Cues from the organism's environment influence many of an organism's traits. While these aspects are referred to as phenotypically plastic traits, they are also essential in allowing an organism to cope with unpredictable environments. However, what is the genetic mechanisms underlying these traits?
An associate professor of biology at the University of Rochester, Jennifer Brisson and Benjamin Parker, her former postdoctoral student, now an assistant professor of microbiology at University of Tennessee, studied phenotypically plastic traits in pea aphids and uncovered, for the first time, genes that influence whether aphids produce wingless or winged offspring in response to their environment. The team published their findings in the journal Current Biology, and it shed light on how phenotypically plastic traits evolve and address critical questions about the evolution of environmentally sensitive characters.
As insects, pea aphids reproduce rapidly and typically give birth to offspring that do not have wings. As many gardeners aware, aphids can quickly overwhelm and kill the host plants on which they live and feed. When an environment becomes too crowded with other aphids, the female begins producing offspring that have wings, rather than the typical wingless offspring. The winged offspring can then fly to and colonize new, less crowded plants.
Brisson explained that aphids have been doing this trick for millions of years. Some aphids, however, are more sensitive to crowding than others. To figure out the reason is critical to understanding how this textbook example of phenotypic plasticity works.
The scientists utilized methods from evolutionary genetics and molecular biology to identify genes that determine the level to which aphids respond to crowding. To their surprise, the genes they uncovered are from a virus that then became incorporated into the aphids genome. The virus, which is from a group of insect viruses called densoviruses, cause its host to produce offspring with wings.
The virus does this, as the researchers believed, to facilitate its dispersal. As Brisson and Parker discovered, the gene from the virus retained the same function of producing winged offspring even after it was transferred and incorporated into the aphid genome.
Parker noted that this is a new role for viral genes that are co-opted by the genome for another purpose, like modulating plastic phenotypes. Microbial genes can become incorporated into the animal genome, and this process is essential to evolution.
The team discovered a clear case in which genes from outside an organism were co-opted by the organism's genome to modify the strength of a plastic response to environmental cues. Brisson said further that even in ancient traits like the one studied here, new genes could start to play a role in shaping plastic traits and can help organisms cope with an unpredicted environment.
