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.
Highlights
Three extant polecat species of the subgenus Putorius are recognized: the European polecat (Mustela putorius L., 1758), the steppe polecat (M. eversmanii Lesson, 1827) and the black-footed ferret (M. nigripes (Audubon et Bachman, 1851))
M. eversmanii likely diverged from M. putorius approximately 1.5 million years ago based on the nuclear DNA region inter-receptor binding protein (IRBP), though cytochrome b (CytB) transversions indicate a younger date of 430,000 years (Sato et al 2003)
The discriminant scores applied to the identification of M. eversmanii and M. putorius mostly agreed with the determinations based on the assessment of museum catalogues, qualitative pelage and cranial characters (Table 4) as all but three individuals were correctly classified into their respective species groups
Summary
Three extant polecat species of the subgenus Putorius are recognized: the European polecat (Mustela putorius L., 1758), the steppe polecat (M. eversmanii Lesson, 1827) and the black-footed ferret (M. nigripes (Audubon et Bachman, 1851)). M. eversmanii likely diverged from M. putorius approximately 1.5 million years ago based on the nuclear DNA region inter-receptor binding protein (IRBP), though cytochrome b (CytB) transversions indicate a younger date of 430,000 years (Sato et al 2003) Since these species are occasionally reported to hybridize where they have an overlap in their distribution, the reality of a true species split has been debated (Blandford 1987), and some authors have considered if M. putorius, M. eversmanii and M. nigripes could be viewed as a single Holarctic species (Anderson 1977; Anderson et al 1986; O’Brien et al 1989). The present study is the first multivariate analysis which includes specimens from the western range of the steppe polecat (including the poorly studied subspecies M. eversmanii hungarica) examining the cranial measurements and the geographical distribution and frequency of the external features described by Pocock (1932) and Wolsan (1993b)
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