Brain size affects responsiveness in mating behaviour to variation in predation pressure and sex ratio

Abstract

Despite ongoing advances in sexual selection theory, the evolution of mating decisions remains enigmatic. Cognitive processes often require simultaneous processing of multiple sources of information from environmental and social cues. However, little experimental data exist on how cognitive ability affects such fitness‐associated aspects of behaviour. Using advanced tracking techniques, we studied mating behaviours of guppies artificially selected for divergence in relative brain size, with known differences in cognitive ability, when predation threat and sex ratio was varied. In females, we found a general increase in copulation behaviour in when the sex ratio was female biased, but only large‐brained females responded with greater willingness to copulate under a low predation threat. In males, we found that small‐brained individuals courted more intensively and displayed more aggressive behaviours than large‐brained individuals. However, there were no differences in female response to males with different brain size. These results provide further evidence of a role for female brain size in optimal decision‐making in a mating context. In addition, our results indicate that brain size may affect mating display skill in male guppies. We suggest that it is important to consider the association between brain size, cognitive ability and sexual behaviour when studying how morphological and behavioural traits evolve in wild populations.

Rapid mosaic brain evolution under artificial selection for relative telencephalon size in the guppy (Poecilia reticulata)

“…Although interspecific and intraspecific correlative comparative analyses form an important tool to investigate evolutionary patterns and generate hypotheses 6,10,17 , experimental evidence is needed to fully understand the independent evolutionary potential of brain regions. Artificial selection experiments on mice and fish have revealed that increases in relative brain size can occur quickly and yield important cognitive benefits (increased associative learning [18][19][20][21][22][23] , more accurate mate preferences 24,25 , and more effective predator avoidance 26,27 ), but also high energetic costs (lower offspring production 19 , reduced innate immune response 28 , and shorter intrinsic life-span 29 ). But in line with the mosaic brain hypothesis, relative brain size is a rather crude measure of brain morphology, and evolutionary changes in brain morphology in wild populations are unlikely to target the entire brain 30,31 .…”

Brain size mediates the choice of breeding strategy in the Red-backed shrike Lanius collurio

“…Hence, it was proposed as one of the major forces shaping brain size and cognitive skills 12 . The link between predation and brain size was, in fact, indicated in numerous studies 4,[13][14][15] . What is more, predation, in parallel with food availability, is the main factor of nesting site selection in birds 16 .…”

Brain size mediates the choice of breeding strategy in the Red-backed shrike Lanius collurio

“…Hence, it was proposed as one of the main forces shaping brain size and cognitive skills (Bijl and Kolm 2016). The link between predation and brain size was, in fact, indicated in numerous studies (Herczeg et al 2014;van der Bij et al 2015;Corral-López et al 2020;Møller et al 2020). Moreover, predation, in parallel with food availability, is the main factor of bird nesting site selection (Martin 1993).…”