Considering the impacts of climate change on natural systems, the study of species’ abilities to adapt to such change is critical. To adapt to rapid change, a species must already possess the necessary phenotypic variation. Climate-relevant variation may exist along environmental gradients within a species’ range. Geometric morphometrics (GM) is a powerful interdisciplinary tool that can quantify morphological adaptations of species across climate gradients, and that can assess the capacity of morphology to represent environmental conditions. The aim of this study is to apply GM to investigate the relationship between climate variables and dentition in the California vole (Microtus californicus). We imaged 307 lower first molars (m1s) and 361 upper toothrow specimens, spanning the range of the species. Using the “Geomorph” package in R, we applied generalized Procrustes superimposition to scale and align the m1 images and, separately, toothrow images. We then performed two-block partial least squares (2B-PLS) analysis to quantify the degree of covariation between Worldclim climate variables and toothrow and m1 shapes. We subsequently produced deformation grids to visualize trends in climate-correlated dental shape. Finally, we employed Spearman’s Rank Correlation Coefficient to compare the order of m1 and toothrow images along their PLS axes.
Results/Conclusions
We found significant positive covariation between the climate variables and the first singular toothrow (r = 0.38, p < 0.01) and m1 (r = 0.47, p < 0.01) PLS axes. The mean annual precipitation climate variable carried a greater weight than the mean annual temperature variable in driving these patterns. We also found that in high-temperature, low-precipitation climates, m1s and toothrows are relatively straight, while in low-temperature, high-precipitation climates, they are relatively curved, particularly towards the anterior cap of the m1 and the middle of the toothrow. Lastly, we determined from Spearman’s Rank Correlation Coefficient analysis that the orders of m1 and toothrow specimens along their first PLS axes are strongly correlated (r = 0.99, p < 0.01). These results suggest that climate plays a major role in driving similar trajectories of m1 and toothrow variation in Microtus californicus across space. This indicates that local cranial plasticity may occur in response to climatic conditions. Future research would explore the mechanisms by which climate causes specific dental adaptations. These results will be used to bridge ecological and paleontological datasets to enhance our understanding of natural systems in the face of climate change.