Effects of Herbivory on Male Reproductive Success in Plants

Abstract

The effects of herbivory on plant fitness have been assessed in terms of seed or fruit production whereas the effects on male reproductive success have received much less attention. This female-biased approach has been based on the assumption that the male and female reproductive success in plants are correlated with each other and that the effects of environmental factors on female and male function are equal or at least parallel. However, several studies have suggested that male and female reproductive success are not closely related and they may even be negatively correlated. Here we review the literature and also present an experimental study of the effect of herbivory on pollen-tube growth rates. The literature reviewed shows that the effects of herbivory on plant fitness may vary in relation to the fitness measures used and that herbivory may have differential effects on female and male reproductive functions. These differential effects may have evolutionary consequences, as well as consequences for estimating the selective effects of herbivory. Our experiment with Lobelia siphilitica showed that removal of 50% of the leaves during flower development caused a significant reduction in pollen-tube growth rates. We suggest that assessment of both male and female fitness components will give more accurate estimates of the effects of herbivory on total plant reproductive success. Consequently, the role of herbivory as a selective force can be more accurately estimated.