Genetics of Sargassum from the Great Barrier Reef

Allozyme variation was examined in 175 individuals representing 13 putative species of Sargassum (Sargassum aquifolium, S. carpophyllum, S. decurrens, S. fissifolium, S. ligulatum, S. linearifolium, S. oligocystum, S. opacum, S. parvifolium, S. polycystum, S. siliquosum, S. spinifex, S. swartzii) and 34 populations from the Great Barrier Reef, Australia. Allozyme variability was examined (five polymorphic loci, 12 alleles total), between morphological species and those between different geographical populations of the same taxon. Sargassum decurrens, S. oligocystum, S. parvifolium and S. swartzii + S. aquifolium, were sampled in sympatry. S. carpophyllum and S. polycystum are conspecific. Single populations of 3 different species were thought to be possible misassignments (S. opacum = S. polycystum; S. aquifolium = S. swartzii and S. linearifolium = S. fissifolium), but may be morphological variants of the species with which they clustered. Finally, S. oligocystum (subgenus Eusargassum) clustered with S. decurrens, (subgenus Phyllotrichia) suggesting a revision of subgeneric boundaries in the genus Sargassum is required. Allele frequencies at five loci (GPI, SOD-1, ACO-1, ME-1, PGM-1) were examined. Calculation of gene frequencies and population genetic statistics were carried out using BIOSYS-1 package. Genetic relationships were represented using Nei's genetic distance and Roger's genetic distance, and clustered using the UPGMA method.Collection sites: Cooktown, Cape Tribulation, Alma Bay, Geoffrey Bay, Shute Harbour, Heron Island, One Tree Island
Differentiation of Sargassum taxa by means of allozymes.
Allozyme markers will be useful for species identification of Sargassum within the GBR, as many species are only clearly distinguishable morphologically for a short time of the year (when they have reproductive organs).Voucher specimens were deposited at the Adelaide Herbarium:S. carpophyllum A61833 (Alma Bay, 5 specimens); S. carpophyllum A61834 (Cooktown, 9 specimens); S. carpophyllum A61839 (Alma Bay, 5 specimens); S. decurrens A61807 (Cooktown, 10 specimens); S. decurrens A61808 (Shute Harbour, 5 specimens); S. fissifolium A61817 (Heron Island, 5 specimens); S. fissifolium A61818 (Shute Harbour, 5 specimens); S. fissifolium A61840 (Cooktown, 5 specimens); S. ligulatum A61810 (Heron Island 2 specimens); S. linearifolium A61843 (Alma Bay, 5 specimens); S. oligocystum A61815 (Shute Harbour, 3 specimens); S. oligocystum A61816 (Cooktown, 5 specimens); S. oligocystum A61841 Geoffrey Bay, 1 specimens); S. opacum A61831 (Cooktown, 8 specimens); S. parvifolium A61806 (Shute Harbour, 5 specimens); S. polycystum A61811 (Heron Island, 5 specimens); S. siliquosum A61812 (Shute Harbour, 5 specimens); S. swartzii A61829 (Cooktown, 10 specimens).

本研究对澳大利亚大堡礁（Great Barrier Reef）的13个推定马尾藻（Sargassum）物种，即叶马尾藻（Sargassum aquifolium）、肉托马尾藻（Sargassum carpophyllum）、下枝马尾藻（Sargassum decurrens）、裂叶马尾藻（Sargassum fissifolium）、舌叶马尾藻（Sargassum ligulatum）、线叶马尾藻（Sargassum linearifolium）、少囊马尾藻（Sargassum oligocystum）、暗褐色马尾藻（Sargassum opacum）、小叶马尾藻（Sargassum parvifolium）、多囊马尾藻（Sargassum polycystum）、长角马尾藻（Sargassum siliquosum）、刺叶马尾藻（Sargassum spinifex）、斯氏马尾藻（Sargassum swartzii）的34个种群共175个个体，开展了同工酶（Allozyme）变异分析。

本次研究检测了5个多态性位点，总计12个等位基因，对形态学物种间以及同一分类群不同地理种群间的同工酶变异进行了分析。其中，下枝马尾藻、少囊马尾藻、小叶马尾藻以及斯氏马尾藻+叶马尾藻为同域采样样本。

研究发现肉托马尾藻与多囊马尾藻为同物异名。另有3个物种的单一种群被认为存在鉴定误差：暗褐色马尾藻疑似为多囊马尾藻，叶马尾藻疑似为斯氏马尾藻，线叶马尾藻疑似为裂叶马尾藻，但上述类群也有可能是其聚类所属物种的形态变种。

值得注意的是，少囊马尾藻（真马尾藻亚属，Eusargassum）与下枝马尾藻（毛叶马尾藻亚属，Phyllotrichia）聚类在一起，这提示需对马尾藻属的亚属划分边界进行修订。

本研究检测了5个位点的等位基因频率，分别为葡萄糖磷酸异构酶（GPI）、超氧化物歧化酶-1（SOD-1）、顺乌头酸酶-1（ACO-1）、苹果酸酶-1（ME-1）以及磷酸葡萄糖变位酶-1（PGM-1）。基因频率与种群遗传统计量的计算采用BIOSYS-1软件包完成。遗传关系通过Nei遗传距离与Roger遗传距离进行表征，并采用非加权组平均法（UPGMA）进行聚类分析。

采样地点依次为：库克敦、特里比申角、阿尔玛湾、杰弗里湾、舒特港、赫伦岛、独树岛。

基于同工酶的马尾藻分类群分化研究。

同工酶标记将有助于大堡礁地区马尾藻的物种鉴定，因为多数马尾藻物种仅在具有生殖器官的短暂时间段内，才可通过形态学特征实现清晰区分。

凭证标本存放于阿德莱德植物标本馆，详情如下：
肉托马尾藻A61833（阿尔玛湾，5份标本）；肉托马尾藻A61834（库克敦，9份标本）；肉托马尾藻A61839（阿尔玛湾，5份标本）；下枝马尾藻A61807（库克敦，10份标本）；下枝马尾藻A61808（舒特港，5份标本）；裂叶马尾藻A61817（赫伦岛，5份标本）；裂叶马尾藻A61818（舒特港，5份标本）；裂叶马尾藻A61840（库克敦，5份标本）；舌叶马尾藻A61810（赫伦岛，2份标本）；线叶马尾藻A61843（阿尔玛湾，5份标本）；少囊马尾藻A61815（舒特港，3份标本）；少囊马尾藻A61816（库克敦，5份标本）；少囊马尾藻A61841（杰弗里湾，1份标本）；暗褐色马尾藻A61831（库克敦，8份标本）；小叶马尾藻A61806（舒特港，5份标本）；多囊马尾藻A61811（赫伦岛，5份标本）；长角马尾藻A61812（舒特港，5份标本）；斯氏马尾藻A61829（库克敦，10份标本）。