Bivariance of the Size Structure of Sable and Pine Marten Populations: Gene Flow or Introgression?

A comparative analysis of the size structure of 24 population groups of sable and pine marten was performed using two museum pools of craniometric data: the first is based on a complex of 17 standard traits, and the second is based on a new trait, Δ (“delta”), proposed by us to determine the two species by the skull. Each pool contains more than 3000 specimens. Three groups of traits were identified: four traits by which the sable is always larger than the marten; five traits by which the marten is superior to the sable at any point in its range; the main group is represented by seven traits with special variation: in transgression areas their values are higher for the sable, and in “pure” areas, on the contrary, for the pine marten. In areas of hybridization, the size parameters of the sable increase, while those of the marten, on the contrary, decrease, leading to their partial convergence. Each species demonstrates two variants of size structure: one is realized in allopatric groups (sables are smaller in size), the second is observed in areas of sympatry (sables, on the contrary, are larger), but the convergence of parameters is not absolute, statistically significant differences in size between species persist. The described phenomenon of bivariant dimensional structure is most likely, the result of limited introgression in the zone of sympatry. For the Δ trait, a high level of intersexual differences was found, exceeding the usual values by 3–4 times: 28% for the marten and 30.5% for the sable. In this dimension, the marten exceeds the sable by 33–36%.