PARASITE PRESSURE AND THE EVOLUTION OF AMANITIN TOLERANCE IN DROSOPHILA.

Approximately one-half of the members of the Drosophila quinaria species-group are mycophagous. The mushroom-breeding species D. falleni, D. recens, and D. phalerata are far more tolerant of the mushroom toxin α-amanitin than are D. guinaria, D. palustris, and D. subpalustris, which breed in decaying water plants. The non-mycophagous species, however, are physiologically capable of larval development in mushrooms, showing that high levels of amanitin tolerance are not necessary for mycophagy. A primary selective advantage of amanitin tolerance among the mycophagous species is that it allows them to breed in mushrooms that are toxic to nematodes that infest Drosophila in other fungi and render them infertile. Parasitism, then, may be an important factor governing evolutionary patterns of resource utilization in these species.