Food availability and parasite infection influence mating tactics in guppies (Poecilia reticulata)

Despite the important effects of diet and parasite infectionon male reproductive behavior, few studies have simultaneouslyaddressed their influence on intrasexual selection (male–malecompetition). We examined the synergistic effects of 2 naturallyvarying environmental factors, lifetime food intake and infection,with the monogenean parasite Gyrodactylus turnbulli on the matingtactics and foraging behavior of male guppies (Poecilia reticulata).We allowed fish to interact directly with each other duringobservations and found that unparasitized males won more intermalecontests, courted females more frequently, and received positiveresponses to courtship displays more frequently than males thathad been infected. Infected males devoted more time to foragingand less time to courtship and competition than uninfected males,suggesting that they were energetically limited and could notincrease reproductive effort despite their reduced expectedlifespan. This interpretation was supported by the observationthat greater food intake ameliorated the negative effects ofparasite infection on courtship effort. Our results have bearingon how natural variation in food availability and parasite prevalenceinfluence geographic variation in reproductive behavior.