Stable isotope ratios of carbon and nitrogen in natural populations of Drosophila species and their hosts

1. Stable isotope ratios of carbon (delta(13)C) and nitrogen (delta(15)N) w ere determined in seven species of wild-caught Drosophila (see Patterson & Stone 1952) and their natural hosts in order to assess if any relationships existed between isotope signatures of the flies and their hosts. The speci es included the cosmopolitan D. hydei, D. arizonae, D. simulans and D. pseu doobscura collected from rotting fruit (commercial melons), and the cactoph ilic D. nigrospiracula, D. mojavensis and D. pachea collected from their sp ecific host plants (Saguaro, Organpipe and Senita Cactus, respectively). 2. Isotope signatures were clearly different among the natural hosts, with fruit and each species of cactus segregating into a non-overlapping pattern on plots of delta(13)C vs delta(15)N. 3. Wild-caught Drosophila exhibited interspecific differences in isotope si gnatures that reflected the patterns observed for their natural hosts. For most species, values for delta(15)N were 3.0-5.parts per thousand higher in the flies, in agreement with the expected delta(15)N enrichment with incre ased trophic level. 4. For D. nigrospiracula, changing food resources from the natural host (Sa guaro) to a laboratory diet of yeast for only 24 h resulted in a shift in s table isotope signatures toward the values of the new resource. 5. The results suggest that stable isotope analysis can be a valuable tool in studies of resource ecology and feeding habitats in Drosophila, and is s ensitive enough to detect recent feeding history.