Mirror image stimulation could reverse social-isolation-induced aggressiveness in the high-level subsocial lactating spider

Abstract

Conspecific aggressiveness often increases after social isolation for species that are not entirely solitary, and this increased aggression could also be reversed after resocialization. However, literature on this aggression plasticity refers to either permanently social or low-level subsocial species in invertebrates. Examinations of conspecific aggressiveness reversibility in high-level subsocial invertebrates, in which offspring cohabitate with parents for a certain period of time after sexual maturation, would enhance the understanding of the role of conspecific-aggression plasticity in social evolution. Here, using the lactating spider Toxeus magnus, which exhibits extremely high-level subsociality, we assessed three questions. (1) Is its conspecific aggression affected by social living and/or kinship? The results indicated that conspecific aggression increased after social isolation, while kinship did not affect aggressiveness. (2) Could the social-isolation-induced higher aggression be reversed after resocialization? The results showed that the increased aggression of the spiders could be reversed 3 days after resocialization. (3) What is the proximate mechanism that caused the aggression reversibility by resocialization? A simulated resocialization experiment in which single spider was provided with mirrors demonstrated that the visual cues of conspecifics alone could reverse the aggression after 6 days. These results indicate that the high-level subsocial invertebrate showed aggressiveness reversibility without chemical cues. This is more similar to permanently social species rather than to low-level subsocial species, and visual cues could be vital to induce aggression change. These results suggest that conspecific-aggression reversibility might play a key role in social evolution and may functionally enhance species’ adaptiveness under variable conditions.

Context-dependent and seasonal fluctuation in bottlenose dolphin (Tursiops truncatus) vocalizations

Abstract

A fundamental question in animal behaviour is the role of vocal communication in the regulation of social interactions in species that organise themselves into social groups. Context dependence and seasonality in vocalizations are present in the communication of many species, although very little research has addressed this dependence in marine mammals. The study presented here examined variations in the rate at which free-ranging dyads of bottlenose dolphins emit social-signals in an effort to better understand the relationship between vocal communication and social context. The results demonstrate that changes in the social-signal production in bottlenose dolphins are related to the sex of the partner, mating season and social affiliation between the components of the dyad. In a context of foraging behaviour on the same feeding ground, mixed (male–female) dyads were found to emit more pulsed burst sounds during the mating season. Another relevant aspect of the study seems to be the greater production of agonistic social-signals in the dyads formed by individuals with a lower degree of social affiliation. Overall, this study confirms a clear relationship between dyad composition and context-specific social-signals that could reflect the motivational state of individuals linked to seasonal changes in vocal behaviour.

Through the eyes of a hunter: assessing perception and exclusion performance in ground-hornbills

Abstract

Logical inference, once strictly associated with spoken language, is now reported in some non-human animals. One aspect of logical inference, reasoning by exclusion, has been traditionally explored through the use of the cups task (cup A and cup B, if not cup A, then exclude cup A and select cup B). However, to fully understand the factors that drove the evolution of logical processes in animals, this latter paradigm needs to cover a taxonomically broader spectrum of species. In this study, we aimed to test the capacity of Southern ground-hornbills (Bucorvus leadbeateri) to show exclusion performance in a two-way object-choice task. First, we determined whether subjects could perceive and choose correctly between two containers (one rewarded, one unrewarded) using visual or acoustic cues (sensory phase). If successful, individuals were then presented with three experimental conditions (test phase): Full information (content of both cups revealed), Exclusion (content of the empty cup revealed), and Control (no content revealed). During the sensory phase, ground-hornbills succeeded in choosing the rewarded container only in the visual modality. Birds were able to select the rewarded container more than would be expected by chance in the Full information condition, but their performances were equal to chance in the Control condition. The without-learning performance of two individuals within the Exclusion condition indicates that this task is not trivial, which invites further investigation on this species’ capacity to represent the dependent relationship between the cups (true logical inference).