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

Abstract

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 O2 across the integument for O2 uptake, would nonetheless show changes in oxygen consumption (V̇o2) associated with reproductive mode (sexual or asexual), feeding (specific dynamic action; SDA), temperature (Q10 values), and photoperiod typical of those responses of more complex invertebrates. In the current experiments, routine V̇o2 was measured over the range of 13-28°C in Schmidtea mediterranea and Girardia dorotocephala. At the long-term maintenance temperature of 18°C, routine V̇o2 was ~13 µL O2·g-1·h-1 in the two asexual strains, but approximately twice as high (27 µL O2·g-1·h-1) in the sexual strain of S. mediterranea, suggesting a metabolic cost for sexual reproduction. Metabolic temperature sensitivity, measured by Q10, was about one to three for all three groups. All three groups showed a large (~2- to 3-fold) increase in V̇o2 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.