Colony-level aggression escalates with the value of food resources

BACKGROUND

Theory predicts that the level of escalation in animal contests is associated with the value of the contested resource. This fundamental prediction has been empirically confirmed by studies of dyadic contests but has not been tested experimentally in the collective context of group-living animals. Here, we used the Australian meat ant Iridomyrmex purpureus as a model and employed a novel field experimental manipulation of the value of food that removes the potentially confounding effects of nutritional status of the competing individual workers. We draw on insights from the Geometric Framework for nutrition to investigate whether group contests between neighbouring colonies escalate according to the value to the colony of a contested food resource.

RESULTS

First, we show that colonies of I. purpureus value protein according to their past nutritional intake, deploying more foragers to collect protein if their previous diet had been supplemented with carbohydrate rather than with protein. Using this insight, we show that colonies contesting more highly valued food escalated the contest, by deploying more workers and engaging in lethal 'grappling' behaviour.

CONCLUSION

Our data confirm that a key prediction of contest theory, initially intended for dyadic contests, is similarly applicable to group contests. Specifically, we demonstrate, through a novel experimental procedure, that the contest behaviour of individual workers reflects the nutritional requirements of the colony, rather than that of individual workers.

Evolution of chemical interactions between ants and their mutualist partners

Mutualism is the reciprocal exploitation of interacting participants and is vulnerable to nonrewarding cheating. Ants are dominant insects in most terrestrial ecosystems, and some aphids and lycaenid butterfly species provide them with nutritional nectar rewards and employ ants as bodyguards. In this review, I discuss how chemical communication based on condition-dependent signaling and recognition plasticity regulate the payoff of interacting participants. I argue that the selfishness of both participants explains the signaling and communication among participants and contributes to the stability of these mutualisms. Uncovering the origin and maintenance of mutualistic association of ants will come from future research on ant collective behavior, the genetic and neural basis of cooperation, and a deeper understanding of the costs and benefits of these interactions.

Nutritional regulation influencing colony dynamics and task allocations in social insect colonies

In this paper, we use an adaptive modeling framework to model and study how nutritional status (measured by the protein to carbohydrate ratio) may regulate population dynamics and foraging task allocation of social insect colonies. Mathematical analysis of our model shows that both investment to brood rearing and brood nutrition are important for colony survival and dynamics. When division of labour and/or nutrition are in an intermediate value range, the model undergoes a backward bifurcation and creates multiple attractors due to bistability. This bistability implies that there is a threshold population size required for colony survival. When the investment in brood is large enough or nutritional requirements are less strict, the colony tends to survive, otherwise the colony faces collapse. Our model suggests that the needs of colony survival are shaped by the brood survival probability, which requires good nutritional status. As a consequence, better nutritional status can lead to a better survival rate of larvae and thus a larger worker population.