Rapid evolution of unimodal but not of linear thermal performance curves inDaphnia magna

Abstract

Species may cope with warming through both rapid evolutionary and plastic responses. While thermal performance curves (TPCs), reflecting thermal plasticity, are considered powerful tools to understand the impact of warming on ectotherms, their rapid evolution has been rarely studied for multiple traits. We capitalized on a 2-year experimental evolution trial in outdoor mesocosms that were kept at ambient temperatures or heated 4°C above ambient, by testing in a follow-up common-garden experiment, for rapid evolution of the TPCs for multiple key traits of the water flea Daphnia magna . The heat-selected Daphnia showed evolutionary shifts of the unimodal TPCs for survival, fecundity at first clutch and intrinsic population growth rate toward higher optimum temperatures, and a less pronounced downward curvature indicating a better ability to keep fitness high across a range of high temperatures. We detected no evolution of the linear TPCs for somatic growth, mass and development rate, and for the traits related to energy gain (ingestion rate) and costs (metabolic rate). As a result, also the relative thermal slope of energy gain versus energy costs did not vary. These results suggest the overall (rather than per capita ) top-down impact of D. magna may increase under rapid thermal evolution.

Temperature adaptation and its impact on the shape of performance curves inDrosophilapopulations

“…In any case, our work provides stronger support for the idea that thermodynamic constraints play a major role in shaping thermal responses across populations along a latitudinal gradient, and evolution can only partly compensate for these constraints [47,48]. In this sense, adaptive responses can be detected by comparing the TPCs along the whole temperature range (figure 3 a,d ): cold-adapted populations tend to exhibit higher metabolism and egg-to-adult survival at lower temperatures, whereas the opposite is true for warm temperatures.…”