Hybrid zone dynamics in amphibians

Hybrid zones occur where two species meet and produce offspring (hybrids). Typically, hybrids show a considerable reduction in fitness. In this thesis two hybrid zones are treated.Two species of banded newts (Ommatotriton nesterovi and O. ophryticus) are thought to meet in a hybrid zone in the north of Turkey. In this thesis I confirm the species status of the two banded newt species based on mitochondrial DNA and two nuclear DNA sequences. The location of the hybrid zone is narrowed down to a 60 km wide region. If a hybrid zone is present between O. nesterovi and O. ophryticus, it is narrower than 60 km and it may be geographically stable. An introduced population of hybrid banded newts in Spain provides evidence that the two species can produce fertile offspring. This increases the likelihood that a hybrid zone indeed exists between the two species.Common and spined toads (Bufo bufo and B. spinosus) meet in an 800 km long hybrid zone that runs diagonally across France. A genetic footprint north of the hybrid zone was previously recorded and linked to southward hybrid zone movement, with B. bufo overtaking B. spinosus. To test hypotheses of hybrid zone movement, a transect in northwest France was studied with 31 nuclear markers. The contrasting results suggest that stronger reproductive isolation on the B. spinosus side of the hybrid zone than on the B. bufo side, may be more likely than hybrid zone movement.To continue the research on the Bufo hybrid zone, two distant transects, one in the northwest and one in the southeast of France, were studied using 1200 nuclear markers. Asymmetries which were previously found in the literature and in this thesis, were confirmed for the hybrid zone in northwest France, but not in the southeast, where the gene flow appears to be symmetric, indicating the hybrid zone is stable here. Barrier markers, genetic regions which may be associated with barrier genes, were identified by their relatively restricted gene flow. The barrier markers present in both transects suggest that the two species have evolved a universal genetic barrier to gene flow. The differences in patterns of gene flow between the transects may be caused by genetic divergence within B. bufo, documented in previous phylogeographical work. We can clearly no longer think of hybrid zones as static upon formation; hybrid zones evolve! With the increasing availability of genome resources, detection of more detailed patterns of differential introgression along the genome in hybrid zone studies will reveal the genetic architecture of speciation and the evolution of hybrid zones.Naturali

Molecular data reveal the hybrid nature of an introduced population of banded newts (Ommatotriton) in Spain

The three species of banded newt (genus Ommatotriton) are endemic to the Near East. Recently an introduced banded newt population was discovered in Catalonia, Spain. To determine the species involved and the geographical source, we genotyped 11 individuals for one mitochondrial and two nuclear genetic markers, and compared the observed haplotypes to a range-wide phylogeography of Ommatotriton. All haplotypes identified in Spain are identical to haplotypes known from the native range. The mitochondrial haplotypes derive from O. ophryticus and were originally recorded in northeast Turkey. The nuclear haplotypes reveal that all individuals are genetically admixed between O. ophryticus and O. nesterovi. While the geographical resolution for the nuclear markers is low, the source of the O. nesterovi ancestry must be Turkey, as this species is a Turkish endemic. Species distribution models suggest a large potential distribution for the two Ommatotriton species, extending over northern Iberia and southern France. The ecology of hybrids can differ substantially from that of the parent species, making the impact of the Spanish hybrid banded newt population difficult to predict

Tracing species replacement in Iberian marbled newts

Animal science

A genomic footprint of a moving hybrid zone in marbled newts

Animal science

Hybridisation complicates the conservation of Natrix snakes in the Netherlands

NaturalisAnimal science

Genetic traces of hybrid zone movement across a fragmented habitat

Animal science

The Near East as a cradle of biodiversity: a phylogeography of banded newts (genus Ommatotriton) reveals extensive inter- and intraspecific genetic differentiation

The banded newt (genus Ommatotriton) is widely distributed in the Near East (Anatolia, Caucasus and the Levant) - an understudied region from the perspective of phylogeography. The genus is polytypic, but the number of species included and the phylogenetic relationships between them are not settled. We sequenced two mitochondrial and two nuclear DNA markers throughout the range of Ommatotriton. For mtDNA we constructed phylogenetic trees, estimated divergence times using fossil calibration, and investigated changes in effective population size with Bayesian skyline plots and mismatch analyses. For nuDNA we constructed phylogenetic trees and haplotype networks. Species trees were constructed for all markers and nuDNA only. Species distribution models were projected on current and Last Glacial Maximum climate layers. We confirm the presence of three Ommatotriton species: O. nesterovi, O. ophryticus and O. vittatus. These species are genetically distinct and their most recent common ancestor was dated at ∼25Ma (Oligocene). No evidence of recent gene flow between species was found. The species show deep intraspecific genetic divergence, represented by geographically structured clades, with crown nodes of species dated ∼8-13Ma (Miocene to Early Quaternary); evidence of long-term in situ evolution and survival in multiple glacial refugia. While a species tree based on nuDNA suggested a sister species relationship between O. vittatus and O. ophryticus, when mtDNA was included, phylogenetic relationships were unresolved, and we refrain from accepting a particular phylogenetic hypothesis at this stage. While species distribution models suggest reduced and fragmented ranges during the Last Glacial Maximum, we found no evidence for strong population bottlenecks. We discuss our results in the light of other phylogeographic studies from the Near East. Our study underlines the important role of the Near East in generating and sustaining biodiversity

Two transects reveal remarkable variation in gene flow on opposite ends of a European toad hybrid zone

Microbial BiotechnologyAnimal science

Next-generation phylogeography of the banded newts (Ommatotriton): a phylogenetic hypothesis for three ancient species with geographically restricted interspecific gene flow and deep intraspecific genetic structure

NaturalisAnimal science