Fight or flight: agonistic interactions between females of Acanthogonatus centralis Goloboff 1995 (Araneae, Mygalomorphae)

Using a resident (R)–intruder (I) paradigm, 132 encounters between female Acanthogonatus centralis were investigated in order to study its intrasexual interactions and aggressiveness. We also examined the effect of presumed increased hunger levels on the incidence of killing and cannibalism. We selected 3 groups with different satiation levels: medium group (M), low group (L), and high group (H). Interactions took place in 79.54% of the trials. Aggression by lunges or bites was observed in 21.96% of encounters. Spiders made foreleg vibrations and touched the silk, which functioned as an aggression-attenuating mechanism. Other general behaviors observed include threat behavior and hug behavior. We found significant differences between charges and retreats in the following treatments: M(R)–M(I), L(R)–L(I), H(R)–H(I), and H(R)–M(I). During encounters we observed 9 cases of cannibalism between females. Interactions were predominantly nonaggressive, at least in the resident–intruder paradigm. Intraspecific predation was not a response to presumed increased hunger. Future approaches to agonistic behavior and cannibalism should include analyses of diet characteristics over longer periods and of experience in determining the outcome of encounters between adult females.