http://discovermagazine.com/2007/jul/can-sex-reevolve
"After analyzing various mites' DNA, the duo concluded that the
sexually reproducing Crotoniidae mite is a descendant of Camisiidae
mites, which have reproduced asexually for hundreds of millions of
years since they themselves evolved from a sexually reproducing
ancestor. Through a process called parthenogenesis, Camisiidae females
typically lay eggs that are exact copies of themselves. Although males
are born every once in a while, they are always sterile. Or so it was
thought.
"'Those rare males may have enabled Crotoniidae to reevolve sex,'
says Domes. Usually when traits fall into disuse, their corresponding
genes quickly mutate to code for something else. So when something as
complex as the ability to produce sex gametes is lost, it's likely
never to be developed again. Oddly, the Camisiidae mites seem to have
retained that ability, despite surviving millions of years without
using it."

Budikka

http://discovermagazine.com/2007/jul/can-sex-reevolve
"After analyzing various mites' DNA, the duo concluded that the
sexually reproducing Crotoniidae mite is a descendant of Camisiidae
mites, which have reproduced asexually for hundreds of millions of
years since they themselves evolved from a sexually reproducing
ancestor. Through a process called parthenogenesis, Camisiidae females
typically lay eggs that are exact copies of themselves. Although males
are born every once in a while, they are always sterile. Or so it was
thought.
"'Those rare males may have enabled Crotoniidae to reevolve sex,'
says Domes. Usually when traits fall into disuse, their corresponding
genes quickly mutate to code for something else. So when something as
complex as the ability to produce sex gametes is lost, it's likely
never to be developed again. Oddly, the Camisiidae mites seem to have
retained that ability, despite surviving millions of years without
using it."

Budikka