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Cambridge NERC Doctoral Training Partnerships

Graduate Research Opportunities

Lead Supervisor: Walter Federle, Zoology

Co-Supervisor: Chris Jiggins, Zoology

Brief summary: 
The project will investigate the trade-off between chemical and physical defences in the evolutionary model system of Heliconius caterpillars feeding on Passiflora vines
Importance of the area of research concerned: 
Interactions between plants and herbivores are essential for all land ecosystems, and their diversity is driven by an evolutionary arms race between plant defences and insect counteradaptations. So far, little is known about the role of physical plant defences in this arms race. Is there a trade-off between physical and chemical defences, what counteradaptations have herbivores evolved, and how have these factors influenced the co-evolution of both partners? The project will investigate the trade-off between chemical and physical defences in Heliconius caterpillars feeding on Passiflora vines. Passiflora vines can fend off herbivores chemically via cyanogenic glucosides (CGs) and physically via stiff and sharp hooked trichomes, which can injure or kill herbivores by piercing their cuticle or gut. Heliconius caterpillars can adapt to detoxify CGs and/or sequester them for their own defence, and some species have developed the ability to feed on Passiflora with trichomes, but the underlying mechanisms are still unclear. Unraveling how specialized Heliconius species have adapted to physical and chemical defences is key to understanding the arms race with Passiflora.
Project summary : 
The project aims to investigate the trade-off between chemical and physical defences in the evolutionary model system of Heliconius caterpillars feeding on Passiflora vines. 1) How are specialist and non-specialist Heliconius caterpillars affected by trichomes, and how do they respond to their presence? 2) What morphological adaptations do specialised H. charithonia caterpillars have for handling hooked trichomes? What are the underlying genetic mechanisms? What explains the variation in feeding performance between local populations of H. charithonia? 3) How palatable for specialist and non-specialist Heliconius species are trichome-defended Passiflora leaves when the trichomes are removed? 4) What is the phylogenetic signal in the distribution of CGs and trichomes in the Passiflora-subgenus Decaloba? Are chemical and physical defences negatively correlated?
What will the student do?: 
The project will include fieldwork trips to Panama and laboratory/greenhouse work in Cambridge on selected species. The detailed program can be tailored to the student's specific interests. To investigate the effects of hooked trichomes, the the behaviour, locomotion and growth rate of specialist and non-specialist Heliconius caterpillars will be studied when fed intact vs. trichome-shaved leaves. The trichomes' effects on the caterpillars' cuticle and gut will be studied using light and electron microscopy before and after feeding on leaves with sharp trichomes; the piercing resistance of cuticle and gut will also be quantified using penetrometry. Genetic mechanisms underlying caterpillar adaptations can be studied via RNA-seq transcriptomics of Heliconius midgut cells. Two field trips to Panama will be used to collect specimens and to study local populations of H. charithonia differing in their host range and ability to feed on leaves with hooked trichomes. The CG composition of Passiflora (subg. Decaloba) species will be studied using Liquid Chromatography/Mass Spectrometry (LC-MS). The distribution of trichomes and CGs will be mapped onto existing phylogenies.
References - references should provide further reading about the project: 
Cardoso ZM. 2008. Herbivore handling of a plant's trichome: the case of Heliconius charithonia (L.) (Lepidoptera: Nymphalidae) and Passiflora lobata (Killip) Hutch. (Passifloraceae). Neotropical Entomology 37: 247-252. DOI: 10.1590/S1519-566X2008000300002
de Castro ECP, Zagrobelny M, Zurano JP, Cardoso MZ, 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 9: 5079-5093. DOI: 10.1002/ece3.5062
de Castro ECP, Zagrobelny M, Cardoso ZM & Bak S. 2018. The arms race between heliconiine butterflies and Passiflora plants – new insights on an ancient subject. Biological Reviews 93: 555-573. DOI: 10.1111/brv.12357
You can find out about applying for this project on the Department of Zoology page.
Prof Chris Jiggins
Dr Walter Federle
Department of Zoology Graduate Administrator