Assessing seepage-spring dwelling amphipod and isopod resilience to environmental warming using stable isotopes as a metabolic plasticity proxy

In response to climate change, species may shift their ranges toward the poles, alter their phenotypes, change their physiological resilience to rapidly rising temperatures, or some combination of the three. Physiological resilience is particularly important for species that are unable to migrate. For ectotherms, metabolic rates adjust to environmental temperatures; however, the degree to which their metabolism can adapt to temperature change is not well studied. Assessing invertebrate resilience to a rapidly warming environment is crucial for gauging their ability to adapt to climate change. Resilience to the metabolic stress associated with rapid temperature shifts may be assessed by determining how flexible the metabolic rate is at different temperatures. Here we examine the degree of metabolic plasticity (assessed via stable carbon isotope turnover proxy) for the adults of two species of invertebrates, the amphipod Gammarus minus and the isopod Caecidotea kenki, at temperatures ranging from 5°C to 18°C over the course of 24 days. Not surprisingly, isotope turnover increased with temperature for both species. The carbon isotopic endmembers were maple leaves (−30.4 ± 0.2‰, N = 20) and corn leaves (−12.2 ± 0.4‰, N = 20). Half-lives were between 60 and 90 days at 5°C and between 20 and 35 days at 18°C. G. minus showed a small but significantly greater variation in metabolic response to elevated temperatures than C. kenki, suggesting that it has a greater potential for successfully adapting to a warming climate.