EN
Developmental stability and phenotypic diversity of the bank vole Clethrionomys glareolus Schreber, 1780 were tested in a group of founders collected from natural population in Białowieża National Park (Poland) and in a sample taken from the 20th generation of a laboratory mass-cross strain derived from these founders. Fluctuating asymmetry of 28 skull characters such as the number of foramina were used as a measure of developmental stability. Variance of the foramina on the left and right sides of the skull for the same characters was used as a measure of phenotypic diversity. The data obtained indicate a developmental stability decrease and phenotypic diversity increase as a result of inbreeding during 20 generations in the laboratory.