Evolutionary adjustment of developmental time in mixed populations of flour beetles

IN dense, synchronised laboratory populations of the flour beetle Tribolium castaneum (referred to here as CS), there is a substantial amount of cannibalism of the earliest pupating individuals by large larvae, thus creating the possibility of strong selection pressure against fast development 1–3 . An opportunity to investigate this possibility was provided by the existence of a set of mixed-species cultures that had been maintained for several years. These cultures contain CS and T. confusum (CF) in varying proportions. Since developmental time of CF is from 1–2 d longer than CS 4 , the null hypothesis of no differences in developmental time of CS from the various cultures could be tested against the alternative that developmental time of CS would increase as the proportion of slower developing CF in the culture increases. I report here that developmental times do in fact adjust in mixed populations of these flour beetles.