Assessing the Role of Developmental and Environmental Factors in Chemical Defence Variation in Heliconiini Butterflies

Abstract

Chemical defences in animals are both incredibly widespread and highly diverse. Yet despite the important role they play in mediating interactions between predators and prey, extensive differences in the amounts and types of chemical compounds can exist between individuals, even within species and populations. Here we investigate the potential role of environment and development on the chemical defences of warningly coloured butterfly species from the tribe Heliconiini, which can both synthesize and sequester cyanogenic glycosides (CGs). We reared 5 Heliconiini species in captivity, each on a single species-specific host plant as larvae, and compared them to individuals collected in the wild to ascertain whether the variation in CG content observed in the field might be the result of differences in host plant availability. Three of these species were reared as larvae on the same host plant, Passiflora riparia, to further test how species, sex, and age affected the type and amount of different defensive CGs, and how they affected the ratio of synthesized to sequestered compounds. Then, focusing on the generalist species Heliconius numata, we specifically explored variation in chemical profiles as a result of the host plant consumed by caterpillars and their brood line, using rearing experiments carried out on two naturally co-occurring host plants with differing CG profiles. Our results show significant differences in both the amount of synthesized and sequestered compounds between butterflies reared in captivity and those collected in the field. We also found a significant effect of species and an effect of sex in some, but not all, species. We show that chemical defences in H. numata continue to increase throughout their life, likely because of continued biosynthesis, and we suggest that variation in the amount of synthesized CGs in this species does not appear to stem from larval host plants, although this warrants further study. Interestingly, we detected a significant effect of brood lines, consistent with heritability influencing CG concentrations in H. numata. Altogether, our results point to multiple factors resulting in chemical defence variation in Heliconiini butterflies and highlight the overlooked effect of synthesis capabilities, which may be genetically determined to some extent.

The role of host plant usage and the accumulation of toxic secondary chemical compounds across the life cycle of a passion vine specialist butterfly

“…Accumulation of secondary metabolites by host specialist insect larvae is a dynamic process (Nishida, 2002;Petschenka & Agrawal, 2016), especially among the Heliconiinae (Arias et al, 2016;de Castro et al, 2019de Castro et al, , 2020Engler & Gilbert, 2007;Sculfort et al, 2021). We added to this knowledge by characterising how host plant usage affected the trajectory of secondary chemical accumulation in a specialist Lepidopteran.…”

In silico prediction of microRNA families involved in the biosynthesis of lignans and cyanogenic glycosides in flax (Linum usitatissimum L.)

“…From an evolutionary perspective, ferns and gymnosperms synthesize CG from the aromatic amino acids tyrosine or phenylalanine, whereas angiosperms also utilize aliphatic valine, leucine, or isoleucine (Mobot 2021). Several plants, such as passiflora, have the ability to synthesize them even from cyclopentenyl glycine (Sculfort et al 2021). Although some plants have a high CG content, they are still considered edible (Mosayyebi et al 2020;Jaszczak-Wilke et al 2021).…”

Prediction of MicroRNAs Involved in Lignan and Cyanogenic Glycosides Biosynthesis of Flax (Linum usitatissimum L.)

“…From the evolution point of view, ferns and gymnosperms synthetize CG from aromatic aminoacid tyrosine or phenylalanine whereas angiosperms also from aliphatic valine, leucine or isoleucine (Mobot, 2022). Several plants such as passi ora are able to synthetize them even from cyclopentenyl glycine (Sculfort et al, 2021). In general, all plants produce small amounts of HCN and some of rich in content are edible (Mosayyebi, et al, 2020;Jaszczak-Wilke, 2021).…”