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  • 1.
    Buechel, Séverine D.
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Boussard, Annika
    Stockholm University, Faculty of Science, Department of Zoology.
    Kotrschal, Alexander
    Stockholm University, Faculty of Science, Department of Zoology.
    van der Bijl, Wouter
    Stockholm University, Faculty of Science, Department of Zoology.
    Kolm, Niclas
    Stockholm University, Faculty of Science, Department of Zoology.
    Brain size affects performance in a reversal-learning test2018In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 285, no 1871, article id 20172031Article in journal (Refereed)
    Abstract [en]

    It has become increasingly clear that a larger brain can confer cognitive benefits. Yet not all of the numerous aspects of cognition seem to be affected by brain size. Recent evidence suggests that some more basic forms of cognition, for instance colour vision, are not influenced by brain size. We therefore hypothesize that a larger brain is especially beneficial for distinct and gradually more complex aspects of cognition. To test this hypothesis, we assessed the performance of brain size selected female guppies (Poecilia reticulata) in two distinct aspects of cognition that differ in cognitive complexity. In a standard reversal-learning test we first investigated basic learning ability with a colour discrimination test, then reversed the reward contingency to specifically test for cognitive flexibility. We found that large-brained females outperformed small-brained females in the reversed-learning part of the test but not in the colour discrimination part of the test. Large-brained individuals are hence cognitively more flexible, which probably yields fitness benefits, as they may adapt more quickly to social and/or ecological cognitive challenges. Our results also suggest that a larger brain becomes especially advantageous with increasing cognitive complexity. These findings corroborate the significance of brain size for cognitive evolution.

  • 2.
    Corral-López, Alberto
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Bloch, Natasha I.
    Kotrschal, Alexander
    Stockholm University, Faculty of Science, Department of Zoology.
    van der Bijl, Wouter
    Stockholm University, Faculty of Science, Department of Zoology.
    Buechel, Severine D.
    Stockholm University, Faculty of Science, Department of Zoology.
    Mank, Judith E.
    Kolm, Niclas
    Stockholm University, Faculty of Science, Department of Zoology.
    Female brain size affects the assessment of male attractiveness during mate choice2017In: Science Advances, ISSN 0036-8156, E-ISSN 2375-2548, Vol. 3, no 3, article id e1601990Article in journal (Refereed)
    Abstract [en]

    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.

  • 3.
    Corral-López, Alberto
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Eckerström-Liedholm, Simon
    Stockholm University, Faculty of Science, Department of Zoology.
    Van der Bijl, Wouter
    Stockholm University, Faculty of Science, Department of Zoology.
    Kotrschal, Alexander
    Stockholm University, Faculty of Science, Department of Zoology.
    Kolm, Niclas
    Stockholm University, Faculty of Science, Department of Zoology.
    No association between brain size and male sexual behavior in the guppy2015In: Current Zoology, ISSN 1674-5507, Vol. 61, no 2, p. 265-273Article in journal (Refereed)
    Abstract [en]

    Animal behavior is remarkably variable at all taxonomic levels. Over the last decades, research on animal behavior has focused on understanding ultimate processes. Yet, it has progressively become more evident that to fully understand behavioral variation, ultimate explanations need to be complemented with proximate ones. In particular, the mechanisms generating variation in sexual behavior remain an open question. Variation in aspects of brain morphology has been suggested as a plausible mechanism underlying this variation. However, our knowledge of this potential association is based almost exclusively on comparative analyses. Experimental studies are needed to establish causality and bridge the gap between micro-and macroevolutionary mechanisms concerning the link between brain and sexual behavior. We used male guppies that had been artificially selected for large or small relative brain size to study this association. We paired males with females and scored the full known set of male and female sexual behaviors described in guppies. We found several previously demonstrated associations between male traits, male behavior and female behavior. Females responded more strongly towards males that courted more and males with more orange coloration. Also, larger males and males with less conspicuous coloration attempted more coerced copulations. However, courting, frequency of coerced copulation attempts, total intensity of sexual behavior, and female response did not differ between large-and small-brained males. Our data suggest that relative brain size is an unlikely mechanism underlying variation in sexual behavior of the male guppy. We discuss these findings in the context of the conditions under which relative brain size might affect male sexual behavior

