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How Not to Underestimate Mussel Heart Rate and Thermal Tolerance

Paper Reviewed
Tagliarolo, M. and McQuaid, C.D. 2016. Field measurements indicate unexpected, serious underestimation of mussel heart rates and thermal tolerance by laboratory studies. PLoS ONE: 11(2): e0146341: doi:10.1371/journal.pone.0146341.

Introducing their intriguing study, Tagliarolo and McQuaid (2016) write that "attempts to predict the response of species to long-term environmental change are generally based on extrapolations from laboratory experiments that inevitably simplify the complex interacting effects that occur in the field." So what's to be done about this common but serious problem?

In the case of the two South African researchers -- who studied two genetic lineages of the brown mussel Perna perna over a full tidal cycle in-situ at two different real-world sites, in order to evaluate the cardiac responses of the two genetic lineages that are found along the South African coast to both temperature and the immersion/emersion cycles, where "robomussel" temperature loggers were used to monitor thermal conditions at the two sites over an entire year -- they found that "comparison with live animals showed that robomussels provided a good estimate of mussel body temperatures." And what, more specifically, did their study reveal?

Tagliarolo and McQuaid write that "overall, the results underline the critical importance of performing in-situ experiments on undisturbed animals in order to evaluate the reliability of laboratory experiments as a way of estimating field responses and deriving realistic assessments of the physiology of intertidal species under natural conditions." And this work revealed, as they continue, that "a significant difference in estimated body temperatures was observed between the sites and the results showed that, under natural conditions, temperatures regularly approach or exceed the thermal limits of P. perna identified in the laboratory." In fact, they report that a "comparison of the heart rates measured in the field with data previously measured in the laboratory indicates that laboratory results seriously underestimate heart rate activity," and that they do it "by as much as 75%."

In concluding, the two researchers thus write that "field estimates of body temperatures indicated an ability to tolerate temperatures considered lethal on the basis of laboratory measurements." And they therefore rightly conclude that "real metabolic variability and limits can only be assessed for animals living in the field."

Posted 10 August 2015