British moth species use the region cortex to change color

Researchers learned that three moth species separated by 30-45 million years use a similar genetic master switch for color change.

In the 1800s in Britain’s heavily coal-polluted areas, dark peppered moths began to dominate instead of the white moths with black spots on the body and wings.

At least three species Biston betularia, Phigalia pilosaria and Odontopera bidentate displayed these color changes. In 2016 Ilik J. Saccheri published that the color change in B. betularia was due to a recent (dated to the early 1800s) transposon insertion in the cortex region of B. betularia’s genome.

Since that time Ilik J. Saccheri and his team Arjen E. van't Hof, Louise A. Reynolds, Carl J. Yung, and Laurence M. Cook, have explored the question of whether the locus controlling color in B. betularia also controls color in P. pilosaria and O. bidentata.

What the team discovered from linkage analysis is that the color change of these different moths was attributable to genetic variation in the same area of DNA, cortex, as B. betularia. This work was published on Royal Society Publication’s website in October 2019.

These "results imply the conservation of a developmental master switch for melanism [color] in geometrid moths spanning 30-45 (million years ago), the estimated age of the subfamily ennominae."

This poses the hypothesis that phenotypic variation (color variation in moth wings) may rely on a small subset of control loci acting as master switches. Advantages this might afford to an organism are maximized desired changes and limitation of undesirable off-target effects.

The authors noted, "the absence of a strong association between melanic forms and haplotype in wild-caught samples of P. pilosaria and O. bidentata implies that neither monacharia [light] nor nigra [dark] are owing to a singular mutation event occurring within the past 200-300 years (generations)."

This implies that the color change in P. pilosaria and O. bidentata observed was not due to a recent genetic change as was the case for B. betularia.  Instead it suggests that there was standing variation in these moth populations before the increase in coal soot pollution.  Important future questions raised by the researchers are whether or not the standing variation was due to an older transposon insertion or if it was due to other mutations.