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The impact of human-made ecological changes on the genetic architecture of Daphnia species
↵1N.B. and K.S. contributed equally to this work.
Edited by Nelson G. Hairston, Cornell University, Ithaca, NY, and accepted by the Editorial Board February 2, 2009 (received for review July 24, 2008)

Abstract
The overenrichment (eutrophication) of aquatic ecosystems with nutrients leading to algal blooms and anoxic conditions has been a persistent and widespread environmental problem. Although there are many studies on the ecological impact of elevated phosphorus (P) levels (e.g., decrease in biodiversity and water quality), little is known about the evolutionary consequences for animal species. We reconstructed the genetic architecture of a Daphnia species complex in 2 European lakes using diapausing eggs that were isolated from sediment layers covering the past 100 years. Changes in total P were clearly associated with a shift in species composition and the population structure of evolutionary lineages. Although environmental conditions were largely re-established after peak eutrophication during the 1970s and 1980s, original species composition and the genetic architecture of species were not restored but evolved along new evolutionary trajectories. Our data demonstrate that anthropogenically induced temporal alterations of habitats are associated with long-lasting changes in communities and species via interspecific hybridization and introgression.
Footnotes
- 4To whom correspondence should be addressed. E-mail: k.schwenk{at}bio.uni-frankfurt.de
Author contributions: N.B., T.J., and K.S. designed research; N.B., C.S., D.S., and T.J. performed research; N.B. contributed new reagents/analytical tools; N.B. and K.S. analyzed data; and N.B., D.S., P.S., B.S., and K.S. wrote the paper.
↵2Present address: Institute of Zoology, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland.
↵3Present address: Aarbergstrasse 64c, CH-3250 Lyss, Switzerland.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission. N.G.H. is a guest editor invited by the Editorial Board.
Freely available online through the PNAS open access option.