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Discordant patterns of introgression across a narrow hybrid zone between two cryptic lineages of an Iberian endemic newt
Author(s) -
Sequeira Fernando,
BessaSilva Adam,
Tarroso Pedro,
SousaNeves Tiago,
Vallinoto Marcelo,
Gonçalves Helena,
MartínezSolano Iñigo
Publication year - 2020
Publication title -
journal of evolutionary biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.289
H-Index - 128
eISSN - 1420-9101
pISSN - 1010-061X
DOI - 10.1111/jeb.13562
Subject(s) - introgression , cline (biology) , biology , hybrid zone , reproductive isolation , lineage (genetic) , parapatric speciation , evolutionary biology , species complex , hybrid , incipient speciation , ecology , allopatric speciation , mitochondrial dna , population , genetic structure , gene flow , genetic variation , genetics , phylogenetic tree , gene , demography , botany , sociology
The study of natural hybrid zones can illuminate aspects of lineage divergence and speciation in morphologically cryptic taxa. We studied a hybrid zone between two highly divergent but morphologically similar lineages (south‐western and south‐eastern) of the Iberian endemic Bosca's newt ( Lissotriton boscai ) in SW Iberia with a multilocus dataset (microsatellites, nuclear and mitochondrial genes). STRUCTURE and NEWHYBRIDS analyses retrieved few admixed individuals, which classified as backcrosses involving parental individuals of the south‐western lineage. Our results show asymmetric introgression of mtDNA beyond the contact from this lineage into the south‐eastern lineage. Analysis of nongeographic introgression patterns revealed asymmetries in the direction of introgression, but except for mtDNA, we did not find evidence for nonconcordant introgression patterns across nuclear loci. Analysis of a 150‐km transect across the hybrid zone showed broadly coincident cline widths ( ca. 3.2–27.9 km), and concordant cline centres across all markers, except for mtDNA that is displaced ca. 60 km northward. Results from ecological niche modelling show that the hybrid zone is in a climatically homogenous area with suitable habitat for the species, suggesting that contact between the two lineages is unlikely to occur further south as their distributions are currently separated by an extensive area of unfavourable habitat. Taken together, our findings suggest the genetic structure of this hybrid zone results from the interplay of historical (biogeographic) and population‐level processes. The narrowness and coincidence of genetic clines can be explained by weak selection against hybrids and reflect a degree of reproductive isolation that is consistent with cryptic speciation.