Impact of pollen-feeding on egg-laying and cyanogenic glucoside abundance in red postman butterflies
Pollen-feeding delays reproductive senescence and maintains toxicity of Heliconius erato
Recommendation: posted 07 August 2023, validated 07 August 2023
Growth, development and reproduction in animals are all limited by dietary nutrients. Expansion of an organism’s diet to sources not accessible to closely related species reduces food competition, and eases the constraints of nutrient-limited diets. Adult butterflies are herbivorous insects known to feed primarily on nectar from flowers, which is rich in sugars but poor in amino acids. Only certain species in the genus Heliconius are known to also feed on pollen, which is especially rich in amino acids, and is known to prolong their lives by several months. The ability to digest pollen in Heliconius has been linked to specialized feeding behaviors (Krenn et al. 2009) and extra-oral digestion using enzymes, possibly including duplicated copies of cocoonase (Harpel et al. 2016; Smith et al. 2016 and 2018), a protease used by some moths to digest silk upon eclosion from their cocoons. In this reprint, Pinheiro de Castro and colleagues investigated the impact of artificial and natural diets on egg-laying ability, body weight, and cyanogenic glucoside abundance in adult Heliconius erato butterflies of both sexes.
Previous studies (Dunlap-Pianka et al. 1981) in H. charithonia demonstrated that access to dietary pollen led to extended egg-laying ability among adult female butterflies compared to females deprived of pollen, and compared to Dryas iulia females which feed only on nectar. In the current study, Pinheiro de Castro et al. (2023) examine the impact of diet on both young and old H. erato, over a longer period of time than the earlier work, highlighting the importance of extending the time period over which effects are evaluated. In addition to extending egg-laying ability in older females, the authors found that pollen in the diet appeared to maintain older female body weight, presumably because the pollen contained nutrients depleted during egg-laying.
The authors then investigated the effects of nutrition on the production of cyanogenic glycoside defenses. Heliconius are aposematic butterflies that sequester cyanide-forming defense chemicals from food plants as larvae or synthesize these compounds de novo. The authors found the abundance of cyanogenic glycosides to be significantly greater in butterflies with access to pollen, but again only in older females.
Curiously, field studies of male and female H. charithonia butterflies found that females in the wild collected more pollen than males (Mendoza-Cuenca and Macías-Ordóñez 2005). Taken together, these new findings raise the intriguing possibility that females collect more pollen than males, in part, because pollen has a bigger impact on female survival and reproduction. A small limitation of the study is the use of wing length, rather than body weight, at the zero time point. But the trend is clear in both males and females, and it adds supporting detail to the efficacy of pollen feeding as an unusual strategy for increasing fertility and survival in Heliconius butterflies.
Dunlap-Pianka, Helen, Carol L. Boggs, Lawrence E. Gilbert. (1977) Ovarian dynamics in heliconiine butterflies: Programmed senescence versus eternal youth. Science, 197: 487-490, https://doi.org/10.1126/Science.197.4302.487
Pinheiro de Castro, Erika C., Josie McPherson, Glennis Julian, Anniina L. K. Mattila, Søren Bak, Stephen H. Montgomery, Chris Jiggins. (2023) Pollen-feeding delays reproductive senescence and maintains toxicity of Heliconius erato. bioRxiv, 2023.01.13.523799, ver. 4 peer-reviewed and recommended by Peer Community in Evolutionary Biology. https://doi.org/10.1101/2023.01.13.523799
Krenn, Harald W., Monika J. B. Eberhard, Stefan H. Eberhard, Anna-Laetitia Hikl, Werner Huber, Lawrence E. Gilbert (2009). Mechanical damage to pollen aids nutrient acquisition in Heliconius butterflies (Nymphalidae). Arthropod-Plant Interactions, 3: 203–208. https://doi.org/10.1007/s11829-009-9074-7
Harpel, Desiree, Darron A. Cullen, Swidbert R. Ott, Chris D. Jiggins, James R. Walters (2015) Pollen feeding proteomics: Salivary proteins of the passion flower butterfly, Heliconius melpomene. Insect Biochemistry and Molecular Biology, 63: 7-13, https://doi.org/10.1016/j.ibmb.2015.04.004
Mendoza-Cuenca, Luis, Rogelio Macías-Ordóñez (2005) Foraging polymorphism in Heliconius charitonia (Lepidoptera: Nymphalidae): morphological constraints and behavioral compensation. Journal of Tropical Ecology, 21: 407-415. https://doi.org/10.1017/S0266467405002385
Smith, Gilbert, Aide Macias-Muñoz, John Kelly, Carter Butts, Rachel Martin, Adriana D. Briscoe (2018) Evolutionary and structural analyses uncover a role for solvent interactions in the diversification of cocoonases in butterflies. Proceedings of the Royal Society B, 285: 20172037. https://doi.org/10.1098/rspb.2017.2037
Smith, Gilbert, Aide Macias-Muñoz, Adriana D. Briscoe (2016) Gene duplication and gene expression changes play a role in the evolution of candidate pollen-feeding genes in Heliconius butterflies. Genome Biology and Evolution, 8: 2581-2596. https://doi.org/10.1093/gbe/evw180
Adriana Briscoe (2023) Impact of pollen-feeding on egg-laying and cyanogenic glucoside abundance in red postman butterflies. Peer Community in Evolutionary Biology, 100648. 10.24072/pci.evolbiol.100648
The recommender in charge of the evaluation of the article and the reviewers declared that they have no conflict of interest (as defined in the code of conduct of PCI) with the authors or with the content of the article. The authors declared that they comply with the PCI rule of having no financial conflicts of interest in relation to the content of the article.
