Determinants of Postmolt Size in the American Lobster (Homarus americanus). I. D13 is the Critical Stage

Juvenile American lobster (Homarus americanus) were subjected to induced limb autotomy, eyestalk ablation, and manipulation of container space at different molt stages to test the hypothesis that postmolt size is predetermined at the time of deposition of the epicuticle. Molt increments in autotomized animals that regenerated limbs were reduced by 30–40%. Molt increments were reduced by only 5–10% in autotomized animals that did not regenerate limbs. The critical stage for limb regeneration is D13. Depending on the time of limb autotomy, molt intervals were decreased (stages B–C), increased (stages D11 and D12), or not affected (stages D0, D13, D2, and D3). Eyestalk ablation shortened the molt interval; the change in molt interval was less when ablation was performed near the end of the current molt cycle. Eyestalk-ablated lobsters had larger molt increments compared with intact controls, especially in the chelipeds. This growth-promoting effect disappeared if ablation was conducted at or after D13. Transferring lobsters from small to large container spaces shortened molt intervals and increased molt increments. Increases in molt increments only occurred when transfers were made before D13. We conclude that postmolt size of lobsters is predetermined at D13 when the new epicuticle is produced.