I will never forget 2023, the year I battled my anxiety demons and travelled solo from India to Japan. Little did I know that this move would unleash a 'tsunami' of new experiences, both delightful and challenging.
As my life underwent a complete reboot, I longed for the comforting touch of a cat's fur! As previously shared in my blog post titled 'The Rolling Cats: What Really Happens When Felines Meet Catnip?'—I have always had feline companions for that extra boost of oxytocin, especially during moments of stress.
With animal shelters far from the city and the language barrier adding an extra layer of complexity, I decided to explore the Cat Cafe MOCHA in Shibuya, Tokyo. While the setting was undeniably commercial, the joy I felt was genuine.
I encountered a cat that was friendly and sought my company. As I gently stroked her fur, the worries that had burdened my mind melted away. Yet, amid this serene moment with Ocha (yes, that was her name), questions that weren't contemplated during my relentless days working in India began to surface.
The prominent query that echoed in my thoughts was: What determines the colour and pattern of a cat's coat? With a background in biology, I understood the role of melanin in the pigmentation of hair and skin. However, the intricacies of how melanin produced the various hues intrigued me.
As I bid Ocha goodbye and left the cat cafe, I returned home with a newfound determination to research the ever-evolving field of 'colouration in mammals' and seek answers.
This blog aims to address several questions, helping readers understand coat colouration. Trust me, once you navigate through the information presented, you will never underestimate the power of genes again.
Does the Environment Influence Colouration in Mammals?
The prominent and diverse trait of colouration in mammals results from its environment. Have you ever wondered why a snow leopard has a thick, smoky grey colour adorned with blurred black markings while a tropical leopard has a regular, golden coat with black spots?
What prompts leopards to have spots while tigers exhibit stripes? Additionally, why does your skin possess its particular shade, while the skin of Europeans appears white, Africans' is black, or Asians' range from brown to yellow?
All these questions lead to a common thread: The primary influence on an animal's colouration is the environment it inhabits and adapts to.
The colour of the mammal is scientifically referred to as its 'phenotype' or trait. These traits are intricately tied to the organism's genetic makeup, collectively termed 'genetics.'
Imagine a Himalayan snow leopard in a tropical dry forest. Can it survive? Bookmark this question as I will return to it after explaining the mechanisms that drive the phenotype.
Understanding Pigment Regulation and Patterning in Mammals
The pigment regulation determines colour variation. Let me establish that the colours and patterns are pre-determined during embryogenesis or in an embryo before the mammal's birth. In this blog post, let's stick to furry mammals. In furry mammals, the colour variation is determined by pigment regulation and patterning.
Have you seen a striped or a patchy cat without its coat? Or if you have a cat at home, try to partition its fur where there is a pattern, a stripe or a patch and look at its skin beneath the coat. The skin beneath the patterned coat shall bear the pattern, too.
What is Pigment Regulation and How Does It Affect Colouration?
Picture a game of musical chairs, where the last 'two players' vying for the coveted seat are Agouti and MSH (α-melanocyte stimulating hormone). The 'chair' in question is the melanocortin-1 receptor (Mc1r), and the game's outcome depends on who ultimately claims the seat.
If MSH triumphantly occupies the 'chair,' the celebration unfolds with 'balloons' filled with the black pigment, eumelanin. On the other hand, if Agouti secures the 'chair', 'balloons' containing the pigment pheomelanin mark the celebration.
MSH causes eumelanin production from their interaction with the Mc1r. Eumelanin is the pigment responsible for dark colouration, manifesting as black or brown shades.
Upon interacting with Mc1r, Agouti causes pheomelanin production. In contrast to eumelanin, pheomelanin takes the spotlight for light colouration, giving rise to hues such as red or yellow. This is how the pigment regulation unfolds.
What is Patterning and How is it Determined?
The intricate patterns adorning animals, whether in stripes, spots, or patches, are determined during embryogenesis. Remarkably, a blueprint for the colour pattern is established even before the creature takes its first breath.
The colour pattern 'blueprint' owes its existence to specialised cells known as melanoblasts orchestrated by specific genes.
During embryonic development, the melanoblasts set the foundation for colour patterns by strategically positioning themselves within the epidermis (the outermost layer of the skin) and the hair follicles.
The melanoblasts change into pigment-producing melanocytes. Acting upon the instructions encoded in the creature’s genetics, melanocytes produce pigments, eumelanin or pheomelanin within 'packages' known as melanosomes.
The 'pigment packages' are then delivered to prominent cells known as the keratinocytes within the epidermis. These pigment-containing keratinocytes in the epidermis migrate deeper into the skin to form hair follicles where hair originates and grows.
