When you picture a crocodile, the image of a long, green, lizard-like creature likely springs to mind. And most times, you’d be spot on, but nature occasionally throws us a delightful surprise. Case in point—crocs aren’t always rocking the familiar green hue.
The real curveball? White crocs. Yep, you read that correctly. They’re a thing too. They’re known as albinos.
What are albinos?
Albino animals suffer from a heritable condition known as albinism. Often just referred to as albinos, these animals are generally white due to an inability to produce melanin — a pigment responsible for the coloration of skin, fur, and eyes. However, it’s important to note that while all albino animals are white, not all white animals are albinos. A whole suite of genetic conditions — that we’ll get into in a minute — can result in the expression of a white phenotype (non-science talk: a white look).
What causes albinism?
It all comes down to genes; specifically, recessive genes.
In any living cell, genes determine and shape life. Genes are segments of DNA that encode instructions that tell cells to make vital proteins. There are two types of genes: dominant and recessive. Here’s the low-down on the two:
- Genes and Alleles:
A gene is generally made up of two or more alternative forms known as alleles. Think of genes, like chapters of a book (the DNA). The alleles are different versions of the same chapter. When an organism inherits alleles from its parents, the combination of these alleles—whether identical or different—determines the organism’s traits.
- Dominant Alleles:
A dominant allele is one whose trait always shows up in the organism when the allele is present. In other words, if an individual inherits a dominant allele from either parent, the characteristic encoded by this allele will be expressed. For example, if the allele for brown eyes is dominant, an individual only needs one copy of this allele to have brown eyes.
- Recessive Alleles:
In stark contrast to the dominant allele, a recessive allele cannot express its genetic information unless paired with an identical recessive allele. Recessive alleles are generally only expressed in the absence of a dominant allele. Using the eye color example, if the allele for blue eyes is recessive, an individual needs two copies of this allele (one from each parent) to exhibit blue eyes.
How do genes determine albinism?
Albinism is a genetic condition. It can be passed down from one generation to the next. It’s a family thing. The congenital condition generally follows an autosomal recessive pattern of inheritance. What does this mean? Essentially, to produce an albino progeny, both parents need to have the recessive copy of the albino gene. Hence, the resultant albino progeny contains one copy of the allele from each parent.
The parents themselves don’t have to be albino. That’s because the albino gene is recessive. Without another recessive copy, the parents end up being carriers of the condition as opposed to being albinos themselves.
Is there just one kind of albinism?
Not at all. Although albinism can be distilled down to a lack of pigmentation, this condition can manifest itself in different ways. For instance, humans are mainly prone to two main kinds of albinism: oculocutaneous (OCA) and ocular albinism (OA). Both of these types cause the characteristic loss of melanin but what differs is the extent of depigmentation. With OA, it’s just the eyes that generally bear the brunt of the condition whereas in OCA, the condition can affect the eyes, skin, and hair.
Another important thing to consider is that vertebrates — and living things in general — don’t just produce melanin. It’s only mammals and birds that produce melanin as their primary pigment, and thus melanocytes, as their color-producing cells. Other classes of vertebrates, like reptiles, amphibians, and fish, produce multiple pigments (like carotenoids) and have multiple pigment-producing cells — known as chromatophores. This is why some albinos are partially pigmented; as it’s just melanin production that’s affected by albinism. Other pigments can still be expressed.
There’s not a lot of research on how albinism occurs in the wild, especially in cold-blooded animals. Most scholarly literature is restricted to accounts of opportunistic or anecdotal sightings of albinism in the wild.
Albinism in the wild
There’s a good reason for the dearth of literature on wild albinos: they’re rare. Since the condition is largely regulated by a recessive pattern of inheritance, the likelihood of an animal inheriting both copies of the recessive gene from carrier parents is lower than the chance of inheriting just one copy from either parent.
This makes albinism exceptionally rare in the wild. The rate of albinism ranges from one in 20,000 to one in a million. The “one-off” nature of albinism is also what contributes to its scarcity in literature. The infrequent nature of the condition makes it challenging to study, let alone report.
Odisha: a surprising stronghold for albino crocs
The last known sighting of an albino crocodile in the wild was was 2022. The croc was reported in Odisha, a state in India. The partial albino — with interspersed black scales — named “Sweta” was spotted in a Bhitarkanika National Park, a protected reserve in the state. The white reptile was spotted by Sudhakar Kar, a crocodile researcher.
Sweta, the albino, isn’t exactly ‘wild’ though. She is a product of a concentrated effort to conserve saltwater crocodiles in Odisha. The state, home to over half of India’s saltwater crocs, hosts a dedicated hatchery within the confines of the Bhitarkanika National Park. The hatchery’s work is two-fold: they collect croc eggs from the wild to ensure their incubation and subsequent hatching. Sweta, though hatched from an egg collected in the wild, is a member of the hatchery, where it is carefully monitored.
