title: Shifty salamanders: transient trophic polymorphism and cannibalism within natural populations of larval ambystomatid salamanders.
abstract: BACKGROUND
  Many species of ambystomatid salamanders are dependent upon highly variable temporary wetlands for larval development. High larval densities may prompt the expression of a distinct head morphology that may facilitate cannibalism. However, few studies have characterized structural cannibalism within natural populations of larval salamanders. In this study we used two species of larval salamanders, long-toed (Ambystoma macrodactylum) and ringed salamanders (A. annulatum). Head morphometrics and stable isotopic values of carbon (δ(13)C) and nitrogen (δ(15)N) were used to identify the presence or absence of structural cannibalism. Weather conditions were also analyzed as a potential factor associated with the expression of cannibalistic morphology.
  
  
  RESULTS
  Populations of salamander larvae did not consistently exhibit cannibalistic morphologies throughout collection periods. Larval long-toed salamanders exhibited trophic polymorphisms when relatively lower precipitation amounts were observed. Larval ringed salamanders were observed to be cannibalistic but did not exhibit polymorphisms in this study.
  
  
  CONCLUSIONS
  Structural cannibalism may be transient in both species; however in long-toed salamanders this morphology is necessary for cannibalism. Ringed salamanders can be cannibalistic without morphological adaptations; however the cannibal morph may prolong the viable time period for cannibalism. Additionally, weather conditions may alter pond hydroperiod, subsequently influencing head morphology and cannibalism.
authors.affiliation: Department of Biology, University of Saskatchewan, 112 Science Place, S7N 5E2 Saskatoon, SK Canada.
authors.forename: Dale M
authors.initials: DM
authors.lastname: Jefferson
authors.affiliation: Department of Biomedical Sciences WCVM, University of Saskatchewan, 52 Campus Dr., S7N 5B4 Saskatoon, SK Canada.
authors.forename: Maud Co
authors.initials: MC
authors.lastname: Ferrari
authors.affiliation: Department of Biology, Missouri State University, 65897-0095 Springfield, MO USA.
authors.forename: Alicia
authors.initials: A
authors.lastname: Mathis
authors.affiliation: Environment Canada, S7N 3H5 Saskatoon, SK Canada.
authors.forename: Keith A
authors.initials: KA
authors.lastname: Hobson
authors.affiliation: Department of Biology, Missouri State University, 65897-0095 Springfield, MO USA.
authors.forename: Eric R
authors.initials: ER
authors.lastname: Britzke
authors.affiliation: Department of Biology, University of Saskatchewan, 112 Science Place, S7N 5E2 Saskatoon, SK Canada.
authors.forename: Adam L
authors.initials: AL
authors.lastname: Crane
authors.affiliation: Department of Zoology, Oregon State University, 97331 Corvallis, OR USA.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Blaustein
authors.affiliation: Department of Biology, University of Saskatchewan, 112 Science Place, S7N 5E2 Saskatoon, SK Canada.
authors.forename: Douglas P
authors.initials: DP
authors.lastname: Chivers
keywords: Cannibalism; Carbon-13; Larval salamander; Nitrogen-15; Stable isotope; Trophic polymorphism