An interspecific comparison of variance in sex-based developmental markers
Date
2015
Authors
Morley, Kyle
Journal Title
Journal ISSN
Volume Title
Publisher
University of Oregon
Abstract
Sexual dimorphism varies with the degree of male-male competition among primates. Changes in
body size of both sexes are well known during ontogeny, but less is known about how osteological
developmental markers vary under differing levels of sexual selection. Male-male competition is
reflected in a species’ body size sex ratio: humans are reported to have a 1.2 ratio, while rhesus
macaques have a 1.6 ratio. We predict greater results for larger bodies and canines in macaque males
compared to macaque females and humans as well as greater growth marker variation among
macaque males than in these other groups.
We documented dental eruption and epiphyseal fusion in 292 macaque skeletal specimens and
compared the data to over 25,000 individuals using published human population data.
Two-way ANOVAs without replication were used to test whether species had similar variation in
dental eruption and fusion time. The two species had significantly different eruption variation (males
F=33.71, df=15,1, p <0.0001; females F=119.06, df =15,1, p <0.0001) with macaques more variable
than humans. Both species also had different ranges in fusion time (F=7.28, df=13,1, p <0.05) with
macaque males more variable than human males.
The results support our prediction that macaque males show the greatest variation in these
growth markers. Interspecies comparisons of developmental plasticity, such as this study, allow for
inferences on how growth variation is affected by sexual selection.
Description
Single pdf poster
Keywords
Sexual dimorphism, Primates, Macaques, Male-male competition