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Behavioral Ecology and Sociobiology

, Volume 65, Issue 6, pp 1229–1235 | Cite as

Body size and sexual selection in the koala

  • William A. H. Ellis
  • Fred B. Bercovitch
Original Paper

Abstract

Sexual selection is often characterized by polygynous breeding systems, size dimorphism, and skewed operational sex ratios. Koalas are sexually dimorphic in multiple domains, yet are absent from the literature on sexual selection and the structure of their mating system is unclear. We provide the first documentation of the strength of sexual selection in koalas by using microsatellite markers to identify sires. We combine the genetic data with morphological data in order to assess the role of body size in regulating reproductive output. During our 4-year study, 37% of males were identified as possible sires. Males were significantly larger than females, with sires heavier than non-sires. Male body mass correlated with annual reproductive output, with Crow’s Index of Opportunity for Selection revealing that variation in male reproductive success was threefold higher than that of females. Since it appears that male koalas rarely engage in physical confrontations over access to females, size dimorphism could be based upon non-agonistic competition and/or female mate choice. We propose that size dimorphism in koalas evolved as a consequence of endurance rivalry promoting vocal sexual advertisements that attract females. We suggest that female choice is a key mediator of male reproductive output.

Keywords

Koalas Sexual selection Size dimorphism Reproductive success Mate choice Microsatellite DNA 

Notes

Acknowledgments

This study could not have been completed without the valuable input of Sean FitzGibbon and Alistair Melzer, both of whom contributed data and ideas to this report. The project was funded by The Earthwatch Organization and The San Diego Zoo Institute for Conservation Research. Field work was supported by Queensland Marine Parks Mackay. Kristen Lee oversaw all genetic analyses. Delma Clifton, Gail Tucker, Steve Burke, and Steve Fisher assisted with fieldwork. Queensland Department of Environmental and Resource Management provided the permits to work with koalas (WISP00491302), and the project was carried out under The University of Queensland animal ethics permit (ZOO/ENT/115/04/RT) and approved by the Institutional Animal Care and Use Committee of the Zoological Society of San Diego.

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Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  1. 1.San Diego Zoo Institute for Conservation ResearchZoological Society of San DiegoEscondidoUSA
  2. 2.Koala Ecology Group, School of Biological Sciences and Centre for Mined Land RehabilitationThe University of QueenslandBrisbaneAustralia
  3. 3.Primate Research InstituteKyoto UniversityInuyamaJapan
  4. 4.Wildlife Research CenterKyoto UniversityInuyamaJapan

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