Rapid population sex ratio changes in the moss Ceratodon purpureus

PREMISE OF THE STUDY: Sex ratio variation occurs widely in dioecious plants, but the mechanisms of population sex ratios bias are poorly-understood. In bryophytes, sex ratios are often female-biased, and little information is available about how and when bias forms. METHODS: To test whether population sex ratio variation can emerge during the gametophytic phase, and is not purely a product of spore sex ratios, we created artificial populations of the moss Ceratodon purpureus, with male- and female-biased sex ratios, and placed half under a stress treatment. We hypothesized that male-majority populations would become female-biased, and that stress would increase this transition. After 18 months when sporophytes were initially forming, we used sex-specific molecular markers to determine population sex ratios. KEY RESULTS: Female-majority populations did not differ significantly from their original bias, while male-majority populations became significantly more female-biased. As plants had...