Captura coletiva de presas e interações agonísticas durante o forrageamento em Parawixia bistriata (Araneae: Araneidae)

Abstract

Orb-weavers colonial spiders that form aggregations can get many benefits compared to solitary species. The main benefit of aggregations is foraging success, as aggregated individuals are able to capture larger prey with the ricochet effect and cooperative capture, a phenomenon that occurs in only a few species. However, conflicts can occur during prey capture, even though they are less common than agonistic interactions during web construction or repair. In this context, our study investigated prey capture behavior in Parawixia bistriata (Araneidae), a colonial spider that occurs in the Brazilian Cerrado. We did field natural observations of P. bistriata foraging behavior and identified the main groups of intercepted prey. Additionally, we estimated the frequency of cooperative capture and the occurrence probability of conflicts during capture. We also conducted a field experiment of prey offer to investigate the effect of different vibrations in the web of different orders of insects captured (i.e., Lepidoptera or Orthoptera) and the effect of prey weight in the spider capture behavior and in the occurrence of conflicts. Moreover, intra-colonial weight variation during the development of the spiders was obtained for two generations, being compared between the months and the size of the colonies. The observations of intercepted prey showed variation in the amount and size of prey according to insect order. Cooperative behaviors were more common in small spiders and are replaced by an increase in the occurrence of conflicts as they grow. Both the tendency to cooperation and the occurrence of conflicts during prey capture were dependent on insect order and weight of prey captured. Moths are captured cooperatively more frequently than grasshoppers, and the contrary is observed for conflict interactions. Heavier individuals usually won the conflicts, and individuals that received the prey on their webs only won the conflicts when they were heavier than their competitors were. During the study, 21 colonies were sampled, represented by 3876 individuals (19-600 per colony). The inter-individual weight variation in each colony does not increase throughout their development, and is not dependent on the number of spiders in the colony. This study demonstrates how the social dynamic of this territorial spider species relies on the stage of development of the spiders and the perception of the prey intercepted, both the relationship with its size and behavior on the webs. The weight difference between the individuals on the colonies does not seem to be influenced by the stage of development of the spiders or the size of the colonies, but it is important at the individual level, as they fight for the monopoly of prey, especially when they are close to dispersion, and the bigger tend to win these conflicts over prey.