The maintenance of females among hermaphrodites: the importance of nuclear-cytoplasmic interactions

Abstract

Female plants of Thymus vulgaris produce more seeds than hermaphrodites but their frequency in a population is not determined by the magnitude of this advantage. Instead, the proximity of the population to equilibrium determines the frequency of females: the further from equilibrium, the higher the frequency of females. This trend is due to founder effects occurring among cytoplasmic and nuclear genes determining male sterility. A review of literature supports the conclusions that male sterility in higher plants has a nuclear-cytoplasmic inheritance, that the frequency of female plants is often not at equilibrium, and that populations far from equilibrium (young and/or disturbed) have higher frequencies of females.

Outcrossing rates and inferred levels of inbreeding depression in gynodioecious Cucurbita foetidissima (Cucurbitaceae)

“…However, much work remains to be done to confirm the mode of sex determination in C. foeridissi,na. If sex determination involves cytoplasmic-nuclear interactions, as is known for many plant species, conditions for the maintenance of females are less stringent than under nuclear sex determination (Charlesworth, 1981;Delanney et a!., 1981;Gregorius & Ross, 1984;Ross & Gregorius, 1985;Couvet et a!., 1986;Frank, 1989;Guyon eta!., 1991). While the combined effects of selfing and inbreeding depression appear to contribute strongly to the maintenance of females in C. foetidissima, this is by no means a general result in studies of gynodioecious taxa.…”

Genetics of male-sterility in gynodioecious Cortaderia (Gramineae)

“…The genetics of malesterility in gynodioecious species has not been easily or often solved. Early interpretations were of control by nuclear genes (Lewis and Crowe, 1956;Ross, 1969;Connor, 1965b) but nuclear gene control has been more firmly supplanted by nuclear-cytoplasmic explanations (Kheyr-Pour, 1980;Charlesworth, 1981;Van Damme, 1983;Kesseli and Jam, 1984;Couvet et a!., 1986;Sun, 1987). Such a conclusion was predicted by Simmonds (1971).…”

Effects of environmental heterogeneity on the distribution of sexes within and among populations in a gynodioecious species, Geranium maculatum

“…Although the requirements and mechanisms of increased seed fitness in females have been frequently studied in populations containing both sexes, fitness differences in these populations speak little to the absence of females in other populations. One proposed explanation for the distribution of sexes among populations is that the frequent establishment and loss of populations does not allow populations to reach equilibrium, leading to the maintenance of females on a metapopulation level even if females have less of a fitness increase than typically required (Couvet et al, 1986;Gouyon & Couvet, 1987;Belhassen et al, 1989;Pannell, 1997). Metapopulation dynamics have had limited support, but are more likely to apply to a select group of species with high turnover rates in natural populations (Belhassen et al, 1989;Olson et al, 2005).…”