The three-year-old croc isn’t the only albino to come out of the Bhitarkanika National Park. A recent census conducted found that there are around 15 or so albinos in the area.
“During the census last year, we counted 1,768 crocodiles, including 15 albino reptiles, in the rivers, creeks, and other water bodies of Bhitarkanika,” said Kar, in a news report. The first albino croc sighting in Bhitarkanika National Park dates back to 1975. Named Gori, it was another product of the crocodile conservation program in the protected area.
Why albinism hurts crocodiles
Albino animals do not know they’re albino animals. Unaware of their condition, albinos face severe challenges in the wild. Their absence of pigment compromises various physiological processes in their bodies. Functions like the tanning response, visual processes, and even immunological modulation are all severely affected by albinism.
Consider, for instance, albino crocs. All reptiles need to sunbathe. It’s the way these cold-blooded animals regulate their body temperatures. However, with albinos — sun exposure hurts them. They don’t produce any pigment to shield against UV-ray exposure.
It isn’t just a tanning problem either. Pigments, especially melanin, play a significant role in vision. Melanin is present in various eye structures such as the iris, cornea, retina, and optic muscles and nerves. In individuals with albinism, the absence of this pigment leads to progressively poor vision, and, in rare cases, complete blindness.
Albinism versus leucism
Although all albinos lack some form of pigment, this doesn’t necessarily make every albino white. The converse is true as well — not every white animal is albino!
White animals can sometimes result from a condition called leucism. Unlike albinism, where animals have melanocytes but face physiological pathway blockages — like the dysfunction of the enzyme tyrosinase — that block pigment production, leucistic animals appear white due to a lack of melanocytes.
There’s an easy tell to distinguish between albinos and animals with leucism. With albinism, animals aren’t just white. They’re also characterized by pinkish eyes. This is because albinism affects the eyes as well. With leucism, it’s just a pigmentation thing.
| Feature | Albinism | Leucism |
|---|---|---|
| Definition | A genetic condition causing a lack of melanin, the pigment that gives color to the skin, hair, and eyes. | A partial loss of pigmentation, which affects various types of pigment, not just melanin. |
| Caused by | Mutations in genes involved in the production of melanin. | Mutations in genes that affect pigment cell differentiation and/or migration. |
| Appearance | Individuals have very pale skin, white or light hair, and often red or light-blue eyes due to the lack of pigment in the iris. | Animals show a reduction in pigment, leading to white, pale, or patchy coloration of the skin, hair, or feathers, but normally colored eyes. |
| Pigment Absence | Complete absence of melanin in the skin, hair, and eyes. | Partial lack of pigmentation; some pigment may be present, leading to patchy or diluted coloration. |
| Eyes | Often red or light blue due to the transparency of the iris and visible blood vessels. | Usually normal in color, because eye pigmentation is less affected. |
| Inheritance | Typically inherited in an autosomal recessive manner. | Can vary, but often inherited; the specific pattern can depend on the species and the genes involved. |
| Impact on Health | Increased risk of sunburn and skin cancer due to lack of melanin. Possible vision problems. | Generally, no direct health issues, although they may be more visible to predators in the wild. |
| Species Affected | Can affect humans, mammals, birds, reptiles, fish, and amphibians. | Mostly observed in birds and mammals, but can occur in other species as well. |
Recent advances in albinism research
It’s not just a crocodile thing. Any research on albinism, especially in animal systems, is scant. Recently, however, a group of scientists from the University of Georgia used CRISPR-Cas9 gene-editing technology to create albino anole lizards. The research is significant in two ways. Not only is it new albinism research; but it’s also novel reptile model systems research.
The genetically-edited albinos, the first of their kind, were the result of a concentrated effort to provide alternative techniques for gene editing. The objective? To create a reptilian model for gene editing, rather than using established animal models — like mice and zebrafish.
Doug Menke, one of the researchers on the team, relayed why the team chose to experiment with anole lizards specifically in a press release.
“We wanted to explore anole lizards to study the evolution of gene regulation, since they’ve experienced a series of speciation events on Caribbean islands, much like Darwin’s finches of the Galapagos,” explained Menke.
Menke explained that albinism’s non-lethal loss of pigmentation, coupled with the condition’s association with visual problems, contributed to the team’s choosing to create albino anoles. They reasoned that they could use the albino anoles as a model to study how the loss of the albino gene may affect retina development.
“Humans and other primates have a feature in the eye called the fovea, which is a pit-like structure in the retina that’s critical for high-acuity vision. The fovea is absent in major model systems, but is present in anole lizards, as they rely on high-acuity vision to prey on insects,” said Menke in a press release.
