Geographical Variation in Skull Morphology of a Wild Rodent (Orientallactaga sibirica) Across Environmental Gradients

Orientallactaga sibirica (O. sibirica), a member of the family Dipodidae, is widely distributed across Central Asia and plays a significant role in grassland ecosystems. Although substantial ecological data exist for this species in China, research on intraspecific cranial variation is limited, and no comprehensive surveys have been conducted across its distribution range in China. This study aims to address this gap by collecting specimens of O. sibirica from various geographic regions in China, conducting geometric morphometric analyses of their skulls, and examining the influence of current climatic conditions on cranial morphology. Our results show that significant cranial variation in O. sibirica is observed in the nasal, parietal, and maxillary regions near the nasal end, as well as the zygomatic arch and preorbital bridge. These differences cause skulls from northeastern China to cluster distinctly from those from the Qinghai-Tibet Plateau. Regression analyses indicated that skull size is primarily associated with annual precipitation, whereas skull shape is significantly associated with altitude. Our findings reveal a distinct morphological pattern in the Qinghai-Tibet Plateau population, suggesting a high degree of geographic differentiation that warrants further investigation. Characterizing environment-associated intraspecific variation provides a baseline for understanding morphological diversity in O. sibirica across China.