PARENT SESSION
Oral Session 6: Herbivory I: Dynamics, Communities, and Photosynthesis.
Presiding: C Ivey
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room B 114.
Herbivory differential direct and indirect effects on male and female fitness of an annual plant.
Mariano, Néstor*,1, Dirzo, Rodolfo2, 1 Departamento de Ecología, Cuernavaca, MOR, Mexico2 Departamento de Ecología Evolutiva, Mexico, DF, Mexico
ABSTRACT- Leaf herbivory can have direct negative effects on plants by reducing gamete and seed production; and indirect negative effects by decreasing resource allocation to pollinator-attraction structures. In cosexual plant species both impacts may differentially affect male and female plant fitness. This study explored the consequences of herbivory on both fitness functions and the three-way relationship herbivory-flower traits-pollinator response. In a field experiment with the monoecious wild Cucurbita sororia, we applied three defoliation levels (0, 25 and 75%) and measured flower and fruit number, male flower size, nectar and pollen production, and frequency of visits/foraging time of pollinators. Herbivory reduced female flower and fruit production, but not fruit set. In contrast, plants maintained male flower production and increased pollen number per flower. As a consequence of the observed direct effects, herbivory increased maleness in plants. Leaf damage reduced flower size and nectar production but not in a linear fashion; rather, it followed the pattern 0>25=75%. Accordingly, pollinators significantly responded to this effect: frequency of visitation changed in the same direction (0>25=75%). Thus, leaf damage reduced visitation rate due to changes in flower traits relevant for pollinators. Our results suggest that while plants compensated for direct effects on male fitness, leaf damage had direct negative impacts on female fitness. Considering that reduction in pollinator visitation affect disproportionately more male than female function, we argue that herbivory had an indirect impact on male fitness, but not on female fitness. We discuss these results in terms of an optimization fitness model through differential adjusting of male and female components in response to increasing leaf damage stress.
Key words: male-female fitness, indirect effects, leaf damage, direct effects