Meeting Abstract
P1.81 Jan. 4 Potential molecular basis for lower salinity limits in the euryhaline green crab, Carcinus maenas HENRY, R.P.; Auburn University henryrp@auburn.edu
The green crab, Carcinus maenas, is a euryhaline marine crustacean that is found in salinities as low as 10 ppt. It can be acclimated to as low as 5 ppt, but this is near the species� lower lethal limit. The physiological mechanism, which determines lower salinity limits of this and other marine species, has not been systematically investigated. Since the green crab is a moderately strong osmotic/ionic regulator, a breakdown in this mechanism may be what sets the lower salinity limit. The enzyme carbonic anhydrase (CA) is a central molecular component of low salinity adaptation in the gills of C. maenas. CA is induced up to 10 fold, depending on acclimation salinity. In this study, CA induction was used as an indicator of the up-regulation of the branchial ion transport mechanism in response to low salinity. Crabs were collected from 32 ppt and transferred to each of the following salinities (15, 12.5, 10, and 7.5 ppt) for a period of 4 and 7 days. Anterior (G4) and posterior (G8) gills were then dissected out for CA assay, and total RNA extraction for analysis of CA mRNA expression via real time PCR. At 32 ppt, CA activity and mRNA abundance were low in both gills. Transfer to 15 ppt for 7 days resulted in a 10 fold induction of CA activity and an 8 fold induction of mRNA abundance. Transfer to the lower salinities resulted in significantly lower levels of both CA induction and mRNA expression. A similar pattern was seen for crabs transferred for 4 days. Transfer to 5 ppt virtually eliminated CA induction and caused 50% mortality. CA activity and mRNA expression did not change in G3, and the expression of a control gene, arginine kinase, also did not change. These initial results indicate that the up-regulation of expression of CA breaks down below a critical salinity, suggesting that lower salinity limits might be set by a failure at the transcriptional level. Supported by NSF IBN 02-30005.
