There are few greater obstacles to sexual reproduction than the rarity or absence of one sex. Limited or no sexual reproduction can result in a species inability to adapt to a changing environment, leading to population declines and eventually species extinction. Yet among plants, specifically bryophytes, rarity or absence of one sex occur frequently. An illustration of this pattern occurs in the liverwort Acrobolbus ciliatus Mitt. which is found as males in Japan and females in the Appalachian mountains in the USA . Although intriguing, the underlying causes of these patterns have infrequently been investigated. My research program focuses on elucidating the factors resulting in an entire species or population being dominated by one sex. Such factors include variation in offspring sex ratios and sex differences in clonal expansion that are a function of differential growth, asexual reproduction, colonization and survival as well as sex differences in sex expression.
To study the causes and consequences of sex ratio variation we use an unusually broad array of techniques, including molecular-genetic analysis, physiological methods, greenhouse and growth chamber experiments, field experiments and monitoring, and mathematical modeling. We consider the structure and dynamics of individuals, local clusters of individuals (patches), and patch assemblages, and interactions among them and the environment.