Coevolutionary arms race between a specialist brood parasite, the Screaming Cowbird, and its host, the Baywing.

DE MÁRSICO, M.C.; URSINO, C.A.; SCARDAMAGLIA, R.; REBOREDA, J. C.

Journal of Onithology

Springer

Lugar: Berlin; Año: 2019 vol. 160 p. 1221 - 1233

2193-7192

Interspecific brood parasites exploit the parental care from individuals of other species, the hosts. This exploitation entails fitness costs for the hosts, which favor the evolution of antiparasitic defenses. Host defenses select for counterdefenses in the parasites, which in turn select for improved host defenses, thus resulting in a coevolutionary arms race that may operate at each stage of the nesting cycle of the host. Most studied examples of coevolutionary arms races in brood parasites are restricted to the eggs stage, with relatively few studies showing coevolution between hosts and parasites at the nestling or fledgling stages, and studies on the whole set of host defenses and potential parasite?s counterdefenses at each stage of the breeding cycle are still lacking. Systems in which parasites are host-specialist are particularly well-suited to examine pairwise coevolutionary interactions before, during and after host?s egg-laying, and how those interactions have shaped host resistance or tolerance to parasitism. The Screaming Cowbird (Molothrus rufoaxillaris) is one of the most specialized brood parasites, using mainly a single host species, the Grayish Baywing (Agelaioides badius). Parasitism rates of baywing nests are extremely high, with most nests multiply parasitized. Several traits of this host-parasite system suggest ancient coevolutionary relationships encompassing the entire nesting cycle. In this paper we summarize the main results of a long-term study on the costs of Screaming Cowbird parasitism on Baywing?s reproductive success and how these costs have favored reciprocal adaptations and counteradaptations at each stage of the nesting cycle.