Lowland amphibians - recalculation of data on effects of diluted thyroxine

Our previous paper described methodological problems and a generally acceptable pooling method for metamorphosis experiments and application of that method to the results of multicentre experiments performed over the course of two decades (1990 - 2010) on highland amphibians (Rana temporaria) treated with a homeopathically prepared high dilution of thyroxine (“30x”). Differences between treatment groups thus calculated were in line with those obtained with other pooling methods: Thyroxine 30x does slow down metamorphosis in highland amphibians. This follow up paper provides a broader background on metamorphosis physiology and describes application of the pooling method to experiments with Rana temporaria from lowland biotopes both with a moderate dilution of thyroxine (“8x”) and with 30x. Analogously prepared water was used for control (water 8x or 30x). Development was, again as above, monitored by documenting the number of animals that had entered the 4-legged stage. Experiments were carried out between 1990 and 2000 by different researchers independently and in blind. As it is well known, metamorphosis can be speeded up by thyroxine 10-8 mol/l; interestingly, thyroxine 8x may produce a reverse, i.e. inhibiting effect (p < 0.01). In contrast to the inhibiting effect of thyroxine 30x on highland larvae (see above), 2-legged lowland larvae did not react to thyroxine 30x (p > 0.05). However, an inhibiting effect on lowland larvae was found when animals were treated from the spawn stage on (p < 0.01).