ABSTRACT Thermal performance curves are commonly used to investigate the effects of heat acclimation on thermal tolerance and physiological performance. However, recent work indicates that the metrics of these curves heavily depend on experimental design and may be poor predictors of animal survival during heat events in the field. In intertidal mussels, cardiac thermal performance (CTP) tests have been widely used as indicators of animals' acclimation or acclimatization state, providing two indices of thermal responses: critical temperature (Tcrit; the temperature above which heart rate abruptly declines) and flatline temperature (Tflat; the temperature where heart rate ceases). Despite the wide use of CTP tests, it remains largely unknown how Tcrit and Tflat change within a single individual after heat acclimation, and whether changes in these indices can predict altered survival in the field. Here, we addressed these issues by evaluating changes in CTP indices in the same individuals before and after heat acclimation. For control mussels, merely reaching Tcrit was not lethal, whereas remaining at Tcrit for ≥10 min was lethal. Heat acclimation significantly increased Tcrit only in mussels with an initially low Tcrit (<35°C), but improved their survival time above Tcrit by 20 min on average. Tflat increased by ∼1.6°C with heat acclimation, but it is unlikely that increased Tflat improves survival in the field. In summary, Tcrit and Tflat per se may fall short of providing quantitative indices of thermal tolerance in mussels; instead, a combination of Tcrit and tolerance time at temperatures ≥Tcrit better defines changes in thermal tolerance with heat acclimation.
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) Impact of heating rate on cardiac thermal tolerance in the California mussel, Mytius californianus.
Intertidal communities of wave-swept rocky shores have served as a
powerful model system for experiments in ecology, and mussels (the
dominant competitor for space in the mid-intertidal zone) play a
central role in determining community structure in this physically
stressful habitat. Consequently, the ability to account for mussels’
physiological responses to thermal stress affects ecologists’ capacity
to predict the impacts of a warming climate on this ecosystem. Here,
we examined the effect of heating rate on cardiac thermal tolerance in
the ribbed mussel, Mytilus californianus, comparing populations from
high and low sites in the intertidal zone where emersion duration
leads to different mean daily heating rates. Two temperature-related
cardiac variables were examined: (1) the critical temperature (Tcrit)
at which heart rate (HR) precipitously declines, and (2) flatline
temperature (FLT) where HR reaches zero. Mussels were heated in
air at slow, moderate and fast rates, and HR was measured via an
infrared sensor affixed to the shell. Faster heating rates significantly
increased Tcrit in high- but not low-zone mussels, and Tcrit was higher
in high- versus low-zone mussels, especially at the fastest heating
rate. By contrast, FLT did not differ between zones, and was
minimally affected by heating rate. As heating rate significantly
impacted high- but not low-zone mussels’ cardiac thermal
tolerance, realistic zone-specific heating rates must be used in
laboratory tests if those tests are to provide accurate information for
ecological models attempting to predict the effects of increasing
temperature on intertidal communities.
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- Award ID(s):
- 1655529
- NSF-PAR ID:
- 10135148
- Date Published:
- Journal Name:
- Journal of experimental biology
- Issue:
- 222
- ISSN:
- 0022-0949
- Page Range / eLocation ID:
- 1-12
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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We were particularly interested in
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/doi: 10.1242/jeb.203166
