According to an article that I read in the New Zealand Herald last week, it seems that plants are able to tell relatives apart from strangers. The article suggested that plants are operating on a higher cognitive level than we give them credit for.
I've reprinted it below for your viewing pleasure. It is from the 19 June 2007 edition.
What will the vegans eat now? Researchers at McMaster University have found that plants get fiercely competitive when forced to share their pot with strangers of the same species, but they're accommodating when potted with their siblings. "The ability to recognise and favour kin is common in animals, but this is the first time it has been shown in plants," said Susan Dudley, associate professor of biology at McMaster University in Hamilton, Canada. "When plants share their pots, they get competitive and start growing more roots, which allows them to grab water and mineral nutrients before their neighbours get them. It appears, though, that they only do this when sharing a pot with unrelated plants; when they share a pot with family they don't increase their root growth. Though they lack cognition and memory, the study shows, plants are capable of complex social behaviours such as altruism towards relatives, says Dudley.
If I were looking for a non-biological explanation for this phenomenon, I would mention Rupert Sheldrake's theory of morphic resonance fields, which basically states that invisible energy patterns or morphic fields surround and affect all living things. Organisms that have surrounding energy fields of similar vibrations can communicate telepathically, and perhaps that is what these plants are doing.
However, a more logical explanation would be the biological concept of resource competition. According to the article, a plant grows bigger when it is potted with an unrelated member of its species. One obvious thing to look for is at what time each day the plant absorbs the most water and mineral nutrients. Siblings are likely to all operate to the same schedule, since their genetic makeup is similar. Therefore, they'll use available resources less efficiently than strangers that operate to different schedules.
An alternative explanation is the biological process known as allelopathy, where one plant harms another with specific biomolecules, in order to hinder this plant's growth and further its own. According to Wikipedia, "Although allelopathic science is a relatively new field of study, there exists convincing evidence that allelopathic interactions between plants play a crucial role in both natural and manipulated ecosystems. These interactions are undoubtedly an important factor in determining species distribution and abundance within some plant communities."
In any case, concluding that plants can "recognise" relatives and strangers seems a bit suspect. We have brains to perform this task. Plants do not. The researcher also makes the assumption that plants are capable of complex social behaviours such as altruism towards relatives. That's quite a leap to make. Looks to me like another case of anthropomorphism.
Sunday, June 24, 2007
Plants Can Tell Who's Who
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1 comment:
I agree with you. It would be very premature to suggest benevolent kin altruism on the evidence given.
I'd hesitate to agree with your first biological explanation though. It is true that non-related plants would have different ecological niches (http://en.wikipedia.org/wiki/Ecological_niche) and thus two different plants may thrive together better than two plants of the same species. Thus usually plants of the same species aren't altruistic, but compete more with their kin than different species and would be smaller.
But this experiment was especially interesting from the view that they were all of the same species. Would variation within the same species allow for a difference in ecological niche? That would need to be determined. The experiment suggests that the plant spreads its roots in one situation and not another. For your first explanation, the roots would grow in the direction where the specific nutrients it desires are plentiful, which would be the opposite direction to its kin. This is plausible. But in a limited space where resources are scarce, you'd expect two plants to compete hard woudn't you? So the roots should go everywhere.
Perhaps there is another element at play and that might be what the researchers were suggesting. What if the plants could detect close kinship versus distant kinship as a way of knowing to what degree they should compete?
The selfish gene, as described by Dawkins, could explain the phenomenon. This is genetically-determined favoritism. Since the closest relatives have similar genes, genes to identify the degree to which a neighbour shares its own genes can develop. To compete against kin would be self-defeating from a genetic point of view thus through natural selection such evolution would be unfavoured. Perhaps, plants can identify roots of close kin and not compete for the space (since the strongest competition is intraspecial).
Allelopathy is naturally another example of selfish genes but doesn't usually work within a species but against other species.
This would not mean that they have complex social behaviour; just that they may have the ability to sense genetic resemblance and respond in different ways. Stimulus / response. Plants aren't 'intelligent' because they can react to gravity, nor where the sun is, nor what time of the day it is. All of these responses are beneficial and hence are selected for, just as would kin recognition.
So, I'd say they should get some more well-designed tests to further search out the exact nature of the phenomenon.
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