Biology subjects

Johnstone, R. A.

Publications and source records attributed to Johnstone, R. A..

10 recordsLinked to original sources

bioRxiv2025

A landscape of intergroup conflict shapes den site choice in banded mongooses

BackgroundFor many social animals, intergroup conflict has major impacts on fitness and should therefore influence how groups navigate their environment. Yet most studies of group movement focus on the behaviour of single groups, usually foraging groups studied in isolation of all others. In many systems rival groups present both threats and opportunities, contributing to a landscape of intergroup conflict. This landscape could have a profound impact on group movement. MethodsHere we test how the potential for intergroup conflict influences movement decisions of wild cooperatively breeding banded mongooses, using 14 years of behavioural and GPS data. In this species, encounters between groups can present both risks (e.g. injury/mortality) and opportunities (e.g., extragroup mating). We expected that, to minimise risks and maximise rewards, the motivation to engage in conflict would depend on the groups state. Such that vulnerable groups (those that were babysitting young offspring) would select den sites closer to the core of their territory than groups without young offspring. ResultsWe found support for this pattern; non-babysitting groups were unusually risk prone choosing den locations in areas of frequent use by outgroups. During times of heightened recent conflict even choosing to den closer to the core of their rivals territory than their own. ConclusionsThese results suggest that groups of banded mongooses choose den sites that reflect not only the risks but also the potential rewards of defensive or competitive claims on space. Rival groups thus form an integral part of the social landscape shaping patterns of collective movement.

animal behavior and cognition↗

bioRxiv2025

Spend today or build for tomorrow? Kinship dynamics and the evolution of alternative helping strategies in cooperative breeders.

Cooperatively breeding animal groups are characterised by the presence of helpers, which assist breeders in raising offspring through a variety of behaviours, such as provisioning young or defence against predators. While these systems have been studied to investigate how costly forms of help can evolve, there is little theory explaining the considerable variation in helping strategies observed across such societies. Here, we use mathematical models to investigate the evolution of alternative helping strategies. Helpers in our models can allocate effort to immediate, short-term benefits or durable, long-term benefits. We find that allocation depends on the kinship dynamics within the group. Specifically, where helpers are more related to future breeders than current breeders, often because they themselves become the future breeder, our model typically predicts greater allocation to durable help. Conversely, immediate help is favoured when helpers are less related to future breeders than to current breeders. We use our model to explore how demographic features impact kinship dynamics within the group, identify which factors select for immediate versus durable help, and which amplify conflict between breeders and helpers over helping strategies. The model is a first step towards explaining variation in types of help observed among cooperatively breeding societies.

evolutionary biology↗

bioRxiv2025

Predicting the patterns of kinship dynamics in human societies

By shaping the inclusive fitness effects of behaviours, kinship environments have important implications for social evolution, and studies across non-human animal societies have shown that the patterns of kinship dynamics individuals experience as they age can be predicted by simple demographic parameters relating to sex-specific dispersal patterns, the extent of extra-group mating, and the age-specific patterns of mortality and fertility. However, it remains unclear whether these insights apply within our own species, where we see both extended lifespans in which kinship dynamics can play out, and remarkable variations in cultural practices relating to marriage and residence that influence the patterns of inter-individual relatedness. Here, using a newly developed model of kinship dynamics, we explore how marriage practices and post-marital residence rules, along with the typical survival and fertility schedules of our own species, can predict the emergent patterns of female and male kinship dynamics in human societies. By showing evidence that the model successfully captures the patterns of female and male kinship dynamics underlying human societies, we demonstrate that, despite the diversity in human social organisation, a relatively simple set of parameters relating to male and female rates of dispersal and the prevalence of extra-group mating suffices to capture the qualitative patterns of human kinship dynamics. Given the inclusive fitness implications kinship dynamics have for sex- and age-linked variations in behaviours, our study thus generates new insights into human social evolution.

