Biology subjects

Leimar, O.

Publications and source records attributed to Leimar, O..

9 recordsLinked to original sources

bioRxiv2026

Modelling pairwise and coalitional contests with reinforcement learning

Game theory in biology started as an attempt to model animal contests by making assumptions about the fitness costs individuals pay in aggressive interactions. Among the different approaches, a notable one is to construct mechanistic models, using assumptions about behaviours and cognitive processes. Reinforcement learning is an important cognitive process, and we use it here to model pairwise and coalitional contests. We study situations where territorial neighbours become so-called dear enemies. A defending individual can get help from a neighbour through a defender-neighbour coalition against a challenger attempting territory takeover. In our model, coalition members have an advantage in contests in terms of costs of aggression, with the challenger being exposed to aggression from both members and each member only receiving part of the aggression from the challenger. We find that notable costs of border conflicts between neighbours, together with substantial advantages for coalitions, favour intervention. Neighbours intervene when they can help weaker defenders, in this way avoiding costs of border renegotiation with a new and potentially stronger territory owner. We also introduce different forms of perceived costs into the model, which we show correspond to the range from pure mutual assessment to partial self-assessment.

animal behavior and cognition↗

bioRxiv2025

Evolution of behavioural flexibility and the forming and breaking of habits

The formation of habits, whereby learnt actions come to be performed automatically with repetition and practice, is a well-established focus for studies in psychology. This contrasts with evolutionarily motivated studies of learning, which typically view behavior as either learnt or fixed, to elucidate the ecological conditions where each predominates. Here, we envisage habit formation functioning to free up limited mental resources (e.g., attention), potentially improving an individuals ability to multitask. As an ecologically relevant case, we investigate exploration-exploitation in foraging under predation risk. In our model, a forager does not know the quality of feeding options, but can learn from the rewards they give. When the environment occasionally changes, individuals can attend to exploration of feeding options in the new conditions. The options can then become habitually exploited, freeing attention for antipredatory vigilance. Via evolutionary simulations, we show that evolutionarily stable forming and breaking of foraging habits can substantially reduce mortality from predation, without drastically reducing foraging success, when environmental conditions remain stable enough between changes. We identify factors promoting habit formation, such as the repetition of actions that yield predictable rewards, and also discuss the role of habits more generally, including their relation to ideas about bounded rationality in theories of decision making. In conclusion, we argue that exploration-exploitation strategies involving the forming and breaking of habits are a type of behavioral flexibility that is likely to be selected for under a range of ecological conditions. Significance statementThe forming and breaking of habits has long been a focus of study in psychology, as well as appearing in many discussions about human behavior. Surprisingly, the topic has been virtually absent from evolutionary studies of learning in non-human animals, despite featuring prominently in Darwins discussion of the evolution of species-specific behaviors. Our aim is to change this, by theoretically investigating a possible evolutionary explanation for habits, namely that habits enhance an individuals ability to multitask. We model the combination of foraging and antipredator vigilance, which is important for many animal species in their natural environments. We conclude that the forming and breaking of habits can promote behavioral flexibility, helping animals to achieve important tasks in different environments.

