Impact of blood parasites on immunoglobulin level and parental effort: A medication field experiment on a wild passerine

Abstract

1. Very few studies to date have evaluated experimentally the effects of blood parasites on physiological variables and breeding performance in wild birds. In this study, blood parasitaemias of female Blue Tits Cyanistes caeruleus L. were experimentally manipulated to assess subsequent changes in immunoglobulin level and parental effort during reproduction. 2. At the beginning of the nestling period, female Blue Tits were medicated with a high dose (HD) or a low dose (LD) of the antimalarial Primaquine, or with saline solution (control). Treatment with Primaquine causes a reduction in blood parasitaemias in the study population. 3. Immunoglobulin levels decreased in females from the HD group during the experimental period (10 days), while the levels increased in control females. 4. Only females in the HD group increased significantly their provisioning rates from the early to the late nestling stage. Total (male and female) provisioning rates increased significantly for the HD and LD groups, but not for the control group. 5. Nestlings reared by control females suffered a higher infestation by the ectoparasitic blowfly Protocalliphora azurea (Fallén). 6. Medication and the associated decrease in immunoglobulin levels allow females to allocate more resources towards parental effort. In addition, there is a potential link of medication with the health of the nestlings. 7. This study gives indirect support to the trade-off between reproductive effort and immune defence in avian hosts, and sheds light on the evolutionary significance of the link between parasitism, immunity, life-history decisions and fitness. © 2006 The Authors.