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1 August 2001 Effects of Growth History and Exogenous Thyroxine on Size and Age at Metamorphosis in the Toad Bufo americanus
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Abstract

By using food rations and thyroxine supplements, I manipulated the growth and differentiation of tadpoles of the toad Bufo americanus to test the hypothesis that the plasticity in metamorphic timing can be lost. A significant food effect indicated that tadpoles that grew rapidly during the middle period of the experiment metamorphosed earlier than slow-growing tadpoles. The changes in growth induced early and late in this experiment did not influence metamorphic timing. There was a significant thyroxine effect: all tadpoles treated with thyroxine metamorphosed early. All thyroxine-treated tadpoles metamorphosed at the same time, indicating that differentiation at the time of thyroxine supplementation was independent of growth rate. A food-by-thyroxine interaction provided evidence that the growth rate/differentiation antagonism may have been active at least during the middle of the experiment. This suggests that the growth rate/differentiation antagonism is decoupled or overridden during later stages of larval development. This result implies limits to metamorphic plasticity and is consistent with a fixed-rate model of amphibian metamorphosis.

The American Society of Ichthyologists and Herpetologists
Christopher K. Beachy "Effects of Growth History and Exogenous Thyroxine on Size and Age at Metamorphosis in the Toad Bufo americanus," Copeia 2001(3), 829-834, (1 August 2001). https://doi.org/10.1643/0045-8511(2001)001[0829:EOGHAE]2.0.CO;2
Accepted: 21 January 2001; Published: 1 August 2001
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