A Hox gene, a major developmental gene that regulates the identity of structures on the segments of black-tailed bumblebees (Bombus melanopygus), turns on a complex set of downstream genes that ultimately drive segmental changes in bumblebees’ pigmentation, according to new research.
Bumblebees exhibit exceptional color diversity, with the approximately 260 species displaying more than 400 color patterns.
Bumblebee color is imparted in their dense setal pile covering their head, thorax, and abdomen.
This diversity in color pattern involves multiple colors (e.g., black, orange-red, yellow, white) that are involved in frequent transitions in a sclerite-specific fashion, leading to a wide range of segmental color combinations within and between bumblebee species.
It was previously demonstrated that a Hox gene, Abdominal-B, is the key regulator of the phenotypic switch in one of these species, the black-tailed bumblebee.
“In a previous study, what we couldn’t explain is how a change in the Hox gene called Abdominal-B leads to a change in the pigments that color these bees,” said Dr. Heather Hines, a researcher in the Department of Biology and the Department of Entomology at the Pennsylvania State University.
“In th new study, we were trying to fill in that gap and understand what genes are being targeted by this first gene, and what is the cascade of events that ultimately leads to these mimetic color differences.”
Dr. Hines and colleagues found that genomic targeting of a major developmental gene allows several melanin genes, rather than just one specific enzyme, to be altered to reinforce these color traits.
Their new study adds to the knowledge about the genes involved in the production of a pigment called pheomelanin.
The pigment was known to be involved in red coloration in vertebrates, but only recently was found to occur in insects.
“A lot of work remains on understanding the evolutionary genetics of these bees,” Dr. Hines said.
“Understanding these genes, we now have the potential to look at so many different bee species and how they’ve diversified.”
“So, it’s not a case that once we are finished here that we’re done. Given the diversity in these bees, there’s just so much more that can be done with the discovery. This is just really the first step.”
Scientists tend to use certain organisms when they investigate evolutionary genetics because they are convenient and easy to study.
This is one of the few studies that looked at coloration genes outside of these well-studied organisms, or non-models.
Studying non-model systems allows researchers to understand the evolution of some of nature’s most exceptional diversifications of form, such as this color radiation.
“This really adds to non-model, evolutionary genetic research, which is a growing field and the field is also expanding to be more comparative,” Dr. Hines said.
“As we move forward, researchers will be looking at how genes and gene pathways have evolved across a broader diversity of species.”
The team’s paper was published in the journal Genome Biology and Evolution.
Sarthok Rasique Rahman et al. 2021. Developmental Transcriptomics Reveals a Gene Network Driving Mimetic Color Variation in a Bumble Bee. Genome Biology and Evolution 13 (6): evab080; doi: 10.1093/gbe/evab080
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