Abstract # 146:

Scheduled for Saturday, June 21, 2008 11:00 AM-11:10 AM: Session 16 (Meeting Room 1GHI) Oral Presentation

The enigma of sexual size monomorphism in strepsirrhines: A new explanation

A. E. Dunham and V. Rudolf
Rice University, Department of Ecology and Evolutionary Biology, Houston, TX, USA
     The primate order is among the most sexually dimorphic mammalian taxa with males generally having much larger body size than females. However, within this dimorphic group, the strepsirrhine primates (including lemurs) represent an extreme exception, exhibiting amongst the lowest sexual size-ratio found in mammals. The lack of dimorphism in Madagascar’s polygynous, group-living lemurs is particularly surprising because classical sexual selection theory predicts that characteristics found in these species such as male-biased operational sex ratios and spatially clumped females should lead to strong selection on male size. To address this we developed a model based on sexual selection theory that describes the circumstances for polygynous mammals in which active mate guarding should be less advantageous than other strategies. We tested predictions of the model with data on primate traits from the literature using a phylogenetic regression approach. Results suggest that certain life history traits shared by lemurs and a few haplorrhine taxa may favor an alternative strategy of mate guarding that does not involve male-male combat or selection on male size. In contrast to previous hypotheses involving constraints on male size, our results suggest the pattern of dimorphism found in strepsirrhine taxa is not inconsistent with sexual selection theory. Further research on mate competition strategies within primates and across a broader range of taxa will be informative for further testing our hypothesis.