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SUMMARY PART 1 Remarkable parallelism exists between two groups of shrikes in the genus Malaconotus: (1) small-billed birds (formerly Chlorophoneus) comprising the polymorphic species multicolor and nigrifrons, the dimorphic olivaceus and the monomorphic sulfureopectus; (2) large-billed birds (formerly Malaconotus sensu stricto)—of the species blanchoti, cruentus, lagdeni, gladiator and alius (and including monteiri). Characters and ranges of the various species are set out and parallelisms between the two groups are listed. M. monteiri is thought to be a colour phase of cruentus rather than a race of blanchoti. It is suggested that the parallelisms are due to the two groups having derived from a common ancestor and that the existing “Malaconotus”, which are monomorphic, may derive directly from polymorphic ancestral stock. part 2 The polymorphism in “Chlorophoneus” can be accounted for by three genes with two alleles each, all interacting with polygenic systems. The homology of the morphs with the colour patterns of monomorphic populations is discussed, and their distributions in the two groups summarised. The interaction of polymorphism with continuous variation in determining the proportion of red to yellow carotenoid is discussed. The evidence bearing upon the status of monteiri is considered. The difference in the incidence of polymorphism between the groups is considered in the light of the analysis into dimorphisms. Some suggestions are made on the significance of parallels between the groups. |
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