Evol Ecol Res 11: 79-94 (2009)     Full PDF if your library subscribes.

Ectoparasites help to maintain variation in cell-mediated immunity in the blue tit–hen flea system

Natalia Pitala¹*, Heli Siitari², Lars Gustafsson³ and Jon E. Brommer¹

¹Department of Biological and Environmental Sciences, University of Helsinki, Helsinki, Finland, ²Department of Biological and Environmental Science, University of Jyväskylä, Jyväskylä, Finland and  ³Department of Animal Ecology/Ecology and Evolution, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden

Correspondence: J.E. Brommer, Bird Ecology Unit, Department of Biological and Environmental Sciences, University of Helsinki, PO Box 65 (Viikinkaari), FIN-00014 Helsinki, Finland.
e-mail: jon.brommer@helsinki.fi

ABSTRACT

Hypothesis: Host–parasite interactions have the potential to maintain genetic variation, especially in traits related to defence against parasites.

Organism: Blue tit (Cyanistes caeruleus) nestlings.

Methods: Rear nestlings in artificially created conditions of low and high abundance of ectoparasitic hen fleas (Ceratophyllus gallinae). Cross-foster siblings between these environments to estimate parasite-induced genotype–environment interactions. Measure components of phenotypic variance in morphology (tarsus length and body mass) and in immune defence (plasma immunoglobulins and cell-mediated immunocompetence).

Results: Hen flea infestation lowered growth, cell-mediated immunocompetence, and haematocrit. Genotype–environment interactions were observed in cell-mediated immunocompetence, body mass, and haematocrit, with significant crossing reaction norms for cell-mediated immunocompetence and haematocrit. Immunoglobulin concentrations were unaffected by fleas. Thus, host–parasite interactions constrain the expression and evolvability of some traits, but also create genotype–environment interactions with the potential to maintain genetic variation in immune defence.

Keywords: ecological immunology (immunoecology), ectoparasites, evolutionary quantitative genetics, reciprocal cross-fostering, restricted maximum likelihood linear mixed model.

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