. Bulletin of the British Museum (Natural History). Zoology . 54 P. H. GREENWOOD sauvagei), specialized insectivores (H. chilotes) and a piscivore (H. altigenis) all exhibit the phenomenon. Selective advantages associated with the maintenance of this balanced poly- morphism are unknown (Greenwood, 1956a ; see also discussion in Fryer & lies, 1972), but must be fairly substantial considering both the frequency of polymorph individuals in a population, and the fact that it occurs in so many Fig. 29. Haplochromis barbarae female, showing piebald coloration (see p. 53).
. Bulletin of the British Museum (Natural History). Zoology . 54 P. H. GREENWOOD sauvagei), specialized insectivores (H. chilotes) and a piscivore (H. altigenis) all exhibit the phenomenon. Selective advantages associated with the maintenance of this balanced poly- morphism are unknown (Greenwood, 1956a ; see also discussion in Fryer & lies, 1972), but must be fairly substantial considering both the frequency of polymorph individuals in a population, and the fact that it occurs in so many Fig. 29. Haplochromis barbarae female, showing piebald coloration (see p. 53). The usually complete linkage of piebald coloration to the female sex is disturbed in Macropleurodus bicolor, where two piebald males have been found (Greenwood, 1956a). In one of these fishes the pattern is identical with that of females, but in the other it is less intense and the background coloration is darker. As far as I can determine, the gonads of these atypical males contained only testicular tissue, and provided no evidence to suggest possible protandry in the species (as is suspected for a Malawian genus Labeotropheus fuellebomi [report by Professor H. Peters, quoted in Fryer & lies, 1972 : 172]). A male showing partial female-type piebald colours is also recorded for Hoplotilapia retrodens (Greenwood, 1956a), and I have seen a live Haplochromis chilotes with piebald coloration and well-defined 4 egg dummies1 on the anal fin. Unfortunately it was not possible to dissect the latter specimen, an aquarium fish. The genetic basis for this almost completely sex-limited polychromatism, and its occasional breakdown, has not been determined. Fryer & lies (1972) argue cogently in favour of its being the manifestation of a potency balance between the expression of alleles on autosomes and 'suppressor' alleles on the sex chromosomes. On the assumption that female cichlids are the heterogametic sex (which is also assumed in my explanation of the phenomenon ; Greenwood, 19
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