Laboratory Adaptation of Life History in Drosophila

Abstract

Laboratory adaptation is a potential problem for evolutionary genetic studies unless the species in question can be successfully revived from freezing, which is a major advantage of organisms such as the bacterium Escherichia coli, the yeast Sacchoarmyces cerevisiae, and the nematode worm Caenorhabditis elegans. We (Sgro and Partridge 2000) evaluated the effects of two types of standard laboratory culture, population cages and bottles, on the life history of the fruit fly Drosophila melanogaster. To do this, we collected wild flies at the same field site in three successive years, set up replicated population cage and bottle cultures, and assayed life-history traits at the time of collection of the third wild sample. Matos and Avelar (2001, in this issue) object to the conclusion of the study on two grounds: first, the differences in life-history traits of the populations collected in the 3 yr may have occurred because of variation in the wild flies themselves rather than because of adaptation to the laboratory, and second, even if laboratory adaptation does occur, it poses no complication for interpretation of results of evolutionary studies. Drosophila cannot at present be successfully revived from freezing, which is the best method for direct comparison of populations collected at different times (e.g., Lenski and Travisano 1994). An alternative approach would be to assay each population at the time of collection, but variability between assays for these traits in Drosophila is considerable so that all populations to be compared must be assayed contemporaneously. Direct comparison of lifehistory traits of Drosophila populations collected at dif-