Insulin signaling in the long-lived reproductive caste of ants

Altered insulin signaling in ant queens may endow them with their characteristic longevity, despite being a colony’s sole reproducers, researchers report.

In most living organisms, there exists a trade-off between reproduction and lifespan. This is largely because animals that bear many offspring often allocate important nutritional and metabolic resources for reproduction at the cost of their own longevity.

It’s thought that the insulin and the insulin-like growth factor signaling pathway underlies the anti-correlation between reproduction and shortened lifespan. Ants are an exception to this pattern, however.

In any colonies, reproductive activity is limited to one or a few queens. Reproductive queens can live for decades – many lifetimes beyond a colony’s non-reproductive female workers – and lay millions of eggs.

In some ant species, like Harpegnathos saltator, workers can switch castes and become reproductive pseudo-queens, or gamergates, when a queen dies or is removed. Despite being born as workers, gamergates can live up to five times longer than their previous counterparts. What’s more, gamergates can revert to workers (revertants) when placed in a colony with an established worker caste, returning to a shortened life span.

How this reproduction-associated longevity in these animals is regulated, particularly during active reproduction, remains unclear. To evaluate the relationship between reproduction and longevity, the researchers performed bulk RNA sequencing on tissues important for reproduction and metabolism from worker, gamergate, and revertant H. saltator ants and compared gene expression during caste switching.

As expected, the researchers found that insulin was upregulated to promote oogenesis in gamergates, however, this did not lead to a shorter lifespan as it does in other animals. The authors propose that part of the insulin signaling pathway (the branch that activates the protein kinase AKT) is inhibited in the fat body of gamergates and that this may be mediated by a protein Imp-L2. 

According to the authors, decreased activity of AKT may enable H. saltator queens and pseudo-queens to live longer.