How do sexual expression, reproductive phenology and reproductive success relate to sexual systems in Fissidens Hedw. (Fissidentaceae)? A case study comparing two different sexual systems in mosses.

Reproductive performance is known to differ between co-sexual and non-co-sexual species. Thus, our aim was to determine whether: (i) the distance between sex structures is negatively associated with sex expression; (ii) male gametangia take longer to mature in rhizautoicous species than in gonioautoicous species; and (iii) the gonioautoicous sexual system has greater reproductive success (i.e. percentage of ramets with sporophyte) than the rhizautoicous sexual system. One population each of the mosses Fissidens scariosus and F. submarginatus, rhizautoicous and gonioautoicous, respectively, in a remnant of Atlantic Forest in Brazil were sampled monthly from September 2016 until August 2017. The number and phenophases of antheridia, archegonia and sporophytes were analysed for each species. Sexual expression and reproductive success were calculated, and reproductive phenology compared across environmental variables. As expected, sexual expression was significantly higher for the gonioautoicous species, which produced antheridia throughout the year and archegonia over many months, while gametangia production by the rhizautoicous species occurred only during the rainy season. Mean number of gametangia per perigonium and perichaetium were slightly higher for the rhizautoicous species (6.84 antheridia; 11.38 archegonia) than for the gonioautoicous species (4.39; 7.62). Gametangia and sporophyte production in the rhizautoicous species were markedly seasonal compared to that of the gonioautoicous species, although reproductive success did not differ. Therefore, we infer that the rhizautoicy (i.e. a functional dioicy) promotes lower expression of gametangia compared to gonioautoicy but is more efficient and so obtains the same reproductive success.