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

Abstract

21Genetically similar organisms act as a powerful study system for the subtle differences in various 22 aspects of life histories. The issue of trade-offs among traits is of special interest. We used six 23 parthenogenetic rotifer clones previously exposed to different thermal laboratory conditions. 24 Interclonal differences in female body size were examined in common garden conditions. We 25 estimated the population growth rate and strength of the size-to-temperature response across four 26 thermal regimes. We tested hypotheses on the existence of the relationships between (i) thermal 27 acclimation and species body size, (ii) thermal specialization and fitness and (iii) thermal 28 specialization and strength of the temperature-size rule. Positive verification of (i) would make it 29 justifiable to refer the other investigated traits to thermal preference and, further, to thermal 30 specialization. Addressing the issues (ii) and (iii) is our pioneering contribution to the question on 31 the strength of size-to-temperature response as differing across life strategies. We hypothesized 32 that this plastic response may be affected by the level of thermal specialization and that this 33 pattern may be traded off with the temperature-dependent potential for population growth rate. 34Additionally, we investigated the differences in reproductive strategy (number of eggs laid by a 35 female and female lifetime duration) in one temperature assumed optimal, which acts as an 36 important supplement to the general clonal life strategy. We confirmed that the thermal 37 acclimation of a clone is related to body size, with clones acclimated to higher temperatures 38 being smaller. We also found that warm-acclimated clones have a narrower thermal range (= are 39 more specialized), and that the temperature-size rule is stronger in rotifers acclimated to 40 intermediate thermal conditions than in specialists. Our results contribute into the issue of trade-41 offs between generalist and specialist strategies, in the context of plastic body size respone to 42 different temperatures.43 3 specialization 45 46 Optimal allocation theory states that living organisms optimize their strategies of the allocation of 48 limited resources among the functions associated with maintenance, repair and reproduction. Any 49 given set of abiotic and biotic conditions provides a unique, optimal strategy, and trade-offs 50 among life history traits are at the base of such strategies (Cody ). The pattern of limited resources causing the traits to 52 trade is complex and troublesome with regard to straightforward inferences and conclusions 53 (Acerenza 2016; Lailvaux and Husak 2017; Roff and Fairbairn 2007). Going a step further, 54DeWitt (2016) stressed the importance of including not only trait means but also the shape (i.e., 55 skew) of phenotypic plasticity in studies on life-history optimization in ecological contexts. 56According to the author, the strength of phenotype distribution across environments should be 57 optimized by means of nat...