字幕表 動画を再生する 英語字幕をプリント Plants are a lot like animals, in the sense that they have to get nutrients to grow, fight off anything that wants to eat them, and reproduce. But, unlike most animals, plants can’t just get up and move around… which is why some of them put out nectar to recruit bodyguards. Lots of flowering plants produce sugary nectar, which attracts pollinators like birds, bats, and insects. They take the pollen with them to the next flower, helping the plant reproduce. But a few plants have evolved a completely separate source of nectar. They’re known as extrafloral nectaries, special structures outside of the flower that produce a liquid cocktail of sugars and amino acids -- a lot like the nectar inside flowers, just in a more strategic place. As the nectar-eaters defend their source of food, the plant ends up with bodyguards. Nectars -- both the floral and the extrafloral kind -- are meant to attract and reward animals, creating what's called a mutualistic relationship. The animals benefit from the nectar -- since they get food -- and the plant gets either pollinators or protection. It's a win-win. For instance, in Inga plants in tropical rainforests, ants will get rid of other, plant-eating insects. These outside nectaries are rich in carbohydrates, like sucrose and glucose, as well as proteins and amino acids -- all important nutrients for the ants. In exchange for the food, the ants protect the plants from invaders like caterpillars. They’re pretty good at it, too -- studies have shown that leaves without ants get much more damaged than leaves that do have ants. And, when a plant eater comes to munch on its leaves, the Inga can make extra nectar as a bonus incentive for the ants. The plant’s basically saying “come help, I’m under attack! Here, take more sugar!” Then there’s the Passion flower, a North American plant that has extrafloral nectaries at the base of each leaf and under the flower bud. The passion flower already has poisonous chemicals in its leaves. But some species of butterfly have evolved an immunity to the toxic leaves, and recruiting ants gives the flower another line of defense. In the 1980s, a group of researchers removed the outside sources of nectar from some passion flowers. They found that those plants had fewer ants around them, were attacked more, and made less fruit. Even cotton plants have them -- though they aren’t looking for ants. They’re trying to attract parasitic wasps. These wasps are a lot different from the yellow jackets invading your summer picnic. For one thing, they’re tiny. They also happen to lay their eggs inside caterpillars. The eggs hatch into larvae while they’re still in the caterpillar and start to eat it, eventually clawing their way out through its skin. All while it’s still alive. Then they take over the caterpillar’s mind, forcing it to protect them as they keep growing. Once they fly away, the caterpillar starves to death. As you can probably imagine, it’s an effective way to kill a caterpillar, which is why some cotton farmers use these wasps as a natural pesticide. The cotton plant sets out its nectar as a food source for the mini wasps, and in return for the sugary snack, the parasitic wasps stick around and take over the caterpillars. But nectar’s good for defending against more than just insects. According to a study published in 2009 in The Plant Journal, it also has compounds that protect the plant from invading viruses, bacteria, and fungi. For example, the nectar of certain Acacia plants contains proteins called chitinases that stop invading fungi. Meaning that sometimes the extrafloral nectar itself is a kind of bodyguard. That nectar doesn’t come cheap, though, energy-wise. To make it, the plant has to use energy it could otherwise be using for things like growth and reproduction. But for a lot of plants, it’s worth setting out a nectar pot for a little extra security. Thanks for watching this episode of SciShow, sponsored by Audible. Right now, Audible’s offering SciShow viewers a free 30-day trial membership. Check out audible.com/scishow where you can choose from over 180,000 audio programs and titles like Wicked Plants by Amy Stewart. So, go to audible com SciShow for a free 30-day trial and download a free title today.