Next time you cool off in a lake, try not to think about the fact that you might be surrounded by furry single-celled microbes engaging in some truly peculiar reproductive behavior. Actually, for the most part, Tetrahymena is quite a chaste creature that uses the virginal method of parthenogenesis to populate its fresh-water environs.
But parthenogenesis doesn't create the kind of genetic variation that can help organisms adapt to changing surroundings. So when times are tough, Tetrahymena can actually switch on a dormant sex drive to help it survive. That's when things get very interesting.
If you think keeping track of gender politics is complicated, consider the fact that this little creature has no fewer than seven genders! Scientists have imaginatively termed these genders Types I through VII. A Type I can't mate with another Type I, but not to worry — it can choose from among any one of the remaining six genders.
The new baby Tetrahymena get all the genetic info necessary to become any one of the seven possible types. Then, through a random process, their DNA gets pruned down to a single gender. Pretty complicated stuff for a microscopic microbe!