Sexual dimorphism and sex ratios in Madagascan prosimians

Skull length was used to evaluate the extent of sexual dimorphism in size among 21 taxa of extant Madagascan prosimians. Extraneous sources of variation were controlled by limiting male-female comparisons to museum samples comprised of ten or more wild-caught, adult individuals collected at the same locality (24 samples total). Sexual dimorphism in skull length averaged only 1.31%, with equal probability of males or females being larger. The only statistically significant sexual differences were Lepilemur edwardsi from St. Marie de Marovoay in western Madagascar (P < 0.05; males 4% larger then females = 2.2 mm) and Microcebus murinus from Amboasary-Sud in southern Madagascar (P < 0.001; females 2% larger than males = 0.6 mm). A recent study of body weights of captive animals at Duke University Primate Center also showed that M. murinus displays highly significant sexual dimorphism. These results were examined in the context of factors believed to affect sexual dimorphism in anthropoid primates. The same 24 samples were used to demonstrate that the sex ratio is approximately 1:1 among Madagascan prosimians, and this information was correlated with data from field studies. The correlations between sexual dimorphism, sex ratio, and size are low, indicating that these are independent traits in Madagascan prosimians.