On the relationship between T-cell mediated immunity in bird species and the establishment success of introduced populations

1. The introduction of animals to novel environments has been used as a model system for investigating the factors affecting small populations during their initial period of establishment. Previous studies of introduction success in birds have identified a number of factors associated with successful establishment. 2. We predicted that species with strong non-specific immune responses would have an elevated probability of establishment because they would be better able to cope with parasites in the novel environment. Consistent with this prediction, we found that nestling T-cell mediated immune response, as reflected by the response to a challenge with the mitogenic lectin phytohaemagglutinin, was a reliable estimator of establishment success. In multivariate analyses that took previously identified predictors into account, this was only the case when propagule sizes of introduced birds were large. 3. These findings suggest that host-parasite interactions can be an important component influencing the fate of small populations in novel environments only when severe disease or virulent parasites are more likely to have been introduced as well.