| Titre : | Seasonal decline in cell-mediated immunity of collared flycatcher Ficedula albicollis nestlings: does the sex of offspring matter? |
| Auteurs : | Tomasz Wilk, Auteur ; Anna Dubiec, Auteur ; Mariusz Cichoń, Auteur |
| Type de document : | Article |
| Dans : | Journal of Ornithology (148(2) APR 2007) |
| Article en page(s) : | 199-205 |
| Langues: | Anglais |
| Résumé : | The seasonal decline in offspring performance is a frequently reported phenomenon in species breeding in a temperate zone, but the potential effect of brood sex ratio on such declines has not been studied. Here, we predicted that this decline may occur if the sex that exhibits the lower immune response or lower survival rate tends to be more frequent among late broods. The seasonal patterns of four performance parameters of collared flycatcher Ficedula albicollis nestlings have been examined during 4 years. Sex was assigned to all studied individuals using molecular techniques. We found significant seasonal decline in cell-mediated immune response, tarsus length and survival of the chicks. The lack of interactions between gender and hatching date revealed that both sexes contributed equally to the observed decline. The brood sex ratio did not vary with the laying date. On the basis of available data, we suggest that the breeding date may only exceptionally induce female-driven sex allocation in species with only slight sexual size dimorphism. In consequence, we suggest that seasonal sex ratio shifts do not account for seasonally declining fitness of nestlings in passerines. |



