Shared mechanisms for adaptive white coloration in bees and butterflies

In a recently published paper, the research team led by the Hines Lab explore the genetic mechanisms by which bees in Anatolia repeatedly evolve a distinctive white color pattern.

In eastern parts of Anatolia, multiple bumble bee species genetically shift their yellow color to white to resemble one another. This is a classic example of mimicry, where species converge on the same appearance for protection from predators. These white colors could also confer an advantage to facilitate cooling in this hot and dry region. Each of these color shifts represent replicates useful to address the different genetic paths to the same trait.

To understand how these white colors arose, the researchers sequenced the genomes of yellow and white morphs of the snowy bumble bee – Bombus niveatus – from Turkiye, and determined what gene was involved by finding where in the genome there were differences by color form. They identified a key player: a developmental gene BarH.

In this case, BarH duplicated a section of its regulatory region in the white form, which likely altered gene expression patterns. What was especially exciting, is that this same gene was found to regulate white vs. yellow wings in butterflies! Both these bees and butterflies use the same type of pterin pigments and butterfly wing scales and bee hairs are similar structures evolutionarily, thus through deep time this developmental gene regulates pterin coloration in these cuticular structures.

Other white colored mimetic bumble bee species were also compared for the same mutation and it was found that even though multiple bee species evolved the same white pattern, they did not coopt the same mutation. Different species achieved similar appearances through different genetic changes. Evolution can arrive at the same solution more than once, but it might take different routes to get there.

A Rare Case of a Patchwork Gynandromorph Bee

The study also examined a rare gynandromorph – a “patchwork” bee with a mosaic distribution of yellow and white colors that also contains a mix of tissues of different sexes (some female traits and some male). The researchers determined this bee contained both yellow and white genetic variants and that female tissues were white and contained one white genetic variant and one yellow, making white a dominant trait. In bumble bees, males are have only one chromosome: some single-chromosome male tissues had the yellow and some the white variant, thus male tissues contained both colors. This provided a unique situation where genetic variants could be linked to color differences within an individual.

Furthermore, the yellow forms and white forms were once considered two different species. The presence of both colors in a single bee confirms this indeed is one species.

These findings address the predictability of evolution. The use of the same gene across diverse lineages reveals that some developmental genes have ancient roles. These mimics show there are many ways to get to the same trait and sometimes those means are simple changes. In mimicry, evolution repeatedly finds creative solutions to the same challenge. For these bees, nature doesn’t just copy and paste - it innovates, again and again. Sometimes by just copy-pasting!