Host plant shifts in herbivorous insects often involve facing new environments that may speed up the evolution of oviposition behavior, performance related traits, morphology and, incidentally, reproductive isolation. In the genus Drosophila, cactophilic species of the repleta group include emblematic species in the study of the evolution of host plant utilization. The South American D. buzzatii and its sibling D. koepferae are a model system for the study of differential host plant use. Though these species exhibit a certain degree of niche overlap, the former breeds primarily on decaying cladodes of Opuntia cacti while the D. koepferae main hosts are columnar cacti of the genus Trichocereus. Opuntia sulphurea and T. terscheckii are the among the main hosts in nature. These cacti differ in ecological (spatial and temporal predictability) and chemical characteristics. Particularly relevant is the presence of toxic alkaloids in T. terscheckii. Studies of the effects of these cacti and alkaloids revealed the remarkable impact on oviposition behavior, viability, developmental time, wing morphology, mating success and developmental stability in both species. Recent whole-genome expression studies showed that expression profiles are massively affected by the rearing cactus, and that the presence of alkaloids is the main factor modulating gene expression in D. buzzatii. Functional enrichment analysis indicated that differentially expressed genes are related to detoxification processes and stress response; though genes involved in development are an important part of the transcriptomic response. The implications of our studies in the evolution of host plant use in the repleta group are discussed.

Drosophila koepferae and Drosophila buzzatii are closely related cactophilic species with overlapping distributions in Andean regions. Both species exploit necrotic tissues, and whereas the former breeds and feeds mostly in columnar cacti of Trichocereus and Cereus genera rich in secondary metabolites, the latter primarily exploits a less toxic host of the genus Opuntia. Although secondary metabolites have been related to the pattern of host exploitation, the microbial community associated with necrosis of cacti could also play a key role in the nutrition and/or alkaloid tolerance of the flies. We investigated the interaction between natural alkaloids and a yeast-protein supplement on both fly species raised in each type of cactus separately. We found that alkaloids reduced viability in both species, whereas a diet poor in protein reduced it only in D. buzzatii, especially when raised in Trichocereus. Concerning fitness traits that are related to adulthood, the addition of yeasts had positive effects, whereas the absence of yeasts resulted in strong detrimental effects. We present evidence of antagonistic effects on fitness and an interaction between alkaloids and proteins when these components are present in the diets of the flies.