Caribbean box jellyfish (水母) can learn to spot and avoid obstacles (障碍) despite lacking a central brain, according to a new study. This is the first evidence that jellyfish can do something called associative learning. The nervous systems of Caribbean box jellyfish are fairly simple, including four “rhopalia (视神经束)”on a jellyfish’s body, each of which has six “eyes”, by which the jellyfish judge a mangrove root’s distance based on how dark it looks compared to the water and make their way round it. In common waters, nearby roots have high contrast. Only distant roots fade into the background. But in murky waters, even near-by roots can blend into their surroundings and have low contrast. The researchers wondered if Caribbean box jellyfish could learn that low-contrast objects-which might at first seem distant-were actually close by.
To find out, the team put 12 jellyfish into a round water tank. The tank was surrounded by low-contrast gray and white stripes (条纹), which might appear to a jellyfish like roots in clear water. A camera filmed the animals for about seven minutes. At first, they seemed to see the gray stripes as distant roots and swam away, ending up bumping the tank wall. But those collisions (碰撞) seemed to lead the jellyfish to reconsider the stripes. Soon, the creatures treated the gray stripes more like close roots in murky water-and avoided them.
This suggests that the rhopalia alone can learn that seemingly distant, low-contrast objects are in fact close enough to avoid. That, in turn, hints that these nerve centers are behind Caribbean box jellyfish learning.
“That’s the coolest part of the paper,” says Ken Cheng, a biologist at Macquarie University, Sydney, Australia. “That gets us one step down into the wiring of how it works.” For Gaëlle Botton-Amiot, tracing learning to the rhopalia raises new questions. “They have four of these things in their bodies. So how does that work?” asks this neurobiologist. If a jellyfish loses one of its rhopalia, does it forget everything those eyes saw and the neurons had learned? Or do the other rhopalia remember it?
【小题1】Jellyfish are able to avoid obstacles because ______.| A．they use brain cells to process information gathered |
| B．they rely on different levels of visual signal input |
| C．they have unique organs to measure the distance |
| D．they are driven by excellent survival instinct |
| A．Unusual. | B．Cloudy. | C．Deep. | D．Rapid. |
| A．Jellyfish usually tend to be scared off by the gray color. |
| B．Jellyfish tend to compare stripes with mangrove roots. |
| C．Stimulation in controlled environment backed the finding. |
| D．Rhopalia are in control of the jellyfish’s memory system. |
| A．No brain, no gain? Denies the jellyfish |
| B．Unique “eyes” help jellyfish survive |
| C．Evolution of learning: from nerve to brain |
| D．White or gray? Creature’s decision-making |
