Fig. 9

Schematic of GFCs during the asexual budding cycle. B. schlosseri has a 7-day asexual lifecycle called blastogenesis in which new bodies are formed by budding from existing ones. Three generations exist in a colony at any given time: functioning adult zooids, primary buds undergoing organogenesis, and newly formed secondary buds. This schematic shows germ cells (red) and follicle progenitors (green) in primary buds, secondary buds, and the vasculature (gray) at each of the seven stages: A1, A2, B1, B2, C1, C2, and D. During stages A1–A2, clusters of germ and follicle progenitor cells are almost exclusively found in the primary bud niche, just posterior to the developing secondary buds. At stage B1, GFCs are still predominantly found in the primary bud niches, but smaller GFCs can be detected in the vasculature. At stage B2, many smaller GFCs begin appearing, and GFCs can be found in the secondary buds and vasculature in addition to the primary bud niche. By stage C1, most germ and follicle progenitor cells are found in the secondary bud niches, and small GFCs can still be found in the vasculature. Two main GFCs are present in the secondary buds at this stage, one dorsal and one ventral. At stage C2, nearly all germ and follicle progenitors are found in the secondary bud niches, but some remain in the vasculature. Rotation of the developing secondary buds has oriented the two main GFCs of cells to anterior and posterior locations by this stage. During stage D, removal of the adult zooid occurs, and the secondary bud transitions into a primary bud. The two GFCs of germ and follicle progenitor cells in each secondary bud then seamlessly transition into the new primary bud niches of the next asexual cycle. Axes (gray arrows) show the orientation of the anteroposterior and left–right body axes. Germ cells exhibit left–right asymmetric abundance throughout the blastogenic cycle. A anterior, P posterior, L left, R right