Extensive polyploid clonality was a successful strategy for seagrass to expand into a newly submerged environment

Polyploidy has the potential to allow organisms to outcompete their diploid progenitor(s) and occupy new environments. Shark Bay, Western Australia, is a World Heritage Area dominated by temperate seagrass meadows including Poseidon’s ribbon weed, Posidonia australis. This seagrass is at the northern extent of its natural geographic range and experiences extreme temperatures and salinities. Our genomic and cytogenetic assessments of ten meadows identified geographically restricted, diploid clones (2n = 20) in a single location, and widespread, high heterozygosity, polyploid clones (2n = 40) in all other locations. A single polyploid clone spanned at least 180 km, making it the largest known example of a clone in any environment on earth. Whole genome duplication through polyploidy, combined with clonality, may have provided the mechanism for P. australis to expand into new habitats and adapt to new environments that became increasingly stressful for its diploid progenitor(s). The new polyploid clones likely formed in the shallow waters after inundation of Shark Bay < 8,500 years ago and subsequently expanded via vegetative growth into newly submerged habitats.

多倍体现象（polyploidy）有望使生物体超越其二倍体祖先，进而占据全新的生存环境。西澳大利亚州的鲨鱼湾是一处世界遗产地，其海域以温带海草床为主要生态景观，涵盖海神带草（Poseidon’s ribbon weed，学名*Posidonia australis*，又称澳大利亚海神草）。该海草分布于其自然地理范围的最北端区域，长期经受极端温度与盐度的胁迫。我们对10处海草床开展的基因组学（genomics）与细胞遗传学（cytogenetics）分析结果显示：仅在单一采样点位存在地理分布局限的二倍体克隆（diploid clone，2n=20）；其余所有采样点位均广泛分布着高杂合度的多倍体克隆（polyploid clone，2n=40）。单个多倍体克隆的分布范围至少达180千米，是目前已知全球各类生境中规模最大的克隆体。通过多倍体现象实现的全基因组复制（whole genome duplication），结合克隆生殖特性（clonality），或许为澳大利亚海神草拓展新生境、适应愈发对其二倍体祖先构成胁迫的全新环境提供了关键演化机制。这些新生多倍体克隆很可能形成于距今不足8500年鲨鱼湾被海水淹没后的浅水环境中，随后通过营养生长（vegetative growth）扩散至新形成的水下生境。