A new study suggests that plants may be social organisms, capable of altruism in response to kin and competitive behavior toward strangers. The debate over the nature of altruism and altruism in nature continues.
The concept of altruism -- or apparently unselfish attitudes or behaviors -- has been debated philosophically for ages and studied psychologically for decades. More recently, evolutionary biologists have joined the discussion.
Ph.D. candidate Guillermo Murphy and Dr. Susan Dudley, of the Department of Biology at McMaster University in Ontario, Canada, have have published a paper in the November issue of the American Journal of Botany exploring kin recognition in yellow jewelweed, Impatiens pallida.
A key question from the perspective of natural selection, is why altruism would evolve. Social behavior, kin recognition, and altruism are well known in the animal kingdom. Perhaps any action that improves the chances for a relatives to survive and reproduce increases the chance of an altruistic individual's DNA being passed on.
Plants have been shown to sense and respond to other plants, but can they recognize kin and behave altruistically? This new study by Murphy and Dudley is one of the first to research the possibility of altruistic behavior in plants.
Yellow jewelweed individuals are often found growing in close proximity to related individuals and are known to respond strongly to above-ground competition, making this species a likely candidate for the study of kin recognition and altruism among members of a plant species.
Murphy and Dudley measured plants' responses to changes in light quality (an above-ground cue) and the presence of root neighbors (an underground cue) for plants grown with strangers and with relatives. The researchers found that the response of yellow jewelweed plants differed, depending on whether they grew with relatives or with strangers.
Plants growing among close relatives did not increase resource allocation to roots or leaves, but altered their above-ground morphology by increasing stem elongation and branching. Murphy and Dudley speculate that this may be an example of the plants cooperating with kin, since the plants are acquiring needed resources without shading nearby relatives.
Yellow jewelweed is found in the understory of forests with nutrient-rich soil, where light is the limiting factor for plant growth. A plant competing with its neighbors would be most likely to allocate resources to leaves.
Yellow jewelweed plants grown with strangers increased their resource allocation to their leaves relative to allocation to stems and roots, a competitive response that would shade nearby plants and decrease their light acquisition abilities.
The differences in allocation of resources in response to light based on the presence of kin or strangers were only observed in plants grown with root neighbors, indicating that communication among roots may be necessary for plants to recognize kin and behave altruistically.