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© 1998 International Society for Behavioral Ecology
research-article |
Fitness components associated with alternative reproductive tactics in cliff swallows
Department of Biological Sciences, University of Tulsa 600 S. College Avenue, Tulsa, OK 74104-3189, USA
ABSTRACT
Two common alternative reproductive tactics are intraspecific brood parasitism and extrapair mating. Understanding the evolution of these traits requires estimation of fitness for individuals that do and do not exhibit diem. We analyze fitness components associated with brood parasitism and extrapair mating in cliff swallows (Petrochetidon pyrrhonoto). Annual survival probabilities for females known to be parasites, hosts, and nonparasites/nonhosts differed significantly, with highest survival (0.761) for parasites and lowest (0.289) for host females parasitized by egg laying. Survival probabilities did not differ among males paired to females of different status. First-year survival probabilities in die absence of ectoparasitic swallow bugs (Otdocus vicarius) were 0.546 for young raised in die brood parasites' own nests versus 0.354 for young from all other nests; first-year survival probabilities in die presence of swallow bugs were 0.223 for young raised in host nests versus 0.132 for young from nests not brood parasitized. Males that engaged in extrapair copulation attempts had an annual survival probability of 0.413, signficantly lower than die 0.614 estimated for males that were not seen engaging in extrapair mating. Annual reproductive success, measured as recruitment to breeding age, was greatest for brood parasites and similar among other classes of birds in die absence of swallow bugs and was greater for hosts than for birds not brood parasitized in die presence of swallow bugs, likely because hosts occupied less infested nests. Estimated lifetime reproductive success was highest for parasites and their mates. There were no apparent long-term effects of brood parasitism on survival of adult hosts or offspring from host nests, both because hosts did not have enlarged broods and because clutch and brood size did not affect cliff swallow survival. Brood parasites have greater fitness than hosts and nonparasitized birds, probably because parasites are superior individuals in good condition to start with. That males who participated in extrapair mating had lower expectation of survival suggests that extrapair copulations in cliff swallows are perpetrated by inferior males, and females should probably avoid diem.
Key words: alternative reproductive tactics, brood parasitism, cliff swallows, coloniality, extrapair copulation, fitness, life history, Petrochelidon pyrrhonota, reproductive success, social behavior, survival.