Genetic Analysis of a Cryptic Contact Zone between Mitochondrial Clades of the Eastern Red-Backed Salamander, Plethodon cinereus

Abstract

When evolutionarily divergent lineages adjoin their geographic ranges after a period of isolation, myriad outcomes can occur, from population anastomosis to the evolution of reproductive isolation by way of reinforcement. Hybrid zones represent natural experiments that may indicate whether lineages will maintain their evolutionary independence. Here, we report on a hybrid zone in the Eastern Red-Backed Salamander, Plethodon cinereus, a highly abundant and wide-ranging terrestrial salamander found in the northeastern United States and in southeastern Canada. An earlier study identified six distinct mitochondrial clades across the range of P. cinereus. Populations of two of these clades were as close as 9.6 km apart in Lorain County, Ohio, USA. To investigate the nature of this contact zone, we sampled 316 individuals from 16 sites along a 53-km transect, and analyzed 10 microsatellite loci and one mitochondrial locus. We found a clinal transition for mtDNA haplotypes. In contrast, most studies of terrestrial plethodontid salamanders commonly exhibit sharp boundaries between mtDNA clades. Microsatellite markers, however, revealed little differentiation and weak population structure, suggesting the nuclear cline, if it exists, lies outside of our sampling region. Explanations for the discordance between the mitochondrial DNA and our microsatellite data include lineage sorting, male-biased dispersal, or historical introgression of mtDNA, among other possibilities. We compare our results with other studies of introgression in terrestrial salamanders, and discuss the causes of mitonuclear discordance.

Eastern red-backed salamanders: A comprehensive review of an undervalued model in evolution, ecology, & behavior

“…Waldron et al (2019) found a clinal transition between two of these clades in Ohio, detectable in the mitochondrial cytochrome b gene, but not in the 10 nuclear microsatellite markers used. Waldron et al (2019) suggest two scenarios to explain the discordance between mitochondrial and nuclear data: first the cline could be an artifact of genetic drift or lineage merger and second, that there may yet be a nuclear cline that is outside their sampling transect. The authors note that a genomic study with wider sampling is needed to fully understand the discordance between mitochondrial and nuclear genomes in P. cinereus .…”

“…A recent study has identified six phylogeographic clades within P. cinereus, based on both mitochondrial and nuclear genes (Radomski et al, 2020). Waldron et al (2019) found a clinal transition between two of these clades in Ohio, detectable in the mitochondrial cytochrome b gene, but not in the 10 nuclear microsatellite markers used. Waldron et al (2019) suggest two scenarios to explain the discordance between mitochondrial and nuclear data: first the cline could be an artifact of genetic drift or lineage merger and second, that there may yet be a nuclear cline that is outside their sampling transect.…”

Asymmetric Reproductive Barriers and Gene Flow Promote the Rise of a Stable Hybrid Zone in the Mediterranean High Mountain

“…These hybridizing contact zones have important effects on the evolutionary dynamics of the hybridizing species and the biodiversity in the area where the contact happens (Wielstra, 2019;Alves de Moura et al, 2020). The hybridization is not always evident for human, which could have even more pervasive consequences for the biology of the species and their conservation (Gómez et al, 2015;Waldron et al, 2019).…”