The minimalist life of males in mosses: understanding the reproductive biology of two Schlotheimia species.

Sexual size dimorphism (SSD) is known mainly among animals, while among plants, this feature is found only in mosses. Dwarf males are supposedly advantageous for dioicous mosses because they almost exclusively produce antherozoids and grow on females, decreasing fertilization distances. We evaluated the relationship between dwarf males and spore size classes, number of spores per sporangium and their germination rates of two species of the genus Schlotheimia - S. tecta and S. rugifolia. We also investigated the association between dwarf males and female sexual success (i.e., sporophyte production). The results indicate extreme SSD for S. tecta and S. rugifolia, although regular-sized males of S. tecta were occasionally found in the study area. Schlotheimia rugifolia produced more spores (1.5x), while neither species exhibited anisospory (two size classes of spores). Sexual success was not directly associated with dwarf males on female shoots for either species, but it was affected by phorophytes (i.e., colonies in the same tree). Despite their minimalist existence, dwarf males likely play a crucial role in the reproduction of Schlotheimia, especially in the fertilization of females in S. tecta.