Does body shape of toothed whales foretell fast-slow life histories?

Abstract

AbstractA widespread pattern in vertebrate life-history evolution is for species to evolve towards either fast or slow life histories; however, the possible causes of this pattern are multiple. Toothed whales (Odontoceti) are a particularly speciose group that includes a substantial range of body sizes and life histories and thus represent a model group to test the possible cause of this dichotomy. Using ancestral reconstruction, we find that some groups of odontocetes evolved sleek, presumably fast, body shapes around the same time that killer whales (Orcinus orca) evolved to be a predator of other whales approximately 1 Mya during the Pleistocene. A sleek body shape may have evolved as an adaptation to escape killer whale predation and resulted in a longer life-history events. A cluster analysis of odontocete whales confirmed the dual pattern of life-history traits with one group called ‘reproducers’ characterized by early age of maturity, short gestation, short interbirth interval, and short life, and the other group called ‘bet-hedgers’ with the opposite pattern. However, we found life history grouping relatively unrelated to whale shape (sleek or chunky). Results of mixed effects models incorporating principle components, indicated support for body shape as being positively related to neonate length (investment in progeny) but not significantly related to the temporal life-history traits. Thus, whale body shape is not an adequate explanation for the evolution of fast-slow life histories in odontocete whales.