Female advantage? Investigating female frequency and establishment performance in high-Arctic Silene acaulis

Many Arctic plants overcome limited time budgets and energy budgets by selfing, increasing the risk of inbreeding. Gynodioecious breeding systems allows for selfing by hermaphrodites, whereas enforced outcrossing through females lowers risk of inbreeding. Females persist due to female advantage in the system. Using the gynodioecious species Silene acaulis (L.) Jacq., we compared establishment performance and female frequency in 17 populations in open, sparsely vegetated habitats versus closed, denser vegetated habitats, across a regional climate gradient in high-Arctic Svalbard. For two populations, genetics were performed using microsatellites to compare inbreeding levels between habitats. As S. acaulis is a pioneer species, we expected denser vegetation to represent more competitive environments, reducing establishment performance and increasing female frequency due to female advantage. We expected similar responses to harsher regional climate. Establishment performance was reduced in closed habitats and harsher climate, but female frequency was slightly lower in closed habitats and did not differ between regional climates. High inbreeding levels may indicate that female advantage is counteracted by pollen limitation. However, female frequency increased with latitude. Lower sun angle at higher latitudes reduce the heat-trap effect of the cushion growth form, and female advantage might be expressed as response to reduced microclimate amelioration.