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... Show moreHybrid 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. Show less
Riemsdijk, I. van; Butlin, R.K.; Wielstra, B.; Arntzen, J.W. 2019
Hybrid zone movement may result in substantial unidirectional introgression of selectively neutral material from the local to the advancing species, leaving a genetic footprint. This genetic... Show moreHybrid zone movement may result in substantial unidirectional introgression of selectively neutral material from the local to the advancing species, leaving a genetic footprint. This genetic footprint is represented by a trail of asymmetric tails and displaced cline centres in the wake of the moving hybrid zone. A peak of admixture linkage disequilibrium is predicted to exist ahead of the centre of the moving hybrid zone. We test these predictions of the movement hypothesis in a hybrid zone between common (Bufo bufo) and spined toads (B. spinosus), using 31 nuclear and one mtDNA SNPs along a transect in the northwest of France. Average effective selection in Bufo hybrids is low and clines vary in shape and centre. A weak pattern of asymmetric introgression is inferred from cline discordance of seven nuclear markers. The dominant direction of gene flow is from B. spinosus to B. bufo and is in support of southward movement of the hybrid zone. Conversely, a peak of admixture linkage disequilibrium north of the hybrid zone suggests northward movement. These contrasting results can be explained by reproductive isolation of the B. spinosus and B. bufo gene pools at the southern (B. spinosus) side of the hybrid zone. The joint occurrence of asymmetric introgression and admixture linkage disequilibrium can also be explained by the combination of low dispersal and random genetic drift due to low effective population sizes. Show less
Riemsdijk, I. van; Nieuwenhuize, L. van; Martinez-Solano, I.; Arntzen, J.W.; Wielstra, B.M. 2018
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... Show moreThe 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. Show less
Riemsdijk, I. van; Arntzen, J.W.; Bogaerts, S.; Franzen, M.; Litvinchuk, S.N.; Olgun, K.; Wielstra, B.M. 2017
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... Show moreThe 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 similar to 25 Ma (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 similar to 8-13 Ma (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. (C) 2017 The Authors. Published by Elsevier Inc. Show less
Peptide mass fingerprinting of bone collagen (ZooMS) has previously been proposed as a method to calculate the extent of the non-enzymatic degradation of glutamine into glutamic acid (deamidation).... Show morePeptide mass fingerprinting of bone collagen (ZooMS) has previously been proposed as a method to calculate the extent of the non-enzymatic degradation of glutamine into glutamic acid (deamidation). Temporal and spatial variation of glutamine deamidation at a single site, however, has not been investigated. Here we apply ZooMS screening of Châtelperronian and Early Holocene bone specimens from Quinçay, France, to explore temporal and spatial variation in glutamine deamidation. Our results indicate that chronological resolution is low, while spatial variation is high. Nevertheless, our analysis allows the identification of bone specimens that have undergone diagenetic histories remarkably different (either in length or in type) from spatially related bone specimens. Therefore, ZooMS ammonium-bicarbonate screening is capable of testing bone assemblage homogeneity, which could guide subsequent analysis and interpretation. Show less
