The developmental genetics of polymorphism in the rotiferAsplanchna. I. Dietary vitamin E control of mitosis and morphogenesis in embryos

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Abstract
Cultures ofAsplanchna sieboldifedParamecium aureliaconsist exclusively of parthenogenetically‐reproducing females whose body form is saccate. When such females are fed algae or α‐tocopherol, their offspring developin uterointo humped females with regular outgrowths of the syncytial body wall (hypodermis and cuticle). The hypodermal nuclei are constant in number and position, and can be mapped; such nuclear maps show that saccate and humped females have the same number and arrangement of hypodermal nuclei. The level of dietary vitamin E thus controls differential growth of the hypodermis, without affecting mitosis. Electron micrographs indicate that the hypodermal outgrowths are produced after cell membranes break down in the embryo; the regions of enhanced growth within the hypodermis are therefore not delimited by cell membranes. In contrast, the offspring ofA. sieboldiorA. brightwellifed vitamin E show an increased mean number of nuclei in the vitellarium and gastric glands, organs which are partially freed from the usual rigid control of nuclear number in rotifer tissues. Variations in nuclear number in a tissue might reflect variations in either the number of cells determined to form that tissue or the number of mitotic divisions in the determined primordium. In the former case, reciprocal variations in nuclear number should be found in another tissue. The vitellarium and oocytes are the sole derivatives of a single blastomere; however, counts of oocytes fail to show reciprocal variations. Dietary vitamin E therefore controls, directly or indirectly, the number of mitoses in the vitellarium, and presumably also in the gastric glands.