ECTOPARASITES INCREASE THE COST OF REPRODUCTION IN THEIR HOSTS

1. Parasites are hypothesized to increase the cost of reproduction in their hosts due to their time and energy drain. I experimentally studied the effects of the haematophagous tropical fowl mite (Ornithonyssus bursa, Berlese (Macronyssidae, Gamasida)) on the within-season costs of reproduction in their swallow (Hirundo rustica L.) hosts by simultaneously manipulating (i) the size of first clutches (which were either increased by one egg, kept as a control, or decreased by one egg), and (ii) the mite loads of first clutch nests (nests were either sprayed with a pesticide or kept as controls). 2. The experimental treatments were successful as evidenced from the effect of the clutch size manipulation on clutch and subsequent brood size, and from the effect of the parasite manipulation on subsequent mite loads. 3. Experimental treatments also affected the reproductive effort during the first reproductive event of the season as evidenced from the effects of both treatments on (i) brood size at fledging, (ii) the duration of the incubation period, and (iii) the body mass of offspring. 4. The cost of reproduction was measured as the effect of experimental treatment during first clutches on reproductive events during second clutches. Presence of mites increased the cost of reproduction as evidenced from statistically significant interactions between clutch size treatment and mite treatment for (i) the time of egg laying, (ii) clutch size and brood size at hatching and fledging, and (iii) the body mass of offspring. 5. The increased costs of reproduction due to the parasite treatment of first clutches remained when the effects of the number of mites in second clutch nests were controlled statistically. The tropical fowl mite, therefore, increases the within-season costs of reproduction in its swallow hosts.