In the last days of 2020, Current Biology magazine suddenly became a battleground for scientists divided into two factions when discussing the same issue: whether climate change will make animals have fur or skin color. brighter or darker?
A team of scientists led by Li Tian of the Chinese University of Geosciences and Michael Benton of the University of Bristol said that the answer is darker, as the animals are facing more intense sunlight. and more ultraviolet rays.
Opposing them, Kaspar Delhey, an ornithologist living in Australia and working remotely for the Max Planck Institute in Germany says the answer must be brighter. The reason he gives is that because climate change causes the Earth’s temperature to rise, animals need to equip themselves with a brighter coat or skin to reflect the sunlight and avoid absorbing extra heat. .
After all, who is right in this century-old debate?
The debate is sparked again after 300 years
In fact, debates such as those of Li Tian and Delhey have been sprouted since the 19th century, after a number of biologists of this era have widely identified. “Rule” describes the effect of Earth’s temperature on ecosystems and animal evolutionary models.
One rule, for example, is that animals in hot climates need extra parts such as beaks and larger ears to help them dissipate heat. Some other 19th century scientists said that of any group of animals, the largest species usually inhabited the south and north poles. For example, polar bears have a much larger body than tropical brown bears – because larger bodies make them warmer.
Among the sciences living in the 1800s emerged a German biologist named Constantin Gloger. Gloger has stated a rule bearing his own name that animals in warmer regions tend to appear darker, while animals in cooler regions will always have lighter skin and feathers.
Among mammals, darker skin and fur are believed to have protective effects against harmful ultraviolet rays, which are conditions in sunny equatorial regions. Among birds, specific melanin pigments in dark fur seem to help them resist bacterial invasion, and these bacteria also survive more in the hot and humid tropics.
Starting July 2020, two scientists Li Tian from the Chinese University of Geosciences and Michael Benton from the University of Bristol reiterated Gloger’s rule in a study in the journal Current Biology. They suggest that this rule can be used to predict the impact of climate change on animal body trends.
Among a variety of engravings, Li Tian and Benton re-emphasize that as the Earth warms, most animals will develop darker skin and feathers. But this prompted a host of other scientists, including Kaspar Delhey from the Max Planck Institute for Ornithology in Germany to post their protest.
As it turns out, the story of the animal’s appearance is not so simple for an 18th-century scientist to be summed up into a simple rule like Gloger’s. The question of whether animals will have brighter or darker hair in the future is actually more complicated than you can imagine.
Will climate change make animals appear darker or brighter?
Over the past few years, Delhey has spearheaded a campaign to break Gloger’s rule and replace it with something more precise. He is not afraid to express his unyielding view that the Gloger rule has caused a harmful misunderstanding but can be permanent if no one dares to break it up.
It all started with a book written in 1833 by Constantin Gloger which was remarked very by Delhey “stupid and bad“What Gloger said in the book focuses on two environmental parameters, humidity and temperature.
Increased humidity leads to lush plant growth, providing shade for animals to hide from predators. As a result, animals will have a tendency to evolve with a darker appearance in humid places to camouflage themselves.
It is true that in many warm places, in cool, humid forests like Tasmania we can find the world’s darkest birds, Delhey said.
But he argues on the contrary that if you control the humidity, Gloger’s rules are turned upside down – warming results in animals having to be brighter. That’s especially true of cold-blooded creatures, Delhey said.
Insects and reptiles rely on external heat sources, and in cold places their dark appearance helps absorb sunlight. In warmer climates, those restrictions are loosened and they will have to be brighter. Delhey calls this “theory of heat theory “.
These Delhey arguments are sent back to Tian and Benton’s group, and in a scientific sense both welcome criticism. However, in a response to the Delhey team, Tian and Benton cite instances where their predictions of darker animals in warmer climates are correct.
The Finnish Tawny has a black or light gray coat color, with a gray color that helps camouflage in the snow. But as the Finnish snow cover has decreased, the owl’s dark brown hair density has increased from about 12% in the early 1960s to 40% in 2010.
Tian and Benton acknowledge that predictions of climate-induced hair and skin changes will be difficult to be accurate when both temperature and humidity parameters change. For example, current climate models predict that the Amazon forest will be hotter and drier.
This makes Tian, Benton, and Delhey all agree it will make the animals here have lighter hair and skin.
But in the deep forests of Siberia where the temperature could get hotter and the humidity is getting higher, the two groups of scientists did not reach consensus. Unlike in physics or chemistry, Benton says the laws of biology are “not absolute. It’s not like gravity”.
The answer is still not clear
Even when projections of general animal trends are correct, it is still difficult to predict how individual species’ appearance will change in response to climate change. Lauren Buckley, a biologist at the University of Washington, Seattle, has studied the colors of butterflies in high altitude areas.
Butterflies absorb heat by drying them in the sun, but only a small patch on their underside that actually absorbs the heat.
“Without knowing that, you will likely accidentally quantify all sorts of weird colors on the top of their wings and the problem won’t be resolved.“Buckley said. “We need to think about a big picture of how organisms interact with their habitats.”
Color changes will also likely depend on the animal’s temperature-regulating system – with cold-blooded organisms they often evolve with a brighter appearance. And among birds and mammals, the results can be mixed.
To improve predictions, Buckley recommends biologists use museum specimens, such as animal mummies, to extend the time frame of their follow-up. Although, this can be faced with a deterioration in color over time of the specimen.
For her part, Tian plans to conduct experiments with warmed containers of bugs and mollusks. She will consider how their skin and fur color changes from generation to generation, under different temperature and humidity conditions.
This means that the final answer to this more than 300-year debate still lies ahead. We do not have a final answer in 2021, to a problem that has existed since 1833.
And the problem can be even more serious when more animals are predicted to disappear or become extinct under the impact of climate change. If they can’t exist anymore, it’s pointless to predict whether they’ll be brighter or darker.
“It’s really the one thing that makes us all sad” Delhey said.