animal behavior and cognition↗

bioRxiv2023

Social bond dynamics and the evolution of helping

Empiricists often struggle to apply game theory models to real-life cases of animal cooperation. One reason is that many examples of cooperation occur in stable groups, where costs and benefits of helping depend on several factors. Among these are variable investments, fitness interdependencies, learning, memory, reciprocity, and partner choice, including the formation of social bonds with specific group members. Here, we present a game theory model exploring the conditions under which social bonds between group members can promote cooperation, with reciprocal acts of helping. In the model, bonds build up from exchanges of help in a similar way as the strength of association increases in learning, as in the Rescorla-Wagner rule. The bonds in turn affect partner choice and influence helping amounts. The model has a mechanism of reciprocity for bonded pairs, which can evolve towards either loose or strict reciprocation. Several aspects of the model are inspired by observations of food sharing in vampire bats. We find that small social neighbourhoods are required for the evolutionary stability of helping, either as small group sizes, or if members of larger groups can form temporary (daily) smaller groupings. The evolutionary outcome is a fairly low cost helping, while the benefit of receiving help can be substantial. Individuals in need request help based on bond strength, but there is also an evolved preference for initiating bonds with new group members. In contrast, if different groups come into temporary contact with each other, the evolved tendency is to avoid forming bonds between groups. Popular science summaryThe search for evolutionary explanations of cooperation between members of social groups has long been a high profile endeavour. A case of particular interest is when individuals develop a network of friends and exchange help through these social bonds. The question of helping between friends was given emphasis already from the start of the evolutionary study of cooperation, more than 50 years ago, but it has remained without any decisive progress since that time. Here we present a game-theory analysis of helping through the build-up of social bonds. We find that there is reciprocity in socially bonded pairs, which is neither immediate nor very strict, and that relatively small social neighbourhoods are required for the evolutionary stability of helping.

animal behavior and cognition↗

bioRxiv2023

Flexibility of learning in complex worlds

Learning to adjust to changing environments is an important aspect of behavioral flexibility. Here we investigate the possible advantages of flexible learning rates in volatile environments, using learning simulations. We compare two established learning mechanisms, one with fixed learning rates and one with flexible rates that adjust to volatility. We study three types of ecological and experimental volatility: transitions from a simpler to a more complex foraging environment, reversal learning, and learning set formation. For transitions to a complex world, we use developing cleaner fish as an example, having more types of client fish to choose between as they become adult. There are other similar transitions in nature, such as migrating to a new and different habitat. Performance in reversal learning and in learning set formation are commonly used experimental measures of behavioral flexibility. Concerning transitions to a complex world, we show that both fixed and flexible learning rates perform well, losing only a small proportion of available rewards in the period after a transition, but flexible rates perform better than fixed. For reversal learning, flexible rates improve the performance with each successive reversal, because of increasing learning rates, but this does not happen for fixed rates. For learning set formation, we find no improvement in performance with successive shifts to new stimuli to discriminate for either flexible or fixed learning rates. Flexible learning rates might thus explain increasing performance in reversal learning, but not in learning set formation. We discuss our results in relation to current ideas about behavioral flexibility.

animal behavior and cognition↗

bioRxiv2022

Effects of local versus global competition on reproductive skew and sex differences in social dominance behaviour

Social hierarchies are often found in group-living animals. The hierarchy position can influence reproductive success (RS), with a skew towards high-ranking individuals. The amount of aggression in social dominance varies greatly, both between species and between males and females within species. Using game theory we study this variation by taking into account the degree to which reproductive competition in a social group is mainly local to the group, emphasising within-group relative RS, or global to a larger population, emphasising an individuals absolute RS. Our model is similar to recent approaches in that reinforcement learning is used as a behavioural mechanism allowing social-hierarchy formation. We test two hypotheses. The first is that local competition should favour the evolution of mating or foraging interference, and thus of reproductive skew. Second, decreases in reproductive output caused by an individuals accumulated fighting damage, such as reduced parenting ability, will favour less intense aggression but should have little influence on reproductive skew. From individual-based simulations of the evolution of social dominance and interference, we find support for both hypotheses. We discuss to what extent our results can explain observed sex differences in reproductive skew and social dominance behaviour.

animal behavior and cognition↗

bioRxiv2021

Reproductive skew, fitness costs, and winner-loser effects in social-dominance evolution

