GENETICS OF A COLOR POLYMORPHISM IN THERIDION GRALLATOR (ARANEAE, THERIDIIDAE), THE HAWAIIAN HAPPY-FACE SPIDER, FROM GREATER MAUI

Theridion grallator, the Hawaiian happy-face spider, a species endemic to four islands in the Hawaiian archipelago, exhibits an exuberant co lour and pattern polymorphism involving both the carapace and opisthos oma (abdomen). Laboratory crosses and broods from wild-mated females d emonstrate that the opisthosomal morphs on Maul (and probably on Molok a'i as well) act as if they are determined by alleles at one autosomal locus, although control by more than one linked locus cannot be elimi nated. With the exception of the White morph, dominance results from t he superimposition of one pattern on another. All morphs are found equ ally in males and females. Carapace morphs are also shown to be determ ined by alleles at one locus. The close association between particular carapace and opisthosomal patterns observed both in the field and in the laboratory is probably a result of linkage between loci rather tha n pleiotropic effects of alleles at one locus. A one-to-one matching o f red- and black-pigmented areas on the opisthosoma with underlying gu anine deposits, which produce a white backcloth against which the pigm ents are displayed, strongly suggests that the polymorphism in this sp ecies has evolved for its visual effects.