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Reassessment of the environmental mechanisms controlling developmental polyphenism in spadefoot toad tadpoles

Abstract

Identifying the environmental mechanism(s) controlling developmental polyphenism is the first step in gaining a mechanistic and evolutionary understanding of the factors responsible for its expression and evolution. Tadpoles of the spadefoot toad Spea multiplicata can display either a “typical” omnivorous or a carnivorous phenotype. Exogenous thyroxine and feeding on conspecific tadpoles have been accepted as triggers for development of the carnivorous phenotype on the basis of a series of studies in the early 1990s. I repeated the thyroxine and conspecific-feeding assays and demonstrated that neither exogenous thyroxine nor feeding on conspecifics induces the carnivorous phenotype. Previous researchers used simple ratio statistics to argue that field-collected carnivores and thyroxine-treated tadpoles are similar, and my results supported these claims if I used the same simple ratio methodology. However, investigation of trait developmental trajectories and allometries for field-collected carnivores and thyroxine-treated and conspecific-fed tadpoles show that these phenotypes are profoundly different.

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Acknowledgements

Many thanks to Joseph Travis, Anne B. Thistle, Alice A. Winn, Shonna R. Storz, Gregory M. Erickson, Scott J. Steppan, Thomas A. Houpt, and four anonymous reviewers for reviews, comments, and constructive criticism. Thanks to the resident scientists, staff, and volunteers at the Southwestern Research Station (American Museum of Natural History). This research was supported by the Theodore Roosevelt Memorial Fund (AMNH), Sigma Xi, and the Robert B. Short Fellowship (FSU). Collecting permit: Arizona SP710791, Florida not required. All laboratory research was conducted under ACUC protocol 0020 from Florida State University.

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Correspondence to Brian L. Storz.

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Storz, B.L. Reassessment of the environmental mechanisms controlling developmental polyphenism in spadefoot toad tadpoles. Oecologia 141, 402–410 (2004). https://doi.org/10.1007/s00442-004-1672-6

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Keywords

  • Thyroxine
  • Spea multiplicata
  • Polyphenism
  • Carnivore
  • Omnivore