Phytochemical changes in milkweed induced by elevated CO2 alter wing morphology but not toxin sequestration in monarch butterflies

Environmental change has the potential to influence trophic interactions by altering the defensive phenotype of prey.Here, we examine the effects of a pervasive environmental change driver, elevated atmospheric concentrations of CO2 (eCO2), on toxin sequestration and flight morphology of a specialist herbivore.We fed monarch butterfly larvae, Danaus plexippus, foliage from four milkweed, Asclepias, species of varying chemical defence profiles grown under either ambient or eCO2. We also infected a subset of these herbivores with a protozoan parasite, Ophryocystis elektroscirrha, to understand how infection and environmental change combine to alter herbivore defences. We measured changes in phytochemistry induced by eCO2 and assessed cardenolide, toxic steroid, sequestration and wing morphology of butterflies.Monarchs compensated for lower plant cardenolide concentrations under eCO2 by increasing cardenolide sequestration rate, maintaining similar cardenolide composition and concentrations in their wings under both CO2 treatments. We suggest that these increases in sequestration rate are a by‐product of compensatory feeding aimed at maintaining a nutritional target in response to declining dietary quality under eCO2.Monarch wings were more suitable for sustained flight (more elongated) when reared on plants grown under eCO2 or when reared on Asclepias syriaca or Asclepias incarnata rather than on Asclepias curassavica or Asclepias speciosa. Parasite infection engendered wings less suitable for sustained flight (wings became rounder) on three of four milkweed species. Wing loading (associated with powered flight) was higher on A. syriaca than on other milkweeds, whereas wing density was lower on A. curassavica. Monarchs that fed on high cardenolide milkweed developed rounder, thinner wings, which are less efficient at gliding flight.Ingesting foliage from milkweed high in cardenolides may provide protection from enemies through sequestration yet come at a cost to monarchs manifested as lower quality flight phenotypes: rounder, thinner wings with lower wing loading values.Small changes in morphology may have important consequences for enemy evasion and migration success in many animals. Energetic costs associated with alterations in defence and morphology may, therefore, have important consequences for trophic interactions in a changing world.A plain language summary is available for this article.Plain Language SummaryPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/148239/1/fec13270-sup-0006-TableS2.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/148239/2/fec13270-sup-0003-FigS2.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/148239/3/fec13270-sup-0004-FigS3.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/148239/4/fec13270-sup-0002-FigS1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/148239/5/fec13270-sup-0008-TableS4.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/148239/6/fec13270-sup-0005-TableS1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/148239/7/fec13270-sup-0009-AppendixS1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/148239/8/fec13270_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/148239/9/fec13270-sup-0001-Summary.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/148239/10/fec13270.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/148239/11/fec13270-sup-0007-TableS3.pd

The role of plant secondary metabolites in shaping regional and local plant community assembly

The outstanding diversity of Amazonian forests is predicted to be the result of several processes. While tree lineages have dispersed repeatedly across the Amazon, interactions between plants and insects may be the principal mechanism structuring the communities at local scales. Using metabolomic and phylogenetic approaches, we investigated the patterns of historical assembly of plant communities across the Amazon based on the Neotropical genus of trees Inga (Leguminosae) at four, widely separated sites. Our results show a low degree of phylogenetic structure and a mixing of chemotypes across the whole Amazon basin, suggesting that although biogeography may play a role, the metacommunity for any local community in the Amazon is the entire basin. Yet, local communities are assembled by ecological processes, with the suite of Inga at a given site more divergent in chemical defences than expected by chance Synthesis. To our knowledge, this is the first study to present metabolomic data for nearly 100 species in a diverse Neotropical plant clade across the whole Amazonia. Our results demonstrate a role for plant–herbivore interactions in shaping the clade's community assembly at a local scale, and suggest that the high alpha diversity in Amazonian tree communities must be due in part to the interactions of diverse tree lineages with their natural enemies providing a high number of niche dimension

Macroevolutionary patterns in overexpression of tyrosine:An anti‐herbivore defence in a speciose tropical tree genus, Inga (Fabaceae)

