These membrane proteins
might reclaim salt from urine
or suck it from ponds.
Mosquitoes face extraordinary challenges to their salt and water balance during their complex life-cycles. Larva of most species live in freshwater environments in which they lose salt by diffusion and gain water by osmosis. In contrast, adults live in terrestrial environments where water loss is a problem. Finally, female mosquitoes ingest large amounts of salt and water when they take a blood meal.
In vertebrates, the sodium-potassium-chloride cotransporters (NKCCs) participate in both salt secretion and absorption. Whereas secretory roles for this group of transporters are well-described in insects, their roles in salt absorption are less well studied. Piermarini et al (2017) recently identified yellow fever mosquito transport proteins that have sequence similarity to the vertebrate NKCCs. Two of these transporters apparently resulted from gene duplications early in the insect and mosquito lineages, suggesting that they have diverged into roles related to mosquito osmoregulation. The transporters may contribute to salt absorption, because the researchers found them in adult hindgut and larval anal papillae, both tissues that transport salt into the body.
Original research: Piermarini, P. M., Akuma, D. C., Crow, J. C., Jamil, T. L., Kerkhoff, W. G., Viel, K. C. M. F., and Gillen, C. M. (2017) Differential expression of putative sodium-dependent cation-chloride cotransporters in Aedes aegypti. Comp. Biochem. Physiol. A 214, 40-49. https://doi.org/10.1016/j.cbpa.2017.09.007
Chris Gillen teaches animal physiology and science writing at Kenyon College in Gambier, Ohio. He is author of The Hidden Mechanics of Exercise (Harvard, 2014) and Reading Primary Literature (Pearson, 2007).