Friday, July 6, 2012
Tiny green insects known as pea aphids have individual behavior patterns, or “personalities,” despite being clones of one another, scientists say. The researchers found differences in the way each individual responds to a threat. The study was part of a “burgeoning” of scientific interest in animal personality variation, noted the investigators, with the University of Osnabrueck, Germany. But despite this trend, they added, few studies have been done on invertebrates, or simple animals without backbones. Studies on “clonal invertebrates,” which are all genetically identical and would thus be expected to show limited differences in behavior, are “nonexistent,” they added, reporting their findings in the March 1 online issue of the journal Developmental Psychobiology. “This is surprising given the obvious advantages of using invertebrates/clones to tackle the crucial question why such consistent behavioral differences exist,” they went on. Personality differences not attributable to genes are generally presumed to be due to the environment in which an organism formed, though there is also a growing appreciation of epigenetic factors—chemical differences that are not genetic, but that influence gene activity. Pea aphids, scientifically named Acyrthosiphon pisum, are pale little insects typically less than a sixth of an inch (half a centimeter) long that feed on pea plants and their relatives. A cluster of aphids infesting a given plant is typically a genetically identical, or clonal, group produced by one mother without sex, although aphids can also reproduce sexually at certain phases. When a pea aphid is threatened by a predator—of which the species has several including wasps and grubs—it gives off a chemical alarm signal that alerts nearby aphids. They may respond in several ways: they can walk away, drop off the plant or seemingly ignore the signal. The researchers, Wiebke Schuett and colleagues, found that pea aphids can be divided into one of three categories: consistent “droppers,” consistent “non-droppers,” and some that behave unpredictably.