Morphological and functional convergence among herbivorous lizards: A comparative study.

摘要

This work examines convergence among eight lineages of herbivorous lizards and their evolutionary history, and explores possible mechanisms and scenarios for the evolution of herbivory in these groups. Geometric morphometric methods are used to quantify variation in skull and lower jaw shape among lizards, simple lever models are used to quantify functional variation, and new comparative techniques are used to analyze these quantitative data.; After an introduction to herbivorous lizards, the second chapter discusses shape variation in the lizard skull. The relationship between morphology and phylogeny is quantified in several ways and three patterns of similarity among unrelated lizards that occupy the same feeding niche are described. This chapter reveals that lizard skull shape is determined primarily by phylogeny, and erects a framework for subsequent work.; The third chapter examines morphological and functional convergence among lizard skulls and lower jaws. Three patterns indicative of convergence are described, and a new phylogenetically informed method is developed to test instances of convergence. Herbivorous lizards are convergent in skull morphology---all herbivorous lizards diverge from their carnivorous relatives towards a similar area of morphospace. Herbivores are convergent in lower jaw function but not shape.; The fourth chapter tests paedomorphosis as a possible mechanism for the evolution of herbivore skull shape among iguanid lizards. Herbivores, although large, show skull shapes most similar to those of small lizards. However, a finer-scale study of two herbivorous iguanids and a related carnivore does not support the hypothesis that herbivore skulls are paedomorphic. Herbivore skulls do not cluster in the same area of morphospace as juvenile carnivores. In general, herbivorous iguanids show skull shapes that are expected for iguanids their size.; The final research chapter tests a few scenarios that have been proposed to explain the evolution of herbivory in lizards, and also investigates whether herbivorous lizards assemble their convergent traits in the same order. New methods are developed to describe and ordinate the evolution of quantitative traits. No common patterns are seen to the evolution of skull size, skull shape, and lower jaw function; no single hypothesis can explain the evolution of herbivory in all lineages.