Genetic exchange across a hybrid zone within the Iberian endemic golden-striped salamander, Chioglossa lusitanica

The study of hybrid zones resulting from Pleistocene vicariance is central in examining the potential of genetically diverged evolutionary units either to introgress and merge or to proceed with further isolation. The hybrid zone between two mitochondrial lineages of Chioglossa lusitanica is located near the Mondego River in Central Portugal. We used mitochondrial and nuclear diagnostic markers to conduct a formal statistical analysis of the Chioglossa hybrid zone in the context of tension zone theory. Key results are: (i) cline centres are not coincident for all markers, with average widths of ca. 2-15 km; (ii) heterozygote deficit was not observed across loci near the transect centre; (iii) associations of parental allele combinations ('linkage disequilibrium'R) were not detected either across loci or across the transect. These observations suggest that the Chioglossa hybrid zone is not a tension zone with strong selection against hybrids but instead one shaped mostly by neutral mixing. The patterns uncovered suggest a complex history of populations over a small scale that may be common in southern Pleistocene refugia.