Planarians in toxicology. I. Physiology of sexual-only Dugesia dorotocephala: effects of diet and population density on adult weight and cocoon production.

A rare sexual-only race of Dugesia dorotocephala produces offspring from cocoons rather than by fissioning, allowing individuals to be accurately aged. Because each animal possesses fully developed male and female reproductive systems and a true brain with synapses, many types of toxicological studies which normally use vertebrates are possible with these animals. Prior to using this race for toxicological studies, a 3(3) factorial study was carried out to determine the effects of environmental conditions on reproduction and growth. The factors studied were crowding (2, 4, or 8 animals/50 ml medium), age (17, 19, 21 months), and type of dietary protein (soy, liver, cooked egg yolk). Protein composition dramatically affected the numbers of cocoons deposited per planarian, mean weight, and temporal patterns of weight changes. During 65 days of observation, planarians fed liver deposited an average of 3.28 cocoons/planarian while those fed soya or egg yolk deposited an average of 0.24 cocoon/planarian. Crowding, but not age, affected the numbers of cocoons deposited. Statistical analysis showed that protein composition, age, and crowding, alone and in factorial combinations, affected both the absolute weight changes and the temporal patterns in weight changes in each group.