evolutionary biology↗

bioRxiv2025

Predicting kinship dynamics during pre- and post reproductive life stages

Individuals relatedness to their groups often changes with age, potentially favouring age-linked trends in social behaviours, and these kinship dynamics have been invoked to explain the evolution of life history traits such as early reproductive cessation and post-reproductive helping. While models showed that simple demographic parameters (e.g., the rates of male and female philopatry vs dispersal, and of local vs non-local mating) suffice to predict the patterns of kinship dynamics breeders experience, they make the unrealistic assumptions that survival and fecundity are age-independent, thus fail to capture the full complexity of kinship dynamics. In particular, they cannot consistently predict how individuals relatedness to their groups should change during their pre- and post-reproductive phases. Here, we extend existing models of kinship dynamics to allow any age-linked changes in mortality and fecundity of both sexes. We describe the new model, and demonstrate its improved predictive power, by comparing the observed kinship dynamics of the killer whales to the predictions of the previously available models (assuming constant mortality and fecundity) and of our new model (considering any observed age-specific survival and fecundity). We show the new model better predicts the data, successfully capturing the observed three-stage female kinship dynamics: an individuals relatedness to her group decreases initially while juvenile, increases across reproductive lifespan, and decreases again during post-reproductive life. These predictions demonstrate the power of our model in generating new insights into the theory of social life history evolution (e.g., explaining why post-reproductive lifespan evolved yet are constrained).

evolutionary biology↗

bioRxiv2023

Group size modulates kinship dynamics and selection on social traits

An individuals relatedness to its group may change with age due to demographic processes, and such kinship dynamics can shape age-linked social behaviors. Existing models, however, have focused almost exclusively on dispersal and mating, leaving the consequences of group size local variation unexplored. Here, we extend these models to incorporate such variation within a single, genetically connected meta-population. We then contrast predicted kinship dynamics and age-linked selection for helping/harming in coexisting smaller and larger groups in three typical social mammal systems characterized by distinct patterns of dispersal and mating, followed by exploring how group size local variation impacts female and male kinship dynamics across broader demographic contexts to clarify the population-genetic mechanisms. We show that, within the adult reproductive lifespans of these social systems, an individuals age-specific relatedness to others is higher, and changes faster (especially when younger), in smaller groups; consequently, smaller groups favor more extreme helping/harming (especially when younger) -- in social system with bi-sexual philopatry with non-local mating (e.g., whales) that favors female shifts from harming to helping with age (which explains the evolution of menopause and post-reproductive helping), such shifts are earlier in smaller groups. Further explorations suggest that, in a genetically connected population with group size local variation, group size effects on local relatedness are shaped by the relative strengths of ancestry dilution versus lineage coalescence, and kinship dynamics in a group reflect not only its local demographic conditions, but also those in coexisting groups of different size. Collectively, our study generates new insights into how female and male kinship dynamics emerge and vary under within-population group-size heterogeneity, and how such locally dynamic, varying kinship environments may help to explain variation in age-linked trends in social traits, such as the timing of menopause in social mammals.

evolutionary biology↗

bioRxiv2023

The Evolution of Democratic Peace

A major goal in evolutionary biology is to elucidate common principles that drive human and other animal societies to adopt either a warlike or peaceful nature. One proposed explanation for the variation in aggression between human societies is the democratic peace hypothesis. According to this theory, autocracies are more warlike than democracies because autocratic leaders can pursue fights for private gain. However, autocratic and democratic decision-making processes are not unique to humans and are widely observed across a diverse range of non-human animal societies. We use evolutionary game theory to evaluate whether the logic of democratic peace may apply across taxa; specifically adapting the classic Hawk-Dove model to consider conflict decisions made by groups rather than individuals. We find support for the democratic peace hypothesis without mechanisms involving complex human institutions and discuss how these findings might be relevant to non-human animal societies. We suggest that the degree to which collective decisions are shared may explain variation in the intensity of intergroup conflict in nature.

evolutionary biology↗

bioRxiv2019

The evolution of parental effects when selection acts on fecundity versus viability

Most predictions on the evolution of adaptive parental effects and phenotypic memory exclusively focus on the role of the abiotic environment. How parental effects are affected by population demography and life history is less well understood. To overcome this, we use an analytical model to assess whether selection acting on fecundity versus viability affects the evolution of parental effects in a viscous population experiencing a spatiotemporally varying environment. We find that parental effects commonly evolve in regimes of viability selection, but are less likely to evolve in regimes of fecundity selection. In regimes of viability selection, an individuals phenotype becomes correlated with its local environment during its lifetime, as those individuals with a locally adapted phenotype are more likely to survive until parenthood. Hence, a parental phenotype rapidly becomes an informative cue about its local environment, favoring the evolution of parental effects. By contrast, in regimes of fecundity selection, locally maladapted and adapted parents survive at equal rates, so that the parental phenotype, by itself, is not informative about the local environment. Correlations between phenotype and environment still arise, but only when more fecund, locally adapted individuals leave more successfully established offspring to the local patch. Hence, correlations take at least two generations to develop, making them more sensitive to distortion by environmental change or competition with immigrant offspring. Hence, we conclude that viability selection is most conducive to the evolution of adaptive parental effects in spatially structured populations.

