Gynodioecy in Thymus pulegioides L., T. serpyllum L., and their hybrid T. × oblongifolius Opiz (Lamiaceae): Flower size dimorphism, female frequency, and effect of environmental factors

Abstract

Thymus pulegioides L., Thymus serpyllum L., and their hybrid Thymus × oblongifolius Opiz are gynodioecious species: the two sexual phenotypes (female and hermaphrodite) coexist in natural habitats. This study showed that the hermaphrodites of the two species and their hybrid produce larger flowers and pistils than females. Higher variation of corolla width and pistil length observed in hermaphrodites may be associated with pollination ecology and the attraction of a greater diversity of pollinators. Differences in the proportions of females characterized T. pulegioides (70.7% ± SD 24.8), T. serpyllum (28.1% ± SD 24.2), and their hybrid T. × oblongifolius (32.4% ± SD 29.6). Male sterility was more common in T. pulegioides, which (as distinct from T. serpyllum and T. × oblongifolius) is specialized toward generative propagation. Our field tests showed that variation in the frequency of females within the same species was positively affected by the environmental conditions of their habitats: statistically significant negative correlations were detected between herb cover and female frequency among the habitats of T. pulegioides (r = − 0.32, p < 0.05), and between habitat lightness and female frequency in the habitats of the heliophilous species T. serpyllum (r = − 0.49, p < 0.05). Our investigations showed that systems of “parental species+their hybrids” are useful for studying connections between ecology and evolutionary change in gynodioecious species of the Thymus genus.

Keywords::

• Environmental factors
• female frequency
• flower size dimorphism
• gynodioecy
• interspecific hybrid
• Thymus

Notes

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