006
Marcus R. Kronforst
Abstract Introgressive hybridization is an important evolutionary process and new analytical methods provide substantial power to detect and quantify it. In this study we use variation in the frequency of 657 AFLP fragments and DNA sequence variation from 15 genes to measure the extent of admixture and the direction of interspecific gene flow among three Heliconius butterfly species that diverged recently as a result of natural selection for Müllerian mimicry, and which continue to hybridize. Bayesian clustering based on AFLP genotypes correctly delineated the three species and identified four H. cydno, three H. pachinus, and three H. melpomene individuals that were of mixed ancestry. Gene genealogies revealed substantial shared DNA sequence variation among all three species and coalescent simulations based on the Isolation with Migration (IM) model pointed to interspecific gene flow as its cause. The IM simulations further indicated that interspecific gene flow was significantly asymmetrical, with greater gene flow from H. pachinus into H. cydno (2Nm 5 4.326) than the reverse (2Nm 5 0.502), and unidirectional gene flow from H. cydno and H. pachinus into H. melpomene (2Nm 5 0.294 and 0.252, respectively). These asymmetries are in the directions expected based on the genetics of wing patterning and the probability that hybrids of various phenotypes will survive and reproduce in different mimetic environments. This empirical demonstration of extensive interspecific gene flow is in contrast to a previous study which found little evidence of gene flow between another pair of hybridizing Heliconius species, H. himera and H. erato, and it highlights the critical role of natural selection in maintaining species diversity. Furthermore, these results lend support to the hypotheses that phenotypic diversification in the genus Heliconius has been fueled by introgressive hybridization and that reinforcement has driven the evolution of assortative mate preferences. [source]

Introgressive hybridization of human and rodent schistosome parasites in western Kenya

MOLECULAR ECOLOGY, Issue 23 2008
MICHELLE L. STEINAUER
Abstract 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. [source]

Hybridization and Rorippa austriaca (Brassicaceae) invasion in Germany

MOLECULAR ECOLOGY, Issue 7 2003
W. Bleeker
Abstract Introgressive hybridization between the invasive Rorippa austriaca and the native R. sylvestris in Germany has been studied using chloroplast DNA (trnL intron) and amplified fragment length polymorphism. Three hybrid zones between the invasive and native species were located in the Ruhr Valley (Mülheim) and at the River Main near Würzburg (Randersacker, Winterhausen). In each hybrid zone hybridization was indicated by additivity of region-specific amplified fragment length polymorphism markers proving independent hybridization events. The hybrids were either morphologically intermediate (R. × armoracioides) or were close to R. sylvestris. The trnL intron of R. austriaca is characterized by a species-specific deletion. This diagnostic chloroplast marker of R. austriaca was detected in three individuals of R. sylvestris providing evidence for introgression of the invasive chloroplast into the native species. Bidirectional introgression of R. austriaca markers into R. sylvestris and of R. sylvestris markers into R. austriaca was detected in the amplified fragment length polymorphism analysis. Some of the invasive R. austriaca populations showed high within-population variation. A possible association among introgression, within-population variation and invasion success is discussed. The morphologically intermediate hybrid R. × armoracioides is currently spreading in northern Germany. It forms large populations without its parent species R. austriaca and R. sylvestris. It is concluded that hybridization between invasive R. austriaca and native R. sylvestris may lead to the evolution of a new invasive species R. × armoracioides. [source]

Introgressive hybridization in southern African baboons shapes patterns of mtDNA variation

