Hybridization of two ancient salamander lineages: molecular evidence for endemic spectacled salamanders on the Apennine peninsula

Abstract

Current studies indicate that both processes and mechanisms of natural hybridization go far beyond the formation and maintenance of hybrid zones between species. These studies demonstrate that the evolutionary consequences of hybridization can include extinction or extirpation of lineages but may also favor the formation of new hybrid species in an ecological context. The unambiguous identification of occurrences of hybridization in natural populations is a crucial first step in addressing questions related to natural hybridization in both evolutionary and ecological terms. Here, we provide the first molecular evidence of extensive natural hybridization between two ancient sister species of spectacled salamanders -Salamandrina perspicillata in northern and Salamandrina terdigitata in southern Italy. Parental lineages diverged at least 10 million years ago during the Lower Pliocene and represent the most ancient split between any congeneric amphibian species endemic to the Italian peninsula. Analysis of the mitochondrial cytochrome b (Cyt b), nuclear-encoded recombination-activating protein (RAG-1) and propriomelanocortin (POMC) genes of more than 250 individuals from populations of both species and from the contact zone, show clear evidence of ongoing hybridization. Whereas 20% of the individuals from the contact population showed no signs of hybridization for the applied markers, the remainder (80%) were identified as first generation hybrids and backcrossed individuals. Our results suggest that hybridization between these two ancient lineages produces viable and fertile offspring, highlighting the need for research on possible mechanisms that prevent the intermixing and hybridization of parental species on a broader geographical scale.

Extensive unidirectional introgression between two salamander lineages of ancient divergence and its evolutionary implications

“…Furthermore, the high frequencies of several S. terdigitata diagnostic alleles within putatively S. perspicillata samples, together with the occurrence of both HW and linkage equilibria within samples, could have resulted in the misassignment of several individuals to pure S. terdigitata or to a recent hybrid progeny, if each locus had been analysed separately. This could explain, at least in part, the striking discordance between our results, and those of previous reports36 that suggested extensive ongoing gene exchange and syntopy between both species based on mtDNA, and a single nuclear locus of diagnostic value.…”

“…Once regarded as a single species ( S. terdigitata ), they were recently identified as two deeply divergent species based on both nuclear and mitochondrial genetic data313233 and their divergence time was estimated to largely predate the onset of the Pleistocene epoch3233 (but see also34). Recently, a small area was found where both the highly divergent mitochondrial DNA (mtDNA) lineages come into sympatry35, and a preliminary analysis of the hybridization was carried out (based on one sampling location, one mtDNA marker, and one diagnostic and one uninformative nuclear markers)36.…”

Songs, genetics, and morphology: revealing the taxonomic units in the EuropeanCicadetta cerdaniensiscicada group, with a description of new taxa (Hemiptera: Cicadidae)

“…separated slightly north of our distribution limits. The two salamanders of ancient lineages form a hybrid zone (Hauswaldt et al ., ), similar in location to C. sibillae sp. nov. and C. a. lucana ssp.…”

First comprehensive insights into nuclear and mitochondrial DNA based population structure of Near East mountain brook newts (Salamandridae: genus Neurergus) suggest the resurrection of Neurergus derjugini

“…5), but also for comparable studies of other newt (e.g. Pyrenean mountain brook newts of the genus Calotriton; Mila et al, 2009) or salamander species {Salamandra species complex; Steinfartz, Veith and Tautz, 2000;Bonato and Steinfartz, 2005 and Salamandrina species; Hauswaldt et al, 2011Hauswaldt et al, , 2014 which used similar mitochondrial DNA markers. Given that we have only partially explored population structure in A' , strauchii with our sampling design, we assume that a much higher level of diversification across populations ofN.…”