Biology subjects

Kolm, N.

Publications and source records attributed to Kolm, N..

12 recordsLinked to original sources

bioRxiv2025

Brain size reduction in dogs was already established at least by the Late Neolithic of western Europe, 5,000 years ago

The timing and causes of brain size reduction in domestic dogs remain uncertain. Using endocasts volume as a proxy for brain size, this study provides a first insight into long-term brain size evolution in the wolf-dog lineage. We compared endocranial volumes of 185 modern and 22 prehistoric wolves and dogs ranging from Western Europe to Australia, and spanning the Pleniglacial (35 Ky BP) to the Late Neolithic (5 Ky BP). Our results reveal that Pleistocene so called "protodogs" show no brain size reduction compared to coeval Pleistocene wolves. Instead, we observed a slightly larger relative endocranial volume in the 35,000-year-old protodog from Goyet, which could suggest increased behavioural flexibility in the presence of humans. This hypothesis needs to be tested further. In contrast, Late Neolithic dogs show a drastic 46% brain size reduction with an endocranial volumes comparable to modern small terrier and toy breeds. The anxious and wary temperaments of these Late Neolithic dogs, induced by the brain tissue reorganization associated with such a size reduction, could have served an alerting purpose, among the many other potential roles dogs could have played within this Late Neolithic socio-ecosystems.

zoology↗

bioRxiv2025

Male social dominance affects access to mates but not female mate choice in a livebearing fish

Male-male competition and female mate choice are often assumed to act in concert, with male social dominance serving as a reliable cue in female choice reflecting overall male quality. However, few studies have explicitly disentangled the effects of male competition and female mate choice, leaving gaps in our understanding of how these processes interact to shape male fitness. Here, we experimentally separated the effects of male-male competition and female mate choice in the pygmy halfbeak Dermogenys colletei, a small freshwater fish, to test whether i) male social dominance drives access to females in the presence and absence of direct male-male competition, and ii) females prefer socially dominant males. Our results show that dominant males monopolized access to females, spending more time courting females and engaging in more courtship behaviors. Additionally, female halfbeaks did not show a preference for dominant males, providing no evidence that females use male dominance when assessing males. Overall, these findings highlight that when male-male competition facilitates mate monopolization there may be less scope for pre-copulatory female mate choice.

animal behavior and cognition↗

bioRxiv2025

Habitat complexity alters the strength of sexual selection on brain size in a livebearing fish

Animals often reproduce in complex environments, which should generate selection for both enhanced detectability in signaling traits and improved cognitive processing abilities. However, the extent to which signaling and cognitive traits have evolved to overcome the challenges of interacting in complex habitats remains understudied. We examined whether habitat complexity influences sexual selection in the pygmy halfbeak, Dermogenys collettei, a small livebearing freshwater fish. Using free-swimming arenas, we created low- and high-complexity environments and observed mating behaviors in mixed-sex groups. While the opportunity for sexual selection did not differ significantly between environments for either sex, we observed positive selection gradients for both male and female brain size in open arenas, but not in complex habitats. Interestingly, no clear selection on male or female ornamentation was detected in either environment. Our findings suggest that habitat complexity may limit selection pressures on cognitive traits, such as brain size, without significantly affecting visual ornamentations role in mating success.

animal behavior and cognition↗

bioRxiv2025

Inbreeding preference emerges in female guppies in a socially complex setting

Animals are typically expected to avoid mating with relatives due to the costs associated with incestuous matings. Yet for more than four decades, theoretical models have consistently suggested that animals should tolerate, or even prefer, mating with relatives under a broad range of conditions. However, empirical studies that evaluate inbreeding avoidance under alternative social and sexual contexts remain scarce. Here, we investigate how experimental variation in sexual and social complexity influence precopulatory inbreeding avoidance behaviors in the guppy Poecilia reticulata, a species known to experience inbreeding depression. In an integrated set of experiments, we examined if sexual and affiliative behaviors of virgin and experienced females and males were differentially directed towards either related or unrelated individuals. In simplistic social interactions, neither virgin nor experienced females or males showed a preference for related or unrelated partners. In contrast, we detected sex-specific responses to relatives in the more sexually and socially complex free-swimming arenas. Females exhibited a stronger preference towards related males regardless of mating experience, while male preference remained unchanged. Overall, these findings challenge previous reports of preference shifts between virgin and experienced female guppies and suggest that inbreeding avoidance behaviors may be less prevalent in complex social environments than previously thought.

