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 cristatus and T. 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, with T. cristatus‐like populations occurring in the northeast and T. carnifex‐like populations in the southwest. Despite T. cristatus tending to occur in deeper ponds and T. carnifex on localities with more shading, the effect of both ecological parameters on the structure of the zone was minimal. Next, we corroborated that T. carnifex individuals and some hybrids possess mtDNA of T. dobrogicus, whose nuclear background was not detected in the studied hybrid zone. Hybridization between T. carnifex and T. dobrogicus (resulting in unidirectional mtDNA introgression) had to predate subsequent formation of the hybrid zone between T. cristatus and T. 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.

Genetic Divergence Across Glacial Refugia Despite Interglacial Gene Flow in a Crested Newt

“…Yet, given that the same mtDNA haplotype still occurs throughout the range of T. dobrogicus (Wielstra et al 2013) have occurred recently, upon postglacial secondary contact between the two species. Introgression into T. carnifex probably took place in the lowlands near the present day T. dobrogicus-T. carnifex hybrid zone and subsequently surfed (Klopfstein et al 2006) beyond the T. dobrogicus range, in an expanding T. carnifex population (Mačát et al 2019). Postglacial northwards expansion of T. carnifex around the Alps (from the Balkan population) is in line with our species distribution model (Fig.…”

An isolated crested newt population in Dutch coastal dunes: distribution relict or introduction?

“…The Italian crested newt T. carnifex has been introduced throughout Europe and a well-documented introduction in the central Netherlands, in the Veluwe region, may have been initiated as early as the 1970s (Bogaerts, 2002;Meilink et al, 2015;Wielstra et al, 2016). The natural distribution ranges of northern and Italian crested newts meet at a narrow hybrid zone (Maletzky et al, 2010;Mikulíček et al, 2012;Wielstra et al, 2014;Mačát et al, 2019;Fahrbach et al, 2021) and the two species also readily hybridize where T. carnifex has been introduced into the range of T. cristatus (Brede et al, 2000;Arntzen, 2001;Maletzky et al, 2008;Brede, 2015;Dufresnes et al, 2016;Dufresnes et al, 2019;Hinneberg et al, 2022). Therefore, the presence of T. carnifex (alleles) needs to be considered when dealing with a crested newt population of unknown origin.…”