The same species, not the same invader: Metabolic responses of genetically distinct invasive populations of Dikerogammarus villosus (Sowinsky, 1894) and their intraspecific hybrid to environmental stresses

Abstract

1. Climate change has a profound impact on ectotherms, which suffer suboptimum thermal conditions in their native areas or spread to previously unavailable locations. However, it is often neglected that responses to environmental changes are likely a population level, rather than species-specific phenomenon. 2. Two groups (Western and Eastern) of the invasive Ponto-Caspian amphipod Dikerogammarus villosus independently spread in Europe from isolated, genetically distinct source populations living in the Danube and Dnieper deltas, respectively. They are expected to meet in the near future in Polish inland waters. This makes this species a perfect model to investigate the intraspecific variability in responses to environmental changes, as well as effects of hybridization between different genetic units on invasiveness. 3. We scaled maximal metabolic rate (MMR), standard metabolic rate (SMR), and aerobic scope (AS, a measure of physiological performance) of D. villosus at different temperatures and oxygen levels to check differences in responses to environmental changes among the distinct invasive groups and their hybrid. 4. With increasing temperature, the AS scaling exponent of the Western group decreased, whereas AS of the Eastern group was unaffected by temperature. In result, large Western group individuals showed a lower AS at a high temperature, compared to low temperature and to the Eastern group individuals. Oxygen reduction decreased MMR and AS scaling exponents regardless of amphipod group, suggesting that larger individuals experienced a greater reduction in these parameters under low oxygen conditions. Although parental groups reduced their AS in response to oxygen reduction, AS of the hybrid remained stable. 5. In conclusion, organism responses to climate change depend on intraspecific variation, which should be considered in studies related to this topic. Furthermore, D. villosus appears sensitive to oxygen deficits and temperature changes (especially the Western group and large individuals), but intraspecific hybridisation can enhance the environmental tolerance of invaders.