Meeting Abstract

P2.81  Saturday, Jan. 5  Macroevolutionary diversity of amniote limb proportions is congruent with predictions from developmental interactions YOUNG, N.M.; University of California, San Francisco nathan.m.young@gmail.com

Mammals, birds, and reptiles exhibit remarkable diversity in limb proportions. These evolved differences are thought to principally reflect selection on variation in fetal and postnatal segmental growth. However, early conserved developmental events also have the potential to impact the generation of interspecific variation. Experimental evidence indicates that proximo-distal patterning of the limb into segments occurs through a balance between activating signals at the flank and inhibitory signals from the tip. Modeling of this mechanism further predicts that the initial proportions of the developing limb should exhibit tradeoffs between stylopod and autopod and invariance of the zeugopod. To test whether this patterning signal exists and whether it varies over ontogeny, amniote limb proportions were analyzed at both early fetal and adult developmental time points. Results demonstrate that macroevolutionary limb diversity is congruent with predictions of activation-inhibition despite subsequent variation in segmental growth or differences in phylogenetic history and functional adaptation. Ontogeny within species exhibits a similar conservation. These results suggest that developmental mechanisms limit initial zeugopodial proportions while selection on higher order design principles may act to further dampen variation in a wide range of functional limb adaptations, resulting in a persistent developmental signal. Limb diversity therefore reflects selection on variation in a range of developmental processes that combine to generate observed macroevolutionary patterns.