Gynodioecy in Origanum vulgare: Computer Simulation of a Model

Abstract

THE population dynamics of the rare male sterility factors, or of gynodioecious species, which have a characteristically high proportion of female (male-sterile) and hermaphrodite individuals together in a population, is interesting to both evolutionists and plant breeders. Many workers have discussed the evolutionary significance of such a mating system, which promotes outbreeding with the proportion of females regulating the degree of outbreeding (for example, refs. 1–3). In Origanum vulgare (Labiateae), Lewis and Crowe⁴ estimated that nearly 30 per cent, or even as many as 50 per cent, of females occur in various European populations. They showed that two loci govern the gynodioecy system; a dominant factor F causes anther suppression in combination with the recessive class hh to give FFhh and Ffhh as females, whereas HH, Hh suppress factor F to yield the other seven genotypes as hermaphrodites. Furthermore, certain segregation ratios suggested to them that the females are maintained through almost lethality of ffhh, lower viability of HH genotypes and poorer seed output of hermaphrodites than females. Thus if the fitness values are denoted by the matrix their data suggest that z is nearly 0, y = 0.25 to 0.50 and x>w.