The form radnensis in the upper second molar in isolated subpopulations of the root vole (Alexandromys oeconomus arenicola) in the Netherlands

Author: Jan Piet Bekker

Abstract: During a preliminary study of unsorted barn owl pellets from Texel, the Netherlands, twelve out of 140 upper second molars (M2) of the root vole (Alexandromys (Microtus) oeconomus arenicola) were identified as the form radnensis. Besides the regular or normal form (N), four different stages of radnensis are recognized, which show a progressive incision of the lingual field: V1, V2, V3, and V4. The aim of this study is to determine the frequencies of the prevalence of the form radnensis of M2 in the known subpopulations of the root vole in the Netherlands, to establish whether or not these frequencies differ from each other and, if so, whether this can be explained by the age structure of the root vole subpopulation. We analysed the skulls of root voles from owl pellets from all the known subpopulations in the Netherlands. The subpopulation of Texel shows 12.5% radnensis, significantly higher than all the other subpopulations. No link was found with age. It is concluded that the prevalence of the form radnensis is unevenly distributed over the subpopulations of root voles in the Netherlands.