Publications by authors named "Niclas Kolm"

61 Publications

The link between relative brain size and cognitive ageing in female guppies (Poecilia reticulata) artificially selected for variation in brain size.

Exp Gerontol 2021 Apr 26;146:111218. Epub 2020 Dec 26.

Department of Zoology, Stockholm University, Svante Arrhenius väg 18B, 10691 Stockholm, Sweden. Electronic address:

Cognitive ageing is the general process when certain mental skills gradually deteriorate with age. Across species, there is a pattern of a slower brain structure degradation rate in large-brained species. Hence, having a larger brain might buffer the impact of cognitive ageing and positively affect survival at older age. However, few studies have investigated the link between relative brain size and cognitive ageing at the intraspecific level. In particular, experimental data on how brain size affects brain function also into higher age is largely missing. We used 288 female guppies (Poecilia reticulata), artificially selected for large and small relative brain size, to investigate variation in colour discrimination and behavioural flexibility, at 4-6, 12 and 24 months of age. These ages are particularly interesting since they cover the life span from sexual maturation until maximal life length under natural conditions. We found no evidence for a slower cognitive ageing rate in large-brained females in neither initial colour discrimination nor reversal learning. Behavioural flexibility was predicted by large relative brain size in the youngest group, but the effect of brain size disappeared with increasing age. This result suggests that cognitive ageing rate is faster in large-brained female guppies, potentially due to the faster ageing and shorter lifespan in the large-brained selection lines. It also means that cognition levels align across different brain sizes with older age. We conclude that there are cognitive consequences of ageing that vary with relative brain size in advanced learning abilities, whereas fundamental aspects of learning can be maintained throughout the ecologically relevant life span.
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http://dx.doi.org/10.1016/j.exger.2020.111218DOI Listing
April 2021

Rapid evolution of coordinated and collective movement in response to artificial selection.

Sci Adv 2020 Dec 2;6(49). Epub 2020 Dec 2.

Department of Zoology/Ethology, Stockholm University, Stockholm, Sweden.

Collective motion occurs when individuals use social interaction rules to respond to the movements and positions of their neighbors. How readily these social decisions are shaped by selection remains unknown. Through artificial selection on fish (guppies, ) for increased group polarization, we demonstrate rapid evolution in how individuals use social interaction rules. Within only three generations, groups of polarization-selected females showed a 15% increase in polarization, coupled with increased cohesiveness, compared to fish from control lines. Although lines did not differ in their physical swimming ability or exploratory behavior, polarization-selected fish adopted faster speeds, particularly in social contexts, and showed stronger alignment and attraction responses to multiple neighbors. Our results reveal the social interaction rules that change when collective behavior evolves.
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http://dx.doi.org/10.1126/sciadv.aba3148DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7710366PMC
December 2020

Artificial selection for schooling behaviour and its effects on associative learning abilities.

J Exp Biol 2020 Dec 7;223(Pt 23). Epub 2020 Dec 7.

Department of Zoology, Stockholm University, Svante Arrhenius väg 18B, 10691, Stockholm, Sweden.

The evolution of collective behaviour has been proposed to have important effects on individual cognitive abilities. Yet, in what way they are related remains enigmatic. In this context, the 'distributed cognition' hypothesis suggests that reliance on other group members relaxes selection for individual cognitive abilities. Here, we tested how cognitive processes respond to evolutionary changes in collective motion using replicate lines of guppies () artificially selected for the degree of schooling behaviour (group polarization) with >15% difference in schooling propensity. We assessed associative learning in females of these selection lines in a series of cognitive assays: colour associative learning, reversal learning, social associative learning, and individual and collective spatial associative learning. We found that control females were faster than polarization-selected females at fulfilling a learning criterion only in the colour associative learning assay, but they were also less likely to reach a learning criterion in the individual spatial associative learning assay. Hence, although testing several cognitive domains, we found weak support for the distributed cognition hypothesis. We propose that any cognitive implications of selection for collective behaviour lie outside of the cognitive abilities included in food-motivated associative learning for visual and spatial cues.
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http://dx.doi.org/10.1242/jeb.235093DOI Listing
December 2020

The link between selection for function and human-directed play behaviour in dogs.

