Genetic variation within and between populations of Posidonia australis, a hydrophilous, clonal seagrass

Abstract

Allozyme diversity was surveyed at 15 loci across 22 populations of the hydrophilous seagrass Posidonia australis (Hook. f). Substantial genetic variation was detected (HT = 0.311) with a high proportion of this variation partitioned between populations (GST = 0.623). The high value of GST is attributed to large geographical distances between many of the populations and several of the extreme north-western populations having fixed homozygous genotypes. Southwestern populations of P. australis were the most variable and these correlate with the highest species diversity in this genus. Intermediate levels of genetic diversity are observed in P. australis when compared with other hydrophilous angiosperms. Average gene diversity values for hydrophilous taxa surveyed to date indicate lower HT and higher GST values than an average reported for 468 plant taxa. Patterns of genetic variability in different regions of the distribution of P. australis may reflect past evolutionary diversification into novel environments and subsequent dispersal following the rifting of Australia from Antarctica in the early Tertiary.