How does rising atmospheric CO2 affect marine organisms?

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The Thermal Tolerance of a Tropical Lizard Species
Leal, M. and Gunderson, A.R. 2012. Rapid change in the thermal tolerance of a tropical lizard. The American Naturalist 180: 815-822.

The authors write that "the general view is that climate change will have a major impact on biodiversity by increasing the extinction risk of many species or changing their distributions," based on "the implicit assumption that species are relatively fixed entities, unable to respond to rapid changes in ecological conditions, including climatic variables, over an ecological timescale." However, they state that "evidence that some organisms are able to respond to climatic changes over short timescales has begun to emerge (e.g., Grant and Grant, 2002; Walther et al., 2002; Bradshaw and Holzapfel, 2006); so they proceeded to see if they could add some similar evidence to this growing body of work.

What was done
Some 35 years ago, the tropical Caribbean lizard Anolis cristatellus, which is native to an area of xeric forest in northeastern Puerto Rico, was found in Miami, Florida, by Schwartz and Thomas (1975) in a location where minimum temperatures in winter can average 10°C cooler than in Puerto Rico, but where maximum temperatures in summer are much more similar. And taking advantage of this situation, Leal and Gunderson set about to determine if the cold tolerance or critical thermal minimum temperature (CTmin) of the introduced populations had diverged from that of the source populations of A. cristatellus over the 35-year period of their physical separation. And as a check on their experimental procedures, they also conducted studies to see if the critical thermal maximum temperature (CTmax) of the two groups of lizards remained about the same.

What was learned
The two U.S. researchers report that "the introduced population tolerates significantly colder temperatures (by ~3°C) than does the Puerto Rican source population," while at the same time they found that the maximum temperatures tolerated "did not differ."

What it means
In the final sentence of their paper's abstract, Leal and Gunderson write that their results "demonstrate that changes in thermal tolerance occurred relatively rapidly (~35 generations), which strongly suggests that the thermal physiology of tropical lizards is more labile than previously proposed." And, therefore, they write in their paper's final paragraph that "regardless of the mechanism, the adaptive lability of thermal tolerance in A. cristatellus over an ecological timescale" provides "a glimpse of hope for tropical lizards under the current conditions of rapid climate change."

Bradshaw, W.E. and Holzapfel, C.M. 2006. Evolutionary responses to rapid climate change. Science 312: 1477-1478.

Grant, P.R. and Grant, R.B. 2002. Unpredictable evolution in 30-year study of Darwin's finches. Science 296: 707-711.

Schwartz, A. and Thomas, R. 1975. A Check-List of West Indian Amphibians and Reptiles. Carnegie Museum of Natural History Special Publication 1. Carnegie Museum of Natural History, Pittsburgh, Pennsylvania, USA.

Walther, G.-R., Post, E., Convey, P., Menzel, A., Parmesan, C., Beebee, T.J.C., Fromentin, J.-M., Hoegh-Guldberg, O. and Bairlein, F. 2002. Ecological responses to recent climate change. Nature 416: 389-395.

Reviewed 17 April 2013