Phenotypic plasticity in chemical defence of butterflies allows usage of diverse host plants

Abstract

Host plant specialization is a major force driving ecological niche partitioning and diversification in insect herbivores. The cyanogenic defences of Passiflora plants keep most herbivores at bay, but not the larvae of Heliconiu s butterflies, which can both sequester and biosynthesize cyanogenic compounds. Here, we demonstrate that both Heliconius cydno chioneus and H. melpomene rosina have remarkable plasticity in their chemical defences. When feeding on Passiflora species with cyanogenic compounds that they can readily sequester, both species downregulate the biosynthesis of these compounds. By 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 fitness cost for the more specialist H. m. rosina , as adult size and weight for this species negatively correlate with biosynthesis levels, but not for the more generalist H. c. chioneus . By contrast, H. m rosina has increased performance when sequestration is possible on its specialized host plant. In summary, phenotypic plasticity in biochemical responses to different host plants offers these butterflies the ability to widen their range of potential hosts within the Passiflora genus, while maintaining their chemical defences.

Balanced polymorphisms and their divergence in a Heliconius butterfly

“…Differences in mimicry ring compositions and densities between South American and Central America could certainly also contribute to the regional differences we observed in selection pressures. This could be exacerbated by regional differences in differences in toxicity, which is known for several Heliconius species (de Castro et al, 2021 ; Mattila et al, 2021 ; Sculfort et al, 2020 ). Current data show little variation in toxicity of H .…”

Chemical defense acquired via pharmacophagy can lead to protection from predation for conspecifics in a sawfly

“…Many individuals protect themselves against predation using chemical defenses that turn them distasteful, toxic and/or less nutritional [1,2]. Such defensive chemicals can either be synthesized de-novo or acquired extrinsically from their diet [3][4][5]. For example, the oleander aphid, Aphis nerii, sequesters cardenolides from its host plant during feeding and uses these defensive compounds against both vertebrate and invertebrate predators [6].…”

Condition dependence in biosynthesized chemical defenses of an aposematic and mimetic Heliconius butterfly

“…Some of this variation is explained by a balance between plant‐derived cyanogen compound sequestration and de novo biosynthesis. These are negatively correlated traits in Heliconius , such that, on average, increased sequestration is associated with decreased de novo biosynthesis at species and population level, as well as at the level of individuals (de Castro et al, 2019 , 2021 ; Engler‐Chaouat & Gilbert, 2007 ; Sculfort et al, 2020 ). Several studies have also reported evidence of unprotected automimics (Arias et al, 2016 ; Mattila et al, 2021 ; Sculfort et al, 2020 ), which could indicate an important evolutionary role of selection balancing costs and benefits of investing in chemical defenses (Speed et al, 2006 , 2012 ; Svennungsen & Holen, 2007 ).…”