The developmental genetics of polymorphism in the rotifer <i>Asplanchna</i>. II. A method for quantitative analysis of changes in morphogenesis induced by vitamin E, and the short‐term inheritance of the effects of vitamin E

Abstract

Abstract Amictic female Asplanchna sieboldi , reproducing asexually by diploid parthenogenesis, are predominantly saccate in form when fed paramecia. The addition of vitamin E to their diet causes their female offspring to develop regular outgrowths of the body wall, or humps. A continuous spectrum of intermediate forms connects the saccate (S) and fully humped (H) morphotypes. We have shown that this response can be studied quantitatively with the use of an ordinal scale for measuring the degree of hump development: five morphotypes are distinguished and assigned scores (S = 1; I 1 = 2; I 2 = 3; I 3 = 4; H = 5). The response of embryos to exogenous vitamin E, measured with this scale, is proportional to the amount of vitamin E in the diet of their saccate parents. When vitamin E is removed from the diet of humped females, offspring with humps continue to be produced for up to five generations, with a gradual decline in morphotypic score. This short‐term inheritance of an environmentally‐induced trait can be explained by the passive transmission from parent to daughter of a stable endogenous inducer, which may be vitamin E itself. However, the relationship between the magnitude of the response and the concentration of this hypothetical inducer is not a simple one. For example, when females are fed vitamin E for one generation, the mean score of the granddaughters is greater than that of their daughters, which received no additional exogenous vitamin E. The same considerations apply to the inheritance of increased nuclear number in certain organs of A. brightwelli , which is another response to increased levels of dietary vitamin E.