CULLEY, THERESA M.1*, LISA E. WALLACE2, KARLA M. GENGLER-NOWAK2, and DANIEL J. CRAWFORD3. 1Department of Ecology and Evolutionary Biology, University of California-Irvine, Irvine, CA 92697; 2Department of Evolution, Ecology, and Organismal Biology, The Ohio State University, 1735 Neil Avenue, Columbus, OH 43210; 3Department of Ecology and Evolutionary Biology, University of Kansas, 1200 Sunnyside Avenue, Lawrence, KS 66045. - A comparison of two methods of calculating GST, a genetic measure of population differentiation.
GST, a genetic statistic describing differentiation
of populations, has frequently been compared with Hamrick and Godt's
(1989) review of the plant literature. We show here that some
comparisons may be inappropriate if GST was
calculated in a different way than that used by Hamrick and Godt (HG).
The alternative method of Nei (1973) is mathematically different from
the HG technique, occasionally resulting in different
GST values. We reviewed 695 studies that appeared
between 1990 and September, 1999 that cited Hamrick and Godt (1989),
and found that many of these calculated GST
according to Nei's method (46%), with the majority of these papers
(61%) including comparisons to Hamrick and Godt's review. We suggest
that if GST estimates are compared across studies,
it is most appropriate to calculate them the same way. We found that
in most cases the magnitude of difference in GST
values was small, suggesting that qualitative comparisons of
GST estimates between studies are still probably
valid. Nevertheless, we identified theoretical and empirical
situations in which large differences in GST values
are likely to arise. Thus, we advise investigators to carefully
consider which method to use in calculating GST for
a given data set.
Key words: genetic substructure, GST, population differentiation