Investigating the phylogenetic history of toxin tolerance in mushroom-feeding Drosophila

Understanding how and when key novel adaptations evolved is a central goal
of evolutionary biology. Within the immigrans-tripunctata radiation of
Drosophila, many mushroom-feeding species are tolerant of host toxins,
such as cyclopeptides, that are lethal to nearly all other eukaryotes. In
this study, we used phylogenetic and functional approaches to investigate
the evolution of cyclopeptide tolerance in the immigrans-tripunctata
radiation of Drosophila. First, we inferred the evolutionary relationships
among 48 species in this radiation using 978 single copy orthologs. Our
results resolved previous incongruities within species groups across the
phylogeny. Second, we expanded on previous studies of toxin tolerance by
assaying 16 of these species for tolerance to α-amanitin and found that
six of them could develop on diet with toxin. Finally, we asked how
α-amanitin tolerance might have evolved across the immigrans-tripunctata
radiation, and inferred that toxin tolerance was ancestral in
mushroom-feeding Drosophila and subsequently lost multiple times. Our
findings expand our understanding of toxin tolerance across the
immigrans-tripunctata radiation and emphasize the uniqueness of toxin
tolerance in this adaptive radiation and the complexity of biochemical
adaptations.