SCOTT, G.S.*; RICHARDS, J.S.; ROGERS, J.T.; WOOD, C.M.; SCHULTE, P.M.; University of British Columbia, Vancouver; University of British Columbia, Vancouver; McMaster University, Hamilton, ON; McMaster University, Hamilton, ON; University of British Columbia, Vancouver: Intraspecific variation in freshwater ionoregulation in the euryhaline teleost, Fundulus heteroclitus
The common killifish, Fundulus heteroclitus, is a dynamically euryhaline teleost capable of tolerating a wide range of environmental salinities. Recent work in our laboratory has demonstrated transcriptional regulation of gill ion transporters to be an important component of the physiological response to both freshwater and seawater salinity transfer. However, variability in freshwater tolerance exists within this species; F.h. heteroclitus (southern subspecies) suffers significant mortality after freshwater transfer, in contrast toF.h. macrolepidotus (northern subspecies) for which mortality is negligible. Furthermore, southern survivors experience greater deflection of plasma ions after freshwater transfer than northern fish. Using quantitative real-time PCR, we have demonstrated significant differences in the patterns of ion transporter mRNA expression that may underlie the observed differences between subspecies in freshwater tolerance. In particular, southern individuals had consistently lower Na,K-ATPase α1a expression after freshwater transfer. Furthermore, gill Na,K-ATPase activity increased 24 and 96 hours after freshwater transfer in northern fish, whereas no similar elevation existed in southern fish. These results suggest that southern populations of killifish had lower ion uptake, which resulted in greater decreases in plasma ions and higher mortality.