Biol Lett 2020 09 23;16(9):20200366. Epub 2020 Sep 23.

Institute of Ecology and Botany, Centre for Ecological Research, Vácrátót, Hungary.

Human-directed play behaviour is a distinct behavioural feature of domestic dogs. But the role that artificial selection for contemporary dog breeds has played for human-directed play behaviour remains elusive. Here, we investigate how human-directed play behaviour has evolved in relation to the selection for different functions, considering processes of shared ancestry and gene flow among the different breeds. We use the American Kennel Club (AKC) breed group categorization to reflect the major functional differences and combine this with observational data on human-directed play behaviour for over 132 breeds across 89 352 individuals from the Swedish Dog Mentality Assessment project. Our analyses demonstrate that ancestor dogs already showed intermediate levels of human-directed play behaviour, levels that are shared with several modern breed types. Herding and Sporting breeds display higher levels of human-directed play behaviour, statistically distinguishable from Non-sporting and Toy breeds. Our results suggest that human-directed play behaviour played a role in the early domestication of dogs and that subsequent artificial selection for function has been important for contemporary variation in a behavioural phenotype mediating the social bond with humans.
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http://dx.doi.org/10.1098/rsbl.2020.0366DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7532715PMC
September 2020

Different mating contexts lead to extensive rewiring of female brain coexpression networks in the guppy.

Genes Brain Behav 2021 Mar 22;20(3):e12697. Epub 2020 Sep 22.

University of British Columbia, Department of Zoology and Biodiversity Research Centre, Vancouver, Canada.

Understanding the basis of behavior requires dissecting the complex waves of gene expression that underlie how the brain processes stimuli and produces an appropriate response. In order to determine the dynamic nature of the neurogenomic network underlying mate choice, we use transcriptome sequencing to capture the female neurogenomic response in two brain regions involved in sensory processing and decision-making under different mating and social contexts. We use differential coexpression (DC) analysis to evaluate how gene networks in the brain are rewired when a female evaluates attractive and nonattractive males, greatly extending current single-gene approaches to assess changes in the broader gene regulatory network. We find the brain experiences a remarkable amount of network rewiring in the different mating and social contexts we tested. Further analysis indicates the network differences across contexts are associated with behaviorally relevant functions and pathways, particularly learning, memory and other cognitive functions. Finally, we identify the loci that display social context-dependent connections, revealing the basis of how relevant neurological and metabolic pathways are differentially recruited in distinct social contexts. More broadly, our findings contribute to our understanding of the genetics of mating and social behavior by identifying gene drivers behind behavioral neural processes, illustrating the utility of DC analysis in neurosciences and behavior.
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http://dx.doi.org/10.1111/gbb.12697DOI Listing
March 2021

Long life evolves in large-brained bird lineages.

Evolution 2020 12 4;74(12):2617-2628. Epub 2020 Sep 4.

Instituto de Ecología, Universidad Nacional Autónoma de México, Ciudad de México, 04510, México.

The brain is an energetically costly organ that consumes a disproportionate amount of resources. Species with larger brains relative to their body size have slower life histories, with reduced output per reproductive event and delayed development times that can be offset by increasing behavioral flexibility. The "cognitive buffer" hypothesis maintains that large brain size decreases extrinsic mortality due to greater behavioral flexibility, leading to a longer lifespan. Alternatively, slow life histories, and long lifespan can be a pre-adaptation for the evolution of larger brains. Here, we use phylogenetic path analysis to contrast different evolutionary scenarios and disentangle direct and indirect relationships between brain size, body size, life history, and longevity across 339 altricial and precocial bird species. Our results support both a direct causal link between brain size and lifespan, and an indirect effect via other life history traits. These results indicate that large brain size engenders longer life, as proposed by the "cognitive buffer" hypothesis.
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http://dx.doi.org/10.1111/evo.14087DOI Listing
December 2020

Brain size does not predict learning strategies in a serial reversal learning test.

J Exp Biol 2020 08 4;223(Pt 15). Epub 2020 Aug 4.

