Size matters: Antagonistic effects of body size on courtship and digging in a wolf spider with non-traditional sex roles.

Body size, nuptial gift characteristics and courtship behaviour, among other traits, can reflect the quality of a potential mate and, thus, might be under sexual selection. To maximize their mating success, individuals can show behavioural plasticity in sexual context. Allocosa senex is a burrow-digging wolf spider that exhibits reversal in courtship roles and in sexual size-dimorphism expected for spiders. Males construct the mating refuge and females prefer males that build longer burrows, which are considered as nuptial gifts because they are delivered to them after mating. This study aims to determine whether male body size and female reproductive status influence burrow dimensions, courtship displays, female preferences and cannibalism rate in A. senex. For that purpose, we allowed males to construct burrows and performed sexual trials under laboratory conditions. Larger males were more courted by females, and in turn, they expressed more vibratory behaviours during courtship. However, and contrary to our expectations, smaller males constructed longer burrows. We suggest that males of A. senex exhibit size-dependent behavioural plasticity, and when they are smaller, they invest more in burrow construction to compensate their lower opportunities of courting intensively as larger males. In addition, females courted differentially according to their reproductive status, overriding male preferences for virgin females. This study opens several doors to future research regarding mutual choice in A. senex and the traits assessed by males and females during courtship, as well as about the influence of intrinsic and extrinsic factors shaping reproductive decision-making in this and other wandering spider species.

Sex and burrowing behavior and their implications with lytic activity in the sand-dwelling spider Allocosa senex.

The immune response can be costly. Studies in several arthropod species have indicated a trade-off between immunity and other life-history traits, including reproduction. In sexually dimorphic species in which females and males largely differ in their life history strategies and related energetic demands, we can expect to find sex differences in immune functions. Sex differences in immunity are well documented in vertebrates; however, we largely lack data from invertebrate systems. Lytic activity, the immune system's ability to lysate bacteria and viruses, has been widely used as a proxy for the strength of the immune response in several invertebrates. With this in mind, we used the burrowing wolf spider Allocosa senex to test differences in lytic activity between females and males. We also studied whether digging behavior affects the immune responses in this species. While females of A. senex construct simple refuges where they stay during the day, males construct deep burrows, which they donate to females after copulation. In accordance with our hypothesis, females showed higher lytic activity compared with males, and those males who dug showed higher levels of lytic activity than those that did not dig. Furthermore, male body condition and lytic activity did not correlate with burrow length, a trait under female choice in this species. Our results show sexual dimorphism in lytic activity responses, which are likely related to differences in life-history strategies and energetic requirements of each sex in A. senex spiders.

Predation among armored arachnids: Bothriurus bonariensis (Scorpions, Bothriuridae) versus four species of harvestmen (Harvestmen, Gonyleptidae).

Natural selection shapes prey-predator relationships and their behavioral adaptations, which seek to maximize capture success in the predator and avoidance in the prey. We tested the ability of adults of the scorpion Bothriurus bonariensis (Bothriuridae) to prey on synchronous and sympatric adults harvestmen of Acanthopachylus aculeatus, Discocyrtus prospicuus, Parampheres bimaculatus and Pachyloides thorellii (Gonyleptidae). In 72.5% of the cases B. bonariensis tried to prey on the harvestmen. The most successful captures occurred in the trials against A. aculeatus and D. prospicuus. In all the successful attacks the scorpions stung the prey between the chelicerae and consumed them, starting by the anterior portion of their bodies. The harvestmen used different defensive strategies such as fleeing before or after contact with the predator, exudating of chemical substances or staying still at the scorpion's touch. When scorpions contacted the chemical substances secreted by the harvestmen, they immediately rubbed the affected appendix against the substrate. However, exudating of chemical substances did not prevent, in any case, predation on the harvestmen. This is the first study showing the ability of scorpions to prey on different species of harvestmen, as well as the capture and defensive behaviors used by the predator and the prey.