Ecophysiological responses to temperature of the "killer shrimp" Dikerogammarus villosus: is the invader really stronger than the native Gammarus pulex?

With global climate changes, biological invasions are considered to be one of the main causes of the decline of freshwater biodiversity. In this context, predicted increases in global temperature may alter the geographical distributions of native and invasive species. The purpose of our study was to examine the metabolic, behavioral and physiological responses to short-term temperature acclimation of two widely distributed species (the most successful European invader, Dikerogammarus villosus, and its main victim, Gammarus pulex), in order to estimate the potential effect of global warming on its invasion of freshwater ecosystems. Our results show that D. villosus is more vulnerable to high temperatures than G. pulex. The native species seems to be best adapted to intermediate temperatures (10-20°C) with a possibility of adjustment to "extreme" temperatures (5-27°C), whereas the "killer shrimp" D. villosus seems best adapted to lower temperatures (5-10°C) with a limited possibility of adjustment above 20°C. In the light of our results, global warming is likely to be less favorable to the invasive species. However, D. villosus showed reduced metabolic and activity rates, associated with higher glycogen content. This adaptive strategy was interpreted as having functional advantages, allowing D. villosus to successfully invade harsh and/or unpredictable biotopes. In addition, our results show that glycogen stores may be used as a powerful indicator of the optimal thermal window for aquatic ectotherms.