Department of Zoology/Ethology, Stockholm University, Svante Arrhenius väg 18B, 10691 Stockholm, Sweden.

Reversal learning assays are commonly used across a wide range of taxa to investigate associative learning and behavioural flexibility. In serial reversal learning, the reward contingency in a binary discrimination is reversed multiple times. Performance during serial reversal learning varies greatly at the interspecific level, as some animals adopt a rule-based strategy that enables them to switch quickly between reward contingencies. A larger relative brain size, generating enhanced learning ability and increased behavioural flexibility, has been proposed to be an important factor underlying this variation. Here, we experimentally tested this hypothesis at the intraspecific level. We used guppies () artificially selected for small and large relative brain size, with matching differences in neuron number, in a serial reversal learning assay. We tested 96 individuals over 10 serial reversals and found that learning performance and memory were predicted by brain size, whereas differences in efficient learning strategies were not. We conclude that variation in brain size and neuron number is important for variation in learning performance and memory, but these differences are not great enough to cause the larger differences in efficient learning strategies observed at higher taxonomic levels.
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http://dx.doi.org/10.1242/jeb.224741DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7413604PMC
August 2020

The role of common ancestry and gene flow in the evolution of human-directed play behaviour in dogs.

J Evol Biol 2020 03 4;33(3):318-328. Epub 2019 Dec 4.

Department of Zoology, Stockholm University, Stockholm, Sweden.

Among-population variance of phenotypic traits is of high relevance for understanding evolutionary mechanisms that operate in relatively short timescales, but various sources of nonindependence, such as common ancestry and gene flow, can hamper the interpretations. In this comparative analysis of 138 dog breeds, we demonstrate how such confounders can independently shape the evolution of a behavioural trait (human-directed play behaviour from the Dog Mentality Assessment project). We combined information on genetic relatedness and haplotype sharing to reflect common ancestry and gene flow, respectively, and entered these into a phylogenetic mixed model to partition the among-breed variance of human-directed play behaviour while also accounting for within-breed variance. We found that 75% of the among-breed variance was explained by overall genetic relatedness among breeds, whereas 15% could be attributed to haplotype sharing that arises from gene flow. Therefore, most of the differences in human-directed play behaviour among breeds have likely been caused by constraints of common ancestry as a likely consequence of past selection regimes. On the other hand, gene flow caused by crosses among breeds has played a minor, but not negligible role. Our study serves as an example of an analytical approach that can be applied to comparative situations where the effects of shared origin and gene flow require quantification and appropriate statistical control in a within-species/among-population framework. Altogether, our results suggest that the evolutionary history of dog breeds has left remarkable signatures on the among-breed variation of a behavioural phenotype.
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http://dx.doi.org/10.1111/jeb.13567DOI Listing
March 2020

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

J Evol Biol 2020 02 7;33(2):165-177. Epub 2019 Nov 7.

Department of Zoology/Ethology, Stockholm University, Stockholm, Sweden.

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.
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http://dx.doi.org/10.1111/jeb.13556DOI Listing
February 2020

Yes, correct context is indeed the key: An answer to Haave-Audet et al. 2019.

J Evol Biol 2019 12 3;32(12):1450-1455. Epub 2019 Nov 3.

Department of Zoology, Stockholm University, Stockholm, Sweden.

We published a study recently testing the link between brain size and behavioural plasticity using brain size selected guppy (Poecilia reticulata) lines (2019, Journal of Evolutionary Biology, 32, 218-226). Only large-brained fish showed habituation to a new, but actually harmless environment perceived as risky, by increasing movement activity over the 20-day observation period. We concluded that "Our results suggest that brain size likely explains some of the variation in behavioural plasticity found at the intraspecific level". In a commentary published in the same journal, Haave-Audet et al. challenged the main message of our study, stating that (a) relative brain size is not a suitable proxy for cognitive ability and (b) habituation measured by us is likely not adaptive and costly. In our response, we first show that a decade's work has proven repeatedly that relative brain size is indeed positively linked to cognitive performance in our model system. Second, we discuss how switching from stressed to unstressed behaviour in stressful situations without real risk is likely adaptive. Finally, we point out that the main cost of behavioural plasticity in our case is the development and maintenance of the neural system needed for information processing, and not the expression of plasticity. We hope that our discussion with Haave-Audet et al. helps clarifying some central issues in this emerging research field.
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http://dx.doi.org/10.1111/jeb.13548DOI Listing
December 2019

Artificial selection on brain size leads to matching changes in overall number of neurons.

