Abstract:

The recognition and subsequent rejection of brood parasite eggs is one of the most commonly observed defensive behaviors of the host. The brown-and-yellow marshbird (Pseudoleistes virescens) is a common host of the shiny cowbird (Molothrus bonariensis). This host recognizes and rejects immaculate white eggs of the cowbird, but accepts this bird’s spotted eggs. We assessed the acceptance threshold hypothesis which proposes that parasite egg recognition is context-dependent. We experimentally parasitized host nests with a spotted cowbird egg and simultaneously added: (1) one novel egg with spots similar to those of a cowbird egg but on a blue background or (2) one immaculate white cowbird egg. In this setting, 78 % of the novel blue egg with spots and 77 % of the cowbird’s immaculate white eggs were quickly recognized and rejected. The rejection frequency of spotted cowbird eggs was also high (60 %) and was not related to the type of egg which had been added to the host nest together with the spotted cowbird egg. This rejection frequency of spotted cowbird eggs is higher than the 21 % that we previously found in a similar experimental setting but in which the spotted cowbird egg was added singly to the host nest. These results support the acceptance threshold hypothesis that predicts an adaptive modulation of the antiparasite defence when the perceived risk of parasitism is high.

Author affiliation: Mermoz, Myriam Emilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina

Author affiliation: Haupt, Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina

Author affiliation: Fernandez, Gustavo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina

Abstract:

Breeding dispersal is the movement of an individual between breeding attempts and is usually associated with the disruption of the social pair bond, although mates may disperse together as a social unit. In monogamous territorial species, the decision to disperse may be affected by individual attributes such as sex, age and condition of the disperser. However, environmental and social contexts may also play a crucial role in the decision to disperse. We analysed capture-resighting data collected over 9 years to study breeding dispersal and divorce rates of a Southern House Wren Troglodytes aedon musculus population in South Temperate Argentina. Between-season dispersal was more frequent than within-season dispersal, with females dispersing more often than males, both between and within seasons. Both within-season and between-season breeding dispersal probability was affected by territory availability, but not by previous breeding success. When the adult sex ratio (ASR) was more skewed towards males, male between-season dispersal was also affected by mating status, with widowed and single males dispersing more often than paired males. Within-season divorce increased the reproductive success of females but not males, and was affected by the availability of social partners (with increasingly male-skewed ASR). Our results suggest that territorial vacancies and mating opportunities affect dispersal and divorce rates in resident Southern House Wrens, highlighting the importance of social and environmental contexts for dispersal behaviour and the stability of social pair bonds.

Author affiliation: Carro, Mariana Emilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina

Author affiliation: Llambias, Paulo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Provincia de Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Universidad Nacional de Cuyo. Instituto Argentino de Investigaciones de las Zonas Áridas; Argentina

Author affiliation: Fernandez, Gustavo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina