Dreams of interstellar voyages and planetary colonies are the adrenaline of human spaceflight programs. Such dreams imply that humans will reproduce during generations away from earth. Biological research is showing, however, that reproduction in space will be hard, and maybe impossible, and suggests that human physiology may yet be the limiting factor to long duration space missions.
The issue is weightlessness, a central concern since the beginning days of space research. Successfully adapting to it and successfully recovering from it back on earth are essential to a long-term human space presence, but the effects of weightlessness still aren’t completely understood. Therefore, this is an active research topic for every country with a space program. How does weightlessness affect reproduction? NASA and other space agencies aren’t ready to study that with astronauts yet, but some surprising insights are being gained through experiments with plants and animals. It turns out that space isn’t all that conducive to sex.
Things go better with normal gravity
Sexual reproduction first requires the successful transport of a sperm to an egg; everything else is secondary. That transport process has evolved in the “one g” gravity environment of earth and things work well that way. A Canadian research team manipulated that environment for the Japanese Camellia plant, however, and saw some interesting changes.
Plant reproduction involves the transfer of male pollen to the female stigma. When pollen comes in contact with a stigma, it grows a pollen tube that acts as a tunnel to allow sperm cells to reach the egg. The pollen tube is a good object to study because it’s the fastest growing cell in the plant kingdom so any experiment effects can be seen quickly.
The team generated hypergravity (up to 20 times normal) with a centrifuge to simulate the conditions of a large planet. They simulated the microgravity of space by changing the orientation of the plants at random intervals (also known as omnidirectional gravity). The pollen tubes grew thicker under hypergravity and thinner under microgravity; both changes altered the reproductive transport mechanism. More importantly, the internal material transfer processes required for cell growth were interrupted; even fertilization, therefore, can’t ensure normal development under altered gravity. Not a promising foundation for growing babies in space.
Microgravity is a bad start
A more direct study of weightlessness was conducted aboard the Spacelab Life Sciences (SLS-1) mission and involved the moon jellyfish. The purpose of the experiment was to see how the jellyfish developed in microgravity and to study the effects of that development after return to earth.
Although the mission actually occurred in 1991, the analyzed results are getting a lot of attention now.
Like humans, jellyfish orient themselves with gravity using special sense organs. Jellies also have a short growth cycle, convenient for study on limited duration space missions.
Our own sense of up and down is based on the action of otolith organs in our internal ears. As we move, gravity shifts crystals, embedded in fluid, to stimulate hairs. These hairs activate nerves to the brain and give us our perceptions of motion and orientation. Jellies also develop crystals spaced around the edge of their bells. Each crystal is surrounded by a cell pocket coated with specialized hairs. Motion moves the crystals which stimulate the hairs and provide information about up and down.
The mission launched aboard Space Shuttle Columbia with about 2,500 jellyfish polyps. Over the course of the mission, the polyps grew to medusa stage and reproduced (there were 60,000 jellyfish by the end of the 9-day mission). Jellies appeared to develop their crystal and pocket organs normally, but had trouble orienting and moving after returning to earth. The source of the problem hasn’t been isolated yet, and could involve the receptors themselves, the neuromuscular system that acts on the information, or some combination of these. Whatever the underlying event, however, something different happened in space when the jellies were growing.
A different vision for space
Sex is hardly the major problem for astronaut welfare in our current space programs. Plenty of other health issues are still being studied such as radiation, psychological resilience, sensory shifts, and musculoskeletal changes, all of which require near-term accommodations or protections. Reproduction experiments like these, however, will likely have an effect on the approaches taken for long-duration presence in space, the Moon, or Mars – engineering programs that are already being planned.
The most direct implication of these results is practical: Can we successfully grow food in colonies with a different gravity? A lot of space goals would change if food had to accompany every trip from earth.
The broader implication is ethical: If results like these apply to humans, is it fair to allow conception in space? Or to plan expeditions and colonies where it is likely to happen? What happens to those children when they return to earth?
With space tourism slated to start as early as 2016, we may have to decide these issues a lot sooner than we thought.