"Pigment" - what is it, definition of the term
A pigment is a finely divided, insoluble colorant that imparts hue to a substrate by selectively absorbing certain wavelengths of visible light while reflecting others; its molecular framework contains chromophoric groups that dictate the specific shade, and its particulate form enables dispersion in media such as paints, inks, plastics, textiles, and biological tissues.
Detailed information
Biological colorants in arthropods are organic compounds that absorb specific wavelengths of light, producing visible hues. In ticks, the dominant groups are melanin polymers, which confer dark coloration and provide resistance to desiccation and ultraviolet radiation. Melanization proceeds through the oxidation of phenolic precursors by phenoloxidase enzymes, yielding polymeric pigments that embed within the cuticle.
In true bugs, a variety of carotenoid derivatives appear, ranging from yellow to red tones. These pigments are acquired through diet or symbiotic bacteria, then deposited in the exoskeleton and hemolymph. Carotenoids also function as antioxidants, protecting cellular membranes from oxidative stress.
Lice exhibit a distinct set of pteridine pigments, responsible for pale to brown shades. Pteridines originate from the folate pathway and accumulate in the epidermal layers. Their presence correlates with species‑specific patterns used for mate recognition.
Fleas possess both melanins and ommochromes. Ommochromes, derived from tryptophan catabolism, generate orange to brown colors in the abdomen and legs. The combination of melanin and ommochrome layers yields the characteristic mottled appearance of many flea species.
Key chemical categories of these colorants include:
- Melanins: polymeric phenolic substances; provide dark coloration and structural reinforcement.
- Carotenoids: isoprenoid chains; impart yellow to red hues; obtained externally.
- Pteridines: heterocyclic compounds; contribute to pale pigmentation; synthesized internally.
- Ommochromes: tryptophan metabolites; generate orange‑brown shades; involved in visual signaling.
Enzymatic pathways governing synthesis are conserved across arthropod taxa, with variations in gene expression dictating species‑specific pigment profiles. Understanding these compounds aids in taxonomic identification, ecological studies, and the development of control measures targeting visual cues.