Lisi Dámaris Pereira Alvarenga

Sex ratio, spatial segregation, and fertilization rates of the epiphyllous moss Crossomitrium patrisiae (Brid.) Müll.Hal. in the Brazilian Atlantic rainforest

Abstract In order to investigate which mechanisms the epiphyllous moss Crossomitrium patrisiae employs to overcome the typical constraints of dioicy in light of its spatially isolated habitat, we tested the predictions that high fertilization rates are achieved due to (1) high rates of sexual expression, (2) balanced sex ratios, and (3) high co-occurrence of both sexes in the same colony (leaf). Seven hundred and ninety-seven ramets were studied for total length, presence, and number of gametoecia and number of fertilized perichaetia in the female according to spatial segregation at leaf- and shrub-scales. High rates of sexual expression (76%) were confirmed. The other two predictions, however, were not upheld as C. patrisae exhibited a strong male bias (0·43 ♀∶1 ♂ at ramet level, n = 604). Despite considerable spatial segregation (co-occurrence of sexes was seen in 36·7% of shrubs and 12·8% of colonies), this species revealed one of the highest fertilization rates ever reported for a dioicous bryophyte at three spatial scales: nearly 90% of the mixed colonies bore sporophytes, 40% of all female ramets, and 74% of female ramets occurring in mixed colonies bore sporophytes. Thus, the relative rareness of females may be a phenotypic response due to heavy investment in sporophyte maturation as demonstrated by the high fertilization success of females. High rates of sexual expression and the occurrence of fertilization in nearly all cases of coincidence of sexes in common colonies, with low levels of abortion, contribute to the sexual reproductive success and, subsequently, the long-term survival of this species.

Sexual Dimorphism, Vegetative Growth and Reproductive Investment in the Rhizautoicous Moss Fissidens flaccidus (Fissidentaceae, Bryopsida)

Abstract Reproduction is one of the most important and expensive processes in the life history of plants. The cost commonly incurred by reproductive investment in plants with separate sexes may result in sexual dimorphism. Among bryophytes, sexual dimorphism has been observed in some sex-expressing dioicous species and in some sex-expressing monoicous species with a rhizautoicous sexual system. In the present study, we have investigated sexual dimorphism in morphological features and relative reproductive investments in sporophytic female, non-sporophytic female, sex-expressing male and non-expressing ramets in a population of the rhizautoicous Fissidens flaccidus. Morphometric analyses confirmed sexual dimorphism; gemmiform male ramets were smaller than the other ramet morphs, and exhibited greater sexual investment. Sexual reproductive investment was approximately 35% in males, 13% in non-sporophytic females and 25% in sporophytic females. Our results indicate trade-offs between reproductive investment and vegetative growth for both sexes in this species.