Evidence for long isolation among populations of a pacific cycad: genetic diversity and differentiation in Cycas seemannii A.Br. (Cycadaceae).

The genetic structure of Cycas seemannii A.Br. (Cycadaceae), sampled throughout its range in Vanuatu, New Caledonia, Fiji, and Tonga, was studied using starch-gel electrophoresis. Twenty enzyme loci in 13 enzyme systems were examined. Low genetic diversity within populations (A = 1.2, P = 21.3, Ho = 0.047, and He = 0.057) and a high degree of differentiation among populations (F(ST) = 0.594) were found. This, together with low gene flow estimates, suggests genetic drift by isolation to have been most critical to the current genetic structure of the species. Inbreeding may occur to some extent (F(IS) = 0.165). The decline in abundance of C. seemannii, coupled with the low level of genetic diversity, suggest that conservation strategies are urgently needed.