17 October 2019
Deciphering the genetics of a bumblebee costume change
Published online 13 May 2019
A group of genes switches on late in development, causing the differing band patterns of a North American bumblebee species depending on where they live.
Bumblebees can have numerous differently coloured bands, with those living within the same geographic territory adopting styles that closely resemble one another. Research now reveals how diverse genetic mechanisms help choose the palette adorning a given bee.
This similarity amongst bumblebee populations is thought to be an example of ‘Mullerian mimicry’, where animals warn predators that they are unpleasant to eat by acquiring the appearance of other unpalatable species. Researchers from the US and Morocco focused on one North American species, Bombus melanopygus, whose members display yellow and black bands in Pacific coastal regions, but exhibit a distinctive reddish orange abdominal band within populations further inland.
Extensive genetic analysis of bees from the red-banded subpopulation of B. melanopygus revealed an unexpected finding. The colour switch is apparently governed by altered expression of Hox genes, a set of essential genes with a central role in establishing body patterns in development. “These are highly evolutionarily-conserved genes that are not thought to be prone to change,” says entomologist, Heather Hines, of Pennsylvania State University. Changes to Hox genes usually trigger changes in bumblebee abdominal development, but Hines and her team weren’t seeing any. They found that the genes’ effect on the bee’s appearance is exerted late in development, long after the body structure is established.
Remarkably, other local species that copy B. melanopygus’s style do not exhibit the same Hox regulatory variants. “This suggests that different genetic routes are used to get the same outcome,” says Hines, and her team now aim to map out these alternative mimicry mechanisms.
Tian, L. et al. Tinkering outside the Hox: A homeotic shift late in development drives mimetic color variation in a bumblebee. PNAS https://doi.org/10.1073/pnas.1900365116 (2019).