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 1 2010
C. Keller
Abstract Species, as main evolutionary units have long been considered to be morphological entities with limited hybridization potential. The occurrence of taxa which maintain morphological distinctness despite extensive hybridization is an interesting phenomenon. To understand the evolution of these taxa, descriptions of contemporary morphological and genetic variation are essential, also to reconstruct sound phylogenies. Baboons, with their wide geographic range, variant morphotypes, and extensive hybridization offer an intriguing model for those studies. We focus on the complex situation in southern Africa that, in contrast to east Africa, has been neglected in terms of baboon hybridization history. We aim to clarify the distribution and identify possible overlapping zones between different, previously described mitochondrial (mt) DNA clades of baboons that do not match with the ranges of traditionally recognized species. On the basis of the widespread sampling and mitochondrial cytochrome b gene sequencing, we constructed a phylogenetic tree that separates representatives of the two southern African baboon species, yellow and chacma baboons, into six clades: southern, northern and eastern chacmas, Kinda baboons and southern and Luangwa yellow baboons. The ranges of the chacma clades come into close contact or overlap in two regions in the Republic of South Africa and Namibia. Our phylogenetic reconstruction reveals mitochondrial paraphyly for chacma and yellow baboons, which is probably caused by introgressive hybridization and subsequent nuclear swamping, whereby males of the chacma morphotype population from the south invaded the yellow morphotype population in the north bringing their morphotype into a population that maintained its yellow baboon mtDNA. Am J Phys Anthropol 2010. © 2009 Wiley-Liss, Inc. [source]

Role of Genetic Refuges in the Restoration of Native Gene Pools of Brown Trout

CONSERVATION BIOLOGY, Issue 4 2009
ROSA M. ARAGUAS
introgresión de piscifactoría; pautas de manejo; acervos génicas nativas; refugios genéticos; repoblación de peces Abstract:,Captive-bred animals derived from native, alien, or hybrid stocks are often released in large numbers in natural settings with the intention of augmenting harvests. In brown trout (Salmo trutta), stocking with hatchery-reared non-native fish has been the main management strategy used to maintain or improve depleted wild brown trout populations in Iberian and other Mediterranean regions. This measure has become a serious threat to the conservation of native genetic diversity, mainly due to introgressive hybridization. Aware of this risk, the agency responsible for management of brown trout in the eastern Pyrenees (Spain) created "brown trout genetic refuges" to preserve the integrity of brown trout gene pools in this region. Within refuge areas, the prerefuge status with respect to fishing activities has been maintained, but hatchery releases have been banned completely. We evaluated this management strategy through a comparison of the stocking impact on native populations that accounted for stocking histories before and after refuge designations and fishing activities. In particular we examined the relevant scientific, cultural, and political challenges encountered. Despite agency willingness to change fishery policies to balance exploitation and conservation, acceptance of these new policies by anglers and genetic monitoring of refuge populations should also be considered. To improve management supported by genetic refuges, we suggest focusing on areas where the public is more receptive, considering the situation of local native diversity, and monitoring of adjacent introgressed populations. We recommend the use of directional supportive breeding only when a population really needs to be enhanced. In any case, management strategies should be developed to allow for protection within the context of human use. Resumen:,Animales criados en cautiverio derivados de individuos nativos, exóticos o híbridos a menudo son liberados en grandes cantidades en ambientes naturales con la intención de incrementar su explotación. En la trucha común (Salmo trutta), la repoblación con peces no nativos criados en granjas ha sido la principal estrategia de manejo utilizada para mantener o mejorar poblaciones naturales de trucha común en la Peninsula Ibérica y otras regiones Mediterráneas. Esta medida se ha convertido en una seria amenaza para la conservación de la diversidad genética nativa, debido principalmente a la hibridación introgresiva. Consciente de este riesgo, la agencia responsable del manejo de la trucha común en los Pirineos orientales (España) creó"refugios genéticos de trucha común" para preservar la integridad de las acervos genéticos de trucha común en esta región. Dentro de las áreas de refugio, se ha mantenido el estatus previo al refugio con respecto a las actividades pesqueras pero las liberaciones de peces de piscifactoría han sido completamente prohibidas. Evaluamos esta estrategia de manejo mediante la comparación del impacto de la repoblación sobre las poblaciones nativas que registraron historias de repoblación antes y después de la designación de refugios y de actividades pesqueras. En particular, examinamos los significativos retos científicos, culturales y políticos que encontramos. A pesar de la disponibilidad de la agencia para cambiar las políticas de pesca hacia un equilibrio entre la explotación y la conservación, también se debe considerar la aceptación de estas nuevas políticas por los pescadores y el monitoreo genético de las poblaciones en los refugios. Para mejorar el manejo en los refugios genéticos sugerimos centrarse en las áreas donde el público es más receptivo, considerando la situación de la diversidad nativa local y el monitoreo de las poblaciones introgresadas adyacentes. Recomendamos la utilización de la cría de apoyo direccional solo cuando una población realmente requiera ser mejorada. En cualquier caso, se deberían desarrollar estrategias de manejo para permitir la protección en el contexto del uso por el hombre. [source]

