MCLETCHIE, D. NICHOLAS. School of Biological Sciences, 101 Morgan Building, University of Kentucky, Lexington, KY 40502. - Sex-specific life histories and population sex ratios in the dioecious liverwort Marchantia inflexa.
Unisexual, female- or male-biased populations are common among
dioecious bryophytes and the demographic causes of such biases are
unclear. Life history studies can be valuable in understanding the
contribution of each life history stage to a population sex ratio, yet
few studies use this approach. We chose to study the liverwort
Marchantia infexa to investigate the potential effect of various
stages/traits on population sex ratio. Across M. inflexa’s
distribution range, herbarium data suggest female-biased sex ratios.
Field studies in Trinidad & Tobago suggest an overall 1:1 sex ratio
within a single watershed, however, patches can be single-sex,
bisexual or without sex expression. We investigated sex-specific
survival of asexual propagules (lab), clonal expansive traits
(greenhouse) and patterns of sex expression (field & greenhouse). We
found that neither sex had a consistent advantage. Females had higher
propagule survival, lower propagule production and higher growth
rates. Sex expression tended to occur first in males then in females.
These patterns suggest that focusing on any single stage or trait can
result in erroneous conclusions as to the demographic causes of sex
ratio biases. Thus, studies on population sex ratio biases should
incorporate multiple traits and stages.
Key words: Marchantia inflexa , asexual reproduction, life history, liverwort, sex expression, sex ratio