Move on or take the heat: Can life history strategies of freshwater mussels predict their physiological and behavioural responses to drought and dewatering?

Freshwater organisms have developed different physiological, behavioural and life history strategies to cope with drying events. Although freshwater mussels (Unionidae) are endangered and drought and dewatering events pose a major threat, especially in the southern United States, little is known about their responses to such events and how physiology, behaviour and life history strategies may be linked. Our goal was to examine whether and how behavioural responses to dewatering and physiological tolerances to desiccation are linked in five species of freshwater mussels (Unionidae) within Texas, including two state-threatened species (Cyclonaias petrina and Lampsilis bracteata) and one federally endangered species (Popenaias popeii), and to explore how differences in responses relate to life history strategies. We measured horizontal and vertical movements under three dewatering rates and assessed desiccation tolerance by examining survival after emersion at 30 and 40 degrees C with laboratory experiments. Amblema plicata and C. petrina had the lowest horizontal movement rates and the highest desiccation tolerances, whereas L. bracteata and L. teres were less tolerant to desiccation, but more mobile. P. popeii were intermediate in its responses. Our results show that differences between species in their behavioural response to dewatering and physiological tolerance to desiccation tend to be associated with differences in life history strategies or may be explained by differences in adaptation to certain habitat conditions. We propose a life history strategy-based framework for responses of mussels to drying events, which may be applicable to other taxa.