The researchers involved in this project were supported by the following grants: H2020 Marie Skłodowska-Curie Actions (841230), ERC Starter Grant (758508), Biotechnology and Biological Sciences Research Council (BB/R007500), Academy of Finland (Grant no. 286814), UKRI-NERC (NE/N014936/1), UKRI-NERC (NE/W005131/1).
Evaluation round #2
DOI or URL of the preprint: https://doi.org/10.1101/2023.01.13.523799
Version of the preprint: 4
Author's Reply, 04 Aug 2023
Evaluation round #1
DOI or URL of the preprint: https://doi.org/10.1101/2023.01.13.523799
Version of the preprint: 2
Author's Reply, 19 Jun 2023
Decision by Adriana Briscoe, posted 31 Mar 2023, validated 31 Mar 2023
Three reviewers have responded with thoughtful and constructive comments on your manuscript. One reviewer noted the clarity with which the hypothesis was first stated, investigated, and illustrated. Two referees commented that the paper was well-written (with a number of specific comments about where the writing could be strengthened). I have read the manuscript myself and am in agreement with these comments. I enjoyed reading the paper, which investigates the impact of diet on body mass, fertility, and chemical defenses in Heliconius erato, a butterfly species which supplements its adult nectar diet with pollen. I especially appreciated the difficulty of trying to collect data from butterflies over a period of 45 days, as keeping them alive in the greenhouse is no trivial matter. The work, which illustrates the impact of diet on female defenses and fertility, should be of interest to the wider evolutionary biology community, pending revision.
1. All three reviewers wanted more details about the amino acid supplementation. What was the composition of amino acids in the supplement and in the pollen of offered flowers? One reviewer commented that the valine and isoleucine composition should be mentioned. Another observed that whey powder implies that the supplement is a peptide or protein supplement rather than an amino acid supplement. This should be clarified.
2. Related to this, one reviewer noted that the kind and composition of the sugar(s) used in the artificial nectar should be given.
3. Another reviewer stated that more details about which specific cyanogenic glycosides were analyzed are needed.
4. The third reviewer had several comments on the introduction, including some relating to a few studies on the subject that are perhaps unknown to the authors (Boggs 1979, 1981, 1990).
To this I will add my own comment: From the introduction: “Nonetheless, comparative genomics has shown that they are duplicated in all heliconiines, even those that do not pollen feed (Cicconardi et al. 2022).” That cocoonase duplicates are duplicated in non-pollen feeding heliconiines was earlier observed by Smith G, Macias-Muñoz A, Briscoe AD. 2016. Gene duplication and gene expression changes play a role in the evolution of candidate pollen-feeding genes in Heliconius butterflies. Genome Biology and Evolution, 8:2581-2596. This paper should be cited here if that sentence is retained.
5. Reviewer three was also curious about data not mentioned in the paper which might be useful for interpreting the results if available. I do not think it is necessary to include these data as a condition of publication but do think that it would be good if the authors addressed whether or not the amount of pollen collected by butterflies was recorded and whether the males used in the study had an opportunity to mate.
6. The title was commented on as being overly-broad for a study that investigates a single species. I am in agreement with this comment. Perhaps changing Heliconius to Heliconius erato would be the simplest fix.
I look forward to reading your revised manuscript.
All the best,