Meeting Abstract

8.3  Monday, Jan. 4  Rates of morphological evolution vary with habitat use in dragon lizards COLLAR, David; Harvard University dcollar@oeb.harvard.edu

Ecological factors are often implicated to explain differences in diversity between clades because the ecological conditions available to clade members contribute to the mode of natural selection they experience. In particular, habitat use is thought to be important for evolutionary diversification. Differences between habitats in structural complexity, the number of species interactions, and functional demands can result in differential opportunity for ecological and morphological differentiation. I tested the hypothesis that diversification of body and limb form varies as a function of habitat use in the Agamidae lizard radiation. I inferred a phylogenetic tree for 90 agamid species using mtDNA sequences, reconstructed ancestral habitat use for the four habitats used by species in this group (rocks, trees, ground, and both trees and the ground), and then fit multiple evolutionary models to species’ values for morphological traits involved in locomotor performance. My results suggest that habitat use has had a strong effect on diversification. Models in which the rate of morphological evolution varied between lineages using different habitat types fit much better than models that constrained all lineages to the same rate. Moreover, in the best fitting models the evolutionary rate is much slower in rock-dwelling and arboreal lineages than in terrestrial or semi-arboreal lineages. This suggests that terrestrial habitats may facilitate ecomorphological differentiation, while the use of vertical habitats such as trees or rocky surfaces may impose constraints on morphological evolution and thus impede divergence.