Hybrid zone analysis confirms cryptic species of banded newt and does
not support competitive displacement since secondary contact
Abstract
When two putative cryptic species meet in nature, hybrid zone analysis
can be used to estimate the extent of gene flow between them. Two
recently recognized cryptic species of banded newt (genus Ommatotriton)
are suspected to meet in parapatry in Anatolia but a formal hybrid zone
analysis has never been conducted. We sample populations throughout the
range, with a focus on the supposed contact zone, and genotype them for
31 nuclear DNA SNP markers and mtDNA. We determine the degree of genetic
admixture, introgression and niche overlap. We reveal an extremely
narrow hybrid zone, suggesting strong selection against hybrids, in line
with species status. The hybrid zone does not appear to be positioned at
an ecological barrier and there is significant niche overlap. Therefore,
the hybrid zone is best classified as a tension zone, maintained by
intrinsic selection against hybrids. While the two banded newt species
can evidently backcross, we see negligible introgression and the pattern
is symmetric, which we interpret as supporting that the hybrid zone has
been practically stationary since its origin (while extensive hybrid
zone movement has been suggested in other newt genera in the region).
Our study illustrates the use of hybrid zone analysis to test cryptic
species status.