Clonal thermal preferences affect the strength of the temperature-size rule

Abstract

The issue of trade-offs among traits is of special interest in evolutionary ecology. We hypothesized that the temperature-size rule (TSR) may be affected by the level of thermal specialization and that this pattern may be traded off with the temperature-dependent potential for population growth rate. We used six parthenogenetic rotifer clones previously exposed to different thermal conditions. We tested hypotheses on the relationships between (i) thermal acclimation and clone body size, (ii) thermal preference and fitness, and (iii) thermal specialization and strength of the TSR (the slope of response). Positive verification of (i) makes it justifiable to refer the other investigated traits as thermal preference. Addressing the issues (ii) and (iii) is our pioneering contribution to the question of whether the strength of the size-to-temperature response differs across life strategies. Interclonal differences in female body size were examined in common garden conditions at 25 °C. We estimated the population growth rate and strength (= slope) of the size-to-temperature response across four thermal regimes: 15, 20, 25, and 30 °C. Thermal acclimation of the clones was related to body size, with clones acclimated to higher temperatures being smaller. Warm-acclimated clones had a narrower thermal range (= were more specialized). The TSR was stronger in rotifers acclimated to intermediate thermal conditions than in specialists.