Restricted Gene Flow in a Moving Hybrid Zone of the Newts Triturus cristatus and T. marmoratus in Western France

Abstract

Two hybridizing species of newts, Triturus cristatus and T. marmoratus, with overlapping distributions show a parapatric distribution when surveyed in detail. The factors that govern the distribution of cristatus vs. marmoratus in the département (province) of Mayenne in western France are identified as forestation and relief. The parapatric hybrid zone running through Mayenne is narrow but widens to approximately 20 km in an area with mixed habitat. In this area most breeding sites are shared and F hybrids form about 4% of the total population. Analysis of survey data collected about 30 years previously also shows an essentially parapatric distribution. Comparison of past and present distribution maps reveals that cristatus has superseded marmoratus over large areas in the south of Mayenne. An area where marmoratus replaced cristatus also exists, but it is more limited in size. Gene flow between cristatus and marmoratus is analyzed using 10 diagnostic genetic markers [9 protein loci and mitochondrial (mt) DNA]. In syntopic populations nuclear gene flow is bidirectional with a mean frequency of introgressed alleles (f) of 0.3%. In allotopic populations of cristatus and marmoratus gene flow is present in areas of species replacement (f = 0.3%), while gene flow appears to be absent in those areas that have been continuously occupied by a single species. At the biogeographic level, the presence or absence of introgression is paralleled by the persistence or absence, respectively, of pockets of cristatus-marmoratus syntopy. All F hybrids possess the cristatus type mtDNA. This may be due to asymmetric interspecific mate choice and would explain the observed absence of introgression of the maternally inherited mtDNA genome in areas where cristatus replaced marmoratus. The cristatus-marmoratus hybrid zone bears characteristics of both the clinal (parapatric) hybrid zone model and the mosaic hybrid zone model. Such a mixed model-for which we propose the term "reticulate hybrid zone"-can be appreciated only if studied over a two-dimensional geographic area and also through time.

Genetic relationships among suspected contact zone populations of Helix aspersa (Gastropoda: Pulmonata) in Algeria

“…In addition to this spatial component, another limit to our conclusions comes from the lack of information on temporal variation. In such a Table 4 Estimates of Wrights F-statistics according to Weir & Cockerham's (1984) historical context, a hybrid zone should also be analysed over the dimension of time (Arntzen & Wallis, 1991 the Maghreb territory, they have probably been locally eliminated under the effects of genetic drift, mutation and/or selection as a result of their having low frequencies in the ancestral population (Slatkin, 1985). It is, however, surprising to observe so many private alleles among adjoining populations, an average of 19 alleles instead of the 13 ( = 4.1, P = 0.04) found in the remaining Maghreb colonies Guiller, Bellido & Madec, unpublished observations).…”

Empirical study of hybrid zone movement

“…A hybrid zone between lizards Sceloporus tristichus and Sceloporus cowlesi has moved over 1.5 km in around 30 years in favour of the former; correspondingly, S. cowlesi mitochondrial DNA is found introgressed over 8 km into the current range of S. tristichus (Leaché and Cole, 2007). Introgression between newts Triturus cristatus and Triturus marmoratus is found in the area of recent species replacement, but is absent in other areas (Arntzen and Wallis, 1991). At a hybrid zone between two warbler species, predominantly Vermivora chrysoptera mtDNA haplotypes are found in hybrids at the leading edge of a Vermivora pinus expansion (Dabrowski et al, 2005) and cytonuclear disequilibrium is also found at a crayfish Orconectes rustica-Orconectes propinquus hybrid zone.…”

Pliocene and Pleistocene diversification and multiple refugia in a Eurasian shrew (Crocidura suaveolens group)

“…The congruence between genetic data and classical morphological interpretations was then examined. Considering that the mitochondrial genome of a taxon can introgress into another closely related taxon (Arntzen and Wallis, 1991;Ruedi et al, 1997;Tegelstrom, 1987), a fragment of the nuclear gene Breast Cancer Susceptibility 1 (BRCA1) was analysed in certain samples. Using such data from both mitochondrial and nuclear genomes, and considering the molecular clock, the colonisation and diVerentiation of the populations through time and space was reconstructed.…”