Sexual selection impacts brain anatomy in frogs and toads

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.

Brain size evolution in the frog Fejervarya limnocharis supports neither the cognitive buffer nor the expensive brain hypothesis

“…For anurans, variation in absolute brain size can be strongly affected environmentally (Gonda et al ., ; Jiang et al ., ). Absolute brain size has been proposed to account for differences in behavioral abilities among animals (Reader & Laland, ; Yopak et al ., ; Gonda et al ., ; Liu, Zhou & Liao, ; Jin et al ., ; Tsuboi et al ., ; Zeng et al ., ). We found a significant population variation in absolute brain volume for both sexes, suggesting that the differences in brain morphology between habitats are results of drift without any selection acting on them.…”

Large-brained frogs mature later and live longer

“…; Zeng et al. ; ). We supplemented this data set by collecting three new species ( Rana chensinensis , Odorrana nanjiangensis , and Amolops chunganensis ) at Micangshan Nature Reserve during the breeding seasons in 2017; each species was captured in a single population and we used only males.…”

“…; Zeng et al. ; Liao et al. ), as for any other ectothermic taxon, the relationship between brain size and life span is unknown.…”

“…Accordingly, we test the association between brain size and life span across 40 species of frogs by combining skeletochronological life span estimation and phylogenetically controlled comparative analyses. Although comparative studies have recently identified some of the factors driving anuran brain evolution Wu et al 2016;Zeng et al 2016;Liao et al 2016b), as for any other ectothermic taxon, the relationship between brain size and life span is unknown. We may predict that, analogously to homoeothermic vertebrates, larger brained frogs will live longer.…”

Predation pressure shapes brain anatomy in the wild

“…Even though the function of the separate brain regions is still only partly understood and single regions sometimes have multiple functions, we can make predictions about brain region sizes based on previous findings from lesion studies and neuro-ecology studies (Barton and Harvey 2000;Gonda et al 2009;Gonzalez-Voyer et al 2009;Kotrschal et al 1998Kotrschal et al , 2012bKotrschal and Palzenberger 1992;Zeng et al 2016). For instance, the telencephalon integrates complex information and is vital in learning and memory (Striedter 2005).…”