INTRODUCTION: The purpose of this study was to reproduce an experiment with diluted thyroxine and amphibians. A detailed account of the difficulties of this line of research has been published by the initial team (Endler and Scherer-Pongratz). One experiment which has been reported reproducible by the initial team and independent researchers is the effect of extremely diluted agitated thyroxine (T30x) versus analogously prepared water (W30x) in amphibians from biotopes above the tree line (highland amphibians).
(A) The author replicated the experiment. Rana temporaria were taken from an alpine biotope and the methods given in the original protocols were followed. Animals were treated from the 2-legged stage on. (B), the author reanalyzed the results reported by the initial team and by independent researchers (van Wijk, Lassnig, Zausner-Lukitsch, Bach, Harrer).
(A) In the author’s own experiment, there was a clear trend of T30x animals developing more slowly (i.e. up to 6 h within 3 days) than W30x animals. This is in line with the previous experiments. Due to small numbers of animals, the differences in the frequency of larvae reaching the 4-legged stage and the stage with reduced tail were not statistically significant (p > 0.05). The effect size was large (d > 0.08). (B) In the analysis of all available data with regard to the 4-legged stage, pooled T30x values from the initial team were 10.1% smaller than W30x values (100%) and pooled T30x values from the 5 independent researchers were 12.4% smaller (p < 0.01 and d > 0.08). Analogously, the number of animals entering the juvenile stage with reduced tail was smaller for T30x than for W30x.