Effects of ecdysterone, inokosterone and eyestalk ablation on limb regeneration in the fiddler crab, Uca pugilator

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AbstractBilateral ablation of eyestalks or injection of either ecdysterone or inokosterone (two 25‐μg doses or five 10‐μg doses into crabs weighing on an average 1.5 g) caused precocious proecdysis and ecdysis in the fiddler crab, Uca pugilator. On a weight basis ecdysterone was more effective than inokosterone in exerting the effects. Whether the accelerated proecdysis was accompanied by regenerative limb growth depended on the degree of limb bud development at the time of treatment with ecdysones. Ecdysterone and inokosterone blocked the initiation of basal limb growth when administered as two 25‐μg doses into crabs exhibiting scar tissue without any visible limb bud. When injected into crabs with limb buds in various stages of basal limb growth exogenous ecdysones accelerated basal limb growth and led to proecdysial limb growth. The degree of acceleration of limb bud growth noticed within three to six days after injection of ecdysones into crabs with limb buds in early stages of basal limb growth was greater than that resulting from eyestalk ablation. In crabs with limb buds in later stages of basal growth, the degree of acceleration of limb bud growth evoked by exogenous ecdysones was similar to that resulting from eyestalk ablation. The final sizes of the limb buds preceding ecdysis in eyestalkless crabs and crabs injected with ecdysones depended on the proecdysial duration available for regeneration.The rate of proecdysial limb growth has been known to vary with the speed at which the crabs complete the proecdysial stages of the molt cycle. This study shows that the time required for the initiation and completion of the basal limb growth also varies depending on how soon the intact and eyestalkless crabs approach proecdysis and ecdysis.