Effects of assay conditions in life history experiments with Drosophila melanogaster

Selection experiments with Drosophila have revealed constraints on the simu ltaneous evolution of life history traits. However, the responses to select ion reported by different research groups have not been consistent. Two pos sible reasons for these inconsistencies are (i) that different groups used different environments for their experiments and (ii) that the selection en vironments were not identical to the assay environments in which the life h istory traits were measured. We tested for the effect of the assay environm ent in life history experiments by measuring a set of Drosophila selection lines in laboratories working on life history evolution with Drosophila in Basel, Groningen, Irvine and London. The lines measured came from selection experiments from each of these laboratories. In each assay environment, we measured fecundity, longevity, development time and body size. The results show that fecundity measurements were particularly sensitive to the assay environment. Differences between assay and selection environment in the sam e laboratory or differences between assay environments between laboratories could have contributed to the differences in the published results. The ot her traits measured were less sensitive to the assay environment. However, for all traits there were cases where the measurements in one laboratory su ggested that selection had an effect on the trait, whereas in other laborat ories no such conclusion would have been drawn. Moreover, we provide good e vidence for local adaptation in early fecundity for lines from two laborato ries.