A male gift to its partner? Cyanogenic glycosides in the spermatophore of longwing butterflies (Heliconius)
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Males of several insect species transfer nuptial gifts to females during mating, typically in the form of a protein-rich spermatophore. In chemically defended species, males could potentially enhance such a gift with chemicals that help protect the female, her eggs, or both. This was shown for lepidopteran species that accumulate pyrrolizidine alkaloids. Most Heliconius butterflies are presumably protected from predators by virtue of de novo synthesized and/or sequestered cyanogenic glycosides. Males of Heliconius species are known to transfer nutritional gifts to the females but whether defensive chemicals could also be transferred is not known. To ascertain whether transfer of cyanogens occurs, we dissected freshly mated females from nine different Heliconius species and analyzed spermatophores for cyanogenic glycosides. We found cyanogens in the spermatophores of all nine species. This is the first time cyanogenic glycosides are reported in the spermatophores of arthropods. We discuss the implications of these findings for Heliconius biology and for other cyanogenic insects as well. We suggest that chemically defended species commonly lace their nuptial gifts with defensive chemicals to improve gift quality.
KeywordsNuptial gifts Spermatophore Heliconius Cyanogenic glycoside
Thanks to Carol Boggs for supplying the H. charithonia specimens; Krushnameh Kunte and three anonymous referees for comments and suggestions on the manuscript; Phil Schappert and Helene Engler for helping in the colorimetric analysis; CAPES (Brazil) for MZC’s doctoral fellowship, NSF for grants, which provided greenhouse facilities (DEB 790633 and 8315399-LEG); MINAE, SINAC (Costa Rica), and IBAMA (Brazil) for collection permits; and USDA APHIS for importation permits. The experiments comply with the current laws of the United States.
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