Fitness consequences of branching in Verbascum thapsus (Scrophulariaceae).

The reserve meristem hypothesis proposes that strong apical dominance suppresses lateral meristems and branches to escape from predictable damage (herbivory). This hypothesis was tested for Verbascum thapsus and its seed predator the weevil Gynmnetron tetrum by two mensurative experiments. The following predictions were made under this hypothesis: the proportion of individuals branched within a population will increase with increased damage, the main stalk of branched plants will be more damaged, and branching increases net seed production. Fifty populations of V. thapsus were extensively surveyed, and one pair of similar-sized individuals (branched vs. unbranched