Meeting Abstract
Phenotypic integration is a pervasive characteristic of biological organisms. Interactions among morphological traits, termed phenotypic integration, can be readily identified through quantitative analysis of geometric morphometric data from living and extinct organisms. These interactions have been hypothesized to be a fundamental influence on morphological evolution on small to large time scales. Simulations using covariance matrices derived from 3-D landmark data for 97 living and extinct mammalian taxa confirm that trait integration can influence the trajectory and magnitude of response to selection. Phenotypic integration also produces both more and less disparate organisms than would be expected under random walk models by repartitioning variance in preferred directions, thereby increasing occupied morphospace range, but also homoplasy and convergence on macroevolutionary scales. The role of integration in shaping morphological evolution is particularly interesting when combined with the observation from many studies that cranial integration changes through ontogeny and that postcranial integration is correlated with reproductive strategy in mammals. If integration directs morphological variation, functional pressures at various points in ontogeny may differ in consequence depending in part on level and pattern of integration. For example, high integration in early postnatal ontogeny in marsupials, combined with strong functional pressures for crawling and suckling, may have contributed to the low variance observed in early postnatal marsupials and low disparity across marsupials, relative to placentals. Here, I discuss the macroevolutionary consequences of interactions among phenotypic integration, ontogeny, and function for morphological variance and evolution with comparative data from mammals and new data from amphibians.
