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Climate change is bringing about subtle changes in animal colouring. What does it mean for future survival?
Climate change is bringing about subtle changes in animal colouring. What does it mean for future survival?
WHAT IF THE ACCUMULATION OF HUMAN effects on the planet is altering the colour of a greenfinch’s tail feather, the hue of a lizard’s belly, the tint of a trout fin? What if, in other words, we are determining not just the big stuff — whether we still have glaciers and permafrost, where the sea level settles, how many droughts, floods and heat waves we endure — but also the small?
This is the surprising question explored in a new paper in the U.K.’S Proceedings of the Royal Society B by (among others) Andrew Hendry, a biologist at Mcgill University in Montreal. But why do animals have different colours — or any colours — in the first place?
For a lot of reasons, as it turns out. Camouflage is an obvious one: your colouring can make you blend into the background, hiding you from predators, or make you stand out like a tasty sore thumb. Think about the Arctic hare, whose thick fur coat turns snow-white in the frosty winter and bluey-grey — the colour of tundra rocks — in the spring.
Colouration can determine whether you get the mate you want. For example, female cichlid fish in Africa’s Lake Victoria are choosy about the precise hue of metallic blue on their male mates’ dorsal fins.
But the significance of colouring goes far beyond that. Colours, some of which are determined by inherited melanin pigments, have bewilderingly vast effects on how an animal’s body works. For instance, colour can deflect ultraviolet rays or let them in. Colour can soak up heat or push it away.
Darker creatures are generally more physically active and burn more calories. Lighter-coloured animals can make do with less food. Darker colours have the bizarre ability to fend off pollution by toxic heavy metals. Dark feathers don’t degrade under bacterial assault as quickly as light feathers. Colouring helps determine how effective your immune system is, including how many antibodies you make.
But apart from affecting a creature’s inner workings, colour can also affect how an animal behaves. The darker the colour of your fur, feathers, skin and scales, the bolder you are. Darker animals are more socially dominant, more sexually active and more likely to live in groups, for reasons that are not fully understood.
All of these characteristics affect how a creature contracts disease and parasites and how it fends them off.
But as the world warms and changes in a raft of other ways, vertebrates face unprecedented new stresses that make them more susceptible to disease. Sure, all those heat waves, cold snaps, hurricanes and monsoonal rainstorms affect humans, but they affect wild animals, too. Invasive species bring in new bugs. Pollution depresses immune systems. How will colour play out in this new world of pathogenic abundance?
Take greenfinches as an example of the challenges on the horizon. In 2005, a new infectious parasitic disease, Trichomonas gallinae, began killing off vast numbers of greenfinches across the United Kingdom and northern Europe. (Emerging infectious diseases are linked to the warming world.) One small study from Estonia published in 2014 showed that the tail feathers of greenfinches that didn’t die from the disease were 22 per cent darker than those of birds that did. Darker tail feathers somehow protected the birds from the parasite. Perhaps it was because lighter birds didn’t get good access to food and were weakened. Maybe it was something else.
When you look at this finding through the lens of evolution, it means greenfinches with dark tail feathers are more likely to be left alive, more likely to breed, more likely to pass on their genes and colouring. And that means greenfinches are more likely in the future to have darker tails.
Why does that matter? The implications could be far-reaching, but they remain unknown. Will other species also be affected? Likely. Global change is influencing the spread of disease. It may also shift animals’ colouring and their ability to survive infection. How do the two interact? Could biologists begin to use colouration to predict animals’ response to this weird world we’re creating?
This question fascinates me. It speaks to the epic nature of the change humans are unleashing. Now, it’s not just the Biblical plagues that we already notice and track. Now, it goes right down to the colour of the hair in a squirrel’s tail.
We are dabbling in evolution in ways we barely comprehend. There are dangers, of course. But there is also an affront to the soul. If we are getting rid of colours nature has so painstakingly created, what sort of a species can we be?a