Inheritance of Egg-Color Polymorphism in the Village Weaver (Ploceus cucullatus)

Abstract

--Eggs collected from an aviary colony of Village Weavers (Ploceus cucullatus cucullatus) over a 14-year period varied in color among different females from white to emerald or turquoise, and from many spots to few or none. Color and amount of spotting of the eggs of a given female were constant throughout her life (based on 815 eggs from 37 females). Color was judged from the Villalobos Color Atlas. Mendelian analysis of five different hypotheses showed that inheritance of background color of eggs in 20 different crosses was consistent only with a hypothesis of two independent pairs of autosomal alleles for hue. Received 14 September 1992, accepted 25 November 1992. THE EDITORS of a recent book on avian genetics pointed out that, despite widespread interest among ornithologists in plumage polymorphism, evidence of the genetic basis for most of these polymorphisms is sadly lacking (Cooke and Buckley 1987:202). Even less is known about the genetic control of egg-shell-color polymorphisms. My objective is to present evidence on Mendelian inheritance of egg-shell-color polymorphism in a passerine bird. In the domestic fowl (Gallus gallus) for which the first demonstration of Mendelian heredity in the animal kingdom was made by William Bateson (Punnett 1923), a Mendelian analysis of egg-shellcolor polymorphism was done long ago (Punnett and Bailey 1920, Punnett 1923, 1933a), and this classic work is still one of the few published records dealing with this problem (Washburn 1990). There is no reference in the literature giving comparable evidence for any passerine bird. In North America the color of eggs is generally consistent for a given species of bird, and this is particularly true of the passetines (Harrison 1978). This is in strong contrast to the genus Ploceus (Ploceidae, weaverbirds) in which variation in egg color within the species is higher than in any other group of birds (Moreau 1960:446). In the Village Weaver (Ploceus cucullatus) of sub-Saharan Africa, the eggs are among the most variable in color and pattern of any ploceid species (Meise 1983:521). The different races of the Village Weaver have similar variations in egg color and pattern, in which ground color varies from white through blues to greens, and from plain eggs to eggs spotted to varying degrees usually with brown or reddish brown. This pattern of variability is seen in eastern (Mackworth-Praed and Grant 1960), central (Chapin 1954), western (Bannerman 1949), and southern (Maclean 1985) Africa. Bannerman (1949:94) further noted for the Village Weaver: Only one type of coloring ap-