Oviposition preference and life history traits in cactophilic Drosophila koepferae and D-buzzatii in association with their natural hosts

Drosophila koepferae and D. buzzatii are two closely related cactophilic sp ecies inhabiting the arid lands of southern South America. Previous studies have shown that D. buzzatii breeds primarily on the necrotic cladodes of s everal Opuntia cacti and D. koepferae on the rotting stems of columnar cact i of the genera Trichocereus and Cereus. In this paper, we analyze the patt erns of host plant utilization in a locality where both Drosophila species are sympatric. Field studies showed an absence of differential attraction o f adult flies to the rots of two major host cacti: O. sulphurea and T. ters chekii. However, the proportion of D. buzzatii flies emerged from the rotti ng cladodes of O. sulphurea was significantly higher than in T. terschekii. In laboratory experiments, egg to adult viability in single species cultur es varied when both Drosophila species were reared in media prepared with O . sulphurea or T. terschekii. In addition, between-species comparisons of f lies emerged from single species cultures showed that D. buzzatii adults we re smaller and developed faster than D. koepferae. Furthermore, analysis of flies emerged in mixed species cultures showed differences in oviposition preference and oviposition behavior. We discuss the observed between-specie s differences and suggest that these traits are the result of adaptation to specific patterns of spatial and temporal predictability of their respecti ve preferred host plants: columnar are less dense and less ephemeral resour ces, whereas the opuntias are more abundant, and fast rotting cacti.