Effects of temperature on cell size and number in the yellow dung fly Scathophaga stercoraria

Abstract

(1) A number of hypotheses suggest that the temperature-size rule (larger at cooler temperatures), and consequently Bergmann clines in whole-organism body size (larger at higher latitudes), may be a mere consequence of processes at the cellular level, i.e., a physiological constraint. (2) We show that in the yellow dung fly, Scathophaga stercoraria (Diptera: Scathophagidae), the temperature-size rule holds for wing cell and ommatidia size. Increases in cell number made up two-thirds (eye) to three-quarters (wing) of the increase in organ size. Temperature effects on body size can be fully explained by its effects on cell size and number. (3) Our study adds to the generality of previous results in Drosophila spp. The physiological constraint hypothesis remains viable as a proximate, non-adaptive explanation for the temperature-size rule in ectotherms.