Evolução do forrageamento cooperativo em pseudoescorpiões: Efeitos das variações dos tipos de presas sobre a seleção de personalidades

Abstract

The pseudoscorpion Paratemnoides nidificator is a generalist predator that captures large arthropods that live on tree trunks. Few pseudoscorpions species show some degree of sociality. We investigated how colonies of the pseudoscorpion P. nidificator adjust their cooperative capture behavior under a situation of changing prey types as a simulation of variation in prey availability. We hypothesized that colonies would be more efficient at prey capture under repeated exposure to the same prey, and that the change in the availability of prey would be followed by new behavioral adjustments to adequately exploit the new prey. Eight experimental colonies housed in the laboratory received repetitions of three different ant species as prey. The number of pseudoscorpions attacking the prey, the number of behavioral acts, and the time expended subduing prey were evaluated as measures of prey capture performance, in relation to repetitive exposure to the same prey and also in relation to prey type changes. However, only individuals’ recruitment significantly responded to prey type exposure. Prey capture behavior was heterogeneous among colonies, resulting in highly variable behavioral responses. Colonies showed a tendency toward increasing capture success through repeated prey type exposure. However, 50% of the colonies were unable to capture the new prey type and died of starvation. Although it is a generalist predator, prey capture behavior could depend on different coordination components for subduing and handling large prey. Therefore, changes in prey availability could cause the attenuation of a cooperative relationship in some colonies, making them more prone to failure during capture.

Behavioral variation among individuals of the same species is known to be one of the factors that modulates the viability of a social group. In animal species that have complex social lives, individuals who exert more influence over others are called “keystone” individuals within the social structure. The presence of these individuals in the social group can result in greater success during foraging events, increase in body mass, and a higher population survival rate. The pseudoscorpion species Paratemnoides nidificator has elaborated sociality, being a useful object of study to investigate the influence of key individuals on the foraging of the colony. Thus, this study aimed to analyze how the presence of key individuals modulates the dynamics of cooperative hunting in colonies of the social pseudoscorpion P. nidificator. The following hypotheses were tested: if (1) keystone individuals exert influence over the other components of the group, (2) key individuals’ actions can be measured by previous experience, (3) keystone individuals have positive effects on the social group, making the group more efficient during cooperative foraging events. To this end, experimental studies were carried out in a laboratory setting, which allowed the observation of all the behaviors performed during foraging events, and also the isolation of effects such as interference from unwanted prey. The metrics ‘latency to the beginning of prey attack’, the ‘time required to perceive and begin to attack the prey, the ‘number of individuals attacking the prey’ and the ‘success rate and failure rate’ were used to evaluate the ability to subdue prey. These metrics are directly influenced by features of group composition and are often used to evaluate efficiency in social animals. We expected that the keystone presence would positively modify those metrics of the foraging behavior in P. nidificator. We found an increase in the proportion of successful attack events in the presence of keystone individuals. There was a reduction in the latency to the beginning of the attack and in the time required to kill prey, and an increase in the number of individuals participating in the attacks. In addition, the influence of these individuals was more easily visualized when analyzing the predation of the exotic prey Palembus dermestoides, when inferring the number of individuals participating in the attacks. The largest grouping in P. nidificator benefited the group because it enabled reduction in the time and energy spent during each attack event and allowed investment in more foraging events. As a result, there was a greater increase in body mass and less intraspecific aggression. Thus, the influence of keystone individuals on the colonies of P. nidificator seems to have a direct reflection on fitness gain, group plasticity, and group viability.