July 9, 2010
A paper to be published in Science journal, authored by University of Rochester biologist John Jaenike and colleagues, has found that, for the drosophila fly, a recent adaptation against the invasive parasitic nematode came not from a genetic mutation but from a symbiotic relationship with a bacteria called Spiroplasma. More interesting still, the beneficial relationship with the bacteria is being favored by natural selection.
Normally for drosophila, a nematode infection, which begins early in the life of females, results in sterility for the host, as the parasite prevents them from producing eggs. However, the presence of Spiroplasma greatly weakens infecting nematodes, preventing the fly from becoming sterile.
The reproductive benefit conferred to the fly, in turn, has lead to the bacteria being passed on to subsequent generations. The study found that while only 10% of the population had the beneficial bacteria, the number has jumped to 80% by 2008. Scientists
For more on the study, see the article in PhysOrg.