Female choice may be linked to population density if expected encounter rates with potential mates affects choosiness (energy and risk engaged to express mate preferences). Choosiness should covary with male availability, which could be assessed using social cues available during development. We tested whether exposure of juvenile females to cues of male density affected mechanisms of choosiness of adult Latrodectus hasselti spiders in two experiments simulating natural contexts. Juvenile females were exposed to (1) volatile chemicals from two densities of adult males (airborne cues), and (2) tactile, vibrational, and chemical cues from adult males or other females (cohabitation cues). As adults, females mated readily, regardless of treatment, but there was strong evidence for post-copulatory mechanisms of choosiness in females exposed to cues of high male availability. These included abbreviated matings (both experiments), cannibalism of males before mating was complete (cohabitation), and, remarkably, a reduction in the successful placement of internal sperm plugs (cohabitation). These shifts decrease the likelihood that the first mate would monopolize paternity if the female chose to mate again. We conclude that female choosiness may impose strong selection on males despite high mating rates, and these effects can hinge on cues of male availability detected by juveniles.

Data are from two laboratory studies using the outbred offspring of field-captured female redback spiders (Latrodectus hasselti). Both studies examine how exposure to cues of male density while a juvenile affects the behaviour of adult females in terms of mating behaviours related to pre- and post-copulatory mechanisms of choosiness.

Study 1. Airborne pheromone experiment: This simulates conditions for females maturing in the field, which may be exposed to airborne pheromones from nearby males and other females. Females in their final two juvenile instars were held in a two-by-two design in which they were maintained on a high or low nutrient diet and exposed to airborne phermones from a high or low density of males (while female density was held constant). Ten family lines were used with four females from each family line randomly assigned to one of the four treatments. After females became sexually mature, each was paired with a single male from a different family line for mating trials, where males were size-matched across the 4 treatments to control for size-related differences in mating outcomes (see below). 

Study 2. Cohabitation experiment: This simulates the naturally-occuring encounters between final-instar females and with other spiders that live on their webs (juvenile females or adult males). This period of 'cohabitation' provides females with airborne, vibratory and direct contact cues from cohabitants. Females were randomly assigned to one of three treatments: a control with no cohabitants, a 'female' treatment with a juvenile female cohabitant, and a 'male' treatment with an adult male cohabitant (see paper for detailed methods). Females were checked daily for moulting and the total duration of the female's final instar was recorded, as well as the number of different spiders that had cohabited with the female prior to maturity. After females became sexually mature, each was paired with a single male from a different family line for mating trials (see below). In this experiment, males were not size-matched across treatments, so male mass was recorded as a measure of size and used as a covariate in analyses of mating outcomes.

Mating Trials: A common procedure was used for mating trials. Each female was placed on a frame to build a web. Males were introduced to the web and the interactions observed as well as video-recorded. Trials ended after 8 hours, when the male was dead, or when 2 hrs had passed following a copulation with no additional courtship. Mating outcome and progress variables were recorded as the trials proceeded, with some elements confirmed after trials by reviewing recordings. After mated females produced egg sacs, they were euthanized and their genitalia dissected to visualize the presence and location of sperm plugs.

Mating variables: In both experiments, we recorded the latency to the first copulation (min) for pairs that mated successfully, the number of copulations achieved, and the number of successfully placed sperm plugs (in this species, females have 2 sperm storage organs and a complete mating requires 2 copulations). In the cohabitation experiment, we also recorded whether sexual cannibalism occurred during trials and if so, whether the male was killed after a single copulation.

Data are in an excel spreadsheet, one tab per experiment. Missing values occur occasionally if observations were missed during mating trials and could not be extracted from videos, or if errors were made during the dissection of genitalia.