title: Sperm motility adaptation to ion-differing aquatic environments in the Tanganyikan cichlid, Astatotilapia burtoni.
abstract: The cichlid fish, Astatotilapia burtoni, can acclimate and reproduce in both the K(+)-, Na(+)-, and Ca(2+)-rich waters of Lake Tanganyika (pH 8.9-9.2) and the surrounding rivers where K(+), Na(+), and Ca(2+) concentrations are low (pH 6.5). In this study, we compared sperm motility features among A. burtoni inhabiting the lake, those living in the surrounding rivers, and those from rivers that acclimates to lake water. Sperm of all three groups required extracellular Ca(2+) ([Ca(2+)]o) for sperm motility activation. However, involvement of K(+) and Na(+) were different. In sperm motility initiation of lake population, the decrease in Na(+) and increase in K(+) concentrations corresponding to a decrease in [Na(+)]o/[K(+)]o was required. In contrast, sperm motility in both the river population and those acclimated to lake water were activated only by a decrease in [Na(+)]o, suggesting that motility initiation cues regarding Na(+) and K(+) are different among populations within same species. One probable reason why the difference of initiation cues is that the concentration of K(+) in the river water (40 mM) is lower than that in the lake water (110 mM). These results suggest that sperm flagellar activation cascades of river and lake populations within this species differ as a result of adaptations to different ionic environments.
authors.affiliation: Sesoko Station, Tropical Biosphere Research Center, University of the Ryukyus, Motobu, Okinawa, Japan. morita_m0606@yahoo.co.jp
authors.forename: Masaya
authors.initials: M
authors.lastname: Morita
authors.forename: Satoshi
authors.initials: S
authors.lastname: Awata
authors.forename: Tetsumi
authors.initials: T
authors.lastname: Takahashi
authors.forename: Akihiro
authors.initials: A
authors.lastname: Takemura
authors.forename: Masanori
authors.initials: M
authors.lastname: Kohda
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D002412:Cations; D023681:Cichlids / Q000502:physiology*; D017753:Ecosystem; D008297:Male; D013081:Sperm Motility
chemical_list: D002412:Cations