Metabolic physiology of the freshwater planaria Girardia dorotocephela and Schmidtea mediterranea: reproductive mode, specific dynamic action, and temperature

Planarians are widely used animal models for studies in regeneration, developmental biology, neurobiology, and behavior. However, surprisingly little is known about other aspects of their basic biology, even though such information might help validate these flatworms as a general animal model. We hypothesized that planaria, although dependent on simple diffusion of O-2 across the integument for O-2 uptake, would nonetheless show changes in oxygen consumption ((V) over dotO(2)) associated with reproductive mode (sexual or asexual). feeding (specific dynamic action; SDA), temperature (Q(10) values), and photoperiod typical of those responses of more complex invertebrates. In the current experiments, routine (V) over dotO(2) was measured over the range of 13-28 degrees C in Schmidtea mediterranea and Girardia dorotocephala. At the long-term maintenance temperature of 18 degrees C, routine (V) over dotO(2) was similar to 13 mu l O-2.g(-1).h(-1) in the two asexual strains, but approximately twice as high (27 mu l O-2.g(-1).h(-1)) in the sexual strain of S. mediterranea, suggesting a metabolic cost for sexual reproduction. Metabolic temperature sensitivity, measured by Q(10), was about one to three for all three groups. All three groups showed a large (similar to 2- to 3-fold) increase in (V) over dotO(2) within a day following feeding, suggesting a large SDA effect. Starvation, causing degrowth in some planaria, resulted in a loss of one-third of body mass in sexual S. mediterranea but no body mass loss in either asexual strains. Collectively, these data indicate that, while being a relatively simple flatworm with no dedicated respiratory or circulatory system, their metabolic physiological responses are quite similar to those shown by more complex invertebrates and vertebrates, contributing to their validation as an animal model.