MULTILOCUS ANALYSES OF ADMIXTURE AND INTROGRESSION AMONG HYBRIDIZING HELICONIUS BUTTERFLIES

Distribution of genetic variation among chromosomal forms of Anopheles gambiae s.s.: introgressive hybridization, adaptive inversions, or recent reproductive isolation?

INSECT MOLECULAR BIOLOGY, Issue 1 2001
W. C. Black IV
Abstract A series of four papers in this issue explores the reproductive status of the five chromosomal forms of An. gambiae s.s. using molecular techniques to examine the variation among twelve different genes located throughout the An. gambiae s.s. genome. Results of these and previous studies are consistent with a hypothesis of at least partial barriers to gene flow between some chromosomal forms in the Ivory Coast and other West African countries to the north and west, but introgression between S and M types in Benin and countries to the east. Collectively, these studies indicate the need for a broader geographical sampling of An. gambiae s.s., increased research on mechanisms of prezygotic reproductive isolation and field-based studies of survival and fecundity in hybrids to test for postzygotic reproductive isolation. [source]

Complete lack of mitochondrial divergence between two species of NE Atlantic marine intertidal gastropods

JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 10 2009
P. KEMPPAINEN
Abstract Some mitochondrial introgression is common between closely related species, but distinct species rarely show substantial introgression in their entire distribution range. In this study, however, we report a complete lack of mitochondrial divergence between two sympatric species of flat periwinkles (Littorina fabalis and Littorina obtusata) which, based on previous allozyme studies, diverged approximately 1 Ma. We re-examined their species status using both morphology (morphometric analysis) and neutral genetic markers (microsatellites) and our results confirmed that these species are well separated. Despite this, the two species shared all common cytochrome-b haplotypes throughout their NE Atlantic distribution and no deep split between typical L. fabalis and L. obtusata haplotypes could be found. We suggest that incomplete lineage sorting explains most of the lack of mitochondrial divergence between these species. However, coalescent-based analyses and the sympatric sharing of unique haplotypes suggest that introgressive hybridization also has occurred. [source]

Differentiation of morphology, genetics and electric signals in a region of sympatry between sister species of African electric fish (Mormyridae)

JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 4 2008
S. LAVOUÉ
Abstract Mormyrid fishes produce and sense weak electric organ discharges (EODs) for object detection and communication, and they have been increasingly recognized as useful model organisms for studying signal evolution and speciation. EOD waveform variation can provide important clues to sympatric species boundaries between otherwise similar or morphologically cryptic forms. Endemic to the watersheds of Gabon (Central Africa), Ivindomyrus marchei and Ivindomyrus opdenboschi are morphologically similar to one another. Using morphometric, electrophysiological and molecular characters [cytochrome b sequences and amplified fragment length polymorphism (AFLP) genotypes], we investigated to what extent these nominal mormyrid species have diverged into biological species. Our sampling covered the known distribution of each species with a focus on the Ivindo River, where the two taxa co-occur. An overall pattern of congruence among datasets suggests that I. opdenboschi and I. marchei are mostly distinct. Electric signal analysis showed that EODs of I. opdenboschi tend to have a smaller initial head-positive peak than those of I. marchei, and they often possess a small third waveform peak that is typically absent in EODs of I. marchei. Analysis of sympatric I. opdenboschi and I. marchei populations revealed slight, but significant, genetic partitioning between populations based on AFLP data (FST , 0.04). Taken separately, however, none of the characters we evaluated allowed us to discriminate two completely distinct or monophyletic groups. Lack of robust separation on the basis of any single character set may be a consequence of incomplete lineage sorting due to recent ancestry and/or introgressive hybridization. Incongruence between genetic datasets in one individual, which exhibited a mitochondrial haplotype characteristic of I. marchei but nevertheless fell within a genetic cluster of I. opdenboschi based on AFLP genotypes, suggests that a low level of recent hybridization may also be contributing to patterns of character variation in sympatry. Nevertheless, despite less than perfect separability based on any one dataset and inconclusive evidence for complete reproductive isolation between them in the Ivindo River, we find sufficient evidence to support the existence of two distinctive species, I. opdenboschi and I. marchei, even if not ,biological species' in the Mayrian sense. [source]