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this record.1.Plant secondary metabolites are a key defence against herbivores, and their evolutionary origin is likely from primary metabolites. Yet for this to occur, an intermediate step of overexpression of primary metabolites would need to confer some advantage to the plant. Here, we examine the evolution of overexpression of the essential amino acid, L‐tyrosine and its role as a defence against herbivores. 2.We examined overexpression of tyrosine in 97 species of Inga (Fabaceae), a genus of tropical trees, at five sites throughout the Neotropics. We predicted that tyrosine could act as an anti‐herbivore defence because concentrations of 4% tyrosine in artificial diets halved larval growth rates. We also collected insect herbivores to determine if tyrosine and its derivatives influenced host associations. 3.Overexpression of tyrosine was only present in a single lineage comprising 21 species, with concentrations ranging from 5% to 20% of the leaf dry weight. Overexpression was pronounced in expanding but not in mature leaves. Despite laboratory studies showing toxicity of L‐tyrosine, Inga species with tyrosine suffered higher levels of herbivory. We therefore hypothesize that overexpression is only favoured in species with less effective secondary metabolites. Some tyrosine‐producing species also contained secondary metabolites that are derived from tyrosine: tyrosine‐gallates, tyramine‐gallates and DOPA‐gallates. Elevated levels of transcripts of prephenate dehydrogenase, an enzyme in the tyrosine biosynthetic pathway that is insensitive to negative feedback from tyrosine, were found only in species that overexpress tyrosine or related gallates. Different lineages of herbivores showed contrasting responses to the overexpression of tyrosine and its derived secondary metabolites in their host plants. 4.Synthesis. We propose that overexpression of some primary metabolites can serve as a chemical defence against herbivores, and are most likely to be selected for in species suffering high herbivory due to less effective secondary metabolites. Overexpression may be the first evolutionary step in the transition to the production of more derived secondary metabolites. Presumably, derived compounds would be more effective and less costly than free tyrosine as anti‐herbivore defences.National Science Foundatio

Retention time and abundance of tyrosine and derivatives in Inga

Tyrosine content and the retention times and abundances of tyrosine, tyramine and DOPA gallate ions for each species and site. The ‘Species code’ is our identifier for both species and site. Codes beginning in 'Ing' are from Barro Colorado Island, Panama; 'LA' are from Los Amigos, Peru, 'M' are from Manaus (Km41), Brazil; 'N' are from Nouragues, French Guiana; and 'T' are from Tiputini, Ecuador. Exp and M are expanding and mature leaves, respectively, with ‘n’ indicating sample size. RT is retention time on the UPLC column. TIC is total ion count or ion abundance. Most species/site combinations had five independent UPLC-MS analyses; the exceptions are noted. All UPLC-MS analyses were as described in ‘Analysis of gallic acid depsides of tyrosine, tyramine and DOPA’. For this table, one sample with the highest signal was analyzed per species/site combination by searching for the m/z values given in Table S2. Since the ion abundances of these amines were consistently higher by factors of 6x to 60x for positive mode relative to negative mode, this analysis exclusively used positive mode data in order to maximize sensitivity

Recorded damage to Inga by insect herbivores separated by site and tyrosine expression

Herbivore damage to expanding leaves for species with and without tyrosine overexpression. Species that contained tyrosine-derivatives in addition to free tyrosine were included in the tyrosine-plus category. Data are from French Guiana (FG), Brazil (B), Peru (Pe) and Ecuador (E). Panama is excluded from the analysis as only one species contained tyrosine. An ANOVA exploring the effect of tyrosine status (T+ or T-) on herbivory showed lower damage for species without tyrosine (p < 0.001)

