# Discovery of an aquaporin (CrAQP2) in the freshwater larval midge, Chironomus riparius and its role in response to road de-icers

## TL;DR

Researchers discovered a water channel protein in midge larvae that helps them survive in salty water caused by road de-icers.

## Contribution

The study identifies and characterizes CrAQP2, a novel aquaporin in Chironomus riparius, and its role in osmoregulation under de-icer exposure.

## Key findings

- CrAQP2 is highly expressed in osmoregulatory organs like Malpighian tubules.
- Knockdown of CrAQP2 reduces midge survival in de-icer and salt-contaminated water.
- Beet juice de-icer affects midges similarly to NaCl in terms of osmoregulation.

## Abstract

•CrAQP2 is expressed in anal papillae and throughout the alimentary canal of the midge.•CrAQP2 expression is altered in response to NaCl in various osmoregulatory organs.•Knockdown of CrAQP2 reduces survival of midges in de-icer contaminated water.•Beet juice de-icer causes similar effects on C. riparius, relative to NaCl in water.

CrAQP2 is expressed in anal papillae and throughout the alimentary canal of the midge.

CrAQP2 expression is altered in response to NaCl in various osmoregulatory organs.

Knockdown of CrAQP2 reduces survival of midges in de-icer contaminated water.

Beet juice de-icer causes similar effects on C. riparius, relative to NaCl in water.

Chironomus riparius midge larvae are ubiquitous in freshwater ecosystems throughout the Northern Hemisphere. Recently, freshwater in temperate regions has experienced a threat from salinization due to the use of road de-icers. As ambient temperatures fluctuate, snow and ice melt carry the de-icers into nearby freshwater and significantly raise salt levels. Recently, organic de-icers including brine beet juice de-icer (BBJD) have been implemented as an “ecofriendly” alternative to traditional road salt. Not much is known about the effects of BBJD on freshwater invertebrates. Aquatic insects respond to salinity by adjusting the ion transport functions of osmoregulatory organs. A key component in insect osmoregulation is the presence of water channel proteins known as aquaporins (AQPs) that allow movement of water along an osmotic gradient. To date, there is limited knowledge on the effects of salinity on AQP function in aquatic insects. In this study, we characterized a water-specific AQP known as CrAQP2 (a PRIP homolog) in the osmoregulatory organs of C. riparius larvae. CrAQP2 was immunolocalized in osmoregulatory organs with greatest transcript abundance in the Malpighian tubules. NaCl caused differential Craqp2 transcript expression in some of the organs, whereas BBJD had little effect on Craqp2 transcript levels. Craqp2 knockdown decreased total body water regardless of treatment and reduced survival of larvae in BBJD and NaCl. Therefore, CrAQP2 appears to be important in maintaining total body water levels stable and likely plays a role in the ability of midge larvae to respond to salinity.