evolutionary biology↗

bioRxiv2018

Coping with strangers: how familiarity and active interactions shape group coordination in Corydoras aeneus

Social groups whose members have had sustained prior experience with each other frequently exhibit improved coordination and outperform groups whose members are unfamiliar with one another. The mechanisms by which familiarity assists coordination are not well known. Prior social experience may simply allow individuals to learn the behavioral tendencies of familiar group-mates and coordinate accordingly. In the absence of prior social experience, it would be adaptive for individuals to develop strategies for coping with unfamiliar others to minimize the disadvantage of unfamiliarity. To explore the dynamics of familiarity in shaping group behaviors, we used a highly social catfish, Corydoras aeneus, that utilizes a distinctive, observable tactile interactions. Here we describe this tactile interaction behavior, physical \"nudges\" that are deployed to initiate group movements and maintain contact with group-mates during group movements. We then report the results of two experiments exploring the relationship between nudges and coordination. First, within triplets of two familiar and one unfamiliar individual, we found no individual differences in nudging rate based on familiarity. Despite all individuals interacting at similar rates, however, unfamiliar individuals failed to coordinate as well as their familiar group-mates, and were more frequently absent from group movements. Second, comparing pairs of familiar with pairs of unfamiliar fish, there was no difference in the level of coordination between pairs. Instead, we found that unfamiliar pairs exhibited significantly higher nudging rates, suggesting that unfamiliar pairs could compensate for their unfamiliarity by nudging more frequently. In contrast, familiar individuals coordinated with comparatively little nudging, presumably because they were experienced with each other. Overall, these results suggest that nudges can be used to improve coordination of group activities, but that their usage is reduced in the case of familiar individuals, implying that these potential signals may be costly.

animal behavior and cognition↗

bioRxiv2018

The Evolution of Early-Life Effects on Social Behaviour - Why Should Social Adversity Carry Over to the Future?

Numerous studies have shown that social adversity in early life can have long-lasting negative consequences for social behaviour in adulthood, consequences that may in turn be propagated to future generations. Given these intergenerational effects, it is puzzling why natural selection might favour such sensitivity to an individuals early social environment. To address this question, we model the evolution of social sensitivity in the development of in helping behaviours, showing that natural selection indeed favours individuals whose tendency to help others is dependent on early-life social experience. We find that natural selection typically favours positive social feedbacks, in which individuals who received more help in early life are also more likely to help others in adulthood, while individuals who received no early-life help develop low tendencies to helping others later in life. This positive social sensitivity is favoured because of an intergenerational relatedness feedback: patches with many helpers tend to be more productive, leading to higher relatedness within the local group, which in turn favours higher levels of help in the next generation.

evolutionary biology↗

bioRxiv2017

Maternal Effects and Parent-Offspring Conflict

Maternal effects can provide offspring with reliable information about the environment they are likely to experience, but also offer scope for maternal manipulation of young when interests diverge between parents and offspring. To predict the impact and outcome of parent-offspring conflict, we model the evolution of maternal effects on local adaptation of young. We find that parent-offspring conflict strongly influences the stability of maternal effects; moreover, the nature of the disagreement between parents and young predicts how conflict is resolved: when mothers favour less extreme mixtures of phenotypes relative to offspring (i.e., when mothers stand to gain by hedging their bets), mothers win the conflict by providing offspring with only limited amounts of information. When offspring favour overproduction of one and the same phenotype across all environments compared to mothers (e.g., when offspring favour a larger body size), neither side wins the conflict and signaling breaks down. Only when offspring favour less extreme mixtures relative to their mothers (the case we consider least likely), offspring win the conflict and obtain full information about the state of the environment. We conclude that a partial or complete breakdown of informative maternal effects will be the norm rather than the exception in the presence of parent-offspring conflict.

evolutionary biology↗