Morphological Variation in the Striped Field Mouse Across Three Countries

Abstract

We assessed the variation in morphological traits in the striped field mouse (Apodemus agrarius) across Slovakia, Lithuania, and Estonia, aiming to understand how geographic gradients influence body size. The body mass, body length, tail length, hind foot length, and ear length were analyzed from nearly 12,000 specimens collected in several decades. Findings suggest that body size increases toward the north, following Bergmann’s rule, which links larger size to better heat conservation in colder climates. Conversely, appendage sizes (e.g., tail, ear) decrease, aligning with Allen’s rule to minimize heat loss. Longitudinal gradients revealed reductions in body length and appendages toward the east, potentially reflecting climatic and habitat variability. Temporal analysis revealed fluctuating body size trends, possibly due to changing environmental pressures. Therefore, our study underscores the importance of geographic and temporal factors in shaping morphological traits and provides valuable insights into the adaptability of A. agrarius to varying climatic conditions.