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Male bimaturism success and reproductive success in Sumatran orang-utans

Utami, S.S.; Goossens, B.; Bruford, M.W.; De Ruiter, J.R.; van Hooff, J.A.R.A.M.

Authors

S.S. Utami

B. Goossens

M.W. Bruford

J.R. De Ruiter

J.A.R.A.M. van Hooff



Abstract

Although orang-utans live solitary lives most of the time, they have a complex social structure and are characterized by extreme sexual dimorphism. However, whereas some adult male orang-utans develop full secondary sexual characteristics, such as cheek flanges, others may stay in an "arrested" unflanged condition for up to 20 years after reaching sexual maturity. The result is a marked bimaturism among adult males. Flanged males allow females to overlap with their home range and often tolerate the presence of unflanged males. However, wherever possible flanged males actively prevent unflanged males from copulating with females. Two competing hypotheses, previously untested, have been advanced to explain male reproductive behavior and bimaturism in orang-utans: (1) the "range-guardian" hypothesis, which asserts that the flanged males are postreproductive and defend a range in which they tolerate sexually active, unflanged male relatives; and (2) the "female choice" hypothesis, which asserts that flanged males tolerate unflanged males in their range because they rely on female preference to favor flanged males. We investigated these hypotheses and a third hypothesis that the two male morphs represent co-existing alternative male reproductive strategies ("sitting, calling, and waiting" for flanged males versus "going, searching, and finding" for unflanged males). Fecal samples were collected from a well-studied population in Indonesia, and eight human microsatellites were analyzed for 30 individuals that have been behaviorally monitored for up to 27 years. By carrying out paternity analysis on 11 offspring born over 15 years, we found that unflanged males fathered about half (6) of the offspring. Relatedness between successful unflanged males and resident dominant males was significantly lower than 0.5, and for some unflanged/flanged male pairs, relatedness values were negative, indicating that unflanged males are not offspring of the flanged males.

Citation

Utami, S., Goossens, B., Bruford, M., De Ruiter, J., & van Hooff, J. (2002). Male bimaturism success and reproductive success in Sumatran orang-utans. Behavioral Ecology, 13(5), 643-652. https://doi.org/10.1093/beheco/13.5.643

Journal Article Type Article
Publication Date May 1, 2002
Deposit Date May 23, 2007
Journal Behavioral Ecology
Print ISSN 1045-2249
Electronic ISSN 1465-7279
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 13
Issue 5
Pages 643-652
DOI https://doi.org/10.1093/beheco/13.5.643
Keywords Fecal analysis, Mating strategies, Mmicrosatellites, Non-invasive sampling, Orang-utans, Paternity, Relatedness, Pongo pygmaeus abelii.