  • 4.
    Hansen Wheat, Christina
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    van der Bijl, Wouter
    Stockholm University, Faculty of Science, Department of Zoology.
    Temrin, Hans
    Stockholm University, Faculty of Science, Department of Zoology.
    Dogs, but not wolves, lose their sensitivity towards novelty with ageManuscript (preprint) (Other academic)
  • 5.
    Kotrschal, Alexander
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Zeng, Hong-Li
    van der Bijl, Wouter
    Stockholm University, Faculty of Science, Department of Zoology.
    Öhman-Mägi, Caroline
    Kotrschal, Kurt
    Pelckmans, Kristiaan
    Kolm, Niclas
    Stockholm University, Faculty of Science, Department of Zoology.
    Evolution of brain region volumes during artificial selection for relative brain size2017In: Evolution, ISSN 0014-3820, E-ISSN 1558-5646, Vol. 71, no 12, p. 2942-2951Article in journal (Refereed)
    Abstract [en]

    The vertebrate brain shows an extremely conserved layout across taxa. Still, the relative sizes of separate brain regions vary markedly between species. One interesting pattern is that larger brains seem associated with increased relative sizes only of certain brain regions, for instance telencephalon and cerebellum. Till now, the evolutionary association between separate brain regions and overall brain size is based on comparative evidence and remains experimentally untested. Here, we test the evolutionary response of brain regions to directional selection on brain size in guppies (Poecilia reticulata) selected for large and small relative brain size. In these animals, artificial selection led to a fast response in relative brain size, while body size remained unchanged. We use microcomputer tomography to investigate how the volumes of 11 main brain regions respond to selection for larger versus smaller brains. We found no differences in relative brain region volumes between large- and small-brained animals and only minor sex-specific variation. Also, selection did not change allometric scaling between brain and brain region sizes. Our results suggest that brain regions respond similarly to strong directional selection on relative brain size, which indicates that brain anatomy variation in contemporary species most likely stem from direct selection on key regions.

  • 6.
    Lehmann, Philipp
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Van der Bijl, Wouter
    Stockholm University, Faculty of Science, Department of Zoology.
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology.
    Wheat, Christopher W.
    Stockholm University, Faculty of Science, Department of Zoology.
    Gotthard, Karl
    Stockholm University, Faculty of Science, Department of Zoology.
    Timing of diapause termination in relation to variation in winter climate2017In: Physiological entomology (Print), ISSN 0307-6962, E-ISSN 1365-3032, Vol. 42, no 3, p. 232-238Article in journal (Refereed)
    Abstract [en]

    In temperate insects, winters are typically endured by entering diapause, which comprises a deep resting stage. Correct timing of diapause termination is vital for synchronization of emergence with conspecifics and for mobilizing resources when conditions for growth and reproduction become favourable. Although critical to survival, the intrinsic and extrinsic drivers of diapause termination timing are poorly understood. In the present study, we investigate diapause development under a range of durations (10-24weeks) spent at different temperatures (-2 to 10 degrees C) in the pupal diapausing butterfly Pieris napi Linnaeus (Lepidoptera: Pieridae). We determine: (i) the maximum cold temperature for diapause development; (ii) if pupae in diapause count cold days or cold sums; and (iii) whether diapause termination is distinct or gradual. The results indicate large and idiosyncratic effects of high and low nonlethal temperatures on diapause development in P. napi. Although all temperatures tested lead to diapause termination, a thermal optimum between 2 and 4 degrees C is observed. Lower temperatures lead to decreased eclosion propensity, whereas higher temperatures slow down development and increase emergence desynchronization. These data suggest that, rather than a simple cold-summing process with a distinct diapause termination point, there are trade-offs between time and temperature at the low and high end of the thermal range, resulting in a nonlinear thermal landscape showing a ridge of increasing eclosion propensity at moderate temperatures. The present study suggests that the effects of temperature on diapause development should be included in projections on post-winter phenology models of insects, including pest species.

