REPRODUCTIVE EFFORT DECREASES ANTIBODY RESPONSIVENESS

The prevalence and intensity of parasitic infection often increases in animals when they are reproducing. This may be a consequence of incre ased rates of parasite transmission due to reproductive effort. Altern atively, endocrine changes associated with reproduction can lead to im munosuppression. Here we provide support for a third potential mechani sm: reduced immunocompetence as a consequence of adaptive reallocation of resources in times of increased energetic demand. In captive zebra finches Taeniopygia guttata, reproductive effort was manipulated thro ugh brood size. Enhanced effort was found to affect the production of antibodies towards sheep red blood cells. In addition, activity of zeb ra finches was manipulated independently of parental care. Experimenta lly increased daily workloads in activity reward schedules also suppre ssed antibody production. Thus, we show that not just the reproductive state, but the increased activity that accompanies reproduction is as sociated With immunocompetence. This mechanism may be sufficient to ex plain the increased parasitism observed in reproducing animals. We sug gest that reduced immunocompetence as a consequence of increased repro ductive effort may be an important pathway for the life history cost o f reproduction.