Developmental stability of skull morphology in European bison Bison bonasus

Abstract

We compared developmental stability and total phenotypic diversity of 25 skull characters in three populations of European bison Bison bonasus (Linnaeus, 1758). Developmental stability was measured by fluctuating asymmetry, which was estimated by the variance of the left-right (1-r) and sealed (1-r)/(1+r) differences between the left (1) and right (r) sides of the skull. Mean number of asymmetrical characters per individual was used as an integrated index of developmental stability. Total phenotypic variability was examined by variance of (1+r) for the same characters. Greater developmental instability and total phenotypic diversity were found in bison from Pszczyna Reserve and Bialowieza Primeval Forest, as compared with those from Okskii Reserve. This indicates the gradual deterioration of developmental stability in the following sequence of the studied populations: Okskii Reserve, Bialowieza Primeval Forest, Pszczyna Reserve. In the Bialowieza population, deterioration of developmental stability could be detected, even though commonly used fitness measures showed no response. In the Pszczyna population, more serious developmental stability disturbance was accompanied by decreased viability, an expression of inbreeding depression. Two samples taken from the Bialowieza population at different times showed similar levels of developmental stability, which indicates the reliability of fluctuating asymmetry. These results suggest developmental stability to be an essential characteristic for monitoring populations and especially for revealing the initial response to stress.