Effects of herbivory and its timing on reproductive success of a tropical deciduous tree.

BACKGROUND AND AIMS: The implications of herbivory for plant reproduction have been widely studied; however, the relationship of defoliation and reproductive success is not linear, as there are many interacting factors that may influence reproductive responses to herbivore damage. In this study we aimed to disentangle how the timing of foliar damage impacts both male and female components of fitness, and to assess when it has greater impacts on plant reproductive success. METHODS: We measured herbivore damage and its effects on floral production, male and female floral attributes as well as fruit yield in three different phenological phases of Casearia nitida (Salicaceae) over the course of two consecutive years. Then we tested two models of multiple causal links among herbivory and reproductive success using piecewise structural equation models. KEY RESULTS: The effects of leaf damage differed between reproductive seasons and between male and female components of fitness. Moreover, the impact of herbivory extended beyond the year when it was exerted. The previous season's cumulated foliar damage had the largest impact on reproductive characters, in particular a negative effect on the numbers of inflorescences, flowers and pollen grains, indirectly affecting the numbers of infructescences and fruits, and a positive one on the amount of foliar damage during flowering. CONCLUSIONS: For perennial and proleptic species, the dynamics of resource acquisition and allocation patterns for reproduction promote and extend the effects of herbivore damage to longer periods than a single reproductive event and growing season, through the interactions among different components of female and male fitness.

FITNESS CONSEQUENCES OF MATERNAL AND NONMATERNAL COMPONENTS OF INBREEDING IN THE GYNODIOECIOUS PHACELIA DUBIA.

I assessed the relationship between the level of inbreeding, F, and fitness, and the effects of nonmaternal and maternal components of inbreeding on fitness in Phacelia dubia. I conducted two generations of controlled crosses and tested the performance of the F2 progeny in field and artificial conditions covering the whole life cycle. Inbreeding significantly decreased the individual contribution of seeds to the next generation in the field, but this decrease apparently is not enough to explain the maintenance of gynodioecy. The inbred progeny contributes significantly to the population genetic structure of P. dubia. Fitness estimates and fitness components tended to decrease, usually monotonically, with F. However, nonmonotonic relationships were found in male fitness components and, in some families, in fitness estimates, seed production per fruit, and establishment. Most of the inbreeding depression takes place at the level of seed establishment in the field, but, in artificial conditions the effects of inbreeding were similar at fecundity and establishment. I studied maternal and nonmaternal components of inbreeding by testing the effects of the relatedness of maternal grandparents and parents on the performance of the progeny. Both components affected fitness. Inbreeding depression was conditioned by the level of inbreeding of the maternal plant, but this interaction varied at different fitness components. Also, the magnitude and even the direction of the relationship between fitness and F changed as a result of the combined effects of maternal and nonmaternal components of inbreeding. Such interactions can render convex or concave fitness functions, giving in the latter case the appearance of a false purging. Maternal effects of inbreeding can result from several processes: maternal investment perhaps with serial adjustments during seed development, purging of recessive deleterious genes, and nucleocytoplasmic interactions. These results illustrate the importance of maternal effects of inbreeding, and the complex effects of inbreeding on fitness. A full understanding of the fitness consequences of inbreeding and, therefore, their potential implications in the evolution of breeding systems, should take into account male and female components as well as transgenerational effects in the context of the particular environment in which fitness is evaluated.