DEVELOPMENTAL GENETICS OF POLYMORPHISM IN ROTIFER ASPLANCHNA .3. QUANTITATIVE MODIFICATION OF DEVELOPMENTAL RESPONSES TO VITAMIN E, BY GENOME, PHYSIOLOGICAL STATE, AND POPULATION DENSITY OF RESPONDING FEMALES

An increase in the level of vitamin E in the diet of amictic female Asplanchna fed paramecia and reproducing by parthenogenesis elicits three responses: (1) the mixis response: a proportion of their offspring develop into mictic females, which reproduce bisexually; (2) the BWO response: the offspring develop regular body‐wall outgrowths and (3) a reduction in fecundity of amictic females. The quantitative control of these responses has been studied. Genotypic modification of the BWO response has been demonstrated by showing consistent quantitative differences in the response of different clones from the same or different natural populations. Variation in the BWO response has also been demonstrated among the progeny of different females from a clone, and among the individual progeny of single females. The age of a female proved to be a significant physiological factor affecting both the BWO and mixis responses as measured in her offspring. The composition of the culture fluid may also modify the BWO response. An environmental variable of special interest is population density. The BWO, mixis and fecundity responses are all enhanced at high densities, and this effect is seen at natural population levels. It is suggested that this effect may help explain the observation that mixis generally coincides with peaks of population density in nature; this variable, rather than levels of dietary vitamin E per se, may be the most significant factor controlling polymorphism in nature. The density effect has been shown to be due to one or more conditioning factors, possibly pheromones, liberated by the female rotifers. Copyright © 1969 Wiley‐Liss, Inc., A Wiley Company