Sex and Gender Dynamics in Jack-in-the-Pulpit, Arisaema Triphyllum (Araceae)

Eleven populations of Arisaema triphyllum (L.) Schott (jack-in-the-pulpit) were stud- ied in 1978-1979. There was a range of population gender ratios, from strongly female biased to strongly male biased; gender dimorphism with respect to body size and phenology was found. The proportion of a plant's biomass found in reproductive and ancillary reproductive organs was determined for plants of each gender. The mean total dry mass of carpellate individuals was 3.5 times greater than that of staminate plants. Reproductive effort was 12% of dry mass for flowering carpellate plants, 17% for staminate plants, and 44% for mature fruiting carpellate plants. Approximately 10% of the reproductive plants in all populations were monoecious. In 1978 and 1979 several environmental factors were measured at four of the sites, and these were related to population gender ratios at each site. Carpellate individuals were predominant in less- shaded sites where both pH and soil nutrient levels were higher. Staminate individuals were concen- trated in darker microsites and in areas of lower pH. A reciprocal replant/transplant experiment was initiated in 1978, using 267 ramets of Arisaema triphyllum, from two sites with contrasting population gender ratios. Staminate, carpellate, and mon- oecious plants, reciprocally, were either replanted at the "home" site, or transplanted to the "alien" site. The gender of ramets was monitored in 1979 and 1980. The sequence of gender change in plants was nondirectional. Plants transplanted to an alien site did not maintain the gender ratio characteristic of the home site. Highly significant effects on gender change could be attributed to the environment in which plants were grown. We support the conclusion that sex change is adaptive where female reproductive costs are greater than male costs. A simple model of gender change for reproductive plants at each site was constructed, based on the results of the transplant experiment. The differential survivorship and patterns of gender flux provide possible explanations of contrasting gender ratios.