Transgenerational effects of plant sex and arbuscular mycorrhizal symbiosis

In gynodioecious plants, females are predicted to produce more and/or better offspring than hermaphrodites in order to be maintained in the same population. In the field, the roots of both sexes are usually colonized by arbuscular mycorrhizal (AM) fungi. Transgenerational effects of mycorrhizal symbiosis are largely unknown, although theoretically expected. We examined the maternal and paternal effects of AM fungal symbiosis and host sex on seed production and posterior seedling performance in Geranium sylvaticum, a gynodioecious plant. We hand-pollinated cloned females and hermaphrodites in symbiosis with AM fungi or in nonmycorrhizal conditions and measured seed number and mass, and seedling survival and growth in a glasshouse experiment. Females produced more seeds than hermaphrodites, but the seeds did not germinate, survive or grow better. Mycorrhizal plants were larger, but did not produce more seeds than nonmycorrhizal plants. Transgenerational parental effects of AM fungi were verified in seedling performance. This is the first study to show transgenerational mycorrhiza-mediated parental effects in a gynodioecious species. Mycorrhizal symbiosis affects plant fitness mainly through female functions with enduring effects on the next generation.