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

In order to test whether high reproductive investments impair immune functi on in naturally breeding collared flycatchers, we performed a brood manipul ation experiment and simultaneously induced an immune response by challengi ng birds with a non-pathogenic antigen - sheep red blood cells (SRBC). Fema les rearing experimentally enlarged number of nestlings showed significantl y lower level of specific anti SRBC antibodies than control females attendi ng unaltered broods, but only in one of the two study years. The haemoconce ntration of leukocytes did not differ between the two groups in both study years. The significant difference in immunological responsiveness between c ontrol and enlarged group coincided with differences in survival probabilit y to the next breeding season: females attending enlarged broods showed low er probability of survival than control females, but there was no relations hip between the level of immune response and survival probability. Our resu lts indicate that reproduction may indeed trade for resources with immune f unctions 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.