Plasticity and the defensive chemistry of Heliconius butterflies

Butterfly

Supervisor: Chris Jiggins FRS

Co-Supervisor: Dr Erika Cristina Pinheiro de Castro 

Project Summary (PhD):

Heliconiine butterflies are bright colored to advertise to predators about their toxicity – they have cyanide-containing compounds called cyanogenic glucosides. These butterflies can both de novo biosynthesize their toxins or sequester them from their obligatory larval hostplant (Passifloraceae) (de Castro et al. 2017). There is a balance between biosynthesis and sequestration in heliconiines (de Castro et al. 2018, Sculfort et al. 2020).

Heliconius reduce biosynthesis when toxins that can be sequestered are available in the hostplant and increase biosynthesis when sequestration is not possible (de Castro et al. 2021). This phenotypic plasticity allows them to maintain their toxicity regardless of the chemical profile of their hostplants. Biochemical plasticity has fitness costs for species/populations specialized in sequestration.
While previous work has uncovered the genetic basis for biosynthesis of cyanogens, we do not know anything about the uptake of cyanogens during sequestration. We hve generated candidate genes from RNA-seq analysis and this project will follow up on these to demonstrate function and explore evolutionary patterns. The project could also explore the  costs and benefits of different defensive compounds against different predators. 

Type of Work:
 

The student will use CRISPR gene knockouts to test candidate genes in Heliconius and measure chemical composition. They will use phylogenetic approaches to reconstruct the history of chmical defences. They will use comparative genomics across Heliconiine genomes to explore gene family evolution and associate patterns of gene evolution with defensive chemistry.

Importance of the area of research concerned: 

Overall the project aims to investigate how plasticity can allow herbivorous insects to diversify and explore new niche space. This is an important area given the great diversity of herbivorous insects and their importance as pests and pollinators.

References:

Castro, É. C. P. de, Musgrove, J., Bak, S., McMillan, W. O. & Jiggins, C. D. Phenotypic plasticity in chemical defence allows butterflies to diversify host use strategies. bioRxiv 2020.04.07.030122 (2020) doi:10.1101/2020.04.07.030122.  Castro, É. C. P. de, Zagrobelny, M., Cardoso, M. Z. & Bak, S. The arms race between heliconiine butterflies and Passiflora plants – new insights on an ancient subject. Biological Reviews 93, 555–573 (2018).  de Castro, É. C. P., Musgrove, J., Bak, S., McMillan, W. O. & Jiggins, C. D. Phenotypic plasticity in chemical defence of butterflies allows usage of diverse host plants. Biology Letters 17, 20200863 (2021).