Widespread introgression does not leak into allotopy in a broad sympatric zone

Abstract

Species that overlap over a large part of their range and habitat requirements are challenging for the study of speciation and hybridization. In this respect, the study of broadscale introgressive hybridization has raised recent interest. Here we studied hybridization between two closely related amphibians Lissotriton helveticus and Lissotriton vulgaris that reproduce over a wide sympatric zone. We used mitochondrial and microsatellite markers on 1272 individuals in 37 sites over Europe to detect hybrids at the individual-level and to analyse Hardy-Weinberg and linkage disequilibria at the population-level. Morphological traits showed a strong bimodal distribution. Consistently, hybrid frequency was low (1.7%). We found asymmetric introgression with five times more hybrids in L. vulgaris than in L. helveticus, a pattern probably explained by an unequal effective population size in a study part wherein L. helveticus numerically predominates. Strikingly, significant levels of introgression were detected in 73% of sites shared by both species. Our study showed that introgression is widespread but remains confined to the sites where the two species reproduce at the same time. This pattern may explain why these species remain genetically distinct over a broad sympatric zone.

Side-by-side secretion of Late Palaeozoic diverged courtship pheromones in an aquatic salamander

“…All species have an overlapping breeding season and were collected in spring from ponds near Ternat, Belgium. Hybridization and introgression between L. vulgaris and L. helveticus can occur in sympatric ponds [ 22 ], but the occurrence of introgressed individuals in our populations would not essentially affect the outcome of this study.…”

Extensive mitochondrial introgression in North American Great Black-backed Gulls (Larus marinus) from the American Herring Gull (Larus smithsonianus) with little nuclear DNA impact

“…Although lack of diagnostic alleles at our suite of nuclear loci precludes equivalent estimation of introgressed alleles frequencies, none of the measures of nuclear introgression indicated a substantial contribution of SMITHSONIANUS alleles to the nuclear gene pool of MARINUS in North America: North American MARINUS were not closer to SMITHSONIANUS than European MARINUS along the FCA axis, and the difference in assignment probabilities was very low and not fully significant after correction for multiple testing. Although we are not aware of any study formally linking genomic admixture and position of individuals along FCA axis (often also called Multiple Correspondence Analysis, see Guinand, 1996) as has been done with Principal Component Analysis (PCA; for example, McVean, 2009), the close analytical similarities of FCA and PCA ensures that admixture would result in a shift of an individual's position on the FCA axis, as it has been observed in several empirical studies (for example, Johanet et al, 2011, Lefebvre et al, 2008. Note that individual genotype data (multiple allelic states at several loci, such as microsatellite data) are not suitable for PCA analyses, hence the use of the FCA here, which is the classical method in this context (Guinand, 1996).…”

Human-mediated processes affecting distribution and genetic structure ofSqualidus multimaculatus, a freshwater cyprinid with small spatial range

“…the Nakdong River) or population JA. Considering that only two diagnostic alleles were used in our study, the overall levels of introgression might be underestimated (Johane et al 2011). The hybridization in population JA could not simply be explained by unidirectional introgression from the alleles of S. g. majimae into the gene pool of S. multimaculatus, because the frequency of S. g. majimae alleles was slightly higher than that of S. multimaculatus in the diagnostic loci.…”