Meeting Abstract
A longstanding question in evolutionary biology is to understand the role of local adaptation, as opposed to neutral processes, in shaping morphological variation among populations. Differentiating between these alternatives for fossil bones and teeth is critical for interpreting the drivers of historical change. However, this work is particularly challenging because molecular indicators of selection and drift are lacking in fossils. Here we used the molars of the extant, insectivorous rodent Onychomys leucogaster as a test case to develop expectations for the fossil record. The similarity across environments of the insects comprising the diet of O. leucogaster, at least with respect to their mechanical properties, suggest that selection on molars, primarily through diet, may be homogeneous across the distribution of the species. We used geometric morphometrics to measure morphology, ddRAD sequencing to estimate population structure, and measures of climate, primary productivity, and phenology to measure environment. We evaluated support for the two hypotheses by comparing morphology, population structure, and environment while accounting for geographic distance via PST-FST-comparisons using multiple matrix regression with randomization. Depending on whether we quantified morphology in terms of size, shape, or size and shape together, we found variably significant relationships between morphology and population structure, but never with environment or geographic distance. In sum, these results indicate that we cannot eliminate drift as the mechanism driving morphological divergence in tooth shape and size.
