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Body size and sexual selection in the koala

William A. H. Ellis & Fred B. Bercovitch

W. A. H. Ellis
San Diego Zoo Institute for Conservation Research, Zoological Society of San Diego, 15600 San Pasqual Valley Road, Escondido, CA 92027, USA
W. A. H. Ellis (
*)
Koala Ecology Group, School of Biological Sciences and Centre for Mined Land Rehabilitation, The University of Queensland, St Lucia, Brisbane, QLD 4072, Australia e-mail:
F. B. Bercovitch
Primate Research Institute, Kyoto University, Inuyama, Aichi 484-8506, Japan
F. B. Bercovitch
Wildlife Research Center, Kyoto University, Inuyama, Aichi 484-8506, Japan


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 Crows 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.

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  • 2013
  • Biogeography
  • Biology
  • Chlamydia
  • Diet
  • Disease
  • Ecology
  • Ellis
  • Eucalyptus
  • Genetics
  • Habitat
  • Infection
  • Interventions
  • Koala
  • Lunney
  • Threats
  • Timms
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