Drought Cues Induce Dispersal in an Aquatic Beetle, Haliplus punctatus (Coleoptera: Haliplidae)

Authors: Natalie Constancio, Sophie Dunkelberger, Lauren Musial, Gaby Ortiz, Elizabeth Ruden, Kate Boersma

Year: 2018

Abstract

Desert-dwelling aquatic invertebrates possess a wide array of behavioral adaptations that allow them to survive harsh and highly variable environmental conditions. Dispersal and burial are two opposing behaviors that have been observed during droughts, but it is unclear which of the many drought-associated environmental cues trigger these behaviors. We investigated this question in a little-studied species of crawling water beetle, Haliplus punctatus. These small beetles inhabit arid-land aquatic habitats with hydroperiods ranging from permanent ponds to temporary streams. They are able to bury and disperse between sites, making them ideal model organisms for examining behavioral responses to extreme environmental conditions. We conducted a fully factorial experiment in which we recorded burial and dispersal behaviors in H. punctatus in response to three levels of three drought-associated environmental variables: temperature (8, 16, and 24°C), conductivity (111, 705, and 2868?S/cm), and evaporation (to 0.5, 1.5, and 2.5cm water depth), for a total of 27 treatments with 10 beetles in each treatment. We observed that neither conductivity nor evaporation affected beetle behavior. Temperature affected both burial and dispersal, although in opposite directions. Beetles were more likely to disperse at high temperature, and bury at low temperature. These observations suggest that beetles have multiple, opposing behavioral strategies that can both be triggered by changes in temperature. Given predictions of more extreme summer temperatures across the North American deserts, our results suggest that we may expect to see more dispersal of crawling water beetles in the future.