Host preference of a haematophagous avian ectoparasite: a micronutrient supplementation experiment to test an evolutionary trade-off

Abstract

Immune responses vary greatly depending on physiological and ecological circumstances, but the causes of this variation and its consequences for host–parasite interactions are not clear. One problem is whether resource trade-offs within hosts affect host choice by macroparasites. We aimed experimentally to disentangle the effects of the nutritional and immunological parameters of the host on the choice of host by a blood-feeding ectoparasitic fly, Carnus hemapterus. We used micronutrient supplementation to enhance host immunity and antioxidant capacity and balance the resource allocation of the host from growth to immune function in nestlings of the European roller, Coracias garrulus. Micronutrient-supplemented nestlings showed lower growth rate and body condition than sham-supplemented nestlings. Nestlings receiving micronutrients also had a higher albumin-to-globulin ratio and β- and γ-globulin concentrations, but lower α1- and α2-globulin concentrations, total protein level and cutaneous response to phytohaemagglutinin. Our results revealed that the phytohaemagglutinin response and β- and γ-globulin concentrations reflect body condition, whereas the strength of the acute phase response (α1- and α2-globulin concentrations) reflects the protein status in nestling European rollers. Ectoparasitic C. hemapterus flies generally chose hosts according to their body condition. However, this choice was moderated by host immunity when the host had poor body condition or posed a high risk for parasites in terms of the acute phase immune response.