Evol Ecol Res 20: 349-363 (2019)     Full PDF if your library subscribes.

Gill Na⁺/K⁺-ATPase in the Threespine stickleback (Gasterosteus aculeatus): changes in transcript levels and sites of expression during acclimation to seawater

Makoto Kusakabe^1,2, Seiichi Mori³ and Jun Kitano⁴

¹Department of Biological Sciences, Faculty of Science, Shizuoka University, Surugaku, Shizuoka, Japan,  ²Department of Marine Bioscience, Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwa, Chiba, Japan,  ³Biological Laboratory, Gifu-keizai University, Ogaki, Gifu, Japan and  ⁴Ecological Genetics Laboratory, National Institute of Genetics, Mishima, Shizuoka, Japan

Correspondence: M. Kusakabe, Department of Biological Sciences, Faculty of Science, Shizuoka University, Surugaku, Shizuoka, Japan. email: kusakabe.makoto@shizuoka.ac.jp

ABSTRACT

Background: Na⁺/K⁺-ATPase (NKA) in the gills is a key contributor to osmoregulation in fishes.

Questions: Does gill NKA contribute to the regulation of salinity tolerance in stickleback? Do gill NKA expression patterns during acclimation to seawater differ among stickleback populations that differ in salinity tolerance?

Organisms: Freshwater Threespine stickleback (Gasterosteus aculeatus) from populations in Ono and Gifu, Japan.

Methods: We gradually acclimated the stickleback to 100% seawater. During acclimation, we monitored changes in plasma Na⁺ concentrations using atomic absorption spectrophotometry and gill NKA transcript levels using qPCR. We determined the sites of gill NKA expression by immunohistochemistry.

Results: Threespine stickleback from Ono were able to acclimate to 100% seawater. In contrast, stickleback from the Gifu population were able to survive in 50% seawater but not 100% seawater. Both ecotypes maintained a plasma Na⁺ concentration of approximately 150 mm during the acclimation process. Patterns of change in NKA transcript and protein expression were similar between the two populations, although they differed in tolerance to salinity. In both populations, gill NKA-positive ionocytes were distributed on the primary filaments and secondary lamellae in fresh water, but during acclimation to seawater the NKA-positive ionocytes on the secondary lamellae disappeared. The cell sizes and densities of NKA-positive ionocytes were higher in fish from Ono than in fish from Gifu, which may explain the difference in salinity tolerance between these two stickleback populations.

Keywords: Gasterosteus aculeatus, gills, Na⁺/K⁺-ATPase, plasma Na⁺, salinity, stickleback.

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