EFFECT OF PARASITIC INFECTION ON MALE COLOR PATTERN AND FEMALE CHOICE IN GUPPIES

We infected male guppies Poecilia reticulata with a naturally occurring monogenean parasite, Gyrodactylus tumbulli, in order to examine effects of parasitism on the expression of color patterns and on attractiveness to females. The color of carotenoid spots and ability to attract females were compared between experimentally infected fish and a control group of their full-sib brothers, which had identical color patterns and were treated identically except for actual exposure to parasites. The orange spots of males that had been infected for 9 days followed by treatment with medication to remove parasites became significantly paler and less saturated. Control males (also treated with medication) showed no significant changes in their orange spots. Females in a divided aquarium choice-apparatus showed no preference between control and infection-treatment males initially, but showed significant discrimination after the infection-disinfection treatment. Females spent less time near males that had been infected and responded to a smaller fraction of their courtship displays relative to control males. There were slight differences in courting rates of males between treatments. Parasitic infection appears to reduce the degree of expression of carotenoid colors in guppies, and females are able to discriminate against recently infected males, probably on the basis of the color change. By avoiding infected males, females may be able to avoid becoming infected themselves, or they may be able to identify mates based on "good genes" for parasite resistance that can be passed on to their offspring.