  • 7. Masahito, Tsuboi
    et al.
    van der Bijl, Wouter
    Stockholm University, Faculty of Science, Department of Zoology.
    Kopperud, Bjørn Tore
    Erritzøe, Johannes
    Voje, Kjetil L.
    Kotrschal, Alexander
    Stockholm University, Faculty of Science, Department of Zoology.
    Yopak, Kara E.
    Collin, Shaun P.
    Hansen, Thomas F.
    Iwaniuk, Andrew
    Kolm, Niclas
    Stockholm University, Faculty of Science, Department of Zoology.
    Breakdown of brain-body allometry and the exceptional encephalization of mammals and birdsManuscript (preprint) (Other academic)
  • 8. Szorkovszky, Alex
    et al.
    Kotrschal, Alexander
    Stockholm University, Faculty of Science, Department of Zoology. Stockholm Univ, Zool Dept, Stockholm, Sweden.
    Herbert-Read, James E.
    Stockholm University, Faculty of Science, Department of Zoology. University of Bristol, U.K..
    Buechel, Severine D.
    Stockholm University, Faculty of Science, Department of Zoology.
    Romenskyy, Maksym
    Rosen, Emil
    van der Bijl, Wouter
    Stockholm University, Faculty of Science, Department of Zoology.
    Pelckmans, Kristiaan
    Kolm, Niclas
    Stockholm University, Faculty of Science, Department of Zoology.
    Sumpter, David J. T.
    Assortative interactions revealed by sorting of animal groups2018In: Animal Behaviour, ISSN 0003-3472, E-ISSN 1095-8282, Vol. 142, p. 165-179Article in journal (Refereed)
    Abstract [en]

    Animals living in groups can show substantial variation in social traits and this affects their social organization. However, as the specific mechanisms driving this organization are difficult to identify in already organized groups typically found in the wild, the contribution of interindividual variation to group level behaviour remains enigmatic. Here, we present results of an experiment to create and compare groups that vary in social organization, and study how individual behaviour varies between these groups. We iteratively sorted individuals between groups of guppies, Poecilia reticulata, by ranking the groups according to their directional alignment and then mixing similar groups. Over the rounds of sorting the consistency of the group rankings increased, producing groups that varied significantly in key social behaviours such as collective activity and group cohesion. The repeatability of the underlying individual behaviour was then estimated by comparing the experimental data to simulations. At the level of basic locomotion, individuals in more coordinated groups displayed stronger interactions with the centre of the group, and weaker interactions with their nearest neighbours. We propose that this provides the basis for a passive phenotypic assortment mechanism that may explain the structures of social networks in the wild.

  • 9.
    van der Bijl, Wouter
    Stockholm University, Faculty of Science, Department of Zoology.
    phylopath: Easy phylogenetic path analysis in R2018In: PeerJ, ISSN 2167-8359, E-ISSN 2167-8359, Vol. 6, article id e4718Article in journal (Refereed)
    Abstract [en]

    Confirmatory path analysis allows researchers to evaluate and compare causal models using observational data. This tool has great value for comparative biologists since they are often unable to gather experimental data on macro-evolutionary hypotheses, but is cumbersome and error-prone to perform. I introduce phylopath, an R package that implements phylogenetic path analysis (PPA) as described by von Hardenberg Gonzalez-Vayer (2113). In addition to the published method, I provide support for the inclusion of binary variables. I illustrate PPA and phylopath by recreating part of a study on the relationship between brain size and vulnerability to extinction. The package aims to make the analysis straight-forward, providing convenience functions, and several plotting methods, which I hope will encourage the spread of the method.

  • 10.
    van der Bijl, Wouter
    Stockholm University, Faculty of Science, Department of Zoology.
    Why and how brain size evolves: Sociality, predation and allometry2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The evolution of the vertebrate brain has remained a topic of intense interest from biologists over many decades. Evolutionary biologists have seen it as an intriguing example of how the size and structure of a trait evolves across large phylogenies and under body size constraints, with both large shifts in deep evolutionary time and continuous smaller scale adaptation. Behavioral ecologists, on the other hand, have put great effort in trying to understand the costs and benefits of brain size and structural variation, usually assuming that the brain morphology of species is the result of a balance between energetic costs and cognitive benefits.

    I discuss two hypotheses that aim to explain under what circumstances a higher cognitive ability yields fitness benefits. The predation avoidance hypothesis states that large brains help to avoid predators. The social brain hypothesis predicts that cognition is especially beneficial for animals living in complex social environments. In practice these hypotheses are difficult to differentiate (paper I), as sociality often evolves in response to predation pressure. Comparative studies on either hypothesis should therefore aim to control for effects of the other hypothesis, and experiments may be especially useful in testing more explicit mechanistic explanations.

    I put the predation hypothesis to the test using two approaches, a comparative analysis and a within-species experiment. The comparative analysis (paper II) used published data on hawk predation and related it to both relative brain size and relative telencephalon size. While sparrowhawk predation was unrelated to brain morphology, birds that experience more goshawk predation had larger brains and telencephali. Next, I performed an experiment (paper III) on guppies that had been artificially selected for relative brain size. The selection lines have demonstrated differences in cognitive ability, as well as a marked survival difference under predation in females. I exposed fish to either a predator model or a novel object control, varying both sex and group size. Large-brained females performed fewer and shorter predator inspections than small-brained females, while keeping a larger distance from the predator model.