Recurrent nuclear DNA introgression accompanies chloroplast DNA exchange between two eucalypt species

MOLECULAR ECOLOGY, Issue 7 2010
G. E. MCKINNON
Abstract Numerous studies within plant genera have found geographically structured sharing of chloroplast (cp) DNA among sympatric species, consistent with introgressive hybridization. Current research is aimed at understanding the extent, direction and significance of nuclear (nr) DNA exchange that accompanies putative cpDNA exchange. Eucalyptus is a complex tree genus for which cpDNA sharing has been established between multiple species. Prior phylogeographic analysis has indicated cpDNA introgression into the widespread forest species Eucalyptus globulus from its rare congener E. cordata. In this study, we use AFLP markers to characterize corresponding nrDNA introgression, on both a broad and fine spatial scale. Using 388 samples we examine (i) the fine-scale spatial structure of cp and nrDNA introgression from E. cordata into E. globulus at a site in natural forest and (ii) broad-scale patterns of AFLP marker introgression at six additional mixed populations. We show that while E. globulus and E. cordata retain strongly differentiated nuclear gene pools overall, leakage of nrDNA occurs at mixed populations, with some AFLP markers being transferred to E. globulus recurrently at different sites. On the fine scale, different AFLP fragments show varying distances of introgression into E. globulus, while introgression of cpDNA is extensive. The frequency of E. cordata markers in E. globulus is correlated with spatial proximity to E. cordata, but departs from expectations based on AFLP marker frequency in E. cordata, indicating that selection may be governing the persistence of introgressed fragments in E. globulus. [source]

Detecting hybridization between wild species and their domesticated relatives

MOLECULAR ECOLOGY, Issue 1 2008
ETTORE RANDI
Abstract The widespread occurrence of free-ranging domestic or feral carnivores (dogs, cats) or ungulates (pigs, goats), and massive releases of captive-reproduced game stocks (galliforms, waterfowl) is raising fear that introgressive hybridization with wild populations might disrupt local adaptations, leading to population decline and loss of biodiversity. Detecting introgression through hybridization is problematic if the parental populations cannot be sampled (unlike in classical stable hybrid zones), or if hybridization is sporadic. However, the use of hypervariable DNA markers (microsatellites) and new statistical methods (Bayesian models), have dramatically improved the assessment of cryptic population structure, admixture analyses and individual assignment testing. In this paper, I summarize results of projects aimed to identify occurrence and extent of introgressive hybridization in European populations of wolves (Canis lupus), wildcats (Felis silvestris), rock partridges and red-legged partridges (Alectoris graeca and Alectoris rufa), using genetic methods. Results indicate that introgressive hybridization can be locally pervasive, and that conservation plans should be implemented to preserve the integrity of the gene pools of wild populations. Population genetic methods can be fruitfully used to identify introgressed individuals and hybridizing populations, providing data which allow evaluating risks of outbreeding depression. The diffusion in the wild of invasive feral animals, and massive restocking with captive-reproduced game species, should be carefully controlled to avoid loss of genetic diversity and disruption of local adaptations. [source]

