Reproductive effort and T-lymphocyte cell-mediated immunocompetence in female pied flycatchers Ficedula hypoleuca

The physiological mechanism underlying the cost of reproduction may consist of immunodepression caused by increased parental effort. Here, we report e ffects of experimental manipulation of clutch size on T-lymphocyte cell-med iated immune response in female pied flycatchers, Ficedolla hypoleuca. Pare nts with reduced broods provisioned at lower rates than those caring for co ntrol and enlarged broods three days after hatching. Parents caring for enl arged broods provisioned nests at higher rates 13 days after chick hatching than those feeding control and reduced broods. Females with enlarged brood s weighed less than females with control or reduced broods. No effect of ex perimental treatment on nestling mass and size was found. The response to t he injection of phytohaemagglutinin in the wing-web of females decreased wi th increasing brood size and with increasing provisioning rate when the chi cks were three days old, when controlling for the negative effect of female mass on response. The T-lymphocyte cell-mediated response decreased from t he reduced to the control, and from this to the enlarged group, when contro lling for female mass. This effect of experimental manipulation of clutch s ize was significant and consistent with a trade-off between maternal effort and immunocompetence.