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.