Meeting Abstract
Colonizations from marine to freshwater (FW) environments constitute major evolutionary transitions and pose osmoregulatory challenges for organisms. The copepod Eurytemora affinis has recently invaded FW habitats multiple times independently in the Northern Hemisphere. We found evolutionary shifts in osmoregulatory capacity in E. affinis, with increased hemolymph osmolality at lower salinities in FW populations relative to their saline ancestors. Novel osmoregulatory structures, the “Crusalis organs,” were located at the 5 pairs of swimming legs. In their ionocytes, immunolocalization and in situ expression revealed the presence of basolateral NKA, apical VHA and apical NHA. VHA expression and activity were higher in FW populations relative to their saline ancestors, which arose from increased abundance of VHA per cell, rather than increased number of ionocytes. For the first time in a crustacean we revealed the presence of NHA, with eight paralogs of NHA in the comprehensive genome of E. affinis. Using specific antibodies, we localized the NHA-7 paralog in ionocytes of the swimming legs where it colocalized apically with VHA. Hence, we propose that NHA is involved in the uptake of Na+ in FW using the electric gradient generated by VHA, in association with the transfer of Na+ to the hemolymph by NKA. Such results provide insights into mechanisms of ionic regulation, with added insights into evolutionary mechanisms underlying physiological adaptation during habitat invasions.
