Population sex ratios, sex-specific clonal traits and tradeoffs among these traits in the liverwort Marchantia inflexa

Unisexual, female- or male-biased populations are common among some clonal plants. Within and among populations, the relative frequencies of males and females can be influenced by sex-specific demographic patterns that, in turn, can be a consequence of life-history characteristics. The objectives of this study were to describe (1) population sex-ratio patterns among habitat patches along a river, and (2) sex-specific patterns of and correlations among life-history clonal traits including: Growth rates, number of meristematic tips and asexual reproduction in the dioecious liverwort, Marchantia inflexa. In Trinidad, a section of a stream was surveyed for the occurrence of female and male sex expressing thalli among habitat patches, and habitat characteristics (canopy openness and patch size) were recorded. The numbers of female and male inflorescences were obtained also. Of the 209 patches observed in the field, 83% did not contain sex expressing thalli, 9% contained thalli of both sexes, and the rest contained only female- (4%) or male-expressing (4%) thalli. Sex expression was less common among small patches, and there was a tendency for sex expression to be less likely among patches with the lowest canopy openness. The proportion of male inflorescences among the bisexual patches ranged from 0.22 to 0.80. In a greenhouse, we planted gemmae (asexual propagules) from field-collected isolates: Ten female and eight male. On six occasions, we harvested replicates of each isolate to estimate isolate trait means. Females grew faster, produced more meristematic tips and had lower levels of asexual reproduction than males. Number of meristematic tips was negatively correlated with asexual reproduction and positively correlated with growth rate. These sex-specific patterns may lead to the high frequency of single sex patches as well as biased adult population sex ratios that are observed in the field.