A comparative analysis of the evolution of variation in appearance of eggs of European passerines in relation to brood parasitism

Host of brood parasites increase the ability of rejecting cuckoo eggs by production of (1) a clutch with little variation among eggs and (2) a clutch that differs the most from the modal phenotype of the population. These hypotheses have been tested by Oien et al. (1995), although they did not control for common phylogenetic ancestry We analyze the evolution of egg color and marking patterns in European passerines, which are potential hosts of the European cuckoo (Cuculus canorus), using Felsenstein's (1985) independent comparative method to control for the effect of common phylogenetic descent. We found a significant positive relationship between interclutch variation in appearance of host eggs and parasitism rate, but this relationship disappeared when hole-nesting species were excluded from the analysis; and we found a highly significant multiple regression between rejection rate and intra- and interclutch variation in egg appearance, even when hole nesters were excluded from the analysis. The partial correlation coefficients were negative for intraclutch variation and positive with interclutch variation in agreement with the hypotheses. Therefore, the use of the independent comparative method strengthens the hypothesis that the evolution of egg patterns in hosts is associated with different stages of coevolution with the brood parasite.