title: Climatic variability in combination with eutrophication drives adaptive responses in the gills of Lake Victoria cichlids.
abstract: Textbook examples of adaptive radiation often show rapid morphological changes in response to environmental perturbations. East Africa's Lake Victoria, famous for its stunning adaptive radiation of cichlids, has suffered from human-induced eutrophication over the past decades. This cultural eutrophication is thought to be partly responsible for the dramatically reduced cichlid biodiversity, but climatic variability in itself might also have contributed to the eutrophication which resulted in low oxygen levels and decreased water transparency. To determine how recent environmental changes have influenced the lake and its cichlids over the past 50 years, we gathered environmental and meteorological variables and compared these with gill surface area of four cichlid species. We found that during the period of severe eutrophication and temperature increase (1980s), reduced wind speeds coincided with a reduction in oxygen levels and a decrease in both water temperature and transparency. The gill surface area in three out of the four cichlid species increased during this period which is consistent with adaptive change in response to increased hypoxia. During the 2000s, wind speeds, oxygen levels, water transparency and water temperature increased again, while cichlid gill surface area decreased. Our results imply that climatic changes and especially wind speed and direction might play a crucial role in tropical lake dynamics. The changes in Lake Victoria's water quality coincide with fluctuations in cichlid gill surface area, suggesting that these fish can respond rapidly to environmental perturbations, but also that climatic variability, together with continued eutrophication, might be detrimental to the lake's cichlid biodiversity.
authors.affiliation: Institute of Biology Leiden, Leiden University, 2300 RA, Leiden, The Netherlands. jacco.vanrijssel@eawag.ch.|Naturalis Biodiversity Center, 2300 RA, Leiden, The Netherlands. jacco.vanrijssel@eawag.ch.|Fish Ecology and Evolution, EAWAG Center of Ecology, Evolution and Biogeochemistry, 6047, Kastanienbaum, Switzerland. jacco.vanrijssel@eawag.ch.|Institute of Ecology and Evolution, University of Bern, 3012, Bern, Switzerland. jacco.vanrijssel@eawag.ch.
authors.forename: Jacco C
authors.initials: JC
authors.lastname: van Rijssel
authors.affiliation: Large Lakes Observatory, University of Minnesota, Duluth, MN, 55812, USA.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Hecky
authors.affiliation: Tanzania Fisheries Research Institute, P.O. Box 9750, Dar es Salaam, Tanzania.
authors.forename: Mary A
authors.initials: MA
authors.lastname: Kishe-Machumu
authors.affiliation: Institute of Biology Leiden, Leiden University, 2300 RA, Leiden, The Netherlands.
authors.forename: Saskia E
authors.initials: SE
authors.lastname: Meijer
authors.affiliation: Institute of Biology Leiden, Leiden University, 2300 RA, Leiden, The Netherlands.
authors.forename: Johan
authors.initials: J
authors.lastname: Pols
authors.affiliation: Institute of Biology Leiden, Leiden University, 2300 RA, Leiden, The Netherlands.
authors.forename: Kaj M
authors.initials: KM
authors.lastname: van Tienderen
authors.affiliation: Institute of Biology Leiden, Leiden University, 2300 RA, Leiden, The Netherlands.
authors.forename: Jan D
authors.initials: JD
authors.lastname: Ververs
authors.affiliation: Institute of Biology Leiden, Leiden University, 2300 RA, Leiden, The Netherlands.|Koeman en Bijkerk bv, Ecological Research and Consultancy, 9750 AC, Haren, The Netherlands.
authors.forename: Jan H
authors.initials: JH
authors.lastname: Wanink
authors.affiliation: Institute of Biology Leiden, Leiden University, 2300 RA, Leiden, The Netherlands.|Naturalis Biodiversity Center, 2300 RA, Leiden, The Netherlands.
authors.forename: Frans
authors.initials: F
authors.lastname: Witte
mesh_terms: D000818:Animals; D044822:Biodiversity; D023681:Cichlids; D005068:Eutrophication; D005880:Gills; D060106:Lakes
keywords: Climate change; Cultural eutrophication; Hypoxia; Morphological adaptation; Wind stress