title: Effect of Clonal Selection on Daphnia Tolerance to Dark Experimental Conditions.
abstract: Recent studies have demonstrated substantial effects of environmental stress that vary among clones. Exposure to ultraviolet radiation (UV) is an important abiotic stressor that is highly variable in aquatic ecosystems due to diel and seasonal variations in incident sunlight as well as to differences in the UV transparency of water among water bodies, the depth distribution of organisms, and the ability of organisms to detect and respond to UV. In contrast to the convention that all UV is damaging, evidence is accumulating for the beneficial effects of exposure to low levels of UV radiation. Whereas UV has been frequently observed as the primary light-related stressor, herein we present evidence that dark conditions may be similarly "stressful" (reduction of overall fitness), and stress responses vary among clones of the freshwater crustacean Daphnia parvula. We have identified a significant relationship between survivorship and reduced fecundity of clones maintained in dark conditions, but no correlation between tolerance of the clones to dark and UV radiation. Low tolerance to dark conditions can have negative effects not only on accumulated stresses in organisms (e.g. the repair of UV-induced damage in organisms with photolyase), but potentially on the overall physiology and fitness of organisms. Our results support recent evidence of the beneficial effects of low-level UV exposure for some organisms.
authors.affiliation: Thomas H. Gosnell School of Life Sciences, Rochester Institute of Technology, Rochester, NY 14623, United States of America.
authors.forename: Sandra J
authors.identifier: http://orcid.org/0000-0001-6599-1413
authors.initials: SJ
authors.lastname: Connelly
authors.affiliation: School of Fisheries, Aquaculture and Aquatic Sciences, College of Agriculture, Auburn University, Auburn, AL 36849, United States of America.|Department of Biology, Miami University, Oxford, OH 45056, United States of America.
authors.forename: James A
authors.initials: JA
authors.lastname: Stoeckel
authors.affiliation: School of Forestry and Wildlife Sciences, Auburn University, Auburn, AL 36849, United States of America.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Gitzen
authors.affiliation: Department of Biology, Miami University, Oxford, OH 45056, United States of America.
authors.forename: Craig E
authors.initials: CE
authors.lastname: Williamson
authors.affiliation: Department of Biology, Miami University, Oxford, OH 45056, United States of America.
authors.forename: Maria J
authors.initials: MJ
authors.lastname: González
mesh_terms: D000222:Adaptation, Physiological / Q000528:radiation effects*; D000818:Animals; D002999:Clone Cells; D003621:Daphnia / Q000502:physiology / Q000528:radiation effects*; D005260:Female; D005298:Fertility / Q000502:physiology / Q000528:radiation effects; D008136:Longevity / Q000528:radiation effects*; D008297:Male; D017440:Photoperiod; D012098:Reproduction / Q000502:physiology / Q000528:radiation effects; D013472:Sunlight; D014466:Ultraviolet Rays