The genetic basis of toxin sequestration in Heliconius butterflies

Supervisor: Professor Chris Jiggins

Project Summary (PhD): 

Heliconiine butterflies are chemically defended by cyanogenic glucosides, and they acquire them in two quite different ways. They synthesise the aliphatic compounds linamarin and lotaustralin from scratch, and they also sequester cyclopentenyl cyanogenic glucosides directly from the Passiflora vines their caterpillars feed on. We have shown that these are not simply alternative strategies but a single plastic system: larvae downregulate biosynthesis when sequestrable toxins are available in the hostplant and step it back up when they are not, so that a butterfly stays toxic across hostplants of radically different chemistry.

That plasticity can be lost. We recently showed that in the Sapho clade the biosynthetic cytochrome P450 CYP405A has degraded into non-functional copies, leaving species that can no longer make their own cyanogenic glucosides and are now obligate sequestration specialists — an unusually clean example of plasticity-first evolution, where an ancestrally flexible phenotype becomes canalised through loss of one of its two routes.

The biosynthetic half of this system is now reasonably well understood. The sequestration half is not. We do not know which genes allow a caterpillar to take a plant cyanogenic glucoside across the gut wall, carry it through the haemolymph, and store it in the tissues without poisoning itself, nor why some heliconiines sequester a broad range of compounds while others sequester almost none. This project sets out to find those genes. You would begin from a set of candidate loci that we have already identified from comparative genomic and transcriptomic analysis across the Heliconiini, and test them directly — establishing which are necessary for sequestration, what each one does, and how the pathway was assembled over the radiation of the tribe.

Type of work:

Comparative genomics and transcriptomics across heliconiine species that differ in sequestration ability; functional testing of candidate genes by CRISPR-Cas9 knockout and RNAi in Heliconius; LC-MS/MS quantification of cyanogenic glucoside profiles in larvae reared on hostplants of contrasting chemistry; and, if it appeals, fieldwork in Ecuador or Colombia sampling wild populations. The balance of computational, laboratory and field work is flexible and would be shaped around the student's interests and strengths.

References

de Castro, É. C. P., Zagrobelny, M., Zurano, J. P., Cardoso, M. Z., Feyereisen, R. & Bak, S. (2019). Sequestration and biosynthesis of cyanogenic glucosides in passion vine butterflies and consequences for the diversification of their host plants. Ecology and Evolution. 10.1002/ece3.5062

de Castro, É. C. P., Demirtas, R., Orteu, A., Olsen, C. E., Motawie, M. S., Cardoso, M. Z., Zagrobelny, M. & Bak, S. (2020). The dynamics of cyanide defences in the life cycle of an aposematic butterfly: biosynthesis versus sequestration. Insect Biochemistry and Molecular Biology, 116, 103259. 10.1016/j.ibmb.2019.103259

de Castro, É. C. P. et al. (2021). Phenotypic plasticity in chemical defence of butterflies allows usage of diverse host plants. Biology Letters, 17(3), 20200863. 10.1098/rsbl.2020.0863

de Castro, É. C. P., Cicconardi, F., Warren, I. A., Rueda-M, N., Salazar, C., Bak, S., Montgomery, S. H. & Jiggins, C. D. (2026). Plasticity-first evolution via CYP405 loss shaped chemical defenses in butterflies. Molecular Biology and Evolution, 43(8), msag197. 10.1093/molbev/msag197

Cicconardi, F. et al. (2023). Evolutionary dynamics of genome size and content during the adaptive radiation of Heliconiini butterflies. Nature Communications, 14, 5620.