Adaptive radiation and genetic differentiation in Hawaiian Bidens.

Abstract

The genus Bidens (Asteraceae) has undergone extensive adaptive radiation on the Hawaiian Islands. The 19 species and 8 subspecies endemic to Hawaii exhibit much more morphological and ecological differentiation than the continental members of the genus, but the Hawaiian taxa have the same chromosome number and retain the capacity to interbreed in all possible combinations. Twenty-two population of 15 Hawaiian taxa and 4 populations of American taxa were compared at 21 loci controlling 8 enzyme systems. Populations of Hawaiian taxa are highly polymorphic, but, little genetic differentiation has occurred among taxa despite the high levels of genetic variability. Populations of the same taxon are genetically more similar than are populations belonging to different taxa, but all values are high. There is no correlation between the isozyme data and morphological data. No groups of taxa are evident in the genetic data, although morphological groups exist. Genetic differentiation at isozyme loci has not occurred at the same rate as the acquisition of presumably adaptive morphological and ecological characters in Hawaiian Bidens. Adaptive radiation may be limited to a few genes controlling morphological and ecological characters.-from Authors