Chronic exposure to danger induces morphological, physiological, and behavioural responses that vary by sex in crayfish

Abstract Prey species show a range of responses to perceived danger in their environments, and these responses can have substantial effects at the population, community, and ecosystem levels. In many aquatic systems, freshwater crayfish are ecologically important and are preyed on by many aquatic and terrestrial species. Their responses to danger, therefore, may play an important role in regulating aquatic communities. We report results of an experiment to examine morphological, physiological, and behavioural responses to extended exposure to alarm cues, and consider effects across ontogenetic stages and between sexes of the crayfish Faxonius virilis. We maintained crayfish over their summer growth period with and without intermittent alarm cue exposure. After they moulted into their autumn reproductive form, we compared measures of growth, morphological colour change, and days to reach reproductive readiness. We also carried out a behavioural assay to examine effects on foraging. Male crayfish with chronic exposure to alarm cues showed significantly less growth in overall body size and chela size, and substantially lower magnitude change in colour of the dorsal chela. These same effects were not noted in females; however, females exposed to alarm cues had significantly delayed time to reproductive readiness. In addition, we found that alarm-cue exposed males, but not females, showed significant differences in their foraging behaviour, and were less likely to consume food within the experimental period than control males. Further investigation is warranted to increase understanding of whether and how these responses to danger cues affect population and community ecology in aquatic systems.