Meeting Abstract
The Threespine Stickleback (Gasterosteus aculeatus) provides an excellent euryhaline fish model for examining the evolution of physiological traits such as ion regulation. Ancestral, oceanic populations of stickleback have become isolated and often landlocked in novel freshwater environments across the Northern Hemisphere, and recent investigations have shown landlocked stickleback exhibit a trend of increased freshwater tolerance when compared to ancestral, oceanic fish, despite both populations being euryhaline. It is likely that differences in ionoregulatory performance are due to differences in expression and regulation of ion transport genes, however it is also possible that divergence in protein sequence has led to changes in structure and function that are favorable for freshwater adaptation. We examined the protein sequence of the Na-Cl cotransporter (NCC) in individuals from oceanic (Rabbit Slough and Resurrection Bay) and freshwater-landlocked populations (Frog Lake and Bear Paw Lake). We determined that NCC of oceanic and freshwater-landlocked stickleback differed consistently at four amino acid positions. Three of these positions (413, 415, 430) were found in the large extracellular loop between transmembrane 7 and 8; a fourth position (682) was located in the large intracellular C-terminus. While the C-terminus’ specific function remains unknown, the large extracellular loop region of NCC is involved in ion transport and trafficking. Future research will examine NCC protein sequence in additional oceanic and freshwater-landlocked populations as well as examine whether identified amino acid differences have led to functional changes in NCC advantageous for physiological adaptation to novel freshwater environments.
