Sexual selection impacts brain anatomy in frogs and toads.

Yu Zeng,Shang Ling Lou,Wen Bo Liao,Alexander Kotrschal,Robert Jehle

doi:10.1002/ece3.2459

Yu Zeng, Shang Ling Lou + Show 3 more

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https://doi.org/10.1002/ece3.2459

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Abstract

Natural selection is a major force in the evolution of vertebrate brain size, but the role of sexual selection in brain size evolution remains enigmatic. At least two opposing schools of thought predict a relationship between sexual selection and brain size. Sexual selection should facilitate the evolution of larger brains because better cognitive abilities may aid the competition for mates. However, it may also restrict brain size evolution due to energetic trade‐offs between brain tissue and sexually selected traits. Here, we examined the patterns of selection on brain size and brain anatomy in male anurans (frogs and toads), a group where the strength of sexual selection differs markedly among species, using a phylogenetically controlled generalized least‐squared (PGLS) regression analyses. The analysis revealed that in 43 Chinese anuran species, neither mating system, nor type of courtship, or testes mass was significantly associated with relative brain size. While none of those factors related to the relative size of olfactory nerves, optic tecta, telencephalon, and cerebellum, the olfactory bulbs were relatively larger in monogamous species and those using calls during courtship. Our findings support the mosaic model of brain evolution and suggest that while the investigated aspects of sexual selection do not seem to play a prominent role in the evolution of brain size of anurans, they do impact their brain anatomy.

Highlights

Most theories of vertebrate brain size evolution consider natural selection as the main evolutionary force shaping its diversification (Striedter, 2005)
When controlling for body size, none of the sexually selected traits were significantly related to the amount of variation in relative brain size, and the same was true in the case of the size of olfactory nerves, optic tecta, telencephalon, and cerebellum (Table 2)
We find no evidence that three prominent aspects of sexual selection are related to the overall brain size of 43 species of amphibians

Summary

| MATERIALS AND METHODS

We collected a total of 200 adult male individuals from 43 anuran species during the breeding seasons 2007–2013 from the Hengduan Mountains of China. The relationships between (log) brain size, size of five brain regions, and three indicators of sexual selection (i.e., mating system, type of courtship, and testes mass) were assessed in a series of phylogenetically controlled linear models. As brains are subject to a wide range of selective pressures that act simultaneously, the relationships between both brain and brain regions and sexually selected traits were assessed using multiple regressions in phylogenetic ANOVAs with body size added as a covariate in all analyses to account for allometric effects. When controlling for body size, none of the sexually selected traits (mating system, type of courtship, testes mass) were significantly related to the amount of variation in relative brain size, and the same was true in the case of the size of olfactory nerves, optic tecta, telencephalon, and cerebellum (Table 2). Olfactory bulbs size was further significantly associated with the type of courtship; calling species exhibiting larger olfactory bulbs than searching species (Table 2; Fig. 5)

| DISCUSSION

Findings

FUNDING INFORMATION