ANGILLETTA, M.J.*; SEARS, M.W.; STEURY, T.D.; Indiana State University, Terre Haute ; Indiana State University, Terre Haute ; Indiana State University, Terre Haute : Temperature, growth rate, and body size in ectotherms: fitting pieces of a life history puzzle

In the majority of ectothermic species studied to date, individuals in warmer environments grow faster but attain a smaller size at maturity than individuals in colder environments. This phenomenon is puzzling because few evolutionary models predict a relatively small size at maturity in environments that are conducive to rapid growth, such as warm environments. Furthermore, those models that do make such a prediction are based on invalid assumptions about physiological and thermal constraints on growth. We attribute the failure to explain thermal reaction norms to three factors. First, optimal thermal reaction norms for growth rate and size at maturity have been modeled separately, but these traits actually evolve in concert. Second, existing theories make unrealistic assumptions about the tradeoffs that influence the evolution of reaction norms. Third, tests of theory rarely consider genetic constraints. We will discuss a theoretical approach that overcomes the limitations of previous approaches. This approach considers thermal reaction norms for growth rate and body size as part of a developmental reaction norm � a multivariate phenotype that provides an ontogenetic perspective to the analysis of body size. We will highlight results to show that this approach might enable one to explain some of the key features of thermal reaction norms for growth rate and body size in ectotherms. Finally, we will consider the roles of functional and genetic constraints in the evolution of thermal reaction norms, emphasizing the need to integrate the two in future studies.