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28 results for “asymmetric introgression”
Experimental introgression in Drosophila: Asymmetric postzygotic isolation associated with chromosomal inversions and an incompatibility locus on the X chromosome
<p>Interspecific gene flow (introgression) is an important source of new genetic variation, but selection against it can reinforce reproductive barriers between interbreeding species. We used an experimental approach to trace the role of chromosomal inversions and incompatibility genes in preventing introgression between two partly sympatric <em>Drosophila virilis</em> group species, <em>D. flavomontana </em>and<em> D. montana</em>. We backcrossed F<sub>1</sub> hybrid females from a cross between <em>D. flavomontana female </em>and<em> D. montana </em>male with the males of the parental species for two generations and sequenced pools of parental strains and their reciprocal 2<sup>nd</sup> generation backcross (BC<sub>2</sub>mon and BC<sub>2</sub>fla) females. Contrasting the observed amount of introgression (mean hybrid index, HI) in BC<sub>2</sub> female pools along the genome to simulations under different scenarios allowed us to identify chromosomal regions of restricted and increased introgression. We found no deviation from the HI expected under a neutral null model for any chromosome for the BC<sub>2</sub>mon pool, suggesting no evidence for genetic incompatibilities in backcrosses towards <em>D. montana</em>. In contrast, the BC<sub>2</sub>fla pool showed high variation in the observed HI between different chromosomes, and massive reduction of introgression on the X chromosome (large X-effect). We find that this observation is compatible with reduced recombination combined with at least one dominant incompatibility locus residing within the X inversion(s). Overall, our study suggests that genetic incompatibilities arising within chromosomal inversions can play an important role in speciation.</p>
Experimental introgression in Drosophila: Asymmetric postzygotic isolation associated with chromosomal inversions and an incompatibility locus on the X chromosome
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Whole-genome sequencing reveals asymmetric introgression between two sister species of cold-resistant leaf beetles
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Asymmetric allelic introgression across a hybrid zone of the coal tit (Periparus ater) in the central Himalayas
<p>In the Himalayas, a number of secondary contact zones have been described for vicariant vertebrate taxa. However, analyses of genetic divergence and admixture are missing for most of these examples. In this study, we provide a population genetic analysis for the coal tit (<i>Periparus ater</i>) hybrid zone in Nepal. Intermediate phenotypes between the distinctive western 'spot-winged tit' (<i>P. a. melanolophus</i>) and e<span class="msoDel">E</span>astern Himalayan coal tits (<i>P. a. aemodius</i>) occur across a narrow range of less than 100 km in western Nepal. As a peculiarity, another distinctive cinnamon-bellied form is known from a single population so far. Genetic admixture of western and eastern mitochondrial lineages was restricted to the narrow zone of phenotypically intermediate populations. The cline width was estimated 46 km only with a center close to the population of the cinnamon-bellied phenotype. In contrast, allelic introgression of microsatellite loci was asymmetrical from eastern <i>P. a. aemodius</i> into far western populations of phenotypic <i>P. a. melanolophus</i> but not vice versa. Accordingly, the microsatellite cline was about 3.7 times wider than the mitochondrial one.</p>
Asymmetric allelic introgression across a hybrid zone of the coal tit (Periparus ater) in the central Himalayas
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Asymmetric acoustic signal recognition led to asymmetric genetic introgression between two parapatric rhacophorid treefrogs
<p><span>Correct discrimination between courtship signals could help maintain genetic integrity between closely related species. However, asymmetric usage of signals might cause asymmetric magnitude of gene flow across the contact zone. <i>Buergeria japonica </i>and <i>B. otai </i>are sibling species with parapatric distribution pattern in Taiwan, forming two narrow contact zones in eastern and western sides of the island. Both species use a shared acoustic signal of calls (Type 1a/1b), whereas <i>B. otai </i>presents another unique call type (Type 2) which never appears in <i>B. japonica</i>. Combining behavioral experiments with genome-wide RAD-seq analyses, we aim to test whether the ability of signal recognition influences genetic introgression across their species boundary. The playback experiments showed that the western population of <i>B. otai</i> has evolved a stronger level of reproductive character displacement by showing the inclusive usage of their unique Type 2 signal. In contrast, the eastern population used both unique and shared signals and has a stronger preference for the latter. Consistent with behavioral difference, genetic introgression across the contact zone was detected only in the eastern boundary but not in the western one. Furthermore, the gene flow in this contact zone tends to be unidirectional from <i>B. japonica</i> toward <i>B. otai</i>. Our results support the prediction that a more specialized signal user might have a higher probability to maintain their genetic integrity compared to a generalized signal user.</span></p>
