Orange plumage and red fur have long been thought to be dangerous evolutionary traits associated with pigments that can increase cellular stress and, in humans, cancer risk.
New research suggests that under certain conditions, the same orange pigment may help protect cells by managing certain dietary challenges.
Controlled study at the Spanish National Research Council (CSIC), biologists studied 65 zebra finches to test whether pigmentation itself could limit metabolic damage.
A team led by Dr. Ismael Galván used this built-in color difference to address a long-standing evolutionary mystery: why pigments that are associated with long-term costs persist so widely.
By manipulating diet and pigment production together, this study investigates whether the orange color functions not only as a signal but also as a cellular strategy for processing sulfur-rich nutrients.
orange pigment cost
Scientists call the orange pigment pheomelaninan orange to red pigment made from sulfur that colors the red hair and feathers of finches.
But the same biology that colors hair red is associated with a higher risk of melanoma, a pattern that has puzzled evolutionary biologists for decades.
If the pigment only added danger, natural selection would normally favor genetic mutations that steer cells toward the safer black melanin.
Galvan’s team tested the long-held idea that producing pheomelanin could also solve nutritional problems.
Too much cysteine in cells
Cells use cysteine, a sulfur amino acid used to build proteins, but excess amounts can disrupt the delicate chemical balance.
Under some conditions, cysteine can be oxidized to cystine, resulting in disulfideptosis, a form of cell death caused by disulfide stress.
Pheomelanin is built from cysteine, so producing more pigment can lock excess cysteine into a stable, harmless form.
This idea is important in pigment cells, where cysteine is also supplied. glutathionea small molecule that helps neutralize reactive chemicals.
Drugs block the dye
To test the cysteine hypothesis, Galvan’s group supplemented some birds with nutrients and inhibited pigment synthesis in others during the same period.
Each treated bird drank water containing approximately 0.013 ounces of cysteine per gallon (0.1 g/L) for one month.
Some men were also given ML349, a drug that inhibits pheomelanin synthesis by keeping pigment receptors active.
Post-treatment blood tests tracked malondialdehyde, a byproduct of lipolysis during oxidation, as a marker of systemic damage.
Damage seen in men
In men, blocking pheomelanin changed the results of cysteine supplementation in a clear direction.
Considering antioxidant capacity, men who received cysteine and ML349 had higher plasma malondialdehyde levels than men who received cysteine alone.
In our analysis, we modulated the activity of antioxidant-regulated genes. melanocytesBefore comparing treatment groups, we examine pigment-producing cells in the skin and feathers.
These results support a simple mechanism in which extra cysteine is used for pigment production, resulting in fewer reactive byproducts that can harm cells.
Women had no safety valve.
Females did not produce orange pheomelanin in their feathers, so they showed a natural contrast.
When females drank water spiked with cysteine, malondialdehyde levels tended to increase compared to controls given plain water.
ML349 did not change the women’s blood markers, consistent with a lack of pheomelanin production in the first place.
Without the pigment pathway, excess cysteine appeared to be more of a burden than a useful nutrient for these birds.
convert amino acids into feathers
Since the same amino acids are used to construct pigments, the formation of pheomelanin can reduce free cysteine in cells.
internal melanosome – Small packages where pigments are assembled – Melanocytes build pheomelanin and transfer it to the growing feather.
“These results indicate that pheomelanin synthesis avoids cell damage by dumping excess cysteine into inactive keratin structures such as feathers,” Galván said.
The problem is that other tissues may not have this pigment pathway, so cysteine processing may be different throughout the body.
What does this mean for redheads?
For humans, the same orange pigment is most compatible with red hair and very fair skin. A 2012 mouse model study found that the pheomelanin pathway can increase melanoma risk even without UV radiation.
Finch’s findings suggest that diet and metabolism may shape that risk by changing the amount of cysteine pigment cells that have to be managed.
The study did not include human trials, so it is not yet possible to determine which foods cause the rise. cysteine level In the skin.
Pigments also act as cell protection
If pheomelanin helps manage excess cysteine, orange plumage may persist because it solves a physiological problem beyond signaling and style.
Even if pigment-related genes come with long-term costs, natural selection may favor pigment-related genes as long as they reduce daily cellular stress under certain dietary or environmental conditions.
This trade-off may help explain why orange and red color patterns frequently appear among birds. mammalian, And reptiles.
The simple health story of pigmentation is also becoming more complex, suggesting that the biological effects of pigmentation may depend not only on genetics but also on environment and diet.
Taken together, the CSIC-driven Finch experiments link the regulation of orange pigmentation and cysteine to measurable markers of cell damage in the blood.
Next, the researchers plan to investigate whether human skin relies on a similar pigment-based storage pathway. The research team will also investigate whether changes in diet or disease can alter cysteine levels, altering the pigment’s protective role.
The research will be published in a journal PNAS Nexus.
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