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Evolutionary Response to Environmental Change in Sockeye Salmon
Crozier, L.G., Scheuerell, M.D. and Zabel, R.W. 2011. Using time series analysis to characterize evolutionary and plastic responses to environmental change: A case study of a shift toward earlier migration date in sockeye salmon. The American Naturalist 178: 755-773.

The authors write that "environmental change can shift the phenotype of an organism through either evolutionary or non-genetic processes," but they say that "despite abundant evidence of phenotypic change in response to recent climate change, we typically lack sufficient genetic data to identify the role of evolution." Thus, they go on to do what it has often been so hard to do in the past.

What was done
Crozier et al. investigated the drivers of a long-term trend toward earlier upstream migration date in adult sockeye salmon (Oncorhynchus nerka Walbaum) that currently migrate up the Columbia River 10.3 days earlier than they did in the 1940s. Noting that water temperature records in the lower river showed a rise of 2.6°C in mean July temperature since 1949, they "developed a functional model relating survival during upstream migration to temperature on the basis of the results of recent studies that tracked individual fish through the migration," after which they "hindcast this function over the historical record to estimate the putative selection differential over the time series." Thereafter, they "assembled a set of possible environmental drivers of interannual variation in migration timing from the literature" and used "a state-space modeling framework to combine selection and these environmental variables as covariates to explain mean population migration date in a formal time-series analysis," using "model-selection techniques to determine which factors best predicted annual migration timing".

What was learned
The three researchers from the Northwest Fisheries Science Center in Seattle, Washington (USA) determined, in their words, that "an evolutionary response to thermal selection was capable of explaining up to two-thirds of the phenotypic trend" they observed, while "adaptive plastic responses to June river flow explain most of the remainder."

What it means
In discussing their findings, Crozier et al. note that the amount of evolutionary change they calculated to have taken place in the situation they studied "is typical of numerous studies of contemporary evolution," citing Hendry and Kinnison (1999) and Kingsolver et al. (2001). And they suggest that evolutionary change "will play an important role in protecting species from extinction during ongoing climate change, as demonstrated in recent simulations of evolution in Fraser River sockeye salmon," citing Reed et al. (2011). Last of all, they conclude by voicing their opinion that "directional environmental changes are very likely to induce more rapid evolution in the future."

Hendry, A.P. and Kinnison, M.T. 1999. Perspective: the pace of modern life: measuring rates of contemporary microevolution. Evolution 53: 1637-1653.

Kingsolver, J.G., Hoekstra, H.E., Hoekstra, J.M., Berrigan, D., Vignieri, S.N., Hill, C.E., Hoang, A., Gibert, P. and Beerli, P. 2001. The strength of phenotypic selection in natural populations. American Naturalist 157: 245-261.

Reed, T.E., Schindler, D., Hague, M., Paterson, D., Meir, E., Waples, R.S. and Hinch, S. 2011. Time to evolve? Potential evolutionary responses of Fraser River sockeye salmon to climate change and effects on persistence. PLoS ONE 6: e20380.

Reviewed 4 April 2012