GENETIC UNIFORMITY IN AMPHIBOLIS-ANTARCTICA, A DIOECIOUS SEAGRASS

Few detailed studies have been published on genetic variation in seagr asses except those on the monoecious Zostera marina L. or the hermaphr odite Posidonia australis Hook. f. This paper presents allozyme, RFLP and reproductive biology data on Amphibolis antarctica (Labill.) Sende r & Aschers, one of the 75 per cent of all seagrass species which are dioecious. Collections were made from approximately one-third of the s pecies range in Western Australia. Its only congener, A. griffithii (J . M. Black) den Hartog, was collected from one site to provide a compa rison. Flowering was observed in 25 per cent of the shoots surveyed an d the average sex ratio was 3.8: 1 (F:M) which it has been suggested i ndicates sexual reproduction. No genetic variation was found within or between populations at 14 allozyme loci. 18S RFLPs and M13 DNA finger printing gave few satisfactory results but also did not exhibit any va riability. Allozyme variation was observed between A. antarctica and A . griffithii, the only congeneric species. The lack of allozyme and DN A variation within A. antarctica indicates a potentially low level of outbreeding, a highly clonal reproductive system or a very efficient g enetic system in A. antarctica. The hypothesis that the dioecious repr oductive system evolved in seagrasses to maximize outbreeding and gene tic variability, proposed by several authors, is questioned in light o f these data.