Data from: Parasite-infected sticklebacks increase the risk-taking behavior of uninfected group members

Trophically transmitted parasites frequently increase their hosts' risk-taking behaviour, to facilitate transmission to the next host. Whether such elevated risk-taking can spill over to uninfected group members is, however, unknown. To investigate this, we confronted groups of six three-spined sticklebacks, Gasterosteus aculeatus, containing 0, 2, 4 or 6 experimentally infected individuals with a simulated bird attack and studied their risk-taking behaviour. As a parasite, we used the tapeworm Schistocephalus solidus, which increases the risk-taking of infected sticklebacks, to facilitate transmission to its final host, most often piscivorous birds. Before the attack, infected and uninfected individuals did not differ in their risk-taking. However, after the attack, individuals in groups with only infected members, showed lower escape responses and higher risk-taking than individuals from groups with only uninfected members. Importantly, uninfected individuals adjusted their risk-taking behaviour to the number of infected group members, taking more risk with an increasing number of infected group members. Infected individuals, however, did not adjust their risk-taking to the number of uninfected group members. Our results show that behavioural manipulation by parasites does not only affect the infected host, but also uninfected group members, shedding new light on the social dynamics involved in host-parasite interactions

Strategic disinformation outperforms honesty in competition for social influence

Competition for social influence is a major force shaping societies, from baboons guiding their troop in different directions, to politicians competing for voters, to influencers competing for attention on social media. Social influence is invariably a competitive exercise with multiple influencers competing for it. We study which strategy maximizes social influence under competition. Applying game theory to a scenario where two advisers compete for the attention of a client, we find that the rational solution for advisers is to communicate truthfully when favored by the client, but to lie when ignored. Across seven pre-registered studies, testing 802 participants, such a strategic adviser consistently outcompeted an honest adviser. Strategic dishonesty outperformed truth-telling in swaying individual voters, the majority vote in anonymously voting groups, and the consensus vote in communicating groups. Our findings help explain the success of political movements that thrive on disinformation, and vocal underdog politicians with no credible program

Season-specific carryover of early life associations in a monogamous bird species

Social relationships can have important fitness consequences. Although there is increasing evidence that social relationships carry over across contexts, few studies have investigated whether relationships formed early in life are carried over to adulthood. For example, juveniles of monogamous species go through a major life history stage transition, pair formation, during which the pair bond becomes a central unit of the social organization. At present, it remains unclear whether pair members retain their early life relationships after pair formation. We investigated whether same-sex associations formed early in life carry over into adulthood and whether carryover was dependent on season, in a monogamous species. We also investigated the role of familiarity, genetic relatedness and aggression on the perseverance of social associations. We studied the social structure before and after pair formation in captive barnacle geese, Branta leucopsis, a highly social, long-lived, monogamous species. We constructed association networks of groups of geese before pair formation, during the subsequent breeding season and in the following wintering season. Next, we studied how these associations carried over during seasonal changes. We found that early life associations in females were lost during the breeding season but resurfaced during the subsequent wintering season. In males, the early life associations persisted across both seasons. Association persistence was not mediated by genetic relatedness or familiarity. The high level of aggressiveness of males, but not females, in the breeding season suggests that males may have played a key role in shaping both their own social environment and that of their partners. We show that early life social relationships can be maintained well into later life. Such relationships can be sustained even if they are temporarily disrupted, for example due to reproductive behaviour. Our findings therefore highlight that the early life social environment can have lifelong consequences for individuals’ social environment.</p

Season-specific carry-over of early-life associations in a monogamous bird species

accepte

Data from: Proto-cooperation: group hunting sailfish improve hunting success by alternating attacks on grouping prey

We present evidence of a novel form of group hunting. Individual sailfish (Istiophorus platypterus) alternate attacks with other group members on their schooling prey (Sardinella aurita). While only 24% of attacks result in prey capture, multiple prey are injured in 95% of attacks, resulting in an increase of injured fish in the school with the number of attacks. How quickly prey are captured is positively correlated with the level of injury of the school, suggesting that hunters can benefit from other conspecifics' attacks on the prey. To explore this, we built a mathematical model capturing the dynamics of the hunt. We show that group hunting provides major efficiency gains (prey caught per unit time) for individuals in groups of up to 70 members. We also demonstrate that a free riding strategy, where some individuals wait until the prey are sufficiently injured before attacking, is only beneficial if the cost of attacking is high, and only then when waiting times are short. Our findings provide evidence that cooperative benefits can be realized through the facilitative effects of individuals' hunting actions without spatial coordination of attacks. Such ‘proto-cooperation’ may be the pre-cursor to more complex group-hunting strategies

Causal evidence for the adaptive benefits of social foraging in the wild

Sociality is a fundamental organizing principle across taxa, thought to come with a suite of adaptive benefits. However, making causal inferences about these adaptive benefits requires experimental manipulation of the social environment, which is rarely feasible in the field. Here we manipulated the number of conspecifics in Trinidadian guppies (Poecilia reticulata) in the wild, and quantified how this affected a key benefit of sociality, social foraging, by investigating several components of foraging success. As adaptive benefits of social foraging may differ between sexes, we studied males and females separately, expecting females, the more social and risk-averse sex in guppies, to benefit more from conspecifics. Conducting over 1600 foraging trials, we found that in both sexes, increasing the number of conspecifics led to faster detection of novel food patches and a higher probability of feeding following detection of the patch, resulting in greater individual resource consumption. The extent of the latter relationship differed between the sexes, with males unexpectedly exhibiting a stronger social benefit. Our study provides rare causal evidence for the adaptive benefits of social foraging in the wild, and highlights that sex differences in sociality do not necessarily imply an unequal ability to profit from the presence of others.</p

Contrasting context-dependence of familiarity and kinship in animal social networks

Highlights • We studied which traits affect foraging associations and mate choice in geese. • We collected data on boldness, dominance, familiarity and genetic relatedness. • During foraging geese associated with familiar and genetically related geese. • During mate choice geese selected unfamiliar individuals. • There was no effect of boldness or dominance during foraging or mate choice. The social structure of a population is a crucial element of an individual's environment, fundamentally influencing the transfer of genes, information and diseases. A central question in social network analysis is how different traits affect associations within populations. However, previous studies of animal social networks have typically focused on a single predictor or stage in the life cycle whereas social interactions within populations are known to be dynamic and not fixed through time and/or context. Relatively few animal network studies have explored how individual traits affect decisions across different ecologically relevant contexts. We collected detailed behavioural data (personality, dominance, familiarity) and high-resolution genetic data from a flock of 43 captive barnacle geese, Branta leucopsis, to understand how these traits affect association patterns in two different evolutionary and ecologically highly relevant contexts: foraging and mate choice. Using a novel analytical framework for node label permutations, we found that barnacle geese preferentially associated with close kin and other individuals familiar from earlier in life when foraging, but selected unfamiliar partners during mate choice. We found no effect of either personality or dominance on foraging associations or mate choice. Our study shows how using social network analysis can increase our understanding of the drivers behind population structure (in our case kin selection and inbreeding avoidance). Moreover, our study demonstrates that social networks can be largely determined by long-term processes, in particular early life familiarity.