Blue coloration is relatively rare in the animal kingdom. While many animals display blue, it is often a structural color resulting from microscopic physical structures that reflect blue wavelengths of light, rather than from actual blue pigment. True blue pigment, arising from pigments that absorb certain wavelengths and reflect blue, is rarer. However, there are a few notable examples of animals that produce blue pigment. In this article, we’ll explore some of the animals that make true blue pigment and discuss the biological mechanisms behind their unique and vibrant coloration.
Marine Invertebrates
Some of the most brilliant true blue colors in nature come from marine invertebrates, particularly crustaceans.
Sapphirina, also known as sea sapphires or glittering copepods, are a genus of copepods that display shimmering shades of blue. These tiny crustaceans contain a unique blue pigment called sapphirin. Sapphirin is an extremely thin, layered pigment contained in sets of reflective plates within the sapphirina’s skin. It reflects light at specific wavelengths to produce metallic blues.
Another vivid blue invertebrate is the blue dragon sea slug. These glaucus atlanticus nudibranchs contain blue pigments in their tissue layered over reflective plates on their skin, resulting in their bright blue hue. They obtain this pigment by feeding on the blue venom of the Portuguese man o’war.
Birds
Many breeds of poultry have been selectively bred to display blue coloration. Some bird species also naturally display true blue colors.
Indigo buntings are a small bright blue songbird native to North America. Their brilliant blue plumage comes from a pigment called indigo. This pigment only occurs in birds and is made up of large molecules called polyenes that strongly absorb yellow and reflect blues.
Some breeds of quail, like the Blue Scale quail, also express a blue pigment for their feathers. This results from selective breeding but shows that blue pigment mutations can occur and be selected for in bird species.
Amphibians
Blue pigment is very rare in amphibians. One of the few examples is the dyeing poison dart frog. This frog, found in Suriname, secretes a blue mucus from its skin that contains unique tetrapyrrole pigments. It is believed this blue hue acts as a visual signal to potential predators advertising its toxicity.
Fish
Many species of fish can appear blue due to structural colors, but true blue pigments are rarer. One example is the mandarin fish. These small, vibrantly colored fish have chromatophores containing blue pigments in their skin. They can rapidly change color by expanding and retracting these pigment cells.
Blue Butterflies and Insects
While common blue butterflies rely on structural color, some species can biosynthesize blue pigments. The blue morpho butterfly has shimmering blue wings. In addition to structural color from wing scales, blue morphos also contain blue pigments formed through complex biochemistry. These include ommochromes, pigments formed from the amino acid tryptophan.
Some other insects also utilize blue pigments. Jewel beetles have an iridescent blue-green color that comes from their elytra containing layers of blue pigment.
Mammals
True blue pigment is extremely rare in mammals. Unlike birds and insects, mammals generally cannot biosynthesize blue pigments from scratch. However, one exception is found in mandrills. These primates develop vibrant blue and purple facial skin through a complex process. Their bodies convert a red pigment called isopentenyl pyrophosphate into blue pigments called polyenes. This only occurs in mature male mandrills.
Cephalopods
While octopuses and squid can appear blue via structural color change, some cephalopods also contain true blue pigment. One example is the blue-ringed octopus, which has blue rings and stripes. These come from chromatophores that contain a pigment from the protein reflectin. When expanded, these pigment cells produce bright blue warning coloration.
Fish
– Mandarinfish contain blue pigment cells in their skin called chromatophores.
Amphibians
– The dyeing poison dart frog secretes blue mucus containing unique tetrapyrrole pigments.
Birds
– Indigo buntings produce the pigment indigo, made of polyenes.
– Some breeds of quail have been selectively bred to express blue feathers.
Insects
– Blue morpho butterflies create blue pigments including ommochromes.
– Jewel beetles contain multilayered blue pigment in their elytra.
Marine Invertebrates
– Sapphirina copepods have the pigment sapphirin that reflects blue light.
– Blue dragon sea slugs take up blue pigments from eating Portuguese man o’ wars.
Mammals
– Mature male mandrills can convert red pigments into blue polyenes.
Cephalopods
– Blue-ringed octopuses contain the protein reflectin that produces blue color.
Conclusion
While structural blue colors are common, true blue pigments are rarer in nature. A handful of unique species, however, have evolved complex biochemical mechanisms to produce these vibrant hues. From marine invertebrates to primates, blue can signal toxicity, social status, or breeding fitness. Understanding the mechanisms behind natural blue coloration continues to reveal fascinating insights into evolution, biochemistry, and visual communication in the animal kingdom.
