Gary Rogers [CC-BY-SA-2.0], via Wikimedia Commons
Plants are more generous to kin than strangers.
How plants are kinder to kin. I'm Bob Hirshon and this is Science Update.
Some plants not only recognize their family members, they even treat them more generously than they treat strangers. Plant ecologists Susan Dudley and Amanda File, of McMaster University in Canada, discovered this among plants called sea rockets.
Normally, when unrelated sea rockets are potted together, they grow longer roots than they would on their own—to better compete for limited water and nutrients. But Dudley says things were different when they potted the plants with their siblings.
The siblings basically didn’t respond to sharing the pots. So they didn’t make this competitive response, while the strangers did.
Since some other plants might share this behavior, Dudley says gardeners may get better results by planting crops near family. I'm Bob Hirshon, for AAAS, the science society.
Making Sense of the Research
Kin recognition, or the ability to recognize genetic relatives, has been studied widely in animals. Although you, as a human, might not be able to tell one squirrel from another, many species can recognize not only their mates and children, but also siblings, aunts, uncles, or cousins.
When an animal not only recognizes its kin but offers it help at some cost to itself, that's called kin selection. Animals of many species, from apes to insects, treat those relatives better than unrelated animals in certain situations. Scientists believe that kin selection occurs because related animals share genes and, therefore, helping their relatives sometimes benefits the genes they carry.
For example, consider a species called the Belding's ground squirrel. When it spots a predator, like a hawk or a snake, a squirrel will sound an alarm call. That warns nearby squirrels to duck into their burrows for safety, but calls attention to the squirrel that sounds the alarm, making it more likely to get eaten. But even if a ground squirrel dies as a result of making the call, that squirrel's genes may be better served by saving several—even dozens—of its close relatives. In fact, studies have shown that these ground squirrels make more alarm calls when relatives are nearby.
Prior to this study, scientists knew that plants could sense one another through their roots, by using chemical signals. When the root of one plant approaches another, it may change its growth pattern to avoid a conflict, or, as in the case of sea rockets, grow more aggressively to compete for its resources. It was also known that roots from the same plant don't try to compete with each other. Corn plants have even been shown to sound their own "alarm calls" when they're attacked by insect predators, by releasing signaling chemicals into the air. Nearby corn plants that get the message ramp up production of their own defensive chemicals that protect against munching insects. But those alarm signals benefit all the plants nearby, not just relatives.
This study, in contrast, found plants being choosy about whom they help, favoring relatives over unrelated plants. What's more, they do it at some cost to themselves as individuals, since presumably, any given plant might be better off stealing its sister's water.
Actually, that's not necessarily true. Scientific models have shown that if all the plants sharing the same pot could somehow agree not to compete for resources, they would end up healthier, as a group, than they would if they did compete. (In competitive environments, one individual often wins big at the expense of many others.)
So it's to an individual plant's advantage not to compete—as long as it can trust its neighbor to restrain itself too. In most situations, this isn't true, so the plants usually move right in on their rivals' territory. But kin recognition may serve as a kind of "secret handshake" that allows plants to refrain from competition without being taken advantage of. As a result, the sibling plants might all enjoy better health in the short term, and promote their genes in the long term.
Now try and answer these questions:
- What is kin selection? How is it different from kin recognition?
- How is the sea rocket plant's kin selection like that of the ground squirrel? How is it different?
- How might the plants use chemical signals to recognize their relatives?
- A group of sea rockets will do better, overall, if they agree to cooperate than if they compete. However, if any one individual tries to compete, the benefit is lost. Can you think of other situations in which this rule applies?
You may want to check out the July 13, 2007, Science Update Podcast to hear further information about this Science Update and the other programs for that week. This podcast's topics include: the importance of bubbles, living on icebergs, family-oriented plants, eye medicine from oven cleaner, and how water gets from your mouth to your muscles.
For another side of plant relationships, read Plants on the Warpath: The Roots of Combat from National Geographic magazine.
National Geographic News also features several news stories on kin help in various animals, including:
- Rattlesnakes Show Strong Family Bonds
- Some Ducks Let Young Be Raised by Relatives
- Ants Practice Nepotism
- Animal "Baby-Sitting" May be Family Affair