Olfactory and gustatory systems play crucial roles in insect survival and reproductive success, mediating responses to food, mates, and oviposition sites (Hallem and Carlson 2006). Their functions and evolutionary pattern have been studied in a genetic model species Drosophila melanogaster and its related species (Anholt 2020). This seminar briefly introduces the evolutionary pattern of the gene repertoire of chemosensory receptors associated with host preference in the Drosophila genus.
Insects can be categorized as generalists and specialists according to their host preferences. The species that utilizes a wide variety of resources is called “generalist”, while the species with a strictly limited diet range is called “specialist” (Futuyma & Moreno, 1988).
The gene loss of chemosensory receptors accelerated in some specialist feeders. McBride (2007) has found a specialist Drosophila sechellia is losing odorant receptor (OR) and gustatory receptor (GR) genes faster than its generalist sibling Drosophila simulans. Six of D. sechellia’s 63 ORs, and thirteen of its 73 GRs exhibited lack-of-function (LOF) mutations that clearly render them pseudogenes, while only two of the 73 GR and none of the OR genes fixed LOF mutations along the D. simulans.
On the other hand, McBride and Arguello (2007) demonstrated some OR duplications in three generalist Drosophila species (Or19a in D. melanogaster, Or65c in D. yakuba, and Or67a in D. simulans and D. yakuba), which possibly leads to evolutionary innovation (Ramdya and Benton 2010).
Furthermore, Ramasamy et al. (2016) reported that Drosophila suzukii, which exhibits a special reproductive preference to fresh fruit, show duplication and loss of several ORs and OBPs than other Sophophora subgenus species which prefer to fermenting fruit. It reveals the big changes in receptor genes following a tremendous preference shift.
In conclusion, the gene loss of chemosensory receptors in some specialist species accelerated more than their generalist sister species. On the contrary, some generalists form gene duplications of chemosensory receptors, which indicates possibility of function changing. However, we still have limited evidence about new receptor gene gain associated with host plant shift events. I expect more research can reveal more about it in the future.
References
Hallem, E. A., Dahanukar, A., & Carlson, J. R. (2006). Insect odor and taste receptors. Annu. Rev. Entomol., 51, 113-135. https://doi.org/10.1146/annurev.ento.51.051705.113646
Anholt, R. R. (2020). Chemosensation and evolution of Drosophila host plant selection. IScience, 23(1), 100799. https://doi.org/10.1016/j.isci.2019.100799
Futuyma, D. J., & Moreno, G. (1988). The evolution of ecological specialization. Annual review of Ecology and Systematics, 19(1), 207-233. https://doi.org/10.1146/annurev.es.19.110188.001231
McBride, C. S. (2007). Rapid evolution of smell and taste receptor genes during host specialization in Drosophila sechellia. Proceedings of the National Academy of Sciences, 104(12), 4996-5001. https://doi.org/10.1073/pnas.0608424104
McBride, C. S., & Arguello, J. R. (2007). Five Drosophila genomes reveal nonneutral evolution and the signature of host specialization in the chemoreceptor superfamily. Genetics, 177(3), 1395-1416. https://doi.org/10.1534/genetics.107.078683
Ramdya, P., & Benton, R. (2010). Evolving olfactory systems on the fly. Trends in Genetics, 26(7), 307-316. https://doi.org/10.1016/j.tig.2010.04.004
Ramasamy, S., Ometto, L., Crava, C. M., Revadi, S., Kaur, R., Horner, D. S., … & Rota-Stabelli, O. (2016). The evolution of olfactory gene families in Drosophila and the genomic basis of chemical-ecological adaptation in Drosophila suzukii. Genome biology and evolution, 8(8), 2297-2311. https://dx.doi.org/10.1093%2Fgbe%2Fevw160