Influence of the nutritional state on repeated head regeneration, growth, and fission in the planarian, Dugesia dorotocephala

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Abstract
Starved and fed animals were repeatedly decapitated to determine the influence of nutritional state on regeneration rate and capacity, growth in length, fission, and formation of abnormal heads in Dugesia dorotocephala. Animals fed at the end of each regenerative period were able to regenerate a maximum of 40 times, with no significant change in regeneration rate compared to controls decapitated once. Growth in length of the whole animal continued throughout the study and fissioning capacity was maintained. Abnormal head formation was minimal. However, starved animals showed a marked reduction in regenerative capacity and were unable to regenerate more than 16 times. There was also a retardation of regeneration rate, decline in growth rate, loss of fissioning capacity, and a 13‐fold increase in formation of abnormal heads compared to fed animals. Fissioning cyclicity was an interesting and unexpected finding in intact fed controls and fed and starved regenerating animals. An apparently inherent four‐week frequency pattern in fission cyclicity was observed in intact fed controls, while regenerating animals exhibited an initial three‐week cycling pattern, but an alteration occurred after eight or nine regenerations and fed animals changed to a two‐week cycle, while starved animals ceased fissioning entirely. The act of decapitation and subsequent regeneration appeared to alter fissioning cyclicity. Comparative analysis of fission, growth, and abnormal head formation in regenerating animals showed different relationships in both groups. In fed animals fission and growth were inversely related the first eight decapitations, then growth leveled off while fissioning frequency changed. After 13 decapitations fission and growth were directly related and cyclic. Starved animals showed initial fissioning cyclicity, but growth steadily declined and leveled off. Head abnormalities began to increase greatly after the ninth decapitation.