Quantum shifts in the genetic control of a colour polymorphism in Theridion grallator (Araneae: Theridiidae), the Hawaiian happy-face spider

Abstract

Theridion grallator, the Hawaiian happy-face spider, endemic to four islands in the Hawaiian archipelago, exhibits an exuberant colour and pattern polymorphism involving both the carapace and opisthosoma (abdomen). Previous work has shown that on Maui (and probably on Moloka'i as well) all colour morphs act as if they are determined by alleles at one autosomal locus (although linked loci cannot be excluded) and all morphs are expressed equally in males and females. Here we demonstrate that on Hawai'i, the youngest island, Yellow and Red front morphs seem to be controlled by a single allele, sex-limited in expression, such that females are Yellow and males Red front. Red blob and Red ring form a similar pair of morphs, again apparently controlled by one allele, with Red blob confined to females, Red ring to males. Morphs Red front+back and Black ring are not sex-limited. Evidence from one brood indicates that two unlinked loci are involved in determining the colour polymorphism on Hawai'i. At least the sex-limitation of Yellow and Red front is shown to be island-wide and suggests that the quantum shifts in the genetic control of the polymorphism among islands probably trace their origins to the founding event when T. grallator colonized Hawai'i from Maui. © 1996 The Genetical Society of Great Britain.