Salinity effects on the microbiome of a Neotropical water strider

Salinization of coastal freshwaters (FWs) due to sea-level rise is a significant stressor for FW biodiversity. However, the effect of changes in salinity on the bacterial microbiome of Neotropical FW insects is less known. We combined field collections and common garden experiments to assess how changes in salinity may affect the microbiome associated with fresh and brackish populations of the water strider Telmatometra withei in Panama. The brackish water (BW) population had higher bacterial diversity and the total communities associated with T. withei were different at each site. Common garden experiments showed that both β diversity and the relative abundance of key taxa varied significantly with changes in salinity, but α diversity remained constant. The BW treatments also showed increased diversity of taxa known to be pathogenic to both insects and humans, including Mycobacterium, Spiroplasma, and Vibrio. Our findings suggest that the host environment is an essential driver of host–microbiome interactions in T. withei. Given the expected increases in sea-level rise, salinity-driven changes in the microbiomes of aquatic insects could trigger important ecological, evolutionary, and pathogenic changes, with consequences for both natural and human populations.