Altitudinal variation in limb size across seven populations of Rana kukunoris (Anura: Ranidae) fails to obey Allen’s rule

Abstract

In terms of body size patterns, most research has focused on studying intra- and interspecific variation following the “Bergmannian” patterns. Allen’s rule, closely connected to these patterns, has historically been given comparatively less attention. In this study, our aim was to assess the validity of Allen’s rule, which suggests that the relative size of limb length should decrease as altitude increases. Here, we investigated the geographical variation in limb length among populations of the Plateau Brown Frog, Rana kukunoris, across seven distinct altitudes on the eastern Tibetan plateau. Our findings demonstrated a significant positive correlation between forelimb length of males relative to body size and altitude, contradicting the pattern predicted by Allen’s rule. In our study system, we observed a negative correlation between elevation and temperature seasonality as well as water deficit, but a positive correlation with annual total precipitation, speculating that alternative selective forces may play a role in driving the increase in extremity length at high elevations. Long forelimbs only appear in high-altitude environments, not in aggregations with a high operational sex ratio (OSR), suggesting that individuals in stressful environments (e.g., high altitude or latitude) would drive the differentiation in relative extremity length.