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The Forefront of Space Science

Search for Life in Space, See Space in Life -Theme of Biological Sciences in Space- Masamichi Yamashita, ISAS
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See space in life - Life, a small universe

Now, the latter half of the catchphrase for biological sciences in space is "See Space in Life." The reason why the world of biology is affluent is to address the evolution of living things that have differentiated into a variety of forms and created a prosperous biosphere. The theme of planetary biology and gravitational biology is to elucidate: how the environment that Earth as a planet has given to living things works on life activity as a pressure for natural selection and as a driving force for evolution; and how gravity has been involved in various functions of living things and interactions between individual living things. "See Space in Life" is to decode how degree life and its evolutionary process depend on space history and the environment of the sun-earth system from the history engraved in living things. The history can be found in the biochemical process of cell. Also, specific predominance may exist in each hierarchy of individuals, group of individuals, and biogeocenosis.

Space/gravitational biology of amphibians


The phenomenon and living species that should be selected for research have been repeatedly considered. One candidate is amphibians. Amphibians were the first vertebrates that moved on land about 400 million years ago. To live on land, some conditions were necessary such as movements supporting the body against gravity, drought-resistance, air-breathing mechanism, and so on. The groups of living things that moved on land have created their living environments variously and affluently, and achieved the adaptive radiation explosively.

Amphibians preserve the figures of the initial vertebrates that began to live on land. Tadpoles primarily inhabit the water and follow the history of transition to living on land at their metamorphosis. Adaptation to living on land is found in various stages. There are rare species that do not inhabit the water in their larval stage and directly develop. Amphibians have differentiated into a wide variety of species, and they display various habits and behaviors comparable to number of the species. In terms of habitat areas, there are many amphibian species, which inhabit the surfaces near waterfronts, trees, underground, and the water, in addition to the surface. Diverse adaptation to gravity is demanded corresponding to animalsÐ habits and activity world. In water or on trees, activity world of animals is three-dimensional and gravity serves as a reference coordinate axis to recognize their activity world. By methodically selecting some amphibian species which have various habits and habitat areas, and then comparing the configurations and functions of their bodies and organs, behavior of individuals, and others, we can know the process of moving on land and adaptation to gravity.

Individual animal's activity/physiology and gravity

Animals seek food, escape from predators, meet partners for reproduction, and select environments suitable to survive. Animal's activity means the behavior that individual animal displays on its own. When a frog jumps to a free space under microgravity, it stretches its four limbs, bends backward, and inflates its belly sideways. On the ground, when jumping down from a high place, a frog experiences microgravity condition. While falling, the frog inflates its belly to increase its body's cross section against the flow, bends its four limbs backward to shift the center of hydrodynamic drag from the center of gravity to the back, and descends stably with its venter down. It is estimated that, when a frog floats in free space in space, it shows the same posture as that under microgravity condition on the ground.

The Japanese tree frog frequently shows a posture bending its head strongly backward when sitting on a surface in space. This is similar to the posture shown when a frog increases abdominal pressure in order to vomit. Zero gravity flight experiments by aircraft have demonstrated that susceptibility to motion sickness depends on species ecology. Species that inhabit trees and jump down from high places, and accordingly have attitude control programs under microgravity, throw up very frequently when they have undergone microgravity for a long time. This coincides with the presumption that astronauts began to get space sickness, since they began to conduct space walks in wide spaceship cabin, due to the confusion of the labyrinthine sensation and input information from the sense of vision and others at the central nervous system. Individual of living things shows reactions in order to increase its survival and adaptive capability. Vomiting is to throw up poisonous foods from the stomach and is a physiologically adaptive response. Plants eaten by animals create poisons. Some animals preserve them in their bodies and use them to protect themselves from other animal species. Vomiting by space sickness is caused by stimulus of vomiting center. There are some indexes such as nausea, sudation, and changes or fluctuations of the ventricular rate. These are comprehensive reactions of living things, which are present as a small universe.

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