Allozyme Divergence and Evolution in Tetramolopium (Compositae: Astereae) on the Hawaiian Islands

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Abstract
Tetramolopium is a genus of shrubby to suffrutescent perennial Compositae known only from New Guinea and the Hawaiian Islands. Evidence from biogeography suggests the genus was introduced into Hawaii from New Guinea recently, and perhaps originated from a single introduction. The morphological and ecological diversity of Tetramolopium in the Hawaiian Islands suggest there has been rapid divergence associated with adaptive radiation. Despite the diversity, all taxa are completely interfertile with fertile F-1, F-2, and F-3 hybrids having been obtained. An electrophoretic study of allozymes revealed little divergence at 22 genes coding soluble enzymes. The mean genetic identity for pairwise comparisons of 19 populations from seven species is 0.95, a very high value normally obtained for conspecific plant populations. The results for Tetramolopium contrast sharply with other instances of high genetic identity between species, where taxa are similar morphologically and usually reproductively isolated. The enzyme data also support the hypothesis of recent, rapid divergence in Hawaiian Tetramolopium.