Morphological variability of baculum (os penis) in the polecat Mustela putorius

Abstract. The study presents the morphological variation in three traits of the baculum (os penis) in the polecat (Mustela putorius Linnaeus, 1758), based on an analysis of 108 males (7 juveniles and 101 adults) collected in NE Slovakia between 1958-1978. Adult individuals had a significantly larger baculum (length, width and distal tip size) than juveniles. All three measured baculum traits correlated significantly with each other. However, these relationships only explained from 10% (width – distal tip size relationship) up to 51% (length – width relationship) of the variance between the studied traits. Therefore, evolutionary analysis based on baculum variation should take into account not only baculum size, but also base width, which may be a measure of baculum developmental stage. Moreover, coefficients of variation were 10.2%, 30.2% and 11.4%, respectively for length, width and distal tip size of the baculum, much greater than the known variation of cranial measurements. Therefore, more data on the variability among individuals, as well as between measured traits, are needed for a better understanding of the evolutionary processes which influence baculum size and shape.