Limb regeneration in anuran tadpoles following repeated amputations

Limbs were amputated through the thigh in stages from V onward in Rana pipiens, R. sylvatica, and Pseudacris nigrita tadpoles to establish regenerative capacity. Normal regenerates were produced through stages XII, XI, and XIII, respectively, for the three species. However, hypomorphic forms with reduced toe numbers or a single spikelike spur, or nonregeneration, could appear as early as stages VII or VIII, and increased in frequency thereafter. Pseudacris produced the largest fraction of hypomorphs and R. sylvatica the smallest. Regenerated limbs of various stages were reamputated just distad of the initial transection level and produced regenerates with almost the same frequency as did the initial amputees. In R. pipiens reamputation and regeneration was followed for up to six sequences, with but little change in frequency or quality of regeneration, even when the contralateral control limbs were in stages XIV-XVII, well beyond the possibility of regeneration after transection through the thigh. Clearly, the hormonal milieu did not limit regeneration, though rate of regeneration accelerated as metamorphic climax was approached. Foot sizes were measured in R. pipiens, and were seen in control animals to be correlated to both stage and to tadpole length. Regenerated feet tended to be slightly larger than control feet of the same stage, showed comparable relationships between length and width, but correlated more poorly with tadpole length.