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-specific differences in clonal expansion that are a function of differential growth, asexual reproduction, colonization and survival as well as sex-specific differences in sex expression.

I have two main projects investigating the occurrences, causes and consequences of sex-sex ratio variation. The first is a collaborative project (with Philip Crowley) and focuses on detecting tradeoffs in life-history traits and the effects of these differences on the maintenance of sexual reproduction in Marchantia inflexa. The second project is a collaborative project [with Lloyd Stark ( University of Nevada at Las Vegas ) and Brent Mishler ( University of California at Berkeley )] and focuses on, sex specific regeneration in Syntrichia caninervis.

These projects 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 (patches), and patch assemblages, and interactions among them the environment.

• Stark, L. R. and D. N. McLetchie. 2005. Gender Specific Heat Shock Tolerance of Hydrated Leaves in the Desert Moss Syntrichia caninervis. Physiologia Plantarum (In press).
• Crowley, P. H., C. Stieha, and D. N. McLetchie. 2005. Overgrowth competition, fragmentation and sex-ratio dynamics: a spatially explicit, sub-individual-based model Journal of Theoretical Biology 233: 25-42.
• Crowley, P. H. and D. N. McLetchie. 2002. Tradeoffs and spatial life-history strategies in classical metapopulations The American Naturalist 159: 190-208.
• McLetchie, D. N., G. Garcia-Ramosand P. H. Crowley. 2002. A model of local sex-ratio dynamics and spore production in the dioecious liverwort Marchantia inflexa. Evolutionary Ecology, 15: 231-254
• Fuselier L and D. N. McLetchie. 2002Maintenance of sexually dimorphic pre-adult traits in Marchantia inflexa (Marchantiacae). American Journal of Botany 89: 592-601.
• McLetchie, D. N. and A. L. Collins. 2001. Identification of DNA regions specific to the X and Y chromosomes in Sphaerocarpos texanus Aust. The Bryologist 104: 543-547).
• Stark L. R., B. D. Mishler and D. N. McLetchie. 2000. The cost of realized sexual reproduction: assessing patterns of reproductive allocation and sporophyte abortion in a desert moss. American Journal of Botany. 87: 1599-1608.
• McLetchie, D. N. and M. N. Puterbaugh. 2000. Population sex ratios, sex-specific clonal traits and tradeoffs among these traits in the liverwort, Marchantia inflexa. Oikos 90: 227-237.