Data from: 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 only just produced their first spores, these sex ratio changes occurred during the gametophytic generation due to sex-specific growth or survival. Sporophytes only occurred in populations with female-biased final sex ratios, suggesting that females in male-majority populations may have invested energy in ramets rather than sporophyte production. The stress treatment was mild and had no effect on sex ratio. CONCLUSIONS: Our results suggest that female-bias can be generated during the gametophytic generation, before plants reach sexual maturity. These results, combined with previous work, suggest that both the gametophytic and sporophytic stages drive population sex ratios in C. purpureus, indicating multiple mechanisms operate to create biased population sex ratios