Meeting Abstract
Mammals living in deserts are often considered well-adapted to the unique ecological pressures of their arid environments. Often, these strong selective pressures drive convergent morphological evolution between distantly related and geographically isolated species, such as the large ears of hares and fennec foxes. As bipedal hoppers with long hindlimbs, kangaroo rats (Heteromyidae) and jerboas (Dipodidae) are often discussed as examples of convergence in desert rodents. Such convergence is thought to extend to the auditory apparatus, as enlarged tympanic bullae amplify low-frequency signals used to avoid predators and detect prey. Here, we test for convergence in the conductive auditory system for five species each of heteromyids and dipodids. We use microCT scans and linear measurements to examine trait evolution for external pinna length and tympanic bulla volume. Phylogenetic trait mapping and ancestral character estimation reveal different tradeoffs for each group: bullae are relatively large and pinnae are small in heteromyids, whereas the inverse is seen in dipodids. We then use evolutionary allometry to model the relationship between pinna length vs. ear volume, finding the PGLS regression lines to be orthogonal (mjerboa= -0.178; mkrat= 4.58). We therefore reject the hypothesis that the auditory system is broadly convergent in these two groups of desert rodents, instead identifying inverse tradeoffs in the conductive hearing apparatus in response to similar selective pressures.
