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Metabolic plasticity and critical temperatures for aerobic scope in a eurythermal marine invertebrate (Littorina saxatilis, Gastropoda: Littorinidae) from different latitudes
Lab. Ecophysiology and Ecotoxicology, Alfred-Wegener-Institute for Polar and Marine Research, Columbusstr., 27568 Bremerhaven, Germany
* Author for correspondence at present address: Biology Dept, University of North Carolina at Charlotte, 9201 University City Blvd, Charlotte, NC 28223, USA (e-mail: isokolov{at}email.uncc.edu)
Accepted 26 September 2002
Effects of latitudinal cold adaptation and cold acclimation on metabolic
rates and aerobic scope were studied in the eurythermal marine gastropod
Littorina saxatilis from temperate North Sea and sub-arctic White Sea
areas. Animals were acclimated for 6-8 weeks at control temperature (13°C)
or at 4°C, and their respiration rates were measured during acute
temperature change (1-1.5°C h-1) in a range between 0°C and
32°C. In parallel, the accumulation of anaerobic end products and changes
in energy status were monitored. Starting from 0°C, aerobic metabolic
rates of L. saxatilis rose quickly with increasing temperatures up to
a point at or slightly above the respective acclimation temperature. Beyond
this value, thermal sensitivity of oxygen consumption rate
(
O2) greatly
decreased in a wide, 15°C range of experimental temperatures. This change
in metabolic regulation was also reflected in the activation energy of aerobic
metabolism (Ea), which was approximately seven times lower
at temperatures above Arrhenius breakpoint temperatures (ABTs) than at
temperatures below ABTs. Warming progressively led to a discrepancy between
energy demand and energy production, as demonstrated by a decrease in the
levels of high-energy phosphates [phosho-L-arginine (PLA) and ATP], and
resulted in the onset of anaerobiosis at critically high temperatures,
indicating a limitation of aerobic scope. The comparison of aerobic and
anaerobic metabolic rates in L. saxatilis in air and water suggests
that the heat-induced onset of anaerobiosis is due to the insufficient oxygen
supply to tissues at high temperatures. Cold acclimation led to an increase in
aerobic metabolic rates and a considerable downward shift of the upper
critical temperature in North Sea L. saxatilis but not in White Sea
L. saxatilis. Limited metabolic plasticity in response to cold
acclimation in sub-arctic White Sea snails as compared with their temperate
North Sea counterparts suggests that metabolic depression occurs during
overwintering under the more extreme winter conditions at the White Sea.
Key words: temperature adaptation, aerobic scope, critical temperatures, respiration, metabolic cold compensation, Littorina
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