Intra- and interspecific morphological variation in sympatric and allopatric populations of Mustela putorius and M. eversmanii (Carnivora: Mustelidae) and detection of potential hybrids

Abstract

European mustelids include the European polecat, Mustela putorius, and the steppe polecat, M. eversmanii. Both occur sympatrically in the Pannonian Basin, where M. eversmanii hungarica represents the westernmost part of the latter species and they allegedly hybridize. We investigated the morphological relationships in sympatric and allopatric populations of these mustelids with representative sampling, taxonomic and geographic coverage. We evaluated inter- and intraspecific patterns of morphological differentiation of 20 cranial measurements and four external traits by distance-based morphometric approaches and multivariate analyses. Our results revealed a considerable heterogeneity in cranial morphology. The two species appeared to be clearly differentiated although sympatric populations were closer to each other and had a slight overlap in the morphometric space. Within M. eversmanii, the subspecies and the nominal taxon only partially overlapped, and M. eversmanii eversmanii was more distant from M. putorius than subspecies hungarica. Although morphometric analyses revealed several intermediate individuals in size in sympatric M. eversmanii and M. putorius populations, only a small fraction of such specimens showed conflict in discrete morphological characters with the diagnostic discriminant function. We interpret these results as an indication of ongoing hybridisation between sympatric populations, but the low number of hybrids identified suggests limited genetic exchange between the species.

Extensive genome introgression between domestic ferret and European polecat during population recovery in Great Britain.

“…Finally, we uncover novel features for the polecats from the European mainland. Firstly, there is evidence of introgression between European polecats and Steppe polecats (Figure 4), supporting previous phenotypic analysis where the two species occur in sympatry (Cserkész et al, 2021). Also, there is a suggestion of genetic structure in mainland Europe (Figure 5) where polecats from Italy show a distinct genetic population structure when compared to that of other countries.…”

A comparison of microsatellites and genome‐wide SNPs for the detection of admixture brings the first molecular evidence for hybridization between Mustela eversmanii and M. putorius (Mustelidae, Carnivora)

“…However, in addition to the two putative hybrids identified by Bayesian clustering (#26626, #26714), sample ‘P01’ ( M. putorius , Felsőszölnök, W Hungary) was added as a potential third admixed specimen in this analysis. All three individuals were identified as M. putorius based on morphology (Cserkész et al, 2021). All other samples were assigned to one of the clusters with more than 90% probability (Figure 4a).…”

“…In agreement with that, it was collected in a barely forested, mainly agricultural lowland region, where the environmental conditions seem to be much suitable for M. eversmanii . Unfortunately, this specimen was not included in the morphometric analyses made by Cserkész et al (2021). Additionally, none of the analyses based on SSRs showed this specimen as backcrossed, which clearly highlights the limitation of a handful of SSRs for detecting backcrosses.…”

“…However, there is no solid evidence in support of continuing hybridization between the two species in the wild. A recent study examined the craniometric and phenotypic diversity of polecats (Cserkész et al, 2021), which indicated several morphologically hybrid individuals. Hybrid identification is based on mixture of parental traits in phenotype and size, but this could be misleading owing to considerable overlap in morphological traits between the two species.…”

Consequences of Hybridization in Mammals: A Systematic Review

“…A classic example of the effect of hybridization on morphological traits are the Darwin finches in Galapagos, where most hybrid individuals have intermediate body size and beak shape compared with the parental species [ 186 ]. Several studies in this review reported intermediate phenotypes, e.g., in cetaceans [ 187 ], mustelids [ 188 ], camelids [ 189 ] and primates [ 181 ]. The presence of admixed individuals with intermediate phenotypes may impede species identification in the field.…”