Did Moths Across Britain Evolve Darker Colors Due To Industrial Revolution Pollution?

The brindled beauty moth. University of Liverpool

 

At the turn of the 19th century in Britain, moths across the country gradually become darker in response to the soot-saturated skies of the Industrial Revolution. But was this change prompted by similar genetic characteristics or something much bigger? Researchers at the University of Liverpool believe they now have the answer.

The Industrial Revolution was a period of mechanical development at the turn of the 1800s marked by heavy pollution that caused coal soot from factories to literally rain from the skies. As the skies darkened, so did the area’s moths in what is known as “industrial melanism,” or a visible response to environmental change. The theory of convergent evolution holds that different species independently evolve under similar selection pressures, but researchers wanted to know if different species of moths who exhibited these similar changes relied on the same gene to adapt.

“Although many people have heard about industrial melanism in the British peppered moth, it is not widely appreciated that dark forms increased in over 100 other species of moths during the period of industrial pollution,” said study author Professor Ilik Saccheri in a statement. “This raises the question of whether they relied on the same or similar genetic mechanism to achieve this color change. This was not a foregone conclusion because melanism in insects may be influenced by many different genes.”

Melanic polymorphism in Biston betularia, Phigalia pilosaria, and Odontopera bidentata. Biology Letters

Writing in Biology Letters, scientists sequenced the genomes of two species of moth, the pale brindled beauty and the scalloped hazel, and compared it against existing information about industrial melanism seen in the peppered moth.

It was previously believed that moths evolved largely in response to coal soot pollution caused by the Industrial Revolution. The researchers found that three species of moth – the peppered moth, the pale brindled beauty, and the scalloped hazel – used the same gene to turn themselves a darker color over time. However, the latter two likely did so much earlier than the peppered moth did in the early 1800s and may even predate the industrial revolution by centuries. Although the darker genes appear to be much older alleles, they could have spread at a much larger scale during the Industrial Revolution. Darker moths would have been more likely to evade would-be predators, thus better equipped at passing on their genes. The mutation for melanism occurred in the same genetic region in all three species.

“Our findings imply that these dark forms can persist at low frequencies in non-polluted environments and lend further support to the idea that adaptive evolution makes repeated use of the same genetic and developmental machinery across deep evolutionary time,” explained Saccheri.

Moths’ ability to adapt to their environment through different color patterns allows them to camouflage against would-be predators. As environmental standards have reduced pollution in many parts of the world, moths are now breeding out the darker coloring to better adapt to their changing environment.

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