WHITKUS, RICHARD* AND TIMOTHY K. LOWREY. Department of Biology, Sonoma State University, Rohnert Park, CA 94928-3609 and Department of Biology, University of New Mexico, Albuquerque, NM 87131. - Genetic marker diversity in Hawaiian and Cook Island Tetramolopium (Asteraceae).
Tetramolopium is a genus of sub-shrubs with an
Australasian-Polynesian distribution. The Hawaiian and Cook Islands
species represent a monophyletic group of three clades, each
recognized by morphological and ecological characteristics and
hypothesized to represent products of adaptive radiation. The genetic
diversity of this group was assessed using RAPD and isozyme genetic
markers, and compared with a previous nuclear RFLP analysis of 38
loci. This report represents the first study using these three
markers in island plants. Twenty isozyme loci and 126 RAPD markers
were surveyed for known populations. Overall diversity is very low
(<0.22), following the general pattern observed in insular species,
and confirming the extremely low diversity for Tetramolopium in
comparison to all other studies. RFLP and RAPD marker diversity is
similar while allozyme diversity is markedly lower. There is greater
differentiation among species within sections than among sections.
Analyses of all three marker sets do not agree with morphology/ecology
based clades. The coefficient of genetic differentiation (Gst) over
all species ranges from 0.558 for RFLP to 0.787 for allozymes and
0.858 in the RAPD data, indicating a high degree of genetic
differentiation among species. The results show that allozyme data
underestimate the total amount of genetic diversity present. The high
Gst values are what would be expected as a result of genetic drift in
small isolated insular populations. The low overall genetic diversity
coupled with the lack of congruence between the morphological and
genetic differentiation firmly establishes that the group has
undergone recent and rapid adaptive radiation. These results suggest
that conservation efforts in this genus need to focus on preserving
all species since they each harbor a distinct set of genetic
diversity.
Key words: genetic diversity, island biology, isozyme, RAPD, RFLP, Tetramolopium