It is the stuff of action movies—researchers have resurrected killer Daphnia from our past. Okay so the Daphnia are only killer in the “killer” = synonym for “awesome” sense (unless you’re a phytoplankton anyway). But this study is still amazing. For the first time, we have a series of snapshots showing evolutionary change over a 1600-year period leading up to a century of rapid human population growth.
In 1860, the human population surrounding South Center Lake, Minnesota USA was a mere 1800 individuals, but increased 30-fold by 2010. By 2013, acreage in agriculture had dramatically increased, and after remaining stable for over 1500 years, phosphorus (P) inputs into this originally P-limited lake increased 5-fold over the past 150 years. By carefully isolating Daphnia from a sediment core, Frisch and coauthors resurrected Daphnia eggs and examined Daphnia DNA from across this time period. The results are stunningly clear. Daphnia phenotypes and their underlying population genetic structure were surprisingly stable from the oldest samples (ca 455 A.D.) to sediments dated to 1855 A.D., but changed dramatically at the precise time that the human population and agricultural acreage exploded in size. Even though few genotypes could be resurrected from the earliest samples, significant decreases in P-use efficiency and P-retention were observed. In fact, these shifts were so dramatic that the oldest Daphnia exhibit P-use phenotypes not seen today in any Daphnia species. Although the approach is correlational and although the study only examined a single population in a single lake, the data are convincing. How many other species brandish the evolutionary signature of human impact?
A millennial-scale chronicle of evolutionary responses to cultural eutrophication in Daphnia. 2014. D. Frisch, P.K. Morton, P.R. Chowdhury, B.W. Culver, J.K. Colbourne, L.J. Weider, P.D. Jeyasingh. Ecology Letters 17:360-368.