Thursday, August 7, 2008 - 3:20 PM

COS 97-6: Individual- and population-level consequences of mating system-dependent transgenerational effects of herbivory in Impatiens capensis

Janette A. Steets, Oklahoma State University, Tiffany M. Knight, Washington University, and Tia-Lynn Ashman, University of Pittsburgh.


Vegetative herbivory is a ubiquitous ecological factor affecting plant populations. To date, most studies examining the effect of herbivory for plant fitness quantify effects on seed number or progeny traits expressed early in development, largely ignoring the consequences of herbivory for offspring fitness-related traits and plant population dynamics. Thus, the potential transgenerational consequences of maternal herbivory largely remain unknown.  In two experiments, we examined the transgenerational effects of herbivory for individual fitness-related traits of progeny from obligately-selfed cleistogamous and facultatively-outcrossed chasmogamous flowers of Impatiens capensis. In addition, we assessed the consequences of transgenerational effects of herbivory for population growth. In the first experiment, we manipulated maternal herbivory levels in a natural I. capensis population and grew cleistogamous and chasmogamous progeny of these plants in the presence or absence of intraspecific competitors in a greenhouse experiment. In the second experiment, we explore the demographic consequences of transgenerational effects of herbivory by following cleistogamous and chasmogamous seeds derived from maternal plants grown under ambient and reduced herbivory conditions throughout their life cycle in two natural I. capensis populations. 


In the greenhouse experiment, we found that maternal plants experiencing ambient herbivory produced progeny that were larger in size, produced more cleistogamous flowers, and tended to reproduce relatively more through chasmogamy than cleistogamy than their reduced herbivory counterparts. In addition, we found significant mating system-dependent maternal effects of herbivory for seedling biomass and cleistogamous and chasmogamous flower production. Chasmogamous seedlings produced by ambient herbivory maternal plants were larger and produced more flowers than cleistogamous offspring produced in the same maternal herbivory environment or either seed type from reduced herbivory mothers. Competition influenced expression of transgenerational effects and mating system-dependent transgenerational effects. In the demographic study, we found that transgenerational effects of herbivory significantly reduced population growth rate. In total, our results demonstrate that maternal effects of herbivory can vary with offspring mating system and competitive context experienced by progeny and these transgenerational effects of herbivory influence population dynamics.