Evolution 2019 09 1;73(9):2003-2012. Epub 2019 Aug 1.

Department of Zoology, Faculty of Science, Charles University, 12844, Prague, Czech Republic.

Neurons are the basic computational units of the brain, but brain size is the predominant surrogate measure of brain functional capacity in comparative and cognitive neuroscience. This approach is based on the assumption that larger brains harbor higher numbers of neurons and their connections, and therefore have a higher information-processing capacity. However, recent studies have shown that brain mass may be less strongly correlated with neuron counts than previously thought. Till now, no experimental test has been conducted to examine the relationship between evolutionary changes in brain size and the number of brain neurons. Here, we provide such a test by comparing neuron number in artificial selection lines of female guppies (Poecilia reticulata) with >15% difference in relative brain mass and numerous previously demonstrated cognitive differences. Using the isotropic fractionator, we demonstrate that large-brained females have a higher overall number of neurons than small-brained females, but similar neuronal densities. Importantly, this difference holds also for the telencephalon, a key region for cognition. Our study provides the first direct experimental evidence that selection for brain mass leads to matching changes in number of neurons and shows that brain size evolution is intimately linked to the evolution of neuron number and cognition.
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http://dx.doi.org/10.1111/evo.13805DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6772110PMC
September 2019

On the power to detect rare recombination events.

Proc Natl Acad Sci U S A 2019 06 18;116(26):12607-12608. Epub 2019 Jun 18.

Department of Genetics, Evolution and Environment, University College London, London WC1E 6BT, United Kingdom.

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http://dx.doi.org/10.1073/pnas.1905555116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6601268PMC
June 2019

Large brains, short life: selection on brain size impacts intrinsic lifespan.

Biol Lett 2019 05;15(5):20190137

Department of Zoology/Ethology, Stockholm University , Stockholm , Sweden.

The relationship between brain size and ageing is a paradox. The cognitive benefits of large brains should protect from extrinsic mortality and thus indirectly select for slower ageing. However, the substantial energetic cost of neural tissue may also impact the energetic budget of large-brained organisms, causing less investment in somatic maintenance and thereby faster ageing. While the positive association between brain size and survival in the wild is well established, no studies exist on the direct effects of brain size on ageing. Here we test how brain size influences intrinsic ageing in guppy ( Poecilia reticulata) brain size selection lines with 12% difference in relative brain size. Measuring survival under benign conditions, we find that large-brained animals live 22% shorter than small-brained animals and the effect is similar in both males and females. Our results suggest a trade-off between investment into brain size and somatic maintenance. This implies that the link between brain size and ageing is contingent on the mechanism of mortality, and selection for positive correlations between brain size and ageing should occur mainly under cognition-driven survival benefits from increased brain size. We show that accelerated ageing can be a cost of evolving a larger brain.
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http://dx.doi.org/10.1098/rsbl.2019.0137DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6548732PMC
May 2019

Plastic changes in brain morphology in relation to learning and environmental enrichment in the guppy ().

J Exp Biol 2019 05 21;222(Pt 10). Epub 2019 May 21.

Department of Zoology, Stockholm University, SE-106 91 Stockholm, Sweden.

