SELECTION ON THE COLOR POLYMORPHISM IN HAWAIIAN HAPPY-FACE SPIDERS - EVIDENCE FROM GENETIC-STRUCTURE AND TEMPORAL FLUCTUATIONS

Throughout this century genetic polymorphisms for color have been wide ly used as a research tool to allow insights into key evolutionary pro cesses. Although color variants can often be diverse within population s, frequencies of different morphs may be similar across populations, either as a result of balancing selection or gene how. Under these cir cumstances selection can be extremely difficult to demonstrate. Here w e test for balancing selection on the naturally occurring color forms of the Hawaiian happy-face spider, Theridion grallator with two approa ches. First, allozyme loci are used to generate a null model against w hich to test selection. Frequencies of alleles involved in the color p olymorphism of T. grallator are used to generate another estimate for comparison. The results suggest that statistically similar frequencies of color morphs among populations of T. grallator may be maintained b y some form of balancing selection. Second, we make use of an unusual event in which the normally stable frequencies of unpatterned and patt erned morphs within a population were found to have shifted toward an excess of unpatterned morphs. We scored offspring of all fertilized, u npatterned (bottom-recessive) females found during this period of skew ed morph frequencies and also in a year when morph frequencies were no rmal to deduce paternal color phenotypes. Mating was found to be rando m in the normal year, but in the perturbed year females had mated with rare (patterned) males twice as frequently as expected on the basis o f the frequency of this morph type in the population. Both of these re sults are consistent with selection operating on the color polymorphis m, and we speculate that apostatic selection, perhaps mediated by bird predators, may provide the mechanism.