A research team led by Penn State scientists has identified the gene responsible for the color switch between the red and black color forms of the black-tailed bumblebee (Bombus melanopygus).
The black-tailed bumblebee (Bombus melanopygus). Image credit: Walter Siegmund.
Penn State researcher Heather Hines and colleagues investigated the genetic basis of color in the black-tailed bumblebee, which exhibits two regional color patterns.
Bumblebees that live in the Pacific coastal region are black in the mid-abdomen, whereas those in the Rocky Mountain region are red.
Previous studies suggested that a single gene was driving this color change, although the identity of this gene was unknown.
The team performed a genome-wide association study, where scientists look for variation in DNA sequence associated with variation in a trait.
They identified a regulatory region that changes expression in a gene called Abdominal-B, which drives the shift in color.
“Abdominal-B is located in a highly conserved region of the genome that contains important patterning genes referred to as Hox genes, which act as blueprints for the segments of a developing bee larva,” Dr. Hines said.
“Usually any change to these Hox genes triggers many other important changes in the development of the animal’s segments, but we weren’t seeing those other changes. It turns out that the altered expression of Abdominal-B happens so late in development that it can have very specific effects on color without other consequences.”
The change in the regulatory region resulted in Abdominal-B being expressed in an unusual location late in pupal development; the same time in development that pigment is starting to show up in the bee.
Abdominal-B is usually expressed closer to the tail of the bee, but in red-striped bees it is expressed in segments further up, causing a mid-abdominal color shift.
“It’s possible that the expression of this gene and other Hox genes might move around late in development, allowing the mixing and matching within segments to create the modular color patterning that we see across bumble bees,” Dr. Hines said.
The results will be published in the Proceedings of the National Academy of Sciences.
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Li Tian et al. Tinkering outside the Hox: A homeotic shift late in development drives mimetic color variation in a bumblebee. PNAS, in press; doi: 10.1073/pnas.1900365116
