Meeting Abstract

P3.46  Jan. 6  Evolution of fossoriality in mammals: does burrowing behavior drive an evolutionary ratchet? HOPKINS, SSB; National Evolutionary Synthesis Center shopkins@nescent.org

Some ecomorphological specializations create an evolutionary �ratchet,� a term used to describe irreversible morphological evolution. Hypercarnivory, for example, has evolved many times in the history of mammalian carnivores, and invariably leads to the extinction of the lineage. The phenomenon of an evolutionary ratchet occurs because the specialization creates an anisotropic evolutionary character-space such that it is much easier for the species to become increasingly specialized than for it to become less so. Fossoriality, or burrowing behavior, may provide another example of such an evolutionary ratchet. Fossorial adaptations, such as long, curved digging claws, short, powerful limbs, and reduced eyes, all make it much more difficult for mammals acquiring these features to escape predators using the behaviors of their terrestrial and arboreal ancestors. Running and climbing are very difficult for well-adapted burrowers. Hence, adaptation to a burrowing lifestyle provides a selective regime likely to produce an evolutionary ratchet. Recognizing the pattern of an evolutionary ratchet requires tracing the evolution of morphology across phylogeny. For this study, proxies such as limb bone proportions and craniodental morphology, as well as published behavioral data are used to determine degrees of morphological adaptation for fossoriality. Examining the morphological patterns of fossoriality across phylogenies of a number of extant and extinct burrowing mammalian lineages makes it possible to reconstruct the history of morphological evolution related to burrowing behavior. Preliminary results reveal that this prediction of burrowing as an evolutionary ratchet is generally borne out, although defensive adaptations to deter predation may release the pressure to become more and more fossorial through time.