Meeting Abstract

8.5  Monday, Jan. 4  Tempo and mode of lizard axial evolution. Is body elongation a key innovation? BERGMANN, P.J.*; IRSCHICK, D.J.; University of Arizona; University of Massachusetts Amherst pjbergma@email.arizona.edu

Recent approaches for studying the mode and tempo of trait evolution and diversification allow us to test hypotheses of key innovation with unprecedented rigor. Among vertebrate clades, there is considerable variation in both vertebral number and the degree of constraint on vertebral number. This variation is hypothesized to influence body shape diversity, and ultimately species diversification. We tested the hypothesis that the evolution of a snake-like body represents a key innovation, using a supertree of lizards, a vertebral count dataset including ~1400 species, and a body shape dataset including ~650 species. These data allowed us to calculate rates of morphological evolution, the density of lineages in morphospace, and a new metric that measures the level of dispersion of a clade in morphospace. We found that an elongate body shape does not represent a key innovation, leading to clade diversification. Instead, rapid vertebral number evolution acts to diminish constraints on body shape evolution, and this tends to occur in relatively elongate clades with more trunk vertebrae. However, this phenomenon does not translate into increased rates of species diversification. Our results illustrate how a key innovation can hold sway on some aspects of diversity and not others, suggesting that the role of key innovations may be more complex than previously envisioned.