House sparrows selectively eject parasitic conspecific eggs and incur very low rejection costs |
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Authors: | Manuel Soler Cristina Ruiz-Castellano María del Carmen Fernández-Pinos Anja Rösler Juan Ontanilla Tomás Pérez-Contreras |
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Institution: | 1.Departamento de Biología Animal, Facultad de Ciencias,Universidad de Granada,Granada,Spain;2.Grupo Coevolución, Unidad Asociada al CSIC, Universidad de Granada,Granada,Spain |
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Abstract: | Most host species of obligate interspecific brood parasites are under strong selection because such parasitism, e.g., that
involving evictor nestmates, is highly costly. Egg rejection is one of the most efficient host defences against avian brood
parasites. Many hosts have thus evolved egg-recognition ability and rejection behaviour. However, this defensive mechanism
has not evolved in most species where only intraspecific brood parasitism occurs, probably because (1) the eggs of conspecific
females are very similar in appearance, making egg rejection less likely to emerge, and (2) such parasitism is frequently
less costly than interspecific parasitism. Using a captive population of house sparrows (Passer domesticus) with a low breeding density, we here provide new evidence showing that this species actually has a fine capacity to discriminate
conspecific eggs and to eject them (44.2% of foreign eggs ejected) while incurring very low rejection costs (4.2% of own eggs
ejected). This result contradicts those previously found in high-density house sparrow populations in which very high rejection
costs and very high clutch desertion rates were reported, probably as a consequence of intraspecific competition and infanticide
provoked by the high breeding density. The house sparrow has only rarely been reported as the host of an interspecific brood
parasite, which implies that it is a newly described example of an altricial species in which egg ejection has evolved and
is maintained in response to intraspecific brood parasitism. |
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