WITHIN-POPULATION AND AMONG-POPULATION VARIATION IN OVIPOSITION PREFERENCE FOR UREA-SUPPLEMENTED FOOD IN DROSOPHILA-MELANOGASTER

Oviposition preference for urea-supplemented food was assayed by simul taneous choice trials on five pairs of closely related laboratory popu lations of Drosophila melanogaster, Each pair of populations had been derived from a separate ancestral population about 85 generations prio r to this study, One population in each pair had been subjected to sel ection for larval tolerance to the toxic effects of urea; the other po pulation served as a control. Considerable variation in oviposition pr eference was seen both within and among populations, with four of the ten populations showing a significant mean preference for urea-supplem ented food The degree of specificity shown by individual females was s urprisingly high, leading to a hi-modal distribution of oviposition pr eference in some populations. Overall, selection for larval tolerance to urea did not significantly affect oviposition preference, However, the data indicated that pair-wise comparisons between randomly selecte d populations from the two larval selection regimes would lead to a ra nge of possible outcomes, suggesting, in several cases, that selection for larval urea tolerance had led to significant differentiation of a dult oviposition preference for urea in one or the other direction, Th e results, therefore, highlight the importance of population level rep lication and caution against the practice, common in ecological studie s, of assaying oviposition preference in two populations that utilize different hosts in nature, and then drawing broad evolutionary inferen ces from the results.