Infection-related sexual conflict in mating behaviors of wolf spiders
Description
Resistance to mating by females has been hypothesized as a tactic to assess potential mates and avoid undesirable ones. Previous studies show infection with the pathogenic bacteria, Pseudomonas aeruginosa, triggers a costly immune response and negatively impacts fitness in the wolf spider Schizocosa ocreata (Hentz 1844). Studies also show that infection can be transmitted during copulation, suggesting there are potential fitness costs associated with mating with an infected individual. We examined impacts of infection on mating interactions of male and female S. ocreata. As studies show infection can be detected through chemical cues, we tested whether males or females avoid mating with infected individuals when given the opportunity. We paired infected and uninfected (control) males and females and recorded their behavior. We found that mating outcome was independent of infection for males and females. While higher male courtship rates and more frequent female receptivity displays were associated with successful mating, we saw no direct effect of infection status on mating outcome. However, among spider pairs that did not mate, females were found to be significantly more resistant and aggressive toward infected males than control males. Male aggression, on the other hand, was greater in pairs that did result in mating. These results suggest sexual conflict in mating can be related to infection status, and that females can recognize infected males and alter their behavior in response.
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Steps to reproduce
Experimental infection: Bacteria stocks were kept in Copan Cryovials at -80C and grown on Luria broth media (1.0% Tryptone, 0.5% yeast extract, 1.0%NaCl, 1.5%agar). All plates containing bacteria were cultured prior to treatment and suspended in a sterile water solution with the concentration of 600 Colony forming units of bacteria per microliter determined by McFarland turbidity standards. Treatment occurred two-weeks post-maturity; individuals chosen for study were deprived of water for 24 hours to induce thirst. Then, they were presented with a 1 microliter droplet of either sterile water (control group) or water containing 600 Colony Forming Units (CFUs) of bacteria (infected group). Approximately 24-hours after treatment, males and females were paired for mating in all combinations of infected or control. Males and females were paired at random, while assuring relatively equal representation of each possible pairing; both infected, both uninfected, only male infected, only female infected. The mating arena was constructed using an 20cm diameter cylinder with a circular piece of filter paper lining the bottom as in previous studies (Meyer and Uetz 2019). Females were allowed to explore the arena for 5-10 minutes and lay silk prior to trial start. When trials began, the female was corralled under a vial and a male was introduced into the arena and given a two-minute acclimation period before the female was released. During these two minutes, males typically detected the female presence and began courting. After two minutes, the female was released, and the pair were allowed to interact for up to 1-hour. Trials ended when successful mating occurred or after 1-hour of interaction, allowing for variable trial lengths if mating was the outcome. Videos of mating trials were scored for behaviors of both the male and female subject in each trial. Males were scored for courtship behaviors (latency to court, number of jerky taps and leg waves), and aggressive behaviors (lunge, grab/grapple, forced mount). Females were scored for receptivity displays (slow pivot, tandem leg extend and settle); a sum of the three displays was calculated as a receptivity score as in previous studies. Female resistance (run away, escape male mount attempt) and aggression (lunges and/or cannibalization attempts), were also scored and expressed as counts. All statistical analyses were conducted in JMP® Pro 16 (16.0, SAS). 1. Generalized Linear Model with a binomial distribution(mate y/n) accounting for male and female infection status and their interaction. 2. GLM for mating success using infection status of both the male and the female and all behavioral elements measured. Variables in the model that were significant predictors of mating outcome were analyzed independently. 3. GLM analyses (w/Poisson distributions) were performed on the variables identified in prior model, accounting for both mating outcome and infection status.