Genetic uniformity in Amphibolis antarctica, a dioecious seagrass

Abstract

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

Growth, flowering, and population dynamics of temperate Western Australian seagrasses

“…Studies on seagrass flowering intensity in Western Australian waters demonstrate that flowering is rare in Posidonia spp. (Cambridge & Hocking 1997, Inglis & Lincoln-Smith 1998 and in some Amphibolis antarctica meadows (Waycott et al 1996), which mainly agrees with our findings. However, the studied P. australis meadow flowered profusely when compared with the sparse flowering reported for this species (Cambridge & Hocking 1997, Inglis & LincolnSmith 1998.…”

“…Examination of the genetic variability in this P. australis meadow revealed that it was a multiclonal population, and that it was composed of a high number of genotypes (15 different genotypes within an area of 320 m-2, Waycott 1995). In contrast, the studied A. antarctica meadow was genetically invariant (Waycott et al 1996), ~ndicat-ing that this population was formed by a single or very few genotypes. Waycott et al (1996) attributed the lack of genetic variability in this A, antarctica meadow to Inbreeding rather than to low genet formation rate.…”

“…Hence, quantification of sexual reproduction success, shoot population dynamics and plant growth are the key to estimating productivity, as well as forecasting the expansion, persistence or decline of seagrass meadows (Duarte et al 1994). However, only Clarke & Kirkman (1989), Hillman et al (1995), Waycott et al (1996), Cambridge & Hocking (1997) Figs. 1 & 2).…”

An ancient eelgrass clone in the Baltic

“…Previous studies have also reported genetic uniformity in Zostera marina and other seagrass species at the population level, sometimes over scales of hundreds of kilometres (Z, manna: De Heij & Nienhuis 1992; Posidonia oceanica: Capiomont et al 1996; Arnphibolis antarctica: Waycott et al 1996; Thalassia testudinum: Schlueter & Guttnlan 1998). While such uniformity does not preclude that clones are of a very large size, above data represent no conclusive evidence that clones are, in fact, of such extended sizes.…”

“…Information on clonal diversity in seagrass populations has been hampered in the past by low variability of traditional genetic markers such as allozymes (De Heij & Nienhuis 1992, Capiomont et al 1996, Waycott et al 1996, Schlueter & Guttman 1998. Recent reports using DNA-based genetic markers suggest that the clonal structure in seagrass beds varies within and among species.…”