Colour Dimorphism in Allolobophora chlorotica Sav. (Lumbricidae)

Abstract

The earthworm A. chlorotica has 2 color forms. One form contains a series of porphyrins and a pigment provisionally identified as turboglaucobilin, rendering it green; the other form lacking some of these pigments is pink. Genetic experiments indicated that pink and green worms taken from nature tend to breed true, that pink is dominant over green, that the heterozygous offspring of pinkx green crosses are wholly or partly sterile. Earlier results indicating that the 2 forms do not differ in their sensitivity to u. v. light were confirmed. The frequency distributions of segment numbers in the 2 forms were similar and provided no evidence of cryptic advantage in field populations exposed to bird predation: an aviary experiment indicated a cryptic advantage of the green over the pink form under conditions of exposure to bird predation. Soil samples taken in the very dry summer of 1959 from sites where field populations had been sampled indicated that the pink form tended to occur in drier sites and the the green form in the wetter sites. The 2 forms generally occur in mono-morphic populations. The polymorphism of mixed populations appears to lack a stabilizing mechanism and therefore to be transient in character. Swining selection favoring the green form in wet seasons and the pink form in dry seasons may ensure the prolonged persistence of polymorphic populations.