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

摘要

Theridion grallator, the Hawaiian happy-face spider, a species endemic to four islands in the Hawaiian archipelago, exhibits an exuberant colour and pattern polymorphism involving both the carapace and opisthosoma (abdomen). Laboratory crosses and broods from wild-mated females demonstrate that the opisthosomal morphs on Maul (and probably on Moloka'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 eliminated. With the exception of the White morph, dominance results from the superimposition of one pattern on another. All morphs are found equally in males and females. Carapace morphs are also shown to be determined 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 than pleiotropic effects of alleles at one locus. A one-to-one matching of red- and black-pigmented areas on the opisthosoma with underlying guanine deposits, which produce a white backcloth against which the pigments are displayed, strongly suggests that the polymorphism in this species has evolved for its visual effects.