Background
The authors write that "measuring variation in physiological traits over broad spatial and temporal scales in an effort to investigate the ecological impacts of these traits (Chown et al., 2004)" can "aid in predicting how species or communities will respond to climate change," citing the confirmatory studies of Baker et al. (2004), Harley et al. (2006), Hassol (2004), Helmuth et al. (2002, 2005), Kennedy et al. (2002), Parmesan (2006), Parmesan and Yohe (2003), Portner et al. (2001) and Stillman (2003).

What was done
Employing this approach in their study of the European green crab (Carcinus maenas), Kelley et al. measured the upper lethal thermal thresholds of two populations of the invasive species living at the southern and northern limits of its current range on the west coast of North America - Sea Drift Lagoon, Stinson Beach California (CA; 37°54'27.82"N) and Pipestem Inlet, Vancouver Island, British Columbia (BC; 49°02.3'N), which are separated from each other by 1200 km of coastline - where "ambient sea surface temperature in the northern part of the North American west coast range is 5 to 10°C lower, depending on the time of year, than near the southern range limit," and where the species expansion from its initial introduction at the south end of its range to its current northern end occurred over a period of only about twenty years.

What was learned
The three U.S. scientists determined that the warm-adapted southern CA group of crabs had the highest level of organismal thermotolerance, as well as the greatest degree of heat shock protein 70 (Hsp70) production; and they additionally discovered that carapace widths of both male and female C. maenas individuals from CA were significantly smaller than those found in BC.

What it means
In the words of Kelley et al., "our findings provide evidence that the northeastern Pacific population of C. maenas has incurred a shift in thermal tolerance compared to its southern counterpart," and that "thermal adaptation at the level of the phenotype is a likely cause due to the short timescale of the invasion and the genetic connectivity of the two populations." These observations thus enabled them to state - and with a good degree of confidence - that over a period of a mere two decades, "it is possible that a large, northern cold-water phenotype may have already arisen," which further suggests that the reverse of this phenomenon could also have occurred over the same length of time if the driving force for phenotypic change had arisen due to the crabs migrating from a cooler to a warmer environment, or - by further inference - that it could have occurred during a period of equivalent climatic warming in the same physical setting without any relocation occurring. Hence, we have another example of a species demonstrating that it has the capacity to do what it needs to do to successfully cope with projected global warming, and without the need to migrate to accomplish it.

References
Baker, A.C., Starger, C.J., McClanahan, T.R. and Glynn, P.W. 2004. Corals' adaptive response to climate change. Nature 430: 741.

Chown, S.L., Gaston, K.J. and Robinson, D. 2004. Macrophysiology: large-scale patterns in physiological traits and their ecological implications. Functional Ecology 18: 159-167.

Harley, C.D.G., Hughes, A.R., Hultgren, K.M., Miner, B.G., Sorte, C.J.B., Thornber, C.S., Rodriguez, L.F., Tomanek, L. and Williams, S.L. 2006. The impacts of climate change in coastal marine systems. Ecological Letters 9: 228-241.

Hassol, S.J. 2004. Impacts of a Warming Arctic. Arctic Climate Impact Assessment. Cambridge University Press, New York, New York, USA.

Helmuth, B., Harley, C.D.G., Halpin, P.M., O'Donnell, M., Hofmann, G.E. and Blanchette, C.A. 2002. Climate change and latitudinal patterns of intertidal thermal stress. Science 298: 1015-1017.

Helmuth, B., Kingsolver, J.G. and Carrington, E. 2005. Biophysics, physiological ecology, and climate change: does mechanism matter? Annual Review of Physiology 67: 177-201.

Kennedy, V.S., Twilley, R.R., Kleypas, J.A., Cowan, J.H. and Steven, S.R. 2002. Coastal and Marine Ecosystems and Climate Change. Potential Effects on U.S. Resources. Pew Center on Global Climate Change. Arlington, Virginia, USA.

Parmesan, C. 2006. Ecological and evolutionary responses to recent climate change. Annual Review of Ecology, Evolution and Systematics 37: 637-669.

Portner, H.O., Berdal, B., Blust, R., Brix, O., Colosimo, A., De Wachter, B., Giuliani, A., Johansen, T., Fischer, T. and Knust, R. 2001. Climate induced temperature effects on growth performance, fecundity and recruitment in marine fish: developing a hypothesis for cause and effect relationships in Atlantic cod (Gadus morhua) and common ellpout (Zoarces viviparous). Continental Shelf Research 21: 1975-1997.

Stillman, J.H. 2003. Acclimation capacity underlies susceptibility to climate change. Science 301: 65.