GENETIC INFLUENCES ON CRANIAL FORM - VARIATION AMONG RANCH AND FERAL AMERICAN MINK MUSTELA-VISON (MAMMALIA, MUSTELIDAE)

Multivariate statistical techniques were used to examine craniometric variation within and between ranch and feral populations of American m ink (Mustela vison). An examination of variation between ranches revea led that differences are greater between ranches than within ranches, although all comparisons were statistically significant. There is high ly significant variation within a population of mink sampled from a si ngle ranch during a short time period; female mink of different pelt c olour are differentiable by their skull shape but not by skull size. T his offers evidence for a genetic background to cranial variation in r anch mink. Cranial sexual dimorphism is reduced in ranch mink, when co mpared to feral populations, and size accounts for a lesser proportion of the variation between the sexes in ranched populations. In additio n, the skulls of ranched mink are larger, have a relatively shorter pa late and a relatively narrower postorbital constriction compared to th eir feral counterparts. We believe this reduced dimorphism to be a pro duct of relaxed sexual selection, lack of resource competition and sel ective breeding for larger specimens of both sexes within ranch popula tions. (C) 1995 The Linnean Society of London.