Metacarpal Ratio and Its Relation to Sexual Dimorphism in Primates with Different Mating Strategies
Semester of Graduation
Master of Arts (MA)
Geography and Anthropology
The digit ratio (2D:4D) is a sexually dimorphic trait in mammalian hands that is a result of levels of prenatal androgen exposure (PNAE) during limb development. Previous studies have shown that females have a higher ratio than males and that sexual dimorphism in the ratio is greater in species with polygynous mating strategies and high levels of intermale aggression compared to monogamous species with low intermale aggression. This study used metacarpals instead of phalanges to test the hypotheses that the metacarpal ratio (2Mc:4Mc) will be higher in females than males within a species and that the ratio would be more sexually dimorphic in species with high intermale competition compared to species with low intermale competition. Intermale competition is defined as the frequency and intensity of aggression found in adult males within a species. Second and fourth metacarpals were measured on skeletonized animals for six species with different mating strategies (M=monogamy; P=polygyny) and levels of intermale aggression (H=high; I=intermediate; L=low; F=female; M=male). All animals used in the study were designated by the museum as wild-caught. Sample sizes for each species including mating strategy and level of intermale aggression were as follows: Aotus azarae (M,L; 9F, 11M), Hylobates lar (M,L; 49F, 51M), Presbytis rubicunda (P,I; 18F, 19M), Trachypithecus cristatus (P,I; 31F, 18M), Alouatta seniculus (P,H; 17F, 19M), and Macaca fascicularis (P,H; 19F, 18M). Results comparing medians fail to reject the null hypotheses that the metacarpal ratio is the same between sex within the species and the ratios will be the same regardless of competition level. The sexes are non-significantly different in metacarpal ratio in A. seniculus, A. azarae, H. lar, and M. fascicularis; males have a significantly higher ratio than females in P. rubicunda, but females have a significantly higher ratio than males in T. cristatus. Results are not consistent with previous research on digit ratios indicating that metacarpals and phalanges may respond differently in their growth and PNAE.
Hart, Emilee, "Metacarpal Ratio and Its Relation to Sexual Dimorphism in Primates with Different Mating Strategies" (2018). LSU Master's Theses. 4708.