Fig. 3

Volvox life cycle. Schematic of the Volvox vegetative and sexual life cycle phases. Vegetative reproduction (grey shaded region) occurs in the haploid (1n) phase and can be synchronized with a 16 h:8 h light:dark diurnal regime (center of diagram), under which one full reproductive cycle is completed every 48 h. Vegetative development starts with mature pre-cleavage adults (~ 3:00 on diagram, corresponding to spheroid in Fig. 2a) and proceeds clock-wise through embryogenesis and then cyto-differentiation of germ cells (gonidia) and somatic cells to form juveniles (~ 9:00 on diagram, corresponding to spheroid in Fig. 2b), hatching of juveniles, and finally maturation to complete the cycle as the next generation of adults. After hatching, the parental somatic cells of the previous generation are discarded and undergo senescence and cell death. Sexual development is triggered by exposure to sex inducer and leads to gonidia undergoing modified embryogenesis and development (not shown) into adult sexual egg-bearing females or adult sexual sperm-packet-bearing males. Sperm packets are released and swim to females where mating takes place with internal fertilization (syngamy), resulting in formation of diploid zygospores. Meiosis occurs upon germination and produces three polar bodies and one haploid progeny that re-enters the vegetative life cycle. This figure was adapted from [10], and reproduced here with permission from the Annual Review of Microbiology, Vol. 73 © 2019 by Annual Reviews, http://www.annualreviews.org