Illustration shows D. sechellia, a fly endemic to the Seychelles, on the noni fruit. Credit: Taylor N. Black
Key points:
- Researchers solved the mystery of why only one fly species feeds on a toxic fruit.
- The ability to eat the fruit without consequences gives the species an evolutionary advantage.
- An understanding of the genetic changes that allow insects to develop tolerance for host plant toxins could be useful for controlling agricultural pests.
Scientists at the University of California, Riverside have solved an interesting mystery—why Drosophila sechellia, a fly endemic to the Seychelles, is the only fly attracted to a fruit growing on this archipelago of islands in the Indian Ocean.
D. sechellia is a species of Drosophila that is highly specialized. It survives on noni (Morinda citrifolia), a fruit-bearing tree that grows in the Seychelles. Noni fruit is toxic to all other Drosophila species because its fatty acids kill their larvae. D. sechellia, however, has evolved a preference for this fruit.
In the study, published in Cell Press, the researchers compared D. sechellia to two generalist fly species, D. melanogaster and D. simulans. The two generalist species avoided feeding on noni fatty acids. D. sechellia, on the other hand, fed on these acids. The researchers determined that noni fatty acids activate bitter taste neurons in the flies and inhibit their sweet taste neurons. In other words, bitterness is activated and sweetness is suppressed.
The bitter sensing neurons send a negative signal in terms of behavior. In D. sechellia, however, these neurons are less sensitive to some of the fatty acids, thus weakening the negative signal. The fatty acids were found also to suppress positive signals by inhibiting the sugar response. This inhibition is weaker in D. sechellia.
“This gives D. sechellia an evolutionary advantage,” said Manali Dey, the lead author of the study.
The researchers say they are interested in expanding their analysis to other Drosophila species.
“Such an analysis could give us clues to the sequence of events that lead to behavioral evolution,” said Anupama Dahanukar, a professor of molecular, cell and systems biology and the corresponding author of the study. “It would be interesting to compare several closely related fly species and piece together what step-by-step process occurred. This could help us understand how variation in taste affects dietary preferences in organisms.”
An understanding of the genetic changes that allow insects to adapt to host plants and develop tolerance for host plant toxins could be useful for controlling agricultural pests.