Despite the common assumption that the brain is malleable to surrounding conditions mainly during ontogeny, plastic neural changes can occur also in adulthood. One of the driving forces responsible for alterations in brain morphology is increasing environmental complexity that may demand enhanced cognitive abilities (e.g. attention, memory and learning). However, studies looking at the relationship between brain morphology and learning are scarce. Here, we tested the effects of both learning and environmental enrichment on neural plasticity in guppies (), by means of either a reversal-learning test or a spatial-learning test. Given considerable evidence supporting environmentally induced plastic alterations, two separate control groups that were not subjected to any cognitive test were included to account for potential changes induced by the experimental setup alone. We did not find any effect of learning on any of our brain measurements. However, we found strong evidence for an environmental effect, where fish given access to the spatial-learning environment had larger relative brain size and optic tectum size in relation to those exposed to the reversal-learning environment. Our results demonstrate the plasticity of the adult brain to respond adaptively mainly to environmental conditions, providing support for the environmental enhancement theory.
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http://dx.doi.org/10.1242/jeb.200402DOI Listing
May 2019

Variation in sexual brain size dimorphism over the breeding cycle in the three-spined stickleback.

J Exp Biol 2019 04 9;222(Pt 7). Epub 2019 Apr 9.

Ecological Genetics Research Unit, Organismal and Evolutionary Biology Research Programme, Faculty of Biological and Environmental Sciences, University of Helsinki, PO Box 65, FI-00014 Helsinki, Finland.

Snapshot analyses have demonstrated dramatic intraspecific variation in the degree of brain sexual size dimorphism (SSD). Although brain SSD is believed to be generated by the sex-specific cognitive demands of reproduction, the relative roles of developmental and population-specific contributions to variation in brain SSD remain little studied. Using a common garden experiment, we tested for sex-specific changes in brain anatomy over the breeding cycle in three-spined stickleback () sampled from four locations in northern Europe. We found that the male brain increased in size (ca. 24%) significantly more than the female brain towards breeding, and that the resulting brain SSD was similar (ca. 20%) for all populations over the breeding cycle. Our findings support the notion that the stickleback brain is highly plastic and changes over the breeding cycle, especially in males, likely as an adaptive response to the cognitive demands of reproduction (e.g. nest construction and parental care). The results also provide evidence to suggest that breeding-related changes in brain size may be the reason for the widely varying estimates of brain SSD across studies of this species, cautioning against interpreting brain size measurements from a single time point as fixed/static.
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http://dx.doi.org/10.1242/jeb.194464DOI Listing
April 2019

Brain size predicts behavioural plasticity in guppies (Poecilia reticulata): An experiment.

J Evol Biol 2019 03 21;32(3):218-226. Epub 2018 Dec 21.

Department of Zoology, Stockholm University, Stockholm, Sweden.

Understanding how animal personality (consistent between-individual behavioural differences) arises has become a central topic in behavioural sciences. This endeavour is complicated by the fact that not only the mean behaviour of individuals (behavioural type) but also the strength of their reaction to environmental change (behavioural plasticity) varies consistently. Personality and cognitive abilities are linked, and we suggest that behavioural plasticity could also be explained by differences in brain size (a proxy for cognitive abilities), since accurate decisions are likely essential to make behavioural plasticity beneficial. We test this idea in guppies (Poecilia reticulata), artificially selected for large and small brain size, which show clear cognitive differences between selection lines. To test whether those lines differed in behavioural plasticity, we reared them in groups in structurally enriched environments and then placed adults individually into empty tanks, where we presented them daily with visual predator cues and monitored their behaviour for 20 days with video-aided motion tracking. We found that individuals differed consistently in activity and risk-taking, as well as in behavioural plasticity. In activity, only the large-brained lines demonstrated habituation (increased activity) to the new environment, whereas in risk-taking, we found sensitization (decreased risk-taking) in both brain size lines. We conclude that brain size, potentially via increasing cognitive abilities, may increase behavioural plasticity, which in turn can improve habituation to novel environments. However, the effects seem to be behaviour-specific. Our results suggest that brain size likely explains some of the variation in behavioural plasticity found at the intraspecific level.
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http://dx.doi.org/10.1111/jeb.13405DOI Listing
March 2019

Early neurogenomic response associated with variation in guppy female mate preference.

Nat Ecol Evol 2018 11 8;2(11):1772-1781. Epub 2018 Oct 8.

Department of Genetics, Evolution and Environment, University College London, London, UK.

Understanding the evolution of mate choice requires dissecting the mechanisms of female preference, particularly how these differ among social contexts and preference phenotypes. Here, we studied the female neurogenomic response after only 10 min of mate exposure in both a sensory component (optic tectum) and a decision-making component (telencephalon) of the brain. By comparing the transcriptional response between females with and without preferences for colourful males, we identified unique neurogenomic elements associated with the female preference phenotype that are not present in females without preference. A network analysis revealed different properties for this response at the sensory-processing and the decision-making levels, and we show that this response is highly centralized in the telencephalon. Furthermore, we identified an additional set of genes that vary in expression across social contexts, beyond mate evaluation. We show that transcription factors among these loci are predicted to regulate the transcriptional response of the genes we found to be associated with female preference.
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http://dx.doi.org/10.1038/s41559-018-0682-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6349141PMC
November 2018

Male-biased gene expression resolves sexual conflict through the evolution of sex-specific genetic architecture.

Evol Lett 2018 Apr 10;2(2):52-61. Epub 2018 Feb 10.

Department of Genetics, Evolution and Environment University College London London United Kingdom.

Many genes are subject to contradictory selection pressures in males and females, and balancing selection resulting from sexual conflict has the potential to substantially increase standing genetic diversity in populations and thereby act as an important force in adaptation. However, the underlying causes of sexual conflict, and the potential for resolution, remains hotly debated. Using transcriptome-resequencing data from male and female guppies, we use a novel approach, combining patterns of genetic diversity and intersexual divergence in allele frequency, to distinguish the different scenarios that give rise to sexual conflict, and how this conflict may be resolved through regulatory evolution. We show that reproductive fitness is the main source of sexual conflict, and this is resolved via the evolution of male-biased expression. Furthermore, resolution of sexual conflict produces significant differences in genetic architecture between males and females, which in turn lead to specific alleles influencing sex-specific viability. Together, our findings suggest an important role for sexual conflict in shaping broad patterns of genome diversity, and show that regulatory evolution is a rapid and efficient route to the resolution of conflict.
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http://dx.doi.org/10.1002/evl3.39DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6089503PMC
April 2018

Breakdown of brain-body allometry and the encephalization of birds and mammals.

Nat Ecol Evol 2018 09 13;2(9):1492-1500. Epub 2018 Aug 13.

Department of Zoology/Ethology, Stockholm University, Stockholm, Sweden.

The allometric relationship between brain and body size among vertebrates is often considered a manifestation of evolutionary constraints. However, birds and mammals have undergone remarkable encephalization, in which brain size has increased without corresponding changes in body size. Here, we explore the hypothesis that a reduction of phenotypic integration between brain and body size has facilitated encephalization in birds and mammals. Using a large dataset comprising 20,213 specimens across 4,587 species of jawed vertebrates, we show that the among-species (evolutionary) brain-body allometries are remarkably constant, both across vertebrate classes and across taxonomic levels. Birds and mammals, however, are exceptional in that their within-species (static) allometries are shallower and more variable than in other vertebrates. These patterns are consistent with the idea that birds and mammals have reduced allometric constraints that are otherwise ubiquitous across jawed vertebrates. Further exploration of ontogenetic allometries in selected taxa of birds, fishes and mammals reveals that birds and mammals have extended the period of fetal brain growth compared to fishes. Based on these findings, we propose that avian and mammalian encephalization has been contingent on increased variability in brain growth patterns.
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http://dx.doi.org/10.1038/s41559-018-0632-1DOI Listing
September 2018

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

J Exp Biol 2018 06 25;221(Pt 12). Epub 2018 Jun 25.

Department of Zoology/Ethology, Stockholm University, Svante Arrhenius väg 18B, SE-10691 Stockholm, Sweden.

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 () 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 ornamentation 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.
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http://dx.doi.org/10.1242/jeb.175240DOI Listing
June 2018

Using activity and sociability to characterize collective motion.

Philos Trans R Soc Lond B Biol Sci 2018 05;373(1746)

Zoology Department, Stockholm University, Stockholm, Sweden.

A wide range of measurements can be made on the collective motion of groups, and the movement of individuals within them. These include, but are not limited to: group size, polarization, speed, turning speed, speed or directional correlations, and distances to near neighbours. From an ecological and evolutionary perspective, we would like to know which of these measurements capture biologically meaningful aspects of an animal's behaviour and contribute to its survival chances. Previous simulation studies have emphasized two main factors shaping individuals' behaviour in groups; attraction and alignment. Alignment responses appear to be important in transferring information between group members and providing synergistic benefits to group members. Likewise, attraction to conspecifics is thought to provide benefits through, for example, selfish herding. Here, we use a factor analysis on a wide range of simple measurements to identify two main axes of collective motion in guppies (): (i) sociability, which corresponds to attraction (and to a lesser degree alignment) to neighbours, and (ii) activity, which combines alignment with directed movement. We show that for guppies, predation in a natural environment produces higher degrees of sociability and (in females) lower degrees of activity, while female guppies sorted for higher degrees of collective alignment have higher degrees of both sociability and activity. We suggest that the activity and sociability axes provide a useful framework for measuring the behaviour of animals in groups, allowing the comparison of individual and collective behaviours within and between species.This article is part of the theme issue 'Collective movement ecology'.
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http://dx.doi.org/10.1098/rstb.2017.0015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5882985PMC
May 2018

Brain size affects performance in a reversal-learning test.

Proc Biol Sci 2018 01;285(1871)

Department of Zoology/Ethology, Stockholm University, Svante Arrhenius väg 18B, 10691, Stockholm, Sweden.

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 () 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.
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http://dx.doi.org/10.1098/rspb.2017.2031DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5805926PMC
January 2018

Brain size does not impact shoaling dynamics in unfamiliar groups of guppies (Poecilia reticulata).

Behav Processes 2018 Feb 14;147:13-20. Epub 2017 Dec 14.

Department of Zoology, Stockholm University, SE-10691, Stockholm, Sweden.

Collective movement is achieved when individuals adopt local rules to interact with their neighbours. How the brain processes information about neighbours' positions and movements may affect how individuals interact in groups. As brain size can determine such information processing it should impact collective animal movement. Here we investigate whether brain size affects the structure and organisation of newly forming fish shoals by quantifying the collective movement of guppies (Poecilia reticulata) from large- and small-brained selection lines, with known differences in learning and memory. We used automated tracking software to determine shoaling behaviour of single-sex groups of eight or two fish and found no evidence that brain size affected the speed, group size, or spatial and directional organisation of fish shoals. Our results suggest that brain size does not play an important role in how fish interact with each other in these types of moving groups of unfamiliar individuals. Based on these results, we propose that shoal dynamics are likely to be governed by relatively basic cognitive processes that do not differ in these brain size selected lines of guppies.
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http://dx.doi.org/10.1016/j.beproc.2017.12.006DOI Listing
February 2018

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

Behav Ecol Sociobiol 2017;71(12):179. Epub 2017 Nov 29.

Department of Zoology/Ethology, Stockholm University, Svante Arrhenius väg 18B, SE-10691 Stockholm, Sweden.

Abstract: 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 () 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.

Significance Statement: Pre-existing perceptual biases can be keys for the development of specific behavioral patterns. Hence, potential differences in sensory systems need to be taken into account in the study of animal behavior. We highlight this necessity concentrating on the visual domain and using experimental data on brain size-selected guppies in which we assessed eye size and visual acuity. Behavioral differences between large-brained and small-brained guppies in learning and mate choice predominantly relied on tests using visual cues. Analyses of visual capabilities in this system are therefore necessary. Furthermore, this system offers the unprecedented opportunity to experimentally test the relationship between brain size, eye morphology, and visual capabilities. Our results show similar visual acuities between large-brained and small-brained guppies. However, the differences observed in eye area between the sexes, together with the observed positive relationship between body size and visual acuity, highlight the need to incorporate perceptive differences in the study of animal behavior.
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http://dx.doi.org/10.1007/s00265-017-2408-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5705735PMC
November 2017

Evolution of brain region volumes during artificial selection for relative brain size.

Evolution 2017 Dec 13;71(12):2942-2951. Epub 2017 Nov 13.

Department of Zoology, Stockholm University, Stockholm, Sweden.

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.
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http://dx.doi.org/10.1111/evo.13373DOI Listing
December 2017

How predation shapes the social interaction rules of shoaling fish.

Proc Biol Sci 2017 Aug;284(1861)

Department of Mathematics, Uppsala University, Uppsala, Sweden.

Predation is thought to shape the macroscopic properties of animal groups, making moving groups more cohesive and coordinated. Precisely how predation has shaped individuals' fine-scale social interactions in natural populations, however, is unknown. Using high-resolution tracking data of shoaling fish () from populations differing in natural predation pressure, we show how predation adapts individuals' social interaction rules. Fish originating from high predation environments formed larger, more cohesive, but not more polarized groups than fish from low predation environments. Using a new approach to detect the discrete points in time when individuals decide to update their movements based on the available social cues, we determine how these collective properties emerge from individuals' microscopic social interactions. We first confirm predictions that predation shapes the attraction-repulsion dynamic of these fish, reducing the critical distance at which neighbours move apart, or come back together. While we find strong evidence that fish align with their near neighbours, we do not find that predation shapes the strength or likelihood of these alignment tendencies. We also find that predation sharpens individuals' acceleration and deceleration responses, implying key perceptual and energetic differences associated with how individuals move in different predation regimes. Our results reveal how predation can shape the social interactions of individuals in groups, ultimately driving differences in groups' collective behaviour.
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http://dx.doi.org/10.1098/rspb.2017.1126DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5577484PMC
August 2017

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

Sci Adv 2017 Mar 22;3(3):e1601990. Epub 2017 Mar 22.

Department of Zoology/Ethology, Stockholm University, Svante Arrhenius väg 18B, SE-10691 Stockholm, Sweden.

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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http://dx.doi.org/10.1126/sciadv.1601990DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5362185PMC
March 2017

Convergent recombination suppression suggests role of sexual selection in guppy sex chromosome formation.

Nat Commun 2017 01 31;8:14251. Epub 2017 Jan 31.

Department of Genetics, Evolution and Environment, University College London, Darwin Building, Gower Street, London WC1E 6BT, UK.

Sex chromosomes evolve once recombination is halted between a homologous pair of chromosomes. The dominant model of sex chromosome evolution posits that recombination is suppressed between emerging X and Y chromosomes in order to resolve sexual conflict. Here we test this model using whole genome and transcriptome resequencing data in the guppy, a model for sexual selection with many Y-linked colour traits. We show that although the nascent Y chromosome encompasses nearly half of the linkage group, there has been no perceptible degradation of Y chromosome gene content or activity. Using replicate wild populations with differing levels of sexually antagonistic selection for colour, we also show that sexual selection leads to greater expansion of the non-recombining region and increased Y chromosome divergence. These results provide empirical support for longstanding models of sex chromosome catalysis, and suggest an important role for sexual selection and sexual conflict in genome evolution.
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http://dx.doi.org/10.1038/ncomms14251DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5290318PMC
January 2017

Predation pressure shapes brain anatomy in the wild.

Evol Ecol 2017 12;31(5):619-633. Epub 2017 May 12.

1Department of Ethology/Zoology, Stockholm University, Svante Arheniusväg 18B, 10691 Stockholm, Sweden.

There is remarkable diversity in brain anatomy among vertebrates and evidence is accumulating that predatory interactions are crucially important for this diversity. To test this hypothesis, we collected female guppies () from 16 wild populations and related their brain anatomy to several aspects of predation pressure in this ecosystem, such as the biomass of the four major predators of guppies (one prawn and three fish species), and predator diversity (number of predatory fish species in each site). We found that populations from localities with higher prawn biomass had relatively larger telencephalon size as well as larger brains. Optic tectum size was positively associated with one of the fish predator's biomass and with overall predator diversity. However, both olfactory bulb and hypothalamus size were negatively associated with the biomass of another of the fish predators. Hence, while fish predator occurrence is associated with variation in brain anatomy, prawn occurrence is associated with variation in brain size. Our results suggest that cognitive challenges posed by local differences in predator communities may lead to changes in prey brain anatomy in the wild.
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http://dx.doi.org/10.1007/s10682-017-9901-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6961500PMC
May 2017