The effect of elevated reproductive effort on humoral immune function in collared flycatcher females

In order to test whether high reproductive investments impair immune function in naturally breeding collared flycatchers, we performed a brood manipulation experiment and simultaneously induced an immune response by challenging birds with a non-pathogenic antigen - sheep red blood cells (SRBC). Females rearing experimentally enlarged number of nestlings showed significantly lower level of specific anti SRBC antibodies than control females attending unaltered broods, but only in one of the two study years. The haemoconcentration of leukocytes did not differ between the two groups in both study years. The significant difference in immunological responsiveness between control and enlarged group coincided with differences in survival probability to the next breeding season: females attending enlarged broods showed lower probability of survival than control females, but there was no relationship between the level of immune response and survival probability. Our results indicate that reproduction may indeed trade for resources with immune functions at least in terms of specific antibody production. However, as in the other studies on reproductive costs, these costs seem not always to be pronounced. (C) 2001 Editions scientifiques et medicales Elsevier SAS.