Extreme temperature events directly and indirectly mediate evolutionary adaptation of zooplankton metabolic rate

Abstract

Under global warming, understanding the evolutionary adaptation of ectotherms resting metabolic rate (RMR) is critical for predicting long-term populations' response to temperature increases. While several studies have evaluated metabolic rate evolution under different thermal context, most focused on space-for-time substitutions rather than assessment of populations' adaptation over time. Here, applying the method of resurrection ecology, we used sediment cores as an archive of populations' evolution and hatched ephippia from different sediment layers to examine the metabolic evolution of modern vs. ancient Daphnia longispina populations. Focusing on an oligotrophic subalpine lake, for which temperature has been monitored for almost a century, we were able to link population response to historical thermal contexts. We demonstrate that modern (2021) clonal lines exhibit a 60% higher RMR than ancient ones (1997) when measured at 20°C. The higher RMR correlated with reduced juvenile growth rates at 20°C but increased survival rates at high temperatures, with a higher thermal limit 2°C higher in modern populations. These findings reflect a trade-off favoring survival over growth under warming and likely result from increased oxygen uptake capacities, which provide an advantage at high temperatures but constrain individual energy budgets at non-stressful temperatures. Overall, this study suggests that survival at extreme weather events, such as heatwaves, may play an important role in shaping the RMR adaptation of Daphnia and, more generally, zooplankton populations.