Environmental effects on sexual size dimorphism of a seed-feeding beetle

R. Craig Stillwell, Charles W. Fox

Research output: Contribution to journalArticlepeer-review

79 Scopus citations


Sexual size dimorphism is widespread in animals but varies considerably among species and among populations within species. Much of this variation is assumed to be due to variance in selection on males versus females. However, environmental variables could affect the development of females and males differently, generating variation in dimorphism. Here we use a factorial experimental design to simultaneously examine the effects of rearing host and temperature on sexual dimorphism of the seed beetle, Callosobruchus maculatus. We found that the sexes differed in phenotypic plasticity of body size in response to rearing temperature but not rearing host, creating substantial temperature-induced variation in sexual dimorphism; females were larger than males at all temperatures, but the degree of this dimorphism was smallest at the lowest temperature. This change in dimorphism was due to a gender difference in the effect of temperature on growth rate and not due to sexual differences in plasticity of development time. Furthermore, the sex ratio (proportion males) decreased with decreasing temperature and became female-biased at the lowest temperature. This suggests that the temperature-induced change in dimorphism is potentially due to a change in non-random larval mortality of males versus females. This most important implication of this study is that rearing temperature can generate considerable intraspecific variation in the degree of sexual size dimorphism, though most studies assume that dimorphism varies little within species. Future studies should focus on whether sexual differences in phenotypic plasticity of body size are a consequence of adaptive canalization of one sex against environmental variation in temperature or whether they simply reflect a consequence of non-adaptive developmental differences between males and females.

Original languageEnglish
Pages (from-to)273-280
Number of pages8
Issue number2
StatePublished - Aug 2007

Bibliographical note

Funding Information:
Acknowledgements We thank L. Hitchcock, D. Johnson, O. Njoku and W. Wallin for help weighing beetles during the experiment. We thank F. Messina for providing the laboratory colonies and D. West-neat for statistical advice. We also thank M. Chappell, D. Fairbairn and one anonymous reviewer for helpful comments on the manuscript. Financial support was provided in part by a National Science Foundation grant (DEB-01-10754) to C. W. F. Institutional guidelines were followed for animal care.


  • Body size
  • Differential- plasticity hypothesis
  • Phenotypic plasticity
  • Seed beetles
  • Sexual size dimorphism

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics


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