skip to content
 

Understanding the Heliconius-Passiflora cyanogen arms race

Supervisor: Prof. Chris Jiggins

Project summary:

This project will study the genetic basis for the chemical interactions between Heliconius and Passiflora that underlie their diversification. We are interested to understand the chemical diversity of Passiflora, and the genes in the butterfly and plant genomes that underlie the synthesis and detoxification of these compounds. The butterflies now have several well-assembled genome sequences and a good phylogenetic framework. We have identified likely genes that are likely involved in synthesis of cyanogens in the Heliconius genome. In contrast little is known about the plant genomes or the genes likely involved in cyanogen synthesis in Passiflora.

Coevolutionary interactions between plants and their insect herbivores are one of the major drivers of diversity, especially in the tropics. Herbivores evolve to overcome plant defences, and in return the plants evolve novel and diverse chemical toxins. This arms race is thought to have been an important driver of biodiversity and also leads to the evolution of a huge diversity of chemical compounds with potential economic importance. The Heliconius butterflies are a well studied component of the neotropical fauna and have specific interactions with the passion vine host plants. Passiflora are chemically defended with cyanogenic compounds, and indeed show the greatest diversity of such compounds known in the plant world. In turn the butterflies use cyanogens in their own defence and both sequester and synthesise these compounds independently of the plants. However, little is known of the genetic basis for these interactions, either in this system or more generally in insect-plant interactions. 

What the student will be doing:

The exact project will depend on the student, but likely avenues include studies of the genetic machinery in Heliconius used to synthesise cyanogens using comparative genomics and CRISPR. We have shown that CRISPR experiments can be used to knock out the function of genes in the butterflies, and preliminary experiments show reduced cyanogen content when key P450 genes are targeted. The student will follow up on these preliminary experiments using behavioural experiments to study the implications of reduced cyanogen content on butterfly mating and behaviour, and comparative genomics to study the evolution of these genes in the broader Heliconius clade. Another potential avenue of research would focus on the Passiflora, using phylogenetics and comparative genomics to study genes likely involved in cyanogen synthesis. The project could also involve fieldwork to study the diversity of cyanogenic compounds across the ranges of both butterflies and their hosts, and how the two have co-evolved. The project benefits from collaboration with a postdoctoral fellow in Cambridge Erika Castro and a group in Copenhagen with expertise in biochemistry under Prof Soren Bak. 

The student will learn genomic techniques for analysis of large sequence data sets and comparative analysis of genome sequences. In addition the student will learn about the application of CRISPR in insects for studying the function of evolutionarily relevant genes. In collaboration with Prof Bak and Dr Castro the student will also learn about the biochemistry of cyanogens and plant defensive compounds. The student will also learn about tropical ecology more broadly and the study of insects in the tropics.

References:

Mazo-Vargas, A. et al. Macroevolutionary shifts of WntA function potentiate butterfly wing-pattern diversity. Proc. Natl. Acad. Sci. U.S.A. 114, 10701–10706 (2017).

de Castro, É. C. P., Zagrobelny, M., Cardoso, M. Z. & Bak, S. The arms race between heliconiine butterflies and Passiflora plants - new insights on an ancient subject. Biol Rev Camb Philos Soc 93, 555–573 (2018).