Abstract # 71:

Scheduled for Thursday, August 9, 2001 11:30 AM-11:45 AM: Session 2 (University Hall 157) Oral Presentation

Dynamics of Testes Size Compensates for Male Body-Size Differences in a Wild Malagasy Primate: The Milne-Edwards’ Sifaka (Propithecus diadema edwardsi) of Ranomafana National Park, Madagascar

S. T. Pochron and P. Wright
Dept of Anthropology, SUNY at Stony Brook, SBS Bldg., 5th floor, Stony Brook, NY 11794-4364, USA
     Sperm competition is typically detected with a linear regression depicting body size and testes volume. The distance of the study species from the regression line indicates the strength of sperm competition relative to the primate average. Using this method in a wild, seasonally breeding strepsirhine is difficult. Comparing a strepsirhine species to a haplorhine norm produces confusing results, and since seasonally breeding primates change testes volume with season, the reference database must use animals measured during their breeding season. Kappeler provides a potential reference database by measuring 18 captive strepsirhine species during their breeding season. However, captivity affects lemur weight and testes volume. To detect sperm competition in a wild sifaka population, we examined the dynamics of testes volume and body size. We hypothesized that if small animals (with small testes) increase testes volume to match large animals (with large testes) with breeding-season onset, sperm competition could be inferred. Between 1986 and 2000, we measured male lemurs 69 times; sixty-two yielded measures of body weight and testes size. We compared the relationship between body size and testes volume in the breeding and non-breeding season. The significant positive relationship found in the non-breeding season dissipates in the breeding season, with heavier males experiencing less testicular growth than lighter males. Implications for sperm competition and female dominance in this species are discussed.