27.4 Wednesday, Jan. 4 Evolution of ionic regulation following invasions into freshwater habitats LEE, Carol Eunmi*; KIERGAARD, Michael; CHARMANTIER, Guy; POSAVI, Marijan; University of Wisconsin, Madison; UW-Madison; Université Montpellier, France; UW-Madison email@example.com
Marine to freshwater transitions constitute formidable physiological barriers for most animal taxa. However, the estuarine copepod Eurytemora affinis has invaded freshwater habitats multiple times independently in the past century. We examined activity and expression of ion transport enzymes V-type H+ ATPase and Na+,K+ ATPase and also hemolymph osmolality for saline and fresh population pairs under common-garden salinities (0, 5, 15 PSU). We found parallel evolutionary shifts across multiple independent invasions. Relative to saline populations, freshwater populations showed evolutionary increases in V-ATPase activity in fresh water (0 PSU) and declines at higher salinity (15 PSU). In contrast, freshwater populations displayed declines in Na,K-ATPase activity across salinities. Results were consistent with expression differences observed in underlying genes. Most notably, ancestral saline populations selected for freshwater tolerance in the lab (12 gen) recapitulated the adaptive shifts in V-ATPase activity observed in natural populations. Hemolymph osmolality increased at low salinity in freshwater populations relative to their saline ancestors. Moreover, the same evolutionary shifts occurred in two independently-derived freshwater populations. Such increases in hemolymph osmolality are consistent with increases in ion uptake found in freshwater populations at low salinity. V-ATPase localization and activity have been hypothesized to be critical for the invasions of fresh water and of land, but evolution of this enzyme during habitat shifts had not been demonstrated. Our findings are consistent with evolution of increased physiological regulation accompanying transitions into stressful environments.