Elevated phytohaemagglutinin‐induced skin‐swelling response at an intermediate number of MHC class II alleles in bluethroat nestlings

Genes of the major histocompatibility complex (MHC) are crucial for adaptive immunity, and theory predicts that optimal number alleles is intermediate rather than maximal. Support such an optimum in MHC allele count has mainly been demonstrated studies on parasite load reproductive traits. In this study we tested if class II (MHCII) based positively selected sites was correlated with increased skin-swelling response to two consecutive injections phytohaemagglutinin (PHA) bluethroat Luscinia svecica nestlings. We found nestlings were closer population mean their had a higher first injection, supporting intermediate, alleles. After second PHA skin swelling associated MHCII only at among-brood level, paternity (extra-pair offspring larger within-pair offspring). therefore conclude partly count, but additional factors must be involved both female extra-pair mate choice species.