Background
The authors write that "it is becoming increasingly apparent that adaptive microevolution can occur rapidly in wild populations (Hendry and Kinnison, 1999; Reznick and Ghalambor, 2001; Carroll et al., 2007; Schoener, 2011)," and they report that there is a "proliferation of evidence suggesting that life-history traits are changing in many populations as a response to global climate change," citing the work of Root et al. (2003) and Parmesan and Yohe (2003).

What was done
Focusing on Auke Creek, a small lake-outlet stream near Juneau, Alaska (USA), where there have been complete daily counts of all adult pink salmon migrating into the creek since 1971, Kovach et al. state that they used "phenotypic data on migration timing, archived genetic samples and data from a marker locus, the allele frequencies of which were experimentally altered more than 30 years ago, to determine whether change in migration timing in a population of pink salmon has a genetic basis (i.e., microevolution)."

What was learned
The three researchers determined that both even- and odd-year adult pink salmon that spawn in the warming Alaskan stream are migrating into freshwater nearly two weeks earlier than they did 40 years ago. They also found that experimental data "support the hypothesis that there has been directional selection for earlier migration timing, resulting in a substantial decrease in the late-migrating phenotype (from more than 30% to less than 10% of the total abundance)." They also report that "from 1983 to 2011, there was a significant decrease - over threefold - in the frequency of a genetic marker for late-migration timing, but there were minimal changes in allele frequencies at other natural loci."

What it means
According to Kovach et al., "these results demonstrate that there has been rapid microevolution for earlier migration timing in this population," which has allowed both the odd- and even-year groups of salmon "to remain resilient to environmental change," as has also been demonstrated by Kinnison and Hairston (2007). And they note in closing that "population abundance in 2011 was the second highest on record," further indicating that the salmon of Auke Creek are "persisting through rapid temperature warming."

References
Carroll, S.P., Hendry, A.P., Reznick, D.N. and Fox, C.W. 2007. Evolution on ecological time-scales. Functional Ecology 21: 387-393.

Hendry, A.P. and Kinnison, M.T. 1999. The pace of modern life: measuring rates of contemporary microevolution. Evolution 53: 1636-1653.

Kinnison, M.T. and Hairston Jr., N.G. 2007. Eco-evolutionary conservation biology: contemporary evolution and the dynamics of persistence. Functional Ecology 21: 444-454.

Parmesan, C. and Yohe, G. 2003. A globally coherent fingerprint of climate change impacts across natural systems. Nature 421: 37-42.

Reznick, D.N. and Ghalambor, C.K. 2001. The population ecology of contemporary adaptations: what empirical studies reveal about the conditions that promote adaptive evolution. Genetica 112: 183-198.

Root, T.L., Price, J.T., Hall, K.R., Schneider, S.H., Rosenzweig, C. and Pounds, J.A. 2003. Fingerprints of global warming on wild animals and plants. Nature 421: 57-60.

Schoener, T.W. 2011. The newest synthesis: understanding the interplay of evolutionary and ecological dynamics. Science 331: 426-429.