    I performed another experiment (paper IV) to investigate differences in social competence. I calculated the duration of contests between random pairs of small- and large-brained males, using movement data. When the loser was large-brained, contests were decided almost 40 minutes earlier than when the loser was small-brained, indicating that the decision for the loser to give up is made quicker with a larger brain.

    This thesis ends with an exploration of variation in the scaling relationship between brain and body size across vertebrates (paper V). The observed scaling between brain and body depends on what taxonomic level is under investigation. This effect, however, exclusively occurs in the two classes with the largest brains, mammals and birds. This indicates that strong developmental constraints have been alleviated in the two highly encephalized classes, but not elsewhere.

    In conclusion, I find evidence that both predator avoidance and social factors may contribute to the evolution of brain size. Further work on explicit behavioral frameworks for cognitive benefit hypotheses is likely to yield significant insight. Constraints in brain size may be hard to overcome and play an especially large role at a larger taxonomic scale.

  • 11.
    van der Bijl, Wouter
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Kolm, Niclas
    Stockholm University, Faculty of Science, Department of Zoology.
    Why direct effects of predation complicate the social brain hypothesis And how incorporation of explicit proximate behavioral mechanisms might help2016In: Bioessays, ISSN 0265-9247, E-ISSN 1521-1878, Vol. 38, no 6, p. 568-577Article in journal (Refereed)
    Abstract [en]

    A growing number of studies have found that large brains may help animals survive by avoiding predation. These studies provide an alternative explanation for existing correlative evidence for one of the dominant hypotheses regarding the evolution of brain size in animals, the social brain hypothesis (SBH). The SBH proposes that social complexity is a major evolutionary driver of large brains. However, if predation both directly selects for large brains and higher levels of sociality, correlations between sociality and brain size may be spurious. We argue that tests of the SBH should take direct effects of predation into account, either by explicitly including them in comparative analyses or by pin-pointing the brain-behavior-fitness pathway through which the SBH operates. Existing data and theory on social behavior can then be used to identify precise candidate mechanisms and formulate new testable predictions.

  • 12.
    van der Bijl, Wouter
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Kotrschal, Alexander
    Stockholm University, Faculty of Science, Department of Zoology.
    Buechel, Séverine D.
    Stockholm University, Faculty of Science, Department of Zoology.
    Kolm, Niclas
    Stockholm University, Faculty of Science, Department of Zoology.
    Cognitive ability and antagonistic social competence: contest duration depends on loser’s brain sizeManuscript (preprint) (Other academic)
  • 13.
    van der Bijl, Wouter
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Thyselius, Malin
    Stockholm University, Faculty of Science, Department of Zoology.
    Kotrschal, Alexander
    Stockholm University, Faculty of Science, Department of Zoology.
    Kolm, Niclas
    Stockholm University, Faculty of Science, Department of Zoology.
    Brain size affects the behavioural response to predators in female guppies (Poecilia reticulata)2015In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 282, no 1812, p. 116-124, article id 20151132Article in journal (Refereed)
    Abstract [en]

    Large brains are thought to result from selection for cognitive benefits, but how enhanced cognition leads to increased fitness remains poorly understood. One explanation is that increased cognitive ability results in improved monitoring and assessment of predator threats. Here, we use male and female guppies (Poecilia reticulata), artificially selected for large and small brain size, to provide an experimental evaluation of this hypothesis. We examined their behavioural response as singletons, pairs or shoals of four towards a model predator. Large-brained females, but not males, spent less time performing predator inspections, an inherently risky behaviour. Video analysis revealed that large-brained females were further away from the model predator when in pairs but that they habituated quickly towards the model when in shoals of four. Males stayed further away from the predator model than females but again we found no brain size effect in males. We conclude that differences in brain size affect the female predator response. Large-brained females might be able to assess risk better or need less sensory information to reach an accurate conclusion. Our results provide experimental support for the general idea that predation pressure is likely to be important for the evolution of brain size in prey species.

  • 14.
    van der Bijl, Wouter
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Tsuboi, Masahito
    Iwaniuk, Andrew N.
    Kolm, Niclas
    Stockholm University, Faculty of Science, Department of Zoology.
    Prey-predator interactions and the evolution of bird brain morphologyManuscript (preprint) (Other academic)
1 - 14 of 14
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