What can genetics tell us about the history of a human-mediated introduction of the golden-striped salamander south of its native range?

Abstract

The golden-striped salamander is a streamside species endemic to the northwestern corner of the Iberian Peninsula. In the first half of the twentieth century, an undisclosed number of individuals of this species were reportedly captured in Buçaco, central Portugal, and deliberately introduced in Serra de Sintra, 170 km south of its native distribution range. The discovery of a breeding population of this salamander in Sintra during 2015 prompted this work: we used neutral genetic markers, the mitochondrial DNA Cytochrome b (cyt b) and seven microsatellite loci to elucidate on the relic/human-introduced nature of Sintra population, identify the potential source population and infer the severity of founder effect. Our results support a human-mediated introduction. First, sequencing analysis of cyt b showed the presence of a unique haplotype (h31) in Sintra, which was detected only in Buçaco and in two additional populations located close to Mondego river. Second, microsatellite analysis showed that Sintra is more closely related with populations in between Douro and Mondego rivers (Central Portugal), instead of its geographically closest populations (southernmost), as would be expected if Sintra were a relic population isolated in an interglacial refuge. Third, Sintra presents both reduced levels of genetic variability and effective population size when compared to native populations, particularly to those of Central Portugal. Consistent with an isolated population funded by a small number of individuals (inferred herein to be ca. 10 salamanders), Sintra forms a geographically coherent genetic unit that is significantly differentiated from the extant native C. lusitanica populations. Although changes in the genetic makeup of Sintra do not allow to track unequivocally the origin of the introduced individuals, genetic signs from both nuclear and mtDNA data provide supporting evidence for Buçaco as the most likely source population, which coincides with the documented history of the introduced population in Sintra.