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, Spa in, and compare our data with previous and original data on the gynodioecio us Thymus vulgaris studied near Montpellier, France. The frequency of femal es is high on average and strongly variable among natural populations and s pecies: 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-cyt oplasmic determination of sex in both Spanish species, as already demonstra ted in T. vulgaris. At the species level, we found a tendency for a positiv e association of the average frequency of females with both the relative fe cundity of females and the relative allocation into male function in hermap hrodites. Among natural populations within each of the three species in con trast, these traits were not significantly related to each other. We propos e that temporal variation of female frequency in natural populations preven ts natural selection from adjusting female frequency and reproductive param eters.