Precopulatory mate guarding affects predation risk in two freshwater amphipod species

Abstract

Contact mate guarding may increase predation risk in the presence of active, size-selective predators by increasing the apparent size or decreasing the escape ability of an individual. These same characteristics may, however, make paired individuals less vulnerable to sit-and-wait, non-size-selective predators. Because the costs and benefits associated with mate guarding are likely to depend on local ecological conditions, species or populations should vary in the duration of the guarding phase. In this study, I investigate whether precopulatory mate guarding increases an individual's predation risk for two freshwater amphipod species within the Hyalella azteca species complex that experience different predators. When larval dragonflies, Anax junius and Tramea lacerata, were used as predators in laboratory trials, single, unpaired individuals were more likely to be consumed than paired individuals. Conversely, predatory fish consumed paired females more often than single females. Therefore, the short precopulatory mate guarding duration observed in the species that co-occurs with predatory fish may be due to habitat-specific, predator-driven costs associated with precopulatory mate guarding. Furthermore, the predation cost associated with precopula was greater for females than males when predatory fish were used as predators, implying that intersexual conflict over the duration of the guarding period may be more intense for the species that co-occurs with predatory fish.