Even newts do it: natural hybridization between the smooth newt (Triturus vulgaris) 
and the Montandon's newt (T. montandoni) (Amphibia, Salamandridae)

Wiesław Babik, Jacek M. Szymura & Jan Rafiński

Department of Comparative Anatomy
Institute of Zoology
Jagiellonian University
Ingardena 6, 30-060 Kraków
email: babik@zuk.iz.uj.edu.pl


We studied natural hybridization between two species of newts, the smooth newt (Triturus vulgaris) 
and the Montandon’s newt (T. montandoni) in southern Poland. The survey area was located in the Magura 
National Park in the Beskind Niski Range. 33 sites, a total of  765 individuals from the area of sympatry 
were sampled. To characterize genotypic composition of the breeding populations at nuclear loci we used 6 
allozymes (1 fixed for different alleles between the species, 1 almost fixed, others showed frequency 
differences) and 1 microsatellite locus (fixed). In addition, we studied mtDNA and species specific sexually 
dimorphic  traits in the males. The nuclear allele frequency changes do not follow a smooth cline. The pattern 
is rather patchy and only weakly correlates with the geographic position of the populations and is not related 
to the habitat characteristics. Such microgeographic pattern is likely to reflect the history of colonization of 
the area, with substantial stochastic components resulting from newt metapopulation dynamics. Distribution of 
the genotypes in the local populations is bimodal. Most of the hybrids are recombinants similar to either 
parental species. We detected strong heterozygote deficit in the populations where both parentals and hybrids 
were present. The simplest explanation of this deficit is assortative mating within the parental species. 
Despite patchy allelic distribution there is nevertheless a concordance between  frequencies of species specific 
alleles among the nuclear loci. MtDNA displayed a different pattern. We found a relative excess of  vulgaris 
mtDNA haplotype in montandoni-like populations in the south-eastern part of the area and an excess of montandoni 
mtDNA haplotype in the western part of the area. Again the simplest explanation of the pattern could be related 
to colonization history. An excess of  vulgaris haplotypes in the south-eastern part may be remnant of relatively 
old hybridization events. 
The morphological hybrid index for males, computed from species specific sexually dimorphic traits, showed very 
strong bimodality. Individuals from intermediate classes were almost lacking, which indicates selection, most 
likely sexual selection against the males with intermediate phenotypes. The detected hybridization pattern 
meets requirements for the reinforcement of prezygotic isolation and offers an opportunity to test this 
hypothesis in detail.