title: Changes in water chemistry can disable plankton prey defenses.
abstract: The effectiveness of antipredator defenses is greatly influenced by the environment in which an organism lives. In aquatic ecosystems, the chemical composition of the water itself may play an important role in the outcome of predator-prey interactions by altering the ability of prey to detect predators or to implement defensive responses once the predator's presence is perceived. Here, we demonstrate that low calcium concentrations (<1.5 mg/L) that are found in many softwater lakes and ponds disable the ability of the water flea, Daphnia pulex to respond effectively to its predator, larvae of the phantom midge, Chaoborus americanus. This low-calcium environment prevents development of the prey's normal array of induced defenses, which include an increase in body size, formation of neck spines, and strengthening of the carapace. We estimate that this inability to access these otherwise effective defenses results in a 50-186% increase in the vulnerability of the smaller juvenile instars of Daphnia, the stages most susceptible to Chaoborus predation. Such a change likely contributes to the observed lack of success of daphniids in most low-calcium freshwater environments, and will speed the loss of these important zooplankton in lakes where calcium levels are in decline.
authors.affiliation: Department of Biology, State University of New York (SUNY) College at Buffalo, Buffalo, NY 14222, USA. riessehp@buffalostate.edu
authors.forename: Howard P
authors.initials: HP
authors.lastname: Riessen
authors.forename: Robert Dallas
authors.initials: RD
authors.lastname: Linley
authors.forename: Ianina
authors.initials: I
authors.lastname: Altshuler
authors.forename: Max
authors.initials: M
authors.lastname: Rabus
authors.forename: Thomas
authors.initials: T
authors.lastname: Söllradl
authors.forename: Hauke
authors.initials: H
authors.lastname: Clausen-Schaumann
authors.forename: Christian
authors.initials: C
authors.lastname: Laforsch
authors.forename: Norman D
authors.initials: ND
authors.lastname: Yan
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D049628:Body Size; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D003621:Daphnia / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004777:Environment; D020387:Food Chain; D018625:Microscopy, Atomic Force / Q000379:methods; D008954:Models, Biological; D010641:Phenotype; D010933:Plankton / Q000502:physiology*; D011235:Predatory Behavior; D013997:Time Factors; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D002118:Calcium