Carotenoids

Definition

A class of lipid-soluble, yellow-to-red terpenoid pigments (tetraterpenes) synthesized by plants, algae, fungi, and some bacteria, and sequestered or metabolized by arthropods. In insects and arachnids, carotenoids serve multiple functions: they produce aposematic and cryptic coloration (often combined with melanins and ommochromes), act as precursors for retinal visual pigments, and function as antioxidants and immunomodulators. Because animals cannot synthesize carotenoids de novo, arthropods must acquire them through diet—herbivores directly from plants, predators from sequestered prey, or via endosymbiotic bacteria—making carotenoid-based coloration a reliable indicator of foraging history and nutritional state.

Etymology

From Latin carota (carrot) + -oid (resembling), reflecting the orange pigment first isolated from carrot roots.

Example

The bright yellow-and-black warning patterns of many Coccinellidae (lady beetles) and the red coloration of some aposematic Lycidae net-winged beetles derive from sequestered dietary carotenoids, often modified by oxidation to ketocarotenoids; these pigments are honest signals of unpalatability because they are costly to acquire and process.

Synonyms

• tetraterpenoid pigments

Related Terms

• ommochromes
• pteridines
• melanins
• aposematism
• Sequestration
• retinal
• xanthophylls
• carotenes
• cryptic coloration
• honest signal

Usage Notes

Distinguished from ommochromes and pteridines, which are nitrogen-containing arthropod pigments synthesized de novo. Carotenoid-based colors are often diet-dependent and can fade in preserved specimens; fresh or frozen material is preferred for color documentation. In arachnology, carotenoids contribute to the green and yellow hues of some jumping spiders (Salticidae) and harvestmen, though documentation is sparser than for insects.