Polymorphism refers to the occurrence of several different discontinuous forms within a single interbreeding population, and frequently involves color. A number of mechanisms have been advanced to explain the occurrence of such polymorphisms, yet the explanations are seldom conclusive. The proposal here focuses on the fact that polymorphism frequently appear in an intermittent fashion among representatives of any given lineage. The study focuses on the Hawaiian spider Theridion grallator which demonstrates a highly visible state of polymorphism. The pattern of inheritance of the polymorphism in T. grallator will be examined in order to determine: (1) why different populations appear to exhibit modes of inheritance of the polymorphism; and (2) whether the observed superficial similarities between T. grallator and Enoplognatha ovata, a distantly related species, have a similar mechanism of inheritance. The study will then examine the distribution of such similar color polymorphism within the spider lineage, and assesses whether similarities among unrelated representatives of the lineage are repeated independent evolutionary events or parallel evolution. Elucidation of the mechanisms underlying the intermittent and widespread occurrence of polymorphism in both natural and applied systems will contribute to the knowledge of how selection operates.
