Ever wondered what attracted your mom to dear ol' dad? Well, if you mom was a guppy (Poecilia reticulata), it might very well have been his bright flashy colors. Turns out that female guppies can use the brightness of a male's spots to assess whether or not he is infected with a parasite, such as Gyrodactylus turnbulli, a common monogenean trematode. Classic work by Anne Houde and others showed that infected male guppies showed less intense orange spots and that female guppies preferred them less in mate-choice experiments. They may be using these cues as a means of avoiding being parasitized themselves, but they are also probably trying to pick males with good genes so that their offspring might be resistant to parasites, too.
Photo by Marilyn Scott and comes from this website.