Allozyme Divergence and the Evolution of Dendroseris (Compositae: Lactuceae) on the Juan Fernandez Islands

Abstract

The genus Dendroseris, consisting of rosette trees or shrubs, is endemic to the Juan Fernandez Islands, Chile. With 11 species it is the largest genus on the Islands. The considerable morphological diversity among the species is reflected by the recognition of three subgenera. The relatively young age of the Islands, ca. four million years for Masatierra and one to two million for Masafuera, indicates that speciation may have occurred recently and rapidly in Dendroseris. An electrophoretic study of 14 enzymes revealed little divergence among the six species examined. The three species in subgenus Dendroseris and the three in subgenus Rea are all monomorphic for the same allele at 21 of the 34 genes. The two subgenera are fixed for different alleles at two genes, which supports their recognition as monophyletic lines. The lack of divergence among the species at genes specifying soluble enzymes is concordant with the hypothesis of rapid speciation, perhaps the result of adaptive radiation into a variety of habitats. The chromosome number of n = 18 in Dendroseris suggests it is a tetraploid. Enzyme electrophoresis revealed extensive gene duplication in Dendroseris indicating the genus likely consists of relatively "young" tetraploids. Data from gene number indicate that polyploidy may have been associated with the origin of Dendroseris from a diploid progenitor, or that polyploidy was established shortly after the origin of the genus.