Diverse Evolutionary Histories Characterise Polyploidy in the Deep-Sea Brittle Star Genus Ophiosabine.

Polyploidy is rare in animals, where it is often associated with unusual modes of reproduction. Here we use phased exon capture data to identify ploidy and investigate the subgenome composition of four polyploid taxa in the deep-sea brittle star genus Ophiosabine (Echinodermata: Ophiuroidea). Of the four, O. anomala and O. vivipara are hybrid allopolyploids, the latter particularly complex comprising at least three progenitor lineages. The other two undescribed taxa are better regarded as autopolyploids. While at first the four appeared to be phylogenetically distinct, closer analysis reveals that they all share at least one subgenome with another. Across this genus, taxa with different reproductive modes-spawning versus brooding, hermaphrodite, separate sexes, and parthenogens-can be closely related. While ~97% of ophiuroids are pentaradial, all the Ophiosabine polyploids have more than 5 arms. At least in the case of O. vivipara, the wide geographic and bioclimatic range spanning that of each of its component subgenomes is consistent with the idea, at least in the short term, that animals gain evolutionary advantage from such a multi-facetted genome.