Gynodioecy and reproductive trait variation in three Thymus species (Lamiaceae)

We studied the general features of the reproductive system of two sympatric species Thymus zygis and Thymus mastichina (Lamiaceae) near Salamanca, Spain, and compare our data with previous and original data on the gynodioecious Thymus vulgaris studied near Montpellier, France. The frequency of females is high on average and strongly variable among natural populations and species: 51% (17-87) in T. zygis, 72% (41-99) in T. mastichina, and 63% (34-88) in T, vulgaris. The high female frequencies in some populations and the strong maternal inheritance of the sexual phenotype indicate a nuclear-cytoplasmic determination of sex in both Spanish species, as already demonstrated in T. vulgaris. At the species level, we found a tendency for a positive association of the average frequency of females with both the relative fecundity of females and the relative allocation into male function in hermaphrodites. Among natural populations within each of the three species in contrast, these traits were not significantly related to each other. We propose that temporal variation of female frequency in natural populations prevents natural selection from adjusting female frequency and reproductive parameters.