BRAIN SIZE, COGNITIVE ABILITY AND SEXUAL SELECTION

My thesis' work  focused on the largely unexplored role that a larger brain might play in mating behavior and mating decisions of individuals through its tight link to improved cognitive ability. Mating decisions require a great deal of information processing from multiple sources and understanding how cognitive ability influences such decisions can advance our knowledge in important questions in a wide spectrum of scientific fields ranging from evolutionary biology to animal behaviour.

Our findings in relation to this work have demonstrated that brain size and cognitive ability are important for optimal decision-making in relation to mating decisions in the guppy, results that have drawn some media attention (for instance here or here). But more importantly they highlight the key role that brain size and cognitive ability might play for the generation and maintenance of the large variation observed in mating preferences and in sexually selected traits across and within species.

 

A selection from Stockholm University publication database

• The link between brain size, cognitive ability, mate choice and sexual behaviour in the guppy (Poecilia reticulata)

  2017. Alberto Corral López, Niclas Kolm, Janette Boughman.

  Thesis (Doc)

  Competition over access for mates has led to the evolution of many striking examples of morphological traits and behaviour in animals. The rapid development of the sexual selection field in recent decades have dramatically advanced our understanding of what traits make individuals more successful in attracting mates and how preferences for mates evolve over time. However, till now, research in this field has put less emphasis on the mechanisms that underlie variation in mate choice and sexual behaviour. Cognitive processes could potentially be key drivers of individual variation in mating preferences and sexual behaviours and therefore deserve further investigation. In this thesis, I used guppies artificially selected for relative brain size as the model system to study the association between brain size, cognitive ability and various aspects of mate choice. Previous studies in this model system showed that large-brained individuals of both sexes outperformed small-brained individuals in cognitive tests. Here I quantified their sexual behaviours and mating preferences to provide novel empirical data concerning the association between brain size, cognitive ability and sexual selection. In dichotomous choice preference tests based on visual cues, comparisons between large-brained and small-brained guppies showed important differences in their assessment of mate quality. These results are not driven by pre-existing visual biases caused by the artificial selection since further investigation of the visual capacity of these fish detected no differences between large-brained and small-brained individuals in their sensitivity to colour or in their capacity to resolve spatial detail. I also quantified sexual behaviour in male guppies artificially selected for relative brain size and found no difference in the behaviours of large-brained and small-brained males in a single male-single female non-competitive scenario. On the contrary, in a more complex social setting I found a reduction in large-brained males in the rate of courtship towards females and dominance displays towards other males when exposed to different degrees of predation threat and different numbers of male competitors. However, this reduction in behavioural intensity did not result in a lower access to copulation with females for large-brained males. I likewise evaluated female sexual behaviour and found that large-brained females had higher behavioural flexibility such that they decreased their receptiveness towards males more strongly under higher levels of predation threat. Together, these results provide novel empirical evidence that brain size and cognitive ability are tightly linked to mating preferences and sexual behaviours. These findings suggest that brain size and cognitive ability might be important mechanisms behind variation in mating preferences and in sexually selected traits across and within species.

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• On the role of body size, brain size, and eye size in visual acuity

  2017. Alberto Corral-López (et al.). Behavioral Ecology and Sociobiology 71 (12)

  Article

  The visual system is highly variable across species, and such variability is a key factor influencing animal behavior. Variation in the visual system, for instance, can influence the outcome of learning tasks when visual stimuli are used. We illustrate this issue in guppies (Poecilia reticulata) artificially selected for large and small relative brain size with pronounced behavioral differences in learning experiments and mate choice tests. We performed a study of the visual system by quantifying eye size and optomotor response of large-brained and small-brained guppies. This represents the first experimental test of the link between brain size evolution and visual acuity. We found that female guppies have larger eyes than male guppies, both in absolute terms and in relation to their body size. Likewise, individuals selected for larger brains had slightly larger eyes but not better visual acuity than small-brained guppies. However, body size was positively associated with visual acuity. We discuss our findings in relation to previous macroevolutionary studies on the evolution of brain morphology, eye morphology, visual acuity, and ecological variables, while stressing the importance of accounting for sensory abilities in behavioral studies.

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• Selection for relative brain size affects context-dependent male preference for, but not discrimination of, female body size in guppies

  2018. Alberto Corral-López, Alexander Kotrschal, Niclas Kolm. Journal of Experimental Biology 221 (12)

  Article

  Understanding what drives animal decisions is fundamental in evolutionary biology, and mate choice decisions are arguably some of the most important in any individual's life. As cognitive ability can impact decision making, elucidating the link between mate choice and cognitive ability is necessary to fully understand mate choice. To experimentally study this link, we used guppies (Poecilia reticulata) artificially selected for divergence in relative brain size and with previously demonstrated differences in cognitive ability. A previous test in our female guppy selection lines demonstrated the impact of brain size and cognitive ability on information processing during female mate choice decisions. Here, we evaluated the effect of brain size and cognitive ability on male mate choice decisions. Specifically, we investigated the preference of large-brained, small-brained and non-selected guppy males for female body size, a key indicator of female fecundity in this species. For this, male preference was quantified in dichotomous choice tests when presented with dyads of females with small, medium and large body size differences. All types of males showed a preference for larger females but no effect of brain size was found in the ability to discriminate between differently sized females. However, we found that non-selected and large-brained males, but not small-brained males, showed a context-dependent preference for larger females depending on the difference in female size. Our results have two important implications. First, they provide further evidence that male mate choice also occurs in a species in which secondary sexual omamentation is present only in males. Second, they show that brain size and cognitive ability have important effects on individual variation in mating preference and sexually selected traits.

  Read more about Selection for relative brain size affects context-dependent male preference for, but not discrimination of, female body size in guppies

• Female brain size affects the assessment of male attractiveness during mate choice

  2017. Alberto Corral-López (et al.). Science Advances 3 (3)

  Article

  Mate choice decisions are central in sexual selection theory aimed to understand how sexual traits evolve and their role in evolutionary diversification. We test the hypothesis that brain size and cognitive ability are important for accurate assessment of partner quality and that variation in brain size and cognitive ability underlies variation in mate choice. We compared sexual preference in guppy female lines selected for divergence in relative brain size, which we have previously shown to have substantial differences in cognitive ability. In a dichotomous choice test, large-brained and wild-type females showed strong preference for males with color traits that predict attractiveness in this species. In contrast, small-brained females showed no preference for males with these traits. In-depth analysis of optomotor response to color cues and gene expression of key opsins in the eye revealed that the observed differences were not due to differences in visual perception of color, indicating that differences in the ability to process indicators of attractiveness are responsible. We thus provide the first experimental support that individual variation in brain size affects mate choice decisions and conclude that differences in cognitive ability may be an important underlying mechanism behind variation in female mate choice.

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Show all publications by Alberto Corral Lopez at Stockholm University