The novel Orshina Rhythm in a colonial urochordate signifies the display of recurrent aging/rejuvenation sequels.

When it comes to aging, some colonial invertebrates present disparate patterns from the customary aging phenomenon in unitary organisms, where a single senescence phenomenon along ontogeny culminates in their inevitable deaths. Here we studied aging processes in 81 colonies of the marine urochordate Botryllus schlosseri each followed from birth to death (over 720 days). The colonies were divided between three life history strategies, each distinct from the others based on the presence/absence of colonial fission: NF (no fission), FA (fission develops after the colony reaches maximal size), and FB (fission develops before the colony reaches maximal size). The study revealed recurring patterns in sexual reproductive statuses (hermaphroditism and male-only settings), colonial vigor, and size. These recurring patterns, collectively referred to as an Orshina, with one or more 'astogenic segments' on the genotype level. The combination of these segments forms the Orshina rhythm. Each Orshina segment lasts about three months (equivalent to 13 blastogenic cycles), and concludes with either the colonial death or rejuvenation, and is manipulated by absence/existing of fission events in NF/FA/FB strategies. These findings indicate that reproduction, life span, death, rejuvenation and fission events are important scheduled biological components in the constructed Orshina rhythm, a novel aging phenomenon.