Sexual Body Size Dimorphism in Small Mammals: A Case Study from Lithuania.

Simple Summary: We studied the differences in body size between males and females of 14 small mammal species in Lithuania. By measuring standard physical traits in voles, mice, and shrews from a large collection of long-term surveys, we updated information published 35 years ago and compared our results with data from other countries. Our results showed that males were larger than females in the yellow-necked mouse, root vole, and three other meadow voles, especially among adults. This pattern is consistent with Rensch's rule, which refers to how size differences between the sexes change with total body size. In contrast, females were larger than males in bank voles and four mouse species, although this was less consistent across age groups. Shrews and the smallest mouse species, the herb field mouse, showed no significant size differences between sexes. In some species, these size differences changed as the animals grew. We are adding data on less common species such as the sibling vole and northern birch mouse, which have not been studied extensively. Our research provides new baseline data for small mammals in the boreal mid-latitudes and serves as a foundation for future studies of how animals adapt to changing ecological conditions or climate change. We assessed the sexual size dimorphism (SSD), analyzing standard morphometric traits in juveniles, subadults, and adults, of 14 species of voles, mice, and shrews in Lithuania on the basis of long-term surveys, updating information published 35 years ago and in the context of data from other countries. ANOVA, t-tests, and a 5% threshold were used in the analyses. Male-biased SSD was observed in Apodemus flavicollis and Alexandromys oeconomus, which was subject to Rensch's rule, and in three other meadow vole species, with the strongest expression in adult individuals. Female-biased SSD was best expressed in Clethrionomys glareolus and was also identified in four mouse species, although patterns were less consistent across age groups. Shrews and the smallest mouse, Apodemus uralensis, exhibited monomorphic traits. The transition of dimorphism during postnatal development was observed in some species. We present an assessment of SSD in Microtus rossiaemeridionalis and Sicista betulina, the less common small mammals not analyzed in publications by other authors, and provide new baseline data for boreal mid-latitude small mammal species as a foundation for future studies on SSD and its adaptive significance under shifting ecological pressures or climate change. [ABSTRACT FROM AUTHOR]