Data from: Asymmetric introgression between Magnolia stellata and M. salicifolia at a site where the two species grow sympatrically
In order to understand the ongoing evolutionary relationships between species, it is important to elucidate patterns of natural hybridization. In the zone where two species are sympatrically distributed, we examined 274 individuals of Magnolia stellata, Magnolia salicifolia, and their putative hybrids by means of 16 nuclear and three chloroplast microsatellite markers. Hybrid classes of individuals were estimated by admixture analyses. Morphological traits were also investigated for 64 of the 274 individuals. Admixture analyses revealed that 66 of the 274 individuals were classified as hybrids, comprising 17 F1 and 19 F2 individuals, 27 backcrosses to M. salicifolia, and 3 individuals of unknown origin. Morphological data from the 64 individuals agreed well with their genetic admixture rates. Spatial locations of F1 and F2 hybrids at the study site were intermediate between the two purebred species, indicating that the site preferences of hybrids are intermediate. The occurrences of F2 and backcross hybrids indicate that F1 hybrids are fertile. The chloroplast DNA haplotypes of all F1 hybrids corresponded to those detected in M. salicifolia, so that maternal parents of the F1 hybrids were all M. salicifolia. Furthermore, no hybrid individuals derived from a backcross to M. stellata were detected. These results suggest that the direction of hybridization and the subsequent introgression have been quite asymmetric and that the introgression occurred from M. stellata into M. salicifolia.
Data from: Sharp acoustic boundaries across an altitudinal avian hybrid zone despite asymmetric introgression
Birdsong is a sexually selected trait that could play an important evolutionary role when related taxa come into secondary contact. Many songbird species however learn their songs through copying one or more tutors, which complicates the evolutionary outcome of such contact. Two subspecies of a presumed vocal learner, the grey-breasted wood-wren (Henicorhina leucophrys), replace each other altitudinally across the western slope of the Ecuadorian Andes. These subspecies are morphologically very similar, but show striking differences in their song. We examined variation in acoustic traits and genetic composition across the altitudinal range covered by both subspecies and between two allopatric populations. The acoustic boundary between the subspecies was found to be highly abrupt across a narrow elevational range with virtually no evidence of song convergence. Mixed singing and use of hetero-subspecific song occurred in the contact zone and was biased towards the use of leucophrys song types. Hetero-subspecific song copying by hilaris and not by leucophrys reflected a previously found asymmetric pattern of response to song playback. Using AFLP markers, we detected hybridization in the contact zone and asymmetric introgression in parapatric populations, with more leucophrys alleles present in hilaris populations than vice versa. This pattern may be a trail of introgression due to upslope displacement of leucophrys by hilaris. Our data suggest that song learning may impact speciation and hybridization in contrasting ways at different spatial scales: while learning may speed up population divergence in songs, thereby enhancing assortative mating and reducing gene flow, it may at a local level also lead to the copying of heterospecific songs, therefore allowing some level of hybridization and introgression.
Data from: Asymmetric introgression between fishes in the Red River basin of Texas is associated with variation in water quality
When ecologically divergent taxa encounter one another, hybrid zones can form when reproductive isolation is incomplete. The location of such hybrid zones can be influenced by environmental variables, and an ecological context can provide unique insights into the mechanisms by which species diverge and are maintained. Two ecologically differentiated species of small benthic fishes, the endemic and imperiled prairie chub, Macrhybopsis australis, and the shoal chub, Macrhybopsis hyostoma, are locally sympatric within the upper Red River Basin of Texas. We integrated population genomic data and environmental data to investigate species divergence and the maintenance of species boundaries in these two species. We found evidence of advanced-generation asymmetric hybridization and introgression, with shoal chub alleles introgressing more frequently into prairie chubs than the reciprocal. Using a Bayesian Genomic Cline framework, patterns of genomic introgression were revealed to be quite heterogeneous, yet shoal chub alleles were found to have likely selectively introgressed across species boundaries significantly more often than prairie chub alleles, potentially explaining some of the observed asymmetry in hybridization. These patterns were remarkably consistent across two sampled geographic regions of hybridization. Several environmental variables were found to significantly predict individual admixture, suggesting ecological isolation might maintain species boundaries.
