Larvae Protect From Cyanide

a butterfly with blue, black and white wings spread open sits on a green leaf

Biological Strategy

Sara longwing butterfly

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Image: Pavel Kirillov / Wikimedia Commons / CC BY - Creative Commons Attribution alone

Protect From Chemicals

Chemicals are everywhere in the bodies of living organisms and their external environments. While most chemicals are valuable or benign, some are toxic, including those used for defense (such as the mucus that protects clownfish from an anemone’s stinging tentacles). Even naturally-occurring chemicals, such as arsenic, must be managed to reduce their impact. Some living systems have strategies to break down harmful chemicals, alter them into less toxic forms, physically prevent chemicals from harming sensitive tissues, and more. For example, some herbivorous mammals can digest toxic compounds in plants because they have a particular enzyme that helps them process poisonous plant compounds.

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Catalyze Chemical Breakdown

Life depends upon the building up and breaking down of biological molecules. Catalysts, in the form of proteins or RNA, play an important role by dramatically increasing the rate of a chemical transformation––without being consumed in the reaction. The regulatory role that catalysts play in complex biochemical cascades is one reason so many simultaneous chemical transformations can occur inside living cells in water at ambient conditions. For example, consider the 10-enzyme catalytic breakdown and transformation of glucose to pyruvate in the glycolysis metabolic pathway.

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Insects

Class Insecta (“an insect”): Flies, ants, beetles, cockroaches, fleas, dragonflies

Insects are the most abundant arthropods—they make up 90% of the animals in the phylum. They’re found everywhere on earth except the deep ocean, and scientists estimate there are millions of insects not yet described. Most live on land, but many live in freshwater or saltwater marshes for part of their life cycles. Insects have three distinct body sections: a head, which has specialized mouthparts, a thorax, which has jointed legs, and an abdomen. They have well-developed nervous and sensory systems, and are the only invertebrate that can fly, thanks to their lightweight exoskeletons and small size.

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Larvae of sara longwing butterflies avoid harm from cyanogenic leaves by metabolizing cyanogenic glycosides enzymatically, preventing cyanide release.

“A neotropical butterfly, Heliconius sara, can avoid the harmful effects of the cyanogenic leaves of Passiflora auriculata (passion vine), on which its larvae feed exclusively. To our knowledge this is the first example of an insect that is able to metabolize cyanogens and thereby prevent the release of cyanide. The mechanistic details of this pathway might suggest new ways to make cyanogenic crops more useful as a food source…We conclude that a unique enzymatic mechanism exists in H. sara for dealing with cyanogenic glycosides.” (Engler et al. 2000:144)

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