Species‐specific habitat preferences do not shape the structure of a crested newt hybrid zone (Triturus cristatus x T. carnifex)

Abstract Reproductive isolation barriers maintain the integrity of species by preventing interspecific gene flow. They involve temporal, habitat or behavioral isolation acting before fertilization, and postzygotic isolation manifested as hybrid mortality or sterility. One of the approaches of how to study reproductive isolation barriers is through the analysis of hybrid zones. In this paper, we describe the structure of a hybrid zone between two crested newt species (Triturus cristatusandT. carnifex) in the southern part of the Czech Republic using morphological, microsatellite, and mitochondrial (mtDNA) markers. Specifically, we tested the hypothesis that the structure of the hybrid zone is maintained by species‐specific habitat preferences. Comparing the genetic structure of populations with geographical and ecological parameters, we found that the hybrid zone was structured primarily geographically, withT. cristatus‐like populations occurring in the northeast andT. carnifex‐like populations in the southwest. DespiteT. cristatustending to occur in deeper ponds andT. carnifexon localities with more shading, the effect of both ecological parameters on the structure of the zone was minimal. Next, we corroborated thatT. carnifexindividuals and some hybrids possess mtDNA ofT. dobrogicus, whose nuclear background was not detected in the studied hybrid zone. Hybridization betweenT. carnifexandT. dobrogicus(resulting in unidirectional mtDNA introgression) had to predate subsequent formation of the hybrid zone betweenT. cristatusandT. carnifex. Populations of crested newts in the southern part of the Czech Republic thus represent a genetic mosaic of nuclear and mitochondrial genomes of three species.