Social hierarchies can increase reproductive skew in group-living animals. Using game theory we investigate how the opportunity for differently ranked individuals to acquire resources influences reproductive skew, costs of hierarchy formation, and winner and loser effects. Individuals adjust their aggressive and submissive behaviour through reinforcement learning. The learning is based on perceived rewards and penalties, which depend on relative fighting ability. From individualbased simulations we determine evolutionary equilibria of traits that control an individuals learning. We examine situations that differ in the extent of monopolisation of contested resources by dominants and in the amounts of uncontested resources that are distributed independently of rank. With costly fighting, we find that stable dominance hierarchies form, such that reproductive skew mirrors the distribution of resources over ranks. Individuals pay substantial costs of interacting, in particular in high-skew situations, with the highest costs paid by intermediately ranked individuals. For cases where dominants monopolise contested resources there are notable winner and loser effects, with winner effects for high ranks and very pronounced loser effects for lower ranks. The effects are instead weak when acquired resources increase linearly with rank. We compare our results on contest costs and winner-loser effects with field and experimental observations.

animal behavior and cognition↗

bioRxiv2020

The evolution of social learning as phenotypic cue integration

Most analyses of the origins of cultural evolution focus on when and where social learning prevails over individual learning, overlooking the fact that there are other developmental inputs that influence phenotypic fit to the selective environment. This raises the question how the presence of other cue channels affects the scope for social learning. Here, we present a model that considers the simultaneous evolution of (i) multiple forms of social learning (involving vertical or horizontal learning based on either prestige or conformity biases) within the broader context of other evolving inputs on phenotype determination, including (ii) heritable epigenetic factors, (iii) individual learning, (iv) environmental and cascading maternal effects, (v) conservative bet-hedging and (vi) genetic cues. In fluctuating environments that are autocorrelated (and hence predictable), we find that social learning from members of the same generation (horizontal social learning) explains the large majority of phenotypic variation, whereas other cues are much less important. Moreover, social learning based on prestige biases typically prevails in positively autocorrelated environments, whereas conformity biases prevail in negatively autocorrelated environments. Only when environments are unpredictable or horizontal social learning is characterised by an intrinsically low information content, other cues such as conservative bet-hedging or vertical prestige biases prevail.

evolutionary biology↗

bioRxiv2020

The evolution of social dominance through reinforcement learning

Groups of social animals are often organised into dominance hierarchies that are formed through pairwise interactions. There is much experimental data on hierarchies, examining such things as winner, loser, and bystander effects, as well as the linearity and replicability of hierarchies, but there is a lack evolutionary analyses of these basic observations. Here I present a game-theory model of hierarchy formation in which individuals adjust their aggressive behaviour towards other group members through reinforcement learning. Individual traits such as the tendency to generalise learning between interactions with different individuals, the rate of learning, and the initial tendency to be aggressive are genetically determined and can be tuned by evolution. I find that evolution favours individuals with high social competence, making use of individual recognition, bystander learning and, to a limited extent, generalising learned behaviour between opponents when adjusting their behaviour towards other group members. The results are in good agreement with experimental data, for instance in finding weaker winner effects compared to loser effects.

animal behavior and cognition↗

bioRxiv2018

Ecological genetic conflict between specialism and plasticity through genomic islands of divergence

There can be genetic conflict between genome elements differing in transmission patterns, and thus in evolutionary interests. We show here that the concept of genetic conflict provides new insight into local adaptation and phenotypic plasticity. Local adaptation to heterogeneous habitats sometimes occurs as tightly linked clusters of genes with among-habitat polymorphism, referred to as genomic islands of divergence, and our work sheds light on their evolution. Phenotypic plasticity can also influence the divergence between ecotypes, through developmental responses to habitat-specificcues. We show that clustered genes coding for ecological specialism and unlinked generalist genes coding for phenotypic plasticity differ in their evolutionary interest. This is an ecological genetic conflict, operating between habitat specialism and phenotypically plastic generalism. The phenomenon occurs both for single traits and for syndromes of co-adapted traits. Using individual-based simulations and numerical analysis, we investigate how among-habitat genetic polymorphism and phenotypic plasticity depend on genetic architecture. We show that for plasticity genes that are unlinked to a genomic island of divergence, the slope of a reaction norm will be steeper in comparison with the slope favored by plasticity genes that are tightly linked to genes for local adaptation.

evolutionary biology↗