A biophysical interpretation of temperature-dependent body size in Drosophila aldrichi and D. buzzatii.

The temperature-size rule, the observation that most ectotherms grow faster but reach smaller size at higher temperatures, has defied a general explanation. Here, the temperature-size rule in Drosophila aldrichi and Drosophila buzzatii is investigated, using data on development rate and adult dry weight at nine temperatures. In both species the linear regression of dry weight on temperature is negative. The data are used to infer the potential for a description of temperature dependent size by biophysical modelling. The biophysical Sharpe-Schoolfield model for biological rates and its derivative model for adult weight yield detailed patterns for the two species' development rate, growth rate, and adult weight. These detailed patterns do not confirm the existence of a simple temperature-size rule. The species differ significantly in the values of the parameters in the Sharpe-Schoolfield model, and as a consequence in different patterns of weight over temperatures. The different parameters of the Sharpe-Schoolfield model play distinct roles in the patterns of weight over temperatures. A temperature-size rule as a negative regression of weight on temperature might statistically follow from an upper temperature boundary for growth that is lower than the upper temperature boundary for development; as such a relation between the upper temperature boundaries for growth and development would lead to a decrease of weight at high temperature.