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

Area of Science:

• Evolutionary Biology
• Speciation and Hybridization Studies
• Amphibian Ecology

Background:

• Studying hybridization in species with overlapping ranges and habitat requirements presents challenges.
• Broadscale introgressive hybridization is an area of growing scientific interest.
• Lissotriton helveticus and Lissotriton vulgaris are closely related amphibians with a wide sympatric zone.

Purpose of the Study:

• To investigate hybridization between Lissotriton helveticus and Lissotriton vulgaris.
• To detect hybrids at the individual level and analyze population-level genetic disequilibria.
• To understand the patterns and extent of introgression across their sympatric range.

Main Methods:

• Utilized mitochondrial and microsatellite markers.
• Analyzed data from 1272 individuals across 37 European sites.
• Assessed Hardy-Weinberg and linkage disequilibria.

Main Results:

• Low overall hybrid frequency (1.7%) despite a wide sympatric zone.
• Asymmetric introgression observed, with more hybrids found in Lissotriton vulgaris.
• Significant introgression detected in 73% of shared sites, but confined to overlapping breeding times.

Conclusions:

• Introgressive hybridization is common in these newt species but spatially and temporally restricted.
• The pattern of introgression, despite widespread overlap, likely contributes to their continued genetic distinctness.
• Asymmetric introgression may be influenced by unequal effective population sizes.