Retention time and abundance of tyrosine and derivatives in Inga

Tyrosine content and the retention times and abundances of tyrosine, tyramine and DOPA gallate ions for each species and site. The ‘Species code’ is our identifier for both species and site. Codes beginning in 'Ing' are from Barro Colorado Island, Panama; 'LA' are from Los Amigos, Peru, 'M' are from Manaus (Km41), Brazil; 'N' are from Nouragues, French Guiana; and 'T' are from Tiputini, Ecuador. Exp and M are expanding and mature leaves, respectively, with ‘n’ indicating sample size. RT is retention time on the UPLC column. TIC is total ion count or ion abundance. Most species/site combinations had five independent UPLC-MS analyses; the exceptions are noted. All UPLC-MS analyses were as described in ‘Analysis of gallic acid depsides of tyrosine, tyramine and DOPA’. For this table, one sample with the highest signal was analyzed per species/site combination by searching for the m/z values given in Table S2. Since the ion abundances of these amines were consistently higher by factors of 6x to 60x for positive mode relative to negative mode, this analysis exclusively used positive mode data in order to maximize sensitivity

Recorded damage to Inga by insect herbivores separated by site and tyrosine expression

Herbivore damage to expanding leaves for species with and without tyrosine overexpression. Species that contained tyrosine-derivatives in addition to free tyrosine were included in the tyrosine-plus category. Data are from French Guiana (FG), Brazil (B), Peru (Pe) and Ecuador (E). Panama is excluded from the analysis as only one species contained tyrosine. An ANOVA exploring the effect of tyrosine status (T+ or T-) on herbivory showed lower damage for species without tyrosine (p < 0.001)

wing.morpho

Dataset that accompanies: Decker, LE; Soule, AJ; de Roode, JC; Hunter, MD, 2018ms. Phytochemical changes in milkweed induced by elevated CO2 alter wing morphology but not toxin sequestration in monarch butterflies. Functional Ecology. We examined the indirect effects of elevated CO2 on toxin sequestration and flight morphology of the monarch butterfly mediated by plant quality. We measured the concentration of cardenolides sequestered by the monarchs fed plants grown under ambient or elevated CO2 and also examined aspects of butterfly wing morphology

Data from: Phytochemical changes in milkweed induced by elevated CO2 alter wing morphology but not toxin sequestration in monarch butterflies

1. Environmental change has the potential to influence trophic interactions by altering the defensive phenotype of prey. 2. Here, we examine the effects of a pervasive environmental change driver, elevated atmospheric concentrations of CO2 (eCO2), on toxin sequestration and flight morphology of a specialist herbivore. 3. We fed monarch butterfly larvae, Danaus plexippus, foliage from four milkweed, Asclepias, species of varying chemical defense profiles grown under either ambient or eCO2. We also infected a subset of these herbivores with a protozoan parasite, Ophryocystis elektroscirrha, to understand how infection and environmental change combine to alter herbivore defenses. We measured changes in phytochemistry induced by eCO2 and assessed cardenolide, toxic steroid, sequestration and wing morphology of butterflies. 4. Monarchs compensated for lower plant cardenolide concentrations under eCO2 by increasing cardenolide sequestration rate, maintaining similar cardenolide composition and concentrations in their wings under both CO2 treatments. We suggest that these increases in sequestration rate are a byproduct of compensatory feeding aimed at maintaining a nutritional target in response to declining dietary quality. 5. Monarch wings were more suitable for sustained flight (more elongated) when reared on plants grown under eCO2 or when reared on A. syriaca or A. incarnata rather than on A. curassavica or A. speciosa. Parasite infection engendered wings less suitable for sustained flight (wings became rounder) on three of four milkweed species. Wing loading (associated with powered flight) was higher on A. syriaca than on other milkweeds, whereas wing density was lower on A. curassavica. Monarchs that fed on high cardenolide milkweed developed rounder, thinner wings, which are less efficient at gliding flight. 6. Ingesting foliage from milkweed high in cardenolides may provide protection from enemies through sequestration yet come at a cost to monarchs manifested as lower quality flight phenotypes: rounder, thinner wings with lower wing loading values. 7. Small changes in morphology may have important consequences for enemy evasion and migration success in many animals. Energetic costs associated with alterations in defense and morphology may, therefore, have important consequences for trophic interactions in a changing world