Sex ratio and sex expression in an urban population of the silver moss, Bryum argenteum Hedw.

ABSTRACT

Introduction. A well-supported pattern among dioicous bryophytes is male rarity. However, few assessments of bryophyte sex ratios have been made across environmental gradients to assess the role of environment in shaping population sex ratios.

Methods. We systematically surveyed 200 shoots from a 20 m² urban population of Bryum argenteum, and regenerated each shoot apex until sex expression occurred (up to 315 days).

Key results. Female shoots outnumbered male shoots 132 to 68, giving a sex ratio of 1.94♀: 1♂. The female bias was found in two transects in higher light environments but not in the third transect, which had a lower light level and an equal sex ratio. Female shoots took longer than male shoots to reach gametangial induction (122 vs. 60 days) and longer to produce 5 inflorescences (120 vs. 80 days). Male shoots produced an average of 10× the total number of inflorescences compared to female shoots (34 vs. 3.5 inflorescences). Despite producing more inflorescences, male plants also produced more regenerant shoots, thus contradicting the prediction that a higher prefertilisation reproductive effort in males trades off with vegetative proliferation. Female plants harboured significantly more associated microbes than male plants.

Conclusions. Our results support the role of light in influencing sex ratios in this species, suggest that trade-offs between reproduction and vegetative growth may not be strong for males, and indicate a potential role of a sex-specific microbiome in influencing sex ratios.

KEYWORDS:

• Gametangial induction
• inflorescence
• microbial associates
• reproductive effort
• shoot regeneration
• silvery-thread moss

Acknowledgements

We thank Rich, Janet, and Anabelle Fortin for providing access to their yard, John Brinda for identification of the species at the site, Gabriela Benito, Wendie Welch, and Paige Merriweather for media, nutrient solution, and water preparation, and R. Riker for assistance with Figure 1.

Notes on contributors

Rick Castetter is a naturalist, field ecologist, and bird enthusiast of south-western USA desert and upland regions.

Nicholas McLetchie is a reproductive plant ecologist focused on explanations of skewed sex ratios in bryophytes.

Sarah Eppley’s interests lie in the ecology and evolution of angiosperms and bryophytes, especially the environmental effects on breeding systems.

Llo Stark is an ecophysiologist with main interests in the desiccation biology and reproductive ecology of bryophytes.