Biology subjects

de Castro, E. C. P.

Publications and source records attributed to de Castro, E. C. P..

3 recordsLinked to original sources

bioRxiv2026

Toxin structure shapes palatability in a chemically defended butterfly

The toxicity of chemical defences is well studied, but the potential contribution of compound structure to predator deterrence remains largely unexplored. Whether predation acts more strongly on toxicity or unpalatability remains largely untested, partly because few systems allow toxin structure to vary independently of quantity. Heliconius sara larvae provide such a system: those reared on Passiflora auriculata sequester cyclopentenyl cyanogenic glucosides (CGs), while those reared on P. biflora biosynthesise comparable quantities of aliphatic CGs. Using two invertebrate predators, Camponotus floridanus ants and Hierodula membranacea mantids, we tested whether this structural difference affects palatability independent of toxicity. Mantids rejected larvae with cyclopentenyl CGs more often than larvae with aliphatic CGs, despite no detectable difference in total CG content. This pattern was mirrored in extract-based assays with ants, independently of cyanide release: extracts with cyclopentenyl CGs remained deterrent, while extracts with aliphatic CGs did not differ in deterrence from water. Live larvae, by contrast, elicited similar responses from ants regardless of CG structure. These results show that variation in toxin structure can strongly affect palatability, with some compounds conferring greater protection than others. This demonstrates the importance of chemical structural diversity in the evolution of chemical defences.

evolutionary biology↗

bioRxiv2025

Caterpillar counter-adaptations to hooked trichomes: does the coevolutionary arms race continue?

Plants protect themselves against herbivory with diverse chemical and physical defences, and many herbivores have evolved counter-adaptations against these defences. So far, little is known about herbivore counter-adaptations to physical plant defences and their underlying mechanisms. Here, we investigated how specialised Heliconiini caterpillars are able to cope with the hooked trichomes of Passiflora adenopoda vines. P. adenopoda trichomes have sharp tips reinforced with silica, in contrast to simpler trichomes of other Passiflora that do not deter Heliconiini larvae. While Heliconius melpomene and H. erato caterpillars placed on P. adenopoda leaves were arrested and their soft cuticle was pierced by the sharp hooked trichomes, H. charithonia and Dryas iulia caterpillars of all sizes could move easily over the leaves without any injury. The superior performance of these two species on trichome-bearing leaves can be explained by their thicker and more puncture-resistant cuticle. Morphological and penetrometry measurements showed that the relevant cuticle regions in H. charithonia and D. iulia caterpillars are significantly thicker and more puncture-resistant than in H. melpomene and H. erato. When we tested the ability of the caterpillars to feed on P. adenopoda leaves with hooked trichomes, only H. charithonia survived, indicating the existence of further, previously unknown post-ingestive adaptations. Understanding insect counter-adaptations to physical plant defences is essential for studying the evolutionary arms-race between plants and insect herbivores.

evolutionary biology↗

bioRxiv2020

Phenotypic plasticity in chemical defence allows butterflies to diversify host use strategies

Hostplant specialization is a major force driving ecological niche partitioning and diversification in insect herbivores. The cyanogenic defences of Passiflora plants keeps most herbivores at bay, but not larvae of Heliconius butterflies, which can both sequester and biosynthesize cyanogenic compounds. Here, we demonstrate that both Heliconius cydno chioneus, a host plant generalist, and H. melpomene rosina, a specialist, have remarkable plasticity in their chemical defence. When feeding on Passiflora species with cyanogenic compounds they can readily sequester, both species downregulate the biosynthesis of these compounds. In contrast, when fed on Passiflora plants that do not contain cyanogenic glucosides that can be sequestered, both species increase biosynthesis. This biochemical plasticity comes at a significant fitness cost for specialist like H. m. rosina, as growth rates for this species negatively correlate with biosynthesis levels, but not for a generalist like H. c. chioneus. In exchange, H. m rosina has increased performance when sequestration is possible as on its specialised hostplant. In summary, phenotypic plasticity in biochemical responses to different host plants offers these butterflies the ability to widen their range of potential host within the Passiflora genus, while maintaining their chemical defences.

evolutionary biology↗