Hybridization between pond turtles (Emys orbicularis) subspecies in natural and human-mediated contact zones

Abstract

Hybridization is particularly important for evolutionary and speciation processes. It promotes evolutionary divergence between lineages by reinforcing reproductive isolation mechanisms to avoid the erosion of the spatial genetic structure and the production of unfit hybrids. Additionally, hybridization creates novel taxa by the fusion of interacting lineages. However, introgressive hybridization leads to conservation problems when introgression happens between threatened lineages and non-native or domesticated lineages. In such cases, introgressive hybridization may lead to the genetic swamping of one lineage and to the loss of the entire taxon. Hybrids often harbour novel genetic combinations and novel adaptations that provide them a higher potential to adapt to environmental changes and colonize new ecological niches. In the future, conservation of hybrids might provide additional genetic diversity for species to cope with alterations in their environment. In my thesis, I investigated hybridization and introgression between European pond turtle subspecies (Emys orbicularis) by combining nuclear microsatellites and mitochondrial cytochrome b gene: I reported that introgressive hybridization between pond turtle subspecies occured in natural and human-mediated contact zones. Outcomes of introgressive hybridization between European pond turtle (Emys orbicularis) subspecies indicated that E. o. orbicularis and E. o. hellenica subspecies and hybrids may have better fitness than E. o. galloitalica subspecies and hybrids under Swiss environmental conditions. Furthermore, I developed an eDNA-based methodology to detect the presence of pond turtles and investigated the efficiency of two water sampling methods. Finally, results of this thesis provided scientific knowledge to the Swiss national conservation programme of the European pond turtle.