Group histories and offspring sex ratios in ringtailed lemurs (Lemur catta) |
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Authors: | C L Nunn Michael E Pereira |
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Institution: | (1) Department of Biology, University of Virginia, 221 Gilmer Hall, Charlottesville, VA 22903-2477, USA e-mail: clnunn@virginia.edu Tel.: +1-804-9825746, Fax: +1-804-9825626, US;(2) Department of Biology, Bucknell University, Lewisburg, PA 17837, USA, US |
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Abstract: | Birth sex ratios were examined for ringtailed lemurs (Lemur catta) at the Duke University Primate Center. This population provides a long-term database of births under a variety of demographic
and management conditions, including two semi-freeranging groups between which males transfer freely and females defend stable
territorial boundaries. We examined three hypotheses usually considered in studies of primate sex ratio bias. The Trivers-Willard
hypothesis predicts that dominant females produce males, local resource competition at the population level (LRC-population)
predicts that the dispersing sex (males) will be overproduced in dense populations, and local resource competition among individuals
(LRC-individual) predicts that dominant females overproduce the philopatric sex (females). We also examined a fourth hypothesis,
local resource enhancement (LRE), which is usually subsumed under LRC-individual in studies of primate sex ratio evolution.
LRE predicts that under certain conditions, females will produce the sex that provides later cooperative benefits, such as
alliance support for within- or between-group competition. Our data provide support for LRE: females overproduce daughters
given prospects of new group formation, either through group fission or threatened expulsion of young mothers. Behavioral
data from Duke and also wild populations show that daughters serve mothers as important allies in this context and LRE effects
also have been documented in other mammals that experience similar group histories. Nonsignificant trends in the data supported
the LRC-population hypothesis, and we suggest that LRC interacts with LRE to explain offspring sex ratios in ringtailed lemurs.
Received: 27 August 1999 / Received in revised form: 6 March 2000 / Accepted: 18 March 2000 |
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Keywords: | Offspring sex ratios Facultative adjustment Local resource enhancement Ringtailed lemurs Lemur catta |
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