Freshwater tolerance and mechanisms of freshwater acclimation in marine sticklebacks (Gasterosteus spp.)

Abstract

Freshwater tolerance has evolved repeatedly in fishes, including in the <i>Gasterosteidae</i> family. However, Blackspotted Stickleback (<i>Gasterosteus wheatlandi</i>) and the endemic Nova Scotian “white” Threespine Stickleback (<i>Gasterosteus aculeatus</i>) ecotype are largely limited to marine environments. I tested if low freshwater tolerance might limit the distribution of these fishes. Freshwater tolerance was assessed in wild caught fish acclimated to 10 ppt and then transferred to freshwater (0 ppt) or control conditions (10 ppt) for a period of 21 days. There was no effect of salinity on survivorship or tissue water content (a proxy for osmoregulatory homeostasis) in either species. mRNA content of candidate gill ion transporters was measured via qPCR in Blackspotted Stickleback, and I found this marine species can initiate the transcriptional changes associated with successful freshwater acclimation in other sticklebacks. These data suggest that acute freshwater tolerance does not limit initial freshwater colonization in these species.