THE INHERITANCE OF CERTAIN COLOR PATTERNS IN WILD POPULATIONS OF LEBISTES RETICULATUS IN TRINIDAD

Pronounced sexual dimorphism of both form and color is characteristic of a number of viviparous teleost fishes of the subfamily Poeciliinae. The condition is perhaps most pronounced in several small related tropical forms, such as Micropoecilia branneri Eigenmann, Micropoecilia parae Eigenmann, Micropoecilia bifurca Eigenmann, and Lebistes reticulatus (Peters), all native to northeastern South America and two to adjacent Caribbean islands, which have, been included by Hubbs (1926) in the tribe Poeciliini. Among these small, largely surface-feeding, viviparous top-minnows the females are characteristically of generalized form and of an unspecialized, gray coloration, with very little body marking in the genus Micropoecilia and with none whatever in Lebistes save the characteristic reticulation. By contrast, the males of these species are brilliantly and characteristically colored and exhibit pronounced and species-specific patterns of courtship and mating behavior. In the genus Micropoecilia, the male color patterns within a single species may show decided variation over a wide geographic range, but they are normally quite constant in populations occupying many square miles of territory. Thus, for example, the males of Micropoecilia parae show an essentially constant color pattern throughout the very numerous populations which inhabit the lagoons and brackish coastal streams and ditches of the islands of Trinidad and Tobago. It is not known how the male color patterns are inherited in the genus Micropoecilia. In Lebistes, as in Micropoecilia, the males are small relative to the females, are of pronouncedly different form, and are of brilliant coloration. But the male color patterns, far from being constant within a given population even of restricted scope, are highly variable-so much so that, under natural conditions, it is difficult to find two individuals which exhibit even approximately similar patterns. Indeed, the males of Lebistes form one of the most highly polymorphic color series known in nature, in sharp contrast to the monotonous phenotypic uniformity of the females. The inheritance of male color patterns in Lebistes has been studied by Schmidt (1920), by Blacher (1927, 1928), by Kirpichinikow (1935), and more extensively by Winge (1921, 1922a, 1922b, 1927, 1930, 1932, 1934) and Winge and Ditlevsen (1938, 1948), in a long series of interesting investigations. As a result of these it seems clear that in Lebistes the male is normally the heterogametic sex and inheritance is typically of the XY pattern. The sex-chromosomes, however, are relatively unspecialized and are not morphologically distinguishable either from one another or from the autosomes. Furthermore, sex determination clearly does not reside entirely with the sex-chromosomes. Normally functional XY females and XX males have been demonstrated by Winge. The haploid chromosome number for the species is 23. Although the males of Lebistes exhibit extreme color polymorphism in their total color patterns, even in restricted wild populations, it is possible to resolve these patterns into a number of components which show clear-cut unifactorial inheritance, together with a number of others