(full paper is archived in the Miller Library)
Title: Thermal tolerance limits of heart function in marine
snail congeners (genus Tegula) from different tidal
heights.
Student Author(s): Stenseng, Emily
Faculty Advisor(s): Somero, George
Pages: 26
Location: Final Papers Biology 175H
Date: June 2004
Abstract: Previous studies have demonstrated that a suite of
physiological and biochemical factors contribute to the establishment
of a species’ thermal tolerance limits and vertical
distribution patterns in the marine intertidal. In this study, the
thermal limits of heart function were determined for three congeneric
marine snail species of the genus Tegula, all inhabiting
discrete vertical zones in the intertidal. T. funebralis is
found in the low- to mid-intertidal, T. brunnea in the
subtidal to low-intertidal, and T. montereyi in the subtidal
zone. Using impedance electrodes, changes in heart rate were
monitored in field-acclimatized and lab-acclimated specimens of each
species, in response to thermal stresses in water. Significant
interspecific differences in Arrhenius break temperature values (ABT,
the temperature at which heart rate began a sharp decline) were
observed. Average ABTs for field-acclimatized T. funebralis,
T. brunnea, and T. montereyi were 31ºC, 25ºC
and 24ºC, respectively, establishing a positive correlation
between cardiac upper thermal tolerance limits and maximum habitat
temperatures. Flatline temperatures, defined as those at which
hearts ceased to beat, followed the same trend-T. funebralis
hearts stopped beating at significantly higher temperatures than the
two subtidal species. In response to cold stress, T.
funebralis maintained cardiac function at lower temperatures than
its congeners, demonstrating that it is more eurythermal. In all
three species, ABTs of specimens lab-acclimated to 22ºC were
higher than those of 14ºC lab-acclimated snails. T.
funebralis, however, showed the smallest ABT difference between
acclimation temperatures, indicating that it may have a lower
capacity for thermal acclimation. The results of this study suggest
that the mid-intertidal species T. funebralis is living closer
to its upper thermal tolerance limits. Thus T. funebralis
populations, and perhaps warm-adapted intertidal species in general,
may be at highest risk in the event of global climate change.
Notes: Published in Biological Bulletin, 2005 208:138-144