The Orshina rhythm in a colonial urochordate: 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 existence/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). Results revealed that sexual reproductive statuses (hermaphroditism and male only settings), colonial vigorousness and sizes, represent coinciding and repeated rhythms of one or more emerged life/death astogenic segments on the whole-genet level, each is termed as Orshina, and the sum of all segments as the Orshina rhythm. Each Orshina segment lasts about three months (containing ca. 13 blastogenic cycles), ends by either the colonial death or rejuvenation, and 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. ### Competing Interest Statement The authors have declared no competing interest.