ANGILLETTA, M.J.*; DUNHAM, A.E.; Indiana State Univ., Terre Haute; Univ. of Pennsylvania, Philadelphia: The temperature-size rule in ectotherms: simple evolutionary explanations may not be general

In many organisms, individuals in colder environments exhibit slower growth but larger adult body size. This widespread pattern is embodied by two well-established rules: Bergmann’s rule and the temperature-size rule. Optimization models predict that organisms should grow to be larger in colder environments if growth efficiency decreases with increasing environmental temperature. Using data from 97 laboratory experiments including 58 species, we demonstrate that there is little evidence that the growth efficiencies of ectotherms are negatively related to environmental temperature within the thermal ranges that are relevant to the temperature-size rule. Instead, growth efficiency was either positively related to or insensitive to environmental temperature in the majority of cases (73/89 and 18/24 cases for gross growth efficiency and net growth efficiency, respectively). Two possibilities merit consideration. First, high temperatures may impose constraints on growth that only arise late during ontogeny; this simple and potentially general explanation is supported by the fact that the thermal optimum for growth efficiency (and growth rate) appears to decrease with increasing body size. Alternatively, there may not be a simple, general explanation for relationships between temperature and body size observed in ectotherms. If the latter possibility is true, the best approach would be to generate and test theories that are tailored specifically to ectotherms with similar behavior and physiology.