FIGURE 3 in Phylogeography of the Habronattus amicus species complex (Araneae: Salticidae) of western North America, with evidence for localized asymmetrical mitochondrial introgression
FIGURE 3. Bayesian majority-rule consensus phylogram resulting from the three partitions analysis. Branch lengths are averaged from across the posterior distribution (post burn-in), and drawn proportional to this average length (an exception is the branch leading to "right hand" clades – this branch is less than one scale unit in length). Clade designations follow those described in text. Asterisks denote posterior probability values> 0.95, although these are not shown for tip clades involving only two haplotypes. Haplotypes derived from different species are represented by different colours; focal site haplotypes are named by location and bolded.
FIGURE 5 in Phylogeography of the Habronattus amicus species complex (Araneae: Salticidae) of western North America, with evidence for localized asymmetrical mitochondrial introgression
FIGURE 5. Neighbor-net haplotype networks. Filled circles denote interior nodes with extant haplotypes. Clade designations follow those described in text. Haplotypes derived from different species are represented by different colours; focal site haplotypes are named by location and bolded. Dashed lines are used for graphical purposes only, linking haplotypes with interior nodes. Networks are drawn at different mutational scales – maximum pairwise observed differences as follows: A Interior amicus II (22), B Interior amicus I (18), C southern II derived (3).
FIGURE 1 in Phylogeography of the Habronattus amicus species complex (Araneae: Salticidae) of western North America, with evidence for localized asymmetrical mitochondrial introgression
FIGURE 1. Distribution of H. amicus group members in western North America. Collection localities are designated by location numbers, corresponding to those found in the Appendix. Sites 60–62 are found further south in Baja California than portrayed on the map. Different species are represented by different colours, except for the OR focal sites where H. amicus and H. ustulatus occur in syntopy. Inset shows the relative locations of OR focal sites (16=Alkali Lake, 17=Fossil Lake, 18=Summer Lake).
FIGURE 7 in Phylogeography of the Habronattus amicus species complex (Araneae: Salticidae) of western North America, with evidence for localized asymmetrical mitochondrial introgression
FIGURE 7. Habitat use by H. amicus and H. ustulatus at OR focal sites. Pie charts depict the proportion of times a member of a species was collected on each of the available substrate types. Mantel R values as follows: Alkali Lake (R = 0.439, P = 0.001), Fossil Lake (R = 0.825, P = 0.001), Summer Lake (R = 0.079, P = 0.105).
FIGURE 4 in Phylogeography of the Habronattus amicus species complex (Araneae: Salticidae) of western North America, with evidence for localized asymmetrical mitochondrial introgression
FIGURE 4. Summary diagram of phylogeny plus phylogeographic clade distributions. For the tree diagram, haplotypes derived from different species are represented by different colours. Clade designations follow those described in text.
FIGURE 6 in Phylogeography of the Habronattus amicus species complex (Araneae: Salticidae) of western North America, with evidence for localized asymmetrical mitochondrial introgression
FIGURE 6. Bivariate scattergram of carapace width (CW) versus length of the first tibia (ITL) for male and female H. amicus and H. ustulatus specimens from OR focal sites. All measurements are in millimeters.
Data from: Y-chromosome evidence supports asymmetric dog introgression into eastern coyotes
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Data from: Asymmetric introgression between fishes in the Red River basin of Texas is associated with variation in water quality
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Asymmetric acoustic signal recognition led to asymmetric genetic introgression between two parapatric rhacophorid treefrogs
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Data from: Females drive asymmetrical introgression from rare to common species in Darwin's tree finches
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Data from: Asymmetric introgression between Magnolia stellata and M. salicifolia at a site where the two species grow sympatrically
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