Jellyfish Romance - (Carybdea sivickisi)
By Christine Hoekenga
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Setting the Scene
For most jellyfish, reproduction is not a particularly romantic affair. Typically, males release sperm into the water so that their genetic material can bump into and fertilize eggs released by female jellyfish in a similar fashion. This behavior, known as mass spawning, allows jellyfish to “mate” without the lovers even needing to meet. But Cheryl (Lewis) Ames, a Research Assistant with the National Systematics Lab of NOAA's Fisheries Service at the Smithsonian, has found that at least one species, called Carybdea sivickisi by scientists, has a more intimate courtship routine.
Carybdea sivickisi medusae are probably not the animals that come to mind when one pictures a jellyfish. They are among the species known as box jellies, or Cubozoa, because their bodies are boxier (Fig 1a) than the more familiar bell-shaped jellyfish that sunbathers usually encounter. Despite their orange banded tentacles and the males’ crimson-colored gonads (Fig 1b), they are easy to miss. The ones Ames collected for study were between four millimeters and ten millimeters across (smaller than a dime), and they can shrink their already small bodies by folding their four tentacles up inside their bells or attaching themselves to seaweed (Fig 2) and flattening like a Chinese lantern (Fig 3).
Using an underwater light to attract these nocturnal jellyfish, Ames scooped up hundreds of Carybdea sivickisi off the coast of Japan, separated males from females, and took their measurements. She grouped them in threes – one female, one smaller male, and one larger male – and put them through “courtship trials” to observe their mate choices and courtship behaviors. “You turn the lights down low,” Ames says jokingly of the experiments. “You put on a bit of music in the background.”
Watching hundreds of these blind dates by flashlight, Ames confirmed something scientists had suspected but never been sure about: these tiny jellies pair up to mate and perform a ritual more akin to copulation seen in higher animals than to the anonymous mass spawning most other jellies engage in. “Over the last twenty or thirty years, scientists had hypothesized that this courtship, ‘wedding dance,’ or interaction between one male and one female might potentially be a form of copulation,” Ames says. “But it was never documented.”
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