Planarians are rather cute little flatworms, although they tend to wreak havoc in fish tanks. Researchers have long been fascinated by their ability to regenerate body parts when injured with the help of adult stem cells. More recently, they have gained attention for their ability to survive long periods of time without eating by “degrowing”, i.e. getting smaller but still keeping their shape and functions intact. I would shrink too if I couldn’t eat for 90 days – although I’m guessing I would look more like a skeleton than simply a tiny version of myself.
Although much is known about these cool attributes, very little is known about their basic physiology. Being a flatworm and all, planarians do not breath air like we do. Rather, they absorb oxygen through their skin. This characteristic made Dr. Melissa Lewallen and Dr. Warren Burggren at the University of North Texas wonder whether the animals change how much oxygen they absorb into their bodies in response to their reproductive mode, feeding, temperature, and photoperiod…like other invertebrates. To examine this, they studied two species of planarians: Schmidtea mediterranea, which include strains that reproduce asexually and sexually, and Girardia dorotocephala, which are asexual.
Their findings, recently published in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology show that sexually reproductive Schmidtea mediterranea had higher oxygen uptake into their bodies than animals that were asexual (Schmidtea mediterranea and Girardia dorotocephala). In addition, asexual and sexual planarians increased oxygen uptake in response to increasing environmental temperatures as well as after eating a meal. These responses are similar to more complex invertebrates that likewise adjust oxygen uptake to meet metabolic demands. Interestingly, while sexual Schmidtea mediterranea shrank during a period of starvation, body mass did not change in asexual animals. That further supports the idea that sexual reproduction may be more costly, metabolically speaking, than asexual reproduction for these animals.
M Lewallen, W Burggren. Metabolic physiology of the freshwater planaria Girardia dorotocephela and Schmidtea mediterranea: reproductive mode, specific dynamic action, and temperature. American Journal of Physiology – Regulatory, Integrative and Comparative Physiology. 319(4): R428-R438, 2020.
DA Felix, O Gutierrez-Gutierrez, L Espada, A Thems, C Gonzalez-Estevez. It is not all about regeneration: Planarians striking power to stand starvation. Seminars in Cell & Developmental Biology. 87: 169-181, 2019.