PARENT SESSION

Systematics/Zoogeography 5 -- Session Chair: Theresa Spradling-- Van Duzer Theater

HOW "HERITABLE" IS THE BODY SIZE OF THE VERY LARGEST MAMMALIAN TAXA? Felisa A. Smith¹, S. Kathleen Lyons² and S.K. Morgan Ernest¹. ¹ Department of Biology, University of New Mexico, Albquerque, NM, USA; ² National Center for Ecological Analysis and Synthesis (NCEAS), Santa Barbara, CA, USA.

ABSTRACT- Recent studies examining the similarity of body size across the mammalian hierarchy have demonstrated extreme conservatism among most nonvolant terrestrial taxa, with broad sense heritability estimates exceeding 0.9. Interestingly, however, the pattern does not hold for the very smallest mammal species (<18g), perhaps because increasingly severe allometric constraints on life history and ecological parameters limit the range of possible adaptations when diversifying. Thus, mammals near the lower body size boundary may adapt to novel ecological conditions by modifying size. Because earlier work was limited to contemporary taxa and did not include aquatic mammals, examination of possible constraints on the evolution of the very largest taxa was precluded. Here, we investigate the body size similarity of large mammals across the taxonomic hierarchy, and across geographic space, using data that include the complete late Quaternary mammalian fauna for four continents (North and South America, Africa and Australia), and all aquatic forms. Thus, we include the largest animal that has ever existed, the blue whale (Balaenoptera musculus) at 190,000 kg, as well as numerous extinct large bodied members of Proboscidea, Gomphotheriidae and Megatheriidae. We suspect that biomechanical, allometric and physiological constraints must influence the evolutionary diversification of the largest mammals, as they apparently do for the very smallest. However, the relative importance of each of these factors probably differs from that faced by small animals, and moreover, may be ameliorated for the aquatic forms. Heritability estimates for both ends of the body size spectrum are compared, as are results for terrestrial versus aquatic mammals.

KEY WORDS: evolution, macroecology, body size, heritability