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.LC-MS analyses were carried out as described in Pinheiro de Castro, É. C., Zagrobelny, M., Zurano, J. P., Zikan Cardoso, M., 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(9), 5079-5093. Each whole butterfly was homogeinized in 1.5 mL methanol 80%. All samples were centrifuged at 10,000 x g for 5 min and the supernatant filtered (Anapore 0.45 µm, Whatman) to remove insoluble components. Samples were diluted 50X and injected (3 uL) in a Agilent 1100 Series LC (Agilent Technologies, Germany) hyphenated to a Bruker HCT-Ultra ion trap mass spectrometer (Bruker Daltonics, Bremen, Germany). Deidaclin/Tetraphyllin A (RT 5.5 min, [M+Na]+ at m/z 294), linamarin (RT 2.4 min, [M+Na]+ at m/z 310), lotaustralin (RT 5.5 min, [M+Na]+ at m/z 284), prunasin (RT 7.0 min, [M+Na]+ at m/z 317) and amygdalin (RT 6.6 min, [M+Na]+ at m/z 480) were detected and their RTs compared to authentic standards (Engler et al. 2000; Jaroszewski et al. 2002; Møller et al. 2016). Tetraphyllin B-sulfate (RT 1.3 min, [M+Na]+ at m/z 390) and passibiflorin (RT 5.8 min, [M+Na]+ at m/z 456) were identified in the plant samples by their m/z, fragmentation pattern (MS/MS) and comparison with data reported in the literature regarding these compounds. Please utilize the software Compass Dataanalysis from Bruker to open the raw chemical data (samples, washed and standards). In the excel file "Cyanogen Datasheet.xlsx", you will find information about the species/diet treatment corresponded to each sample (1-105) as well as the cyanogenic glucoside concentrations in the standard curve (ST1-ST7). README.txt contains a description of all the information in the file "Cyanogen Datasheet.xlsx". A file with all the data Analysed in this srudy is also available as .csv (("alldata.csv"). Funding provided by: European Research CouncilCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100007601Award Number: Grant number: 339873 (Acronym: SpeciationGenetics)Funding provided by: Horizon 2020Crossref Funder Registry ID: http://dx.doi.org/10.13039/501100007601Award Number: Marie Curie Actions, grant award: 841230 (Acronym: CyanideEvolution)Funding provided by: Danmarks Frie ForskningsfondCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100007601Award Number: FNU - 1323-00088This dataset correspond to body measurements (forewing length, body length, adult weight, and pupal weight) and cyanogen concentrations of H. cydno chioneus and H. melpomene rosina raised on P. biflora, P. menispermifolia, P. vitifolia and P. platyloba. The common garden experiment was conducted at the Smithsonian Tropical Research Institute (Panama)