The effect of cyanogenic glucosides and their breakdown products on predation by domestic chicks
2020
Cardoso, Márcio Zikán
Cyanogenic insects release cyanide and other breakdown products that are thought to make them unpalatable to predators. Cyanogenic lepidopterans such as Heliconius butterflies and Zygaena moths are rejected by vertebrate predators, but the role played by these compounds in predator deterrence is poorly explored. Here I report tests undertook with captive domestic chicks (Gallus gallus) to evaluate the effect of cyanoglucosides, linamarin and prunasin and their breakdown products. In insects as well as plants, cyanoglucosides are enzymatically broken down when the tissue is disrupted as in the case of a predator attack. The aliphatic linamarin releases cyanide and acetone upon breakdown, while prunasin is an aromatic cyanoglucoside that releases cyanide and benzaldehyde. Using concentrations that mimicked the concentration of Heliconius butterflies, I ran trials with naïve chicks by offering palatable prey laced with chemicals resulting from cyanoglucoside breakdown. I categorized prey acceptance and compared the behavior of the predators towards test and control prey. Prey coated with cyanide and benzaldehyde were rejected by the birds, while acetone elicited some avoidance behavior. Intact cyanoglucosides were not rejected by the predators presumably because of fast ingestion time or lack of enzymes to break it down. Rejection of cyanide-laced prey confirms the protective nature of cyanoglucosides against a vertebrate predator. The rejection of the pungent but not toxic benzaldehyde and the potential effect of acetone suggest that cyanoglucosides could be detected via smell as well by taste. These results provide support for cyanoglucosides as defensive chemicals of aposematic lepidopterans and related arthropods.
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