Appendage Sizes in Three Rodent Species Are Affected Indirectly by Climate Factors via Their Effects on Body Size

In mammals, temporal and spatial variation in appendage sizes within and among species may be driven by variations in ambient temperature and allometric scaling. Here, we use two decades of morphological data on three rodent species distributed across vast latitudinal gradients in China to estimate temporal and spatial trends of tail, hind-foot, and ear lengths. Further, we test 14 climate variables to identify the critical drivers of these trends and use structural equation modeling (SEM) to analyze whether the effects of climate variables on the appendage lengths are direct or indirect, via effects on body length. Relative to body length, and in contradiction to Allen's rule, all appendage lengths remained unchanged over time and across space. By contrast, absolute appendage lengths increased in one species (Apodemus agrarius) over time and in two species (A. agrarius and Rattus norvegicus) across space; and most of the appendage lengths in the two species were associated with annual mean minimum temperature in the year preceding capture (PreAnnMinTemp). The SEM results suggest that PreAnnMinTemp affected absolute appendage lengths indirectly through body length. In addition, except for tail length in two species and both hind-foot and ear length in one species, absolute appendage lengths scaled allometrically with body length. These results suggest that the distinct temperature-appendage-length patterns among and within species arise from species-specific temperature sensitivities and appendage-specific ontogenetic rates and functions.