By Allison Kubo Hutchison
Jellyfish simulate human ears in microgravity but can’t adjust to Earth gravity after a life in space.
In the early 90’s, a one point there were 60,000 jellyfish orbiting the Earth. Although it sounds like the beginning of a sci-fi novel, this is actually the beginning of a microgravity study, lead by Dororthy Spangberger from the Easter Virginia Medical School. Jellyfish although unlike humans in most ways have an important similarity: jellyfish have the ability to sense up and down, to sense the direction of gravity.
Jellyfish form calcium sulfate crystals in small pockets situated around the cap or bell of the jelly. When their direction relative to gravity changes these sulfate crystals fall and stimulate hair like nerves within the pocket similar to how a ball in a bowl will roll when you tilt the bowl. This mechanism is analogous to how our inner ear senses gravity. Within your inner ear, you have multiple otolithic organs, organs dedicated to sensing linear acceleration, where calcium carbonate crystals brush against sensitive hair cells and give you a sense of balance. This is the reason that a bad ear infection can cause you to feel dizzy and lose your sense of balance.
The goal of the SpaceLab Life Sciences mission was to test how a life in microgravity would affect the jellie’s sense of gravity and give insight into how it would affect our own sense of gravity. In 1991, NASA launched over 2,000 jellyfish polyps on the Space Shuttle Columbia which bred and multiplied over a period of 9 days aboard. The polyps progressed to the medusa stage, the life stage where they develop the umbrella shaped bell and long tentacle. The study then retrieved the jellies and compared them to Earth-raised jellies of the same age.
They found that jellyfish raised in the different environments were morphologically similar and had the same number of tentacles. It appeared that the two populations of jellyfish developed the same gravity receptors. However, the space-raised jellies exhibited “pulsing abnormalities” and ethereal rhythm and grace of jellyfish as they contract and swim was altered by living in space. The space-raised jellyfish exhibited “uncoordinated pulsing, after-twitches,spasms, and arms out of synchronization during pulsing”. These abnormalities in their locomotion may indicate malformed gravity receptors.
This implies that for humans born in microgravity, adjusting to the full gravity of Earth may be tricky. Humans do have one advantage over jellyfish: brains. After experiments abroad the International Space Station, we have learned that humans do suffer consequences in microgravity. Bone density loss, atrophy of muscles, can be combated with exercise regimes and return to normal after returning to Earth. However, the NASA Twins Study revealed some troubling long term results from prolonged space travel. The study observed some limited cognitive decline and genes related to immune response and DNA repair seem to be permanently changed. More work is going into mitigating these issues to prepare for longer voyages to Mars and beyond.