RESPIRATORY VARIATION AND ACCLIMATION IN THE FRESHWATER LIMPET,LAEVAPEX FUSCUS

Abstract

1. From three populations of Laevapex fuscus samples were collected bi-weekly through 1970 to 1972. Oxygen consumption rates at ambient temperature and at 10° C and at 20° C were determined. Other respiration experiments involved decreasing O2 tension at 20° C and the consequences of low oxygen stress.2. At ambient temperatures, respiration during the summer is normally 26 to 36 times the winter respiratory rate.3. After treatment with low oxygen stress there is no overt payment of an oxygen debt in Laevapex, instead there is a general increase in respiratory rate at all oxygen tensions. These rates are maintained for up to 135 hours after return to fully saturated conditions and appear to be in part a short-term acclimation of respiratory rates to low oxygen tensions.4. Measured at 100% oxygen tension at 10° and 20° C, respiration rates are higher in the summer than in the winter for all three populations. Such a respiratory response to temperature has been called reverse acclimation. Laevapex lives in conditions of low oxygen tension during the winter. The respiration experiments with decreasing oxygen tension show that at low oxygen tensions winter-conditioned specimens have a higher respiratory rate than summer-conditioned individuals. Such a response to low oxygen tensions may be interpreted as a positive rather than reverse acclimation.5. A hypothesis is advanced regarding "reverse" acclimation in this species. Reverse acclimation appears to be merely one manifestation of a more general acclimatory change in winter-conditioned Laevapex. These limpets, when winter-conditioned, have a higher respiratory rate at low oxygen tension than do summer-conditioned limpets. Although this acclimatory process appears to be triggered by decreasing temperature, its adaptational significance involves the survival of the inactive overwintering limpet in contact with reducing mud.