title: Metamorphosis enhances the effects of metal exposure on the mayfly, Centroptilum triangulifer.
abstract: The response of larval aquatic insects to stressors such as metals is used to assess the ecological condition of streams worldwide. However, nearly all larval insects metamorphose from aquatic larvae to winged adults, and recent surveys indicate that adults may be a more sensitive indicator of stream metal toxicity than larvae. One hypothesis to explain this pattern is that insects exposed to elevated metal in their larval stages have a reduced ability to successfully complete metamorphosis. To test this hypothesis we exposed late-instar larvae of the mayfly, Centroptilum triangulifer, to an aqueous Zn gradient (32-476 μg/L) in the laboratory. After 6 days of exposure, when metamorphosis began, larval survival was unaffected by zinc. However, Zn reduced wingpad development at concentrations above 139 μg/L. In contrast, emergence of subimagos and imagos tended to decline with any increase in Zn. At Zn concentrations below 105 μg/L (hardness-adjusted aquatic life criterion), survival between the wingpad and subimago stages declined 5-fold across the Zn gradient. These results support the hypothesis that metamorphosis may be a survival bottleneck, particularly in contaminated streams. Thus, death during metamorphosis may be a key mechanism explaining how stream metal contamination can impact terrestrial communities by reducing aquatic insect emergence.
authors.affiliation: Colorado State University, Department of Fish, Wildlife, and Conservation Biology, Fort Collins, Colorado 80523 United States.
authors.forename: J S
authors.initials: JS
authors.lastname: Wesner
authors.forename: J M
authors.initials: JM
authors.lastname: Kraus
authors.forename: T S
authors.initials: TS
authors.lastname: Schmidt
authors.forename: D M
authors.initials: DM
authors.lastname: Walters
authors.forename: W H
authors.initials: WH
authors.lastname: Clements
mesh_terms: D000818:Animals; D004553:Electric Conductivity; D004781:Environmental Exposure; D006244:Hardness; D006863:Hydrogen-Ion Concentration; D007313:Insecta / Q000187:drug effects* / Q000254:growth & development*; D007814:Larva / Q000187:drug effects; D008018:Life Cycle Stages / Q000187:drug effects; D016014:Linear Models; D008675:Metamorphosis, Biological / Q000187:drug effects*; D010100:Oxygen / Q000032:analysis; D012995:Solubility; D013696:Temperature; D014921:Wings, Animal / Q000033:anatomy & histology / Q000187:drug effects; D015032:Zinc / Q000633:toxicity*
chemical_list: D015032:Zinc; D010100:Oxygen