Irene Bisang ^1* Flavien Collart ² Alain Vanderpoorten ³ Lars Hedenäs ¹

• ¹ Swedish Museum of Natural History, Stockholm, Sweden
• ² Département d'écologie et évolution, Faculté de Biologie et de Médecine, Université de Lausanne, Lausanne, Vaud, Switzerland
• ³ Institute of Botany, University of Liege, Liege, Liege, Belgium

Introduction: Plant dispersal and reproduction are tightly associated, while the processes differ between plant lineages due to fundamental life cycle differences. In haploid-dominated plants, sex is manifested, and exposed to the environment, in the gametophyte. In the unisexual perennial moss Abietinella abietina, we asked whether pre-zygotic reproductive attributes in the gametophyte generation and their environmental drivers affect fertilization and thus, long-distance dispersal potential. We postulated a high proportion of non-sex-expressing samples, female gametophyte dominance, and that sporophyte formation depended on the mate distribution and environmental conditions. We expect the sexes to exhibit different topo-climate niches. Methods: We scored 1,080 herbarium specimens, representing individual species’ occurrences in Sweden, as sporophytic, phenotypically female or male, or non-sex expressing. We tested whether reproductive stage and sex ratios were related to latitude. We calculated topographic and climate (MPI, UKESM circulation models) niche differentiation, and modelled the response of sex expression and reproductive success to topo-climate factors. Results: Sixty-three percent of the samples bore sexual structures, 8% of females had sporophytes, and females outnumbered males. The female bias decreased from South to North, i.e., sex ratio increased, due to a higher probability of sex-expressing samples being male than females with increasing latitude. Topographic and climate niches did not differ between sexes, and the presence of sexual organs was not explained by ecological conditions. Sporophyte occurrence was predicted by precipitation and temperature factors and was confined to central Sweden. Discussion: Despite a high sex-expression level, sporophyte formation and thus, long-distance dispersal capacity, were rare and spatially strongly restricted. It depended on mate availability and macro-environmental factors related to moisture conditions. We infer that the distribution of reproductive morphs is governed by interactions between macro- and microscale environmental factors and biological traits. We suggest that traits and environmental conditions at the pre-zygotic stage have lower than expected effects on the overall distribution of this haploid-dominant plant. Modelling environmental data at higher resolution, smaller scale and expanding spatial coverage to include more sporophyte occurrences and comparing genetic diversity in sporophytic with non-sporophytic populations, are future lines of this research.