Since the migrated keratinocytes (which form hair follicles) originated from the epidermis with localised melanoblasts, the skin and the hair adopt the same colour, hence, the pattern. Therefore, any skin region devoid of melanoblast localisation remains bereft of colouration, resulting in a pristine white coat.
Understanding pigment regulation and patterning in mammals
What Determines the Shades of Pigments?
Now that we have understood the intricacies of the pigments responsible for a particular colour and the underlying patterns let's look at the nuances of shades within that colour spectrum. To better understand this, let us revisit the analogy of the musical chair.
Picture a room filled with numerous chairs, and the participants engaged in this whimsical game represent two groups: Agouti and MSH. Each time an individual from either group claims a 'chair,' a 'balloon' with pigments representing the triumphant participant's group materialises.
Think of a scenario where the MSH group successfully secures most of the chairs. As the pigment intensity increases, the colour spectrum transitions dynamically from shades of brown to deep black.
In Agouti, as the pigment intensity increases, the colour spectrum transitions dynamically from hues of yellow to red.
How Gene Expression Influences Melanocyte Differentiation and Pigmentation
Numerous studies have identified specific genes that play a pivotal role in producing isoforms of pigments, giving rise to a spectrum of different hues. Furthermore, specific genes are instrumental in determining the intensity of melanocyte differentiation.
Suppression of the expression of these genes inhibits melanocyte differentiation, consequently resulting in diminished pigment production.
Let's consider another analogy to aid our understanding. Imagine an audio equaliser console. Envision the following:
The entire console represents an animal's body.
Each knob on the equaliser shall not only represent the genes but also the extent to which those genes are expressed.
When a knob is turned up or the genes are expressed more strongly, a heightened level of melanocyte differentiation occurs in that region.
Audio equaliser console analogy to understand how gene expression levels alter melanocyte differentiation. Photo by Big Bag Films/pexels.com
Now, imagine a spectrum of colours associated with these gene expression levels. When the knobs are at the bottom (zero) or the gene expression is absent, the area displays a lighter shade due to affected melanocyte differentiation.
The knobs at various levels or the varied expression of genes lead to a spectrum of colours, from lighter tones to the characteristic deeper shade.
In a Cheetah for example, when the gene Edn3 is expressed strongly in an area, it leads to melanocyte differentiation. More melanocyte differentiation means more melanosomes and pigment production resulting in the distinctive black spot on the Cheetah's body.
Colours of Life: How Animals Use Coat Colour to Adapt and Survive
Look into the bookmarked question to understand the importance of colour and adaptation. I am sure many of you immediately assumed that the snow leopard would not survive in a tropical dry forest. But why?
You are correct if your reasoning centred around the leopard's thick, insulating coat—adapted for colder climates—potentially frustrating the leopard in the heat of a tropical environment (Hitchcock, 2023).
Other factors challenging its survival include the scarcity of specific prey and its less effective grey coat, leaving it exposed and making it susceptible to predators or hampering its hunting abilities.
The pelage (hair, fur, or wool) is crucial in helping animals blend seamlessly with their surroundings. This adaptive camouflage enhances an animal's ability to hunt and evade predators effectively. The colouration of the pelage is linked to genetic factors, providing a foundation for protection.
In tropical regions, animals boasting dark-coloured coats exhibit resistance to abrasion, enjoy antimicrobial advantages and mitigate the risk of UV-induced mutagenesis.
Moreover, the hues present in an animal's skin, feathers, or pelage play a multifaceted role, influencing aspects such as sexual dominance and attraction and serving as a warning to potential predators.
Numerous examples underscore how colour variation in mammals facilitates their adaptation to new environments. Genetic alterations, whether arising from specific mutations or the infusion of new genetic material through crossbreeding, form the basis for natural selection. Species endowed with these genetic changes demonstrate a higher resilience and survival rate in altered environments than those lacking such adaptations.
Does the mechanism governing colouration in humans mirror that of other animals, or does it differ? Let me know your thoughts in the comment, and if you found this topic intriguing, please consider sharing it with others who might enjoy it too!
References
Caro, T., & Mallarino, R. (2020). Coloration in mammals. Trends in Ecology and Evolution, 35(4), 357–366. https://doi.org/10.1016/j.tree.2019.12.008
Hirobe, T. (2014). Keratinocytes regulate the function of melanocytes. Dermatologica Sinica, 32(4), 200-204.
Naik, P. P., & Farrukh, S. N. (2021). Influence of ethnicities and skin color variations in different populations: a review. Skin Pharmacology and Physiology, 35(2), 65–76. https://doi.org/10.1159/000518826
This was incredibly informative. I learned quite a lot from this.
This is fascinating stuff! My family has a real interest in this as horse breeders trying to always breed "paint" horses. I never knew colour has so much significance.
Ha,what an explanation. Explained every question why? When I read the blog. Once again well written blog with every minute details explained. 👍