Understanding how demography affects the intensity and form of sexual selection is a major goal of behavioural ecology. Phiddipus clarus is an ideal model for illucidating such links because there is evidence for inter-and intra-sexual selection during a brief but intense mating season (June August) during which the mode of inter-male competition and the level of female choosiness shifts along with shifts in population density. Our past work on this species has demonstrated that inter-male competition is mediated by body size and signalling behaviours, that inter-female competition over refugia leads to intense, injurious fighting, and that the benefit of large size for males changes over time as demographic parameters and the mode of competition shifts in nature. This season, we will (1) ask how polyandry affects selection on male traits by using field-caught individuals in laboratory studies of paternity, (2) examine how female fighting tactics shift as a function of mating status using field observations and laboratory-staged interactions, and (3) determine correlations between male anatomical traits, longevity, physiological performance, and sperm production. This work will add to our body of work on this species, which we hope to develop into a model system in sexual selection.