Gs. Oxford et Rg. Gillespie, GENETICS OF A COLOR POLYMORPHISM IN THERIDION GRALLATOR (ARANEAE, THERIDIIDAE), THE HAWAIIAN HAPPY-FACE SPIDER, FROM GREATER MAUI, Heredity, 76, 1996, pp. 238-248
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.