Ovigerous Female Amphipods (Gammarus pseudolimnaeus) Face Increased Risks from Vertebrate and Invertebrate Predators

We investigated the mortality rates of male and female amphipods resulting from stickleback fish Culaea inconstans) and dragonfly nymphs (Basiaeschna janata) predation. Both predators consumed significantly more ovigerous female amphipods than non-ovigerous females or males in 24-h trials. Stickleback fish consumed more non-ovigerous females than males, whereas dragonflies consumed more males than non-ovigerous females. These results were consistent across trials conducted under ambient light-dark regimes and those conducted in the absence of light, although overall mortality rates were highest in light trials. There were no significant differences in the recorded behaviors of the two predators. However, the behavior of ovigerous females differed significantly from that of males and non-ovigerous females, which may help to explain the overall differences in mortality. These results suggest that female amphipods incur a significant cost of increased predation risk associated with maternal care.