Parasites and sex: Catching the red queen.

One version of the Red Queen hypothesis suggests that sexual reproduction may be an advantage in a coevolutionary arms race. Antagonistic biotic interactions, especially those between parasite and host, are thought to represent a sufficient evolutionary force to counterbalance the supposed inefficiency of sexual reproduction. Recent experimental studies demonstrate negative frequency-dependent selection, increased parasite load in parthenogenetic races relative to sympatric sexual conspecifics and correlations between recombination rate and frequency of parasitic chromosomes. These studies provide strong empirical evidence that there is an important role for parasites in maintaining sex.