Detecting introgressive hybridization between free-ranging domestic dogs and wild wolves (Canis lupus) by admixture linkage disequilibrium analysis

MOLECULAR ECOLOGY, Issue 10 2006
A. VERARDI
Abstract Occasional crossbreeding between free-ranging domestic dogs and wild wolves (Canis lupus) has been detected in some European countries by mitochondrial DNA sequencing and genotyping unlinked microsatellite loci. Maternal and unlinked genomic markers, however, might underestimate the extent of introgressive hybridization, and their impacts on the preservation of wild wolf gene pools. In this study, we genotyped 220 presumed Italian wolves, 85 dogs and 7 known hybrids at 16 microsatellites belonging to four different linkage groups (plus four unlinked microsatellites). Population clustering and individual assignments were performed using a Bayesian procedure implemented in structure 2.1, which models the gametic disequilibrium arising between linked loci during admixtures, aiming to trace hybridization events further back in time and infer the population of origin of chromosomal blocks. Results indicate that (i) linkage disequilibrium was higher in wolves than in dogs; (ii) 11 out of 220 wolves (5.0%) were likely admixed, a proportion that is significantly higher than one admixed genotype in 107 wolves found previously in a study using unlinked markers; (iii) posterior maximum-likelihood estimates of the recombination parameter r revealed that introgression in Italian wolves is not recent, but could have continued for the last 70 (± 20) generations, corresponding to approximately 140,210 years. Bayesian clustering showed that, despite some admixture, wolf and dog gene pools remain sharply distinct (the average proportions of membership to wolf and dog clusters were Qw = 0.95 and Qd = 0.98, respectively), suggesting that hybridization was not frequent, and that introgression in nature is counteracted by behavioural or selective constraints. [source]

Natural hybridization and the evolution of domesticated, pest and disease organisms

MOLECULAR ECOLOGY, Issue 5 2004
Michael L. Arnold
Abstract The role of natural hybridization in the evolutionary history of numerous species is well recognized. The impact of introgressive hybridization and hybrid speciation has been documented especially in plant and animal assemblages. However, there remain certain areas of investigation for which natural hybridization and its consequences remain under-studied and under-appreciated. One such area involves the evolution of organisms that positively or negatively affect human populations. In this review, I highlight exemplars of how natural hybridization has contributed to the evolution of (i) domesticated plants and animals; (ii) pests; (iii) human disease vectors; and (iv) human pathogens. I focus on the effects from genetic exchange that may lead to the acquisition of novel phenotypes and thus increase the beneficial or detrimental (to human populations) aspects of the various taxa. [source]

Differential patterns of hybridization and introgression between the swallowtails Papilio machaon and P. hospiton from Sardinia and Corsica islands (Lepidoptera, Papilionidae)

MOLECULAR ECOLOGY, Issue 6 2003
R. Cianchi
Abstract Proportions of hybridization and introgression between the swallowtails Papilio hospiton, endemic to Sardinia and Corsica, and the holarctic Papilio machaon, were characterized using nine fully diagnostic and two differentiated allozyme loci and a mitochondrial DNA marker. Very low frequencies of F1 hybrids were detected in both Sardinia (0,4%, average 1.4%) and Corsica (0,3%, average 0.5%), as well as of first generation backcrosses (B1). No F2 were observed, in agreement with the hybrid breakdown detected in laboratory crosses. In spite of this minimal current gene exchange, specimens carrying introgressed alleles were found in high proportions in P. machaon but in lower proportions in P. hospiton. Introgression apparently occurred through past hybridization and repeated backcrossing, as evidenced by hybrid index scores and Bayesian assignment tests. Levels of introgression were low (0,1%) at two sex-linked loci and mitochondrial DNA, limited (0.4,2%) at three autosomal loci coding for dimeric enzymes, and high (up to 43%) at four autosomal loci coding for monomeric enzymes. Accordingly, selective filters are acting against foreign alleles, with differential effectiveness depending on the loci involved. The low levels of introgression at sex-linked loci and mitochondrial DNA are in agreement with Haldane's rule and suggest that introgression in P. machaon proceeds mainly through males, owing to a lower fitness of hybrid females. Papilio machaon populations showed higher levels of introgression in Sardinia than in Corsica. The role of reinforcement in the present reproductive isolation between P. machaon and P. hospiton is examined, as well as the evolutionary effects of introgressive hybridization between the two species. [source]

