Relative brain size is predicted by the intensity of intrasexual competition in frogs

Chun Lan Mai, Wen Bo Liao*, Stefan Lüpold, Alexander Kotrschal

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

17 Citations (Scopus)


Competition over mates is a powerful force shaping trait evolution. For instance, better cognitive abilities may be beneficial in male-male competition and thus be selected for by intrasexual selection. Alternatively, investment in physical attributes favoring male performance in competition for mates may lower the resources available for brain development, and more intense male mate competition would coincide with smaller brains. To date, only indirect evidence for such relationships exists, and most studies are heavily biased toward primates and other homoeothermic vertebrates. We tested the association between male brain size (relative to body size) and male-male competition across N = 30 species of Chinese anurans. Three indicators of the intensity of male mate competition—operational sex ratio (OSR), spawningsite density, and male forelimb muscle mass—were positively associated with relative brain size, whereas the absolute spawning group size was not. The relationship with the OSR and male forelimb muscle mass was stronger for the male than for the female brains. Taken together, our findings suggest that the increased cognitive abilities of larger brains are beneficial in male-male competition. This study adds taxonomic breadth to the mounting evidence for a prominent role of sexual selection in vertebrate brain evolution.

Original languageEnglish
Pages (from-to)169-179
Number of pages11
JournalAmerican Naturalist
Issue number2
Publication statusPublished - 1 Aug 2020


  • Anurans
  • Cognitive abilities
  • Male-male competition
  • Operational sex ratio
  • Spawning-site group size


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