Evidence of restoration cost in the annual gynodioecious Phacelia dubia.

A negative pleiotropic effect on fitness of nuclear sex-determining genes (cost of restoration) could explain nuclear-cytoplasmic gynodioecy but rarely has been demonstrated empirically. In a gynodioecious Phacelia dubia population, maternal lineages produce only hermaphroditic progenies irrespective of the pollen parent (N) or can segregate females (S). Natural progenies of N maternal plants had lower seed viability than that of S. Full-sib progenies of unrelated hermaphrodites from all possible matings between N and S lineages had similar pollen filling but differed in sporophyte performance, mainly at seed germination stage. A discrete multivariate analysis reveals that the performance of N(female symbol) x S(male symbol) progeny at early stages of development was significantly lower than that of the other three types of mating in agreement with the silent-cost-of-restoration hypothesis, affecting the sporophyte. The restoration cost and male sterility appear to be dominant and consequence of nuclear-cytoplasmic incompatibilities that may maintain nuclear-cytoplasmic polymorphism by frequency-dependent selection.