Abstract

• Revealing the environmental pressures determining the frequency of females amongst populations of sexually dimorphic plants is a key research question. Analyses of sex-ratio variation have been mainly done in dioecious plants, which misses key plant sexual systems that might represent intermediate stages in the evolution of dioecy from hermaphroditism.
• We investigated female frequency across populations of sexually dimorphic plant species in relation to environmental stressors (temperature, precipitation), totaling 342 species, 2011 populations, representing 40 orders and 3 different sexual systems (dioecy, gynodioecy, and subdioecy). We also included the biome where the population was located to test how female frequency may vary more broadly with climatic conditions.
• After correcting for phylogeny, our results for gynodioecious systems showed a positive relationship between female frequency and increased environmental stress, with the main effects being temperature-related. Subdioecious systems showed also strong positive relationships with temperature and positive and negative relationships related to precipitation, whilst no significant effects on sex ratio in dioecious plants were detected.
• Combined, we show that female frequencies in intermediate sexual system on the pathway from hermaphroditism to dioecy respond strongly to environmental stressors and have different selective agents driving female frequency.