animal behavior and cognition↗

bioRxiv2023

Social complexity affects cognitive abilities but not brain structure in a Poecilid fish

Complex cognitive performance is suggested to be the out-turn of complex social life, allowing individuals to achieve higher fitness through sophisticated "Machiavellian" strategies. Although there is ample support for this concept, especially when comparing species, most of the evidence is correlative. Here we provide an experimental investigation of how group size and composition may affect brain and cognitive development in the guppy (Poecilia reticulata). For six months, we reared sexually mature female guppies in one of three different social treatments: (i) three female guppies; (ii) three female guppies mixed with three female splash tetras (Copella arnoldi), a species that co-occurs with the guppy in the wild; and (iii) six female guppies. We then tested the guppies performance in inhibitory control, associative learning and reversal learning tasks to evaluate their self-control, operant conditioning and cognitive flexibility capabilities. Afterwards, we estimated their brain size and the size of major brain regions using X-ray imaging technology. We found that individuals in larger groups of six individuals, in both same and mixed species treatments, outperformed individuals from the smaller groups of three guppies in reversal learning, with no apparent differences in the inhibitory control and associative learning tasks. This is rare evidence of how living in larger social groups improves cognitive flexibility, supporting that social pressures play an important role in shaping individual cognitive development. Interestingly, social manipulation had no apparent effect on brain morphology, but relatively larger telencephalons were associated with better individual performance in reversal learning. This suggests alternative mechanisms beyond brain region size enabled greater cognitive flexibility in individuals from larger groups.

animal behavior and cognition↗

bioRxiv2023

Functional convergence of genomic and transcriptomic genetic architecture underlying sociability in a live-bearing fish

The organization and coordination of fish schools provide a valuable model to investigate the genetic architecture of affiliative behaviors and dissect the mechanisms underlying social behaviors and personalities. We used quantitative genetic methods in replicate guppy selection lines that vary in schooling propensity to investigate the genetic basis of sociability phenotypes. Alignment and attraction, the two major traits forming the sociability personality axis in this species, showed heritability estimates at the upper end of the range previously described for social behaviors, with important variation across sexes. Consistent with findings in collective motion patterns, experimental evolution of schooling propensity increases the sociability of female, but not male, guppies when swimming with unfamiliar conspecifics, a highly relevant trait in a species with fission-fusion social systems in natural populations. Our results from PoolSeq and RNASeq convergently identify genes involved in neuron migration and synaptic function, highlighting a crucial role of glutamatergic synaptic function and calcium-dependent signaling processes in the evolution of schooling.

evolutionary biology↗

bioRxiv2022

Evolution of schooling propensity in the guppy drives changes in anti-predator behavior that are linked to neuroanatomy

One of the most spectacular displays of social behavior is the synchronized movements that many animal groups perform to travel, forage and escape from predators. However, elucidating the neural mechanisms underlying the evolution of collective behaviors, as well as their fitness effects, remains challenging. Here, we study anti-predator behavior in guppies experimentally selected for divergence in polarization, an important behavioral aspect of coordinated movement. We find that groups from artificially selected lines remain more polarized than control groups in the presence of a threat. Neuroanatomical measurements of polarization-selected individuals indicated changes in brain regions previously suggested to be important regulators of perception, fear and attention, and motor response. Additional visual acuity and temporal resolution tests performed in polarization-selected and control individuals indicate that observed differences in anti-predator and schooling behavior should not be attributable to changes in visual perception, but rather are more likely the result of the more efficient relay of sensory input in the brain of polarization-selected fish. Our findings highlight that brain morphology may play a fundamental role in the evolution of coordinated movement and anti-predator behavior.

evolutionary biology↗

bioRxiv2021

Artificial mosaic brain evolution of relative telencephalon size improves cognitive performance in the guppy (Poecilia reticulata)

