Effects of food level and fecal material on the plasticity of metamorphic traits in Asiatic toad, Bufo gargarizans, in Central China

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Abstract According to Richards’ hypothesis, the presence of a nonpigmented unicellular alga in the intestinal tract of tadpoles is believed to be the inhibitory factor that affects their growth. It is proposed that thecanimals eat their fecal material containing these algal cells, which are then reintroduced into their systems when the alga is shed with the feces and dropped to the bottom. In this study, we aimed to investigate the plasticity of metamorphic traits in the Asiatic toad (Bufo gargarizans) under different combinations of fecal material and food levels. Our findings revealed that B. gargarizans tadpoles reared at high food levels exhibited accelerated larval periods but had smaller metamorphic sizes compared to those reared at low food levels. This suggests that the tadpoles prioritize rapid development at the expense of body mass during metamorphosis. Furthermore, our study discovered evidence supporting the positive effect of fecal material on tadpole growth, as indicated by the investigation of growth rate. Importantly, the presence of feces did not result in smaller body mass on average for Asiatic toad tadpoles compared to those raised in the absence of fecal material. The difference in body mass between fecal material treatments tended to be smaller at low food levels, implying that feces does not inhibit growth in B. gargarizans tadpoles. Therefore, our results contradict Richards’ hypothesis and provide support for a novel mechanism that is selected for in areas where coprophagy is likely to be advantageous, particularly in times of food scarcity.