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Worker ants, despite their diligence, seldom encounter opportunities for social mobility. In many species, individuals adhere to strict caste roles: queens lay eggs and workers take care of almost everything else, including offspring.
In a new study, published in Science, Rockefeller scientists describe the molecular mechanisms controlling this division of labor. "We wanted to know: what makes the queens lay eggs and the workers sterile?" says Daniel Kronauer, the Stanley S. and Sydney R. Shuman Associate Professor. Kronauer and colleagues report that a gene coding for an insulin-like peptide, ILP2, is instrumental in promoting and suppressing reproduction—a finding that illuminates a possible trajectory for the evolution of specialized castes.
Vikram - Chandra - Ingrid - Fetter-Pruneda - Kronauer
Working with graduate fellow Vikram Chandra and postdoctoral associate Ingrid Fetter-Pruneda, Kronauer first searched for differences in gene expression between reproducing and non-reproducing ants from a variety of species. They discovered that a single gene, which codes for the peptide ILP2, is consistently upregulated in reproducers. ILP2 is the ant version of insulin and, like human insulin, probably regulates metabolism. According to Kronauer, there is a direct link between reproduction and food intake: "If the nutritional state is really low, you can't afford to produce offspring," he says.
Next, the researchers studied the role of insulin in the clonal raider ant Ooceraea biroi. This species lacks distinct queens and workers; all ants simultaneously enter a reproductive phase, followed by a brood care phase in which the insects nurture their young. Transitions between phases are regulated by the presence of larvae: when newborns are around, the ants stop reproducing and shift into caretaking mode.
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When Kronauer's group removed larvae during the brood care phase, adult insulin production increased substantially; and when they introduced larvae during the reproductive phase, insulin production decreased. These results indicate that the presence of larvae suppresses the production of insulin; and without...
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