Introgressive hybridization in southern African baboons shapes patterns of mtDNA variation

Intraspecific genome size variation and morphological differentiation of Ranunculus parnassifolius (Ranunculaceae), an Alpine,Pyrenean,Cantabrian polyploid group

BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 2 2010
EDUARDO CIRES
The aim of this study was to assess genome size variation and multivariate morphometric analyses to ascertain cytotype distribution patterns and the morphological differentiation within the Ranunculus parnassifolius group in the Pyrenees and the Alps. Although divergences in nuclear DNA content among different species within a genus are widely acknowledged, intraspecific variation is still a somewhat controversial issue. Holoploid and monoploid genome sizes (C- and Cx-values) were determined using propidium iodide flow cytometry in 125 plants of R. parnassifolius s.l. distributed across four European countries. Three different DNA ploidy levels were revealed in the study area: diploid (2n , 2x, 57.14%), triploid (2n , 3x, 1.19%), and tetraploid (2n , 4x, 41.67%). The mean population 2C-values ranged from 8.15 pg in diploids to 14.80 pg in tetraploids, representing a ratio of 1 : 1.8. Marked intraspecific/interpopulation differences in nuclear DNA content were found. Diploid populations prevail in the Pyrenees, although tetraploid cytotypes were reported throughout the distribution area. In general, mixed-cytotype populations were not found. The Spearman correlation coefficient did not reveal significant correlations between genome size and altitude, longitude, or latitude. Morphometric analyses and cluster analyses based on genome size variation revealed the presence of three major groups, which exhibited a particular biogeographical pattern. A new cytotype, DNA triploid, was found for the first time. Tetraploid populations showed constant nuclear DNA levels, whereas diploid populations from the Pyrenees, in which introgressive hybridization is suggested as a presumable trigger for genome size variation, did not. Scenarios for the evolution of geographical parthenogenesis in R. parnassifolius s.l. are discussed. Finally, the different levels of effectiveness between plant and animal reference standards are analysed. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 251,271. [source]

Widespread hybridization between the Greater Spotted Eagle Aquila clanga and the Lesser Spotted Eagle Aquila pomarina (Aves: Accipitriformes) in Europe

BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2010
ÜLO VÄLI
Hybridization is a significant threat for endangered species and could potentially even lead to their extinction. This concern applies to the globally vulnerable Greater Spotted Eagle Aquila clanga, a species that co-occurs, and potentially interbreeds, with the more common Lesser Spotted Eagle Aquila pomarina in a vast area of Eastern Europe. We applied single nucleotide polymorphism (SNP) and microsatellite markers in order to study hybridization and introgression in 14 European spotted eagle populations. We detected hybridization and/or introgression in all studied sympatric populations. In most regions, hybridization took place prevalently between A. pomarina males and A. clanga females, with introgression to the more common A. pomarina. However, such a pattern was not as obvious in regions where A. clanga is still numerous. In the course of 16 years of genetic monitoring of a mixed population in Estonia, we observed the abandonment of A. clanga breeding territories and the replacement of A. clanga pairs by A. pomarina, whereby on several occasions hybridization was an intermediate step before the disappearance of A. clanga. Although the total number of Estonian A. clanga × A. pomarina pairs was twice as high as that of A. clanga pairs, the number of pairs recorded yearly were approximately equal, which suggests a higher turnover rate in interbreeding pairs. This study shows that interspecific introgressive hybridization occurs rather frequently in a hybrid zone at least 1700-km wide: it poses an additional threat for the vulnerable A. clanga, and may contribute to the extinction of its populations. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 725,736. [source]