Asymmetric allelic introgression across a hybrid zone of the coal tit (Periparus ater) in the central Himalayas*

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 (Periparus ater) hybrid zone in Nepal. Intermediate phenotypes between the distinctive western spot-winged tit (P. a. melanolophus) and Eastern Himalayan coal tits (P. a. aemodius) occur across a narrow range of <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 P. a. aemodius into far western populations of phenotypic P. a. melanolophus but not vice versa. Accordingly, the microsatellite cline was about 3.7 times wider than the mitochondrial one.

Automated summary

A population genetic analysis was conducted for the coal tit hybrid zone in Nepal, revealing genetic admixture of western and eastern mitochondrial lineages restricted to a narrow zone of phenotypically intermediate populations. Allelic introgression of microsatellite loci was asymmetrical from eastern into far western populations, leading to a wider microsatellite cline than the mitochondrial one.