The telencephalon is a brain region believed to have played an essential role during cognitive evolution in vertebrates. However, till now, all the evidence on the evolutionary association between telencephalon size and cognition stem from comparative studies. To experimentally investigate the potential evolutionary association between cognitive abilities and telencephalon size, we used male guppies artificially selected for large and small telencephalon relative to the rest of the brain. In a detour task, we tested a functionally important aspect of executive cognitive ability; inhibitory control abilities. We found that males with larger telencephalon outperformed males with smaller telencephalon. They showed faster improvement in performance during detour training and were more successful in reaching the food reward without touching the transparent barrier. Together, our findings provide the first experimental evidence showing that evolutionary enlargements of relative telencephalon size confer cognitive benefits, supporting an important role for mosaic brain evolution during cognitive evolution.

ecology↗

bioRxiv2021

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

The vertebrate brain displays enormous morphological variation and the quest to understand the evolutionary causes and consequences of this variation has spurred much research. The mosaic brain evolution hypothesis, stating that brain regions can evolve relatively independently, is an important idea in this research field. Here we provide experimental support for this hypothesis through an artificial selection experiment in the guppy (Poecilia reticulata). After four generations of selection on relative telencephalon volume (relative to brain size) in replicated up-selected, down-selected and control-lines, we found substantial changes in telencephalon size, but no changes in other regions. Comparisons revealed that up-selected lines had larger telencephalon while down-selected lines had smaller telencephalon than wild Trinidadian populations. No cost of increasing telencephalon size was detected in offspring production. Our results support that independent evolutionary changes in specific brain regions through mosaic brain evolution can be important facilitators of cognitive evolution.

evolutionary biology↗

bioRxiv2020

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

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, Poecilia reticulata) for increased social coordination (group polarization), we demonstrate that social interaction rules can evolve remarkably fast. Within just three generations, groups of polarization selected females showed a 15% increase in polarization, coupled with increased cohesiveness, compared to fish from control lines. They did not differ in physical swimming ability or exploratory behavior. However, polarization selected fish adopted faster speeds, particularly in social contexts, and showed stronger alignment and attraction responses to multiple neighbors. Our results demonstrate that animals social interactions can rapidly evolve under strong selection, and reveal which social interaction rules change when collective behavior evolves.

animal behavior and cognition↗

bioRxiv2018

Revisiting the social brain hypothesis: contest duration depends on loser’s brain size

BackgroundBrain size is expected to evolve by a balance between cognitive benefits and energetic costs. Several influential hypotheses have suggested that large brains may be especially beneficial in social contexts. Group living and competition may pose unique cognitive challenges to individuals and favor the evolution of increased cognitive ability. Evidence comes from comparative studies on the link between social complexity and brain morphology, but the strength of empirical support has recently been challenged. In addition, the behavioral mechanisms that would link cognitive ability to sociality are rarely studied. Here we take an alternative approach and investigate experimentally how brain size can relate to the social competence of individuals within species, a problem that so far has remained unresolved. We use the unique guppy brain size selection line model system to evaluate whether large brains are advantageous by allowing individuals to better assess their performance in a social contest situation. Based on theoretical literature, we predict that contest duration should depend on the brain size of the loser, as it is the capitulation of the losing individual that ends the fight.\n\nResultsFirst, we show that studying the movement of competitors during contests allows for precise estimation of the dominance timeline in guppies, even when overt aggression is typically one-sided and delayed. Second, we staged contests between pairs of male that had been artificially selected for large and small relative brain size, with demonstrated differences in cognitive ability. We show that dominance was established much earlier in contests with large-brained losers, whereas the brain size of the winner had no effect. Following our prediction, large-brained individuals gave up more quickly when they were going to lose.\n\nConclusionsThese results suggest that large-brained individuals assess their performance in contests better and that social competence indeed can depend on brain size. Conflict resolution may therefore be an important behavioral mechanism behind macro-evolutionary patterns between sociality and brain size. Since conflict is ubiquitous among group-living animals, the possible effects of the social environment on the evolution of cognition may be more broadly applicable than previously thought.

animal behavior and cognition↗

bioRxiv2017

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

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 inter-sexual 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 leads 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.

evolutionary biology↗