GEOGRAPHICAL VARIATION AND POLYMORPHISM IN CHLOROPHONEUS SHRIKES

Abstract

SUMMARY Chlorophoneus multicolor and C. nigrifrons (possibly conspecific) are polymorphic forest shrikes that are widely but discontinuously distributed over most of tropical Africa. Between them they show five main colour‐phases of the under‐parts (each divisible into sub‐phases), as many as three of which occur together in certain localities. In addition there is geographical variation in other plumage characters and in size.This geographical variation tends to be clinal, but the occurrence of the various colour‐phases and the proportions in which they appear in the various local populations vary without apparent correlation. Moreover the extent to which neighbouring populations differ in regard to the phases represented bears no relation to the distance or to the severity of the ecological barriers between them. At present it is impossible to suggest any adaptive significance in the differences between the populations.The nature of the colour‐phases suggests that they may be controlled by very few genes, but no data are available from the offspring of mixed matings.The colour‐phases appear to be equally distributed in both sexes, except that the black phase, although evidently under different genetical control in East African and West African birds respectively, is known only from males.The whole situation is discussed in relation to other cases of polymorphism.