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

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Abstract
1. Stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) were 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 species included the cosmopolitan D. hydei, D. arizonae, D. simulans and D. pseudoobscura collected from rotting fruit (commercial melons), and the cactophilic D. nigrospiracula, D. mojavensis and D. pachea collected from their specific 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 δ13C vsδ15N.3. Wild‐caught Drosophila exhibited interspecific differences in isotope signatures that reflected the patterns observed for their natural hosts. For most species, values for δ15N were 3·0–5·‰ higher in the flies, in agreement with the expected δ15N enrichment with increased trophic level.4. For D. nigrospiracula, changing food resources from the natural host (Saguaro) to a laboratory diet of yeast for only 24 h resulted in a shift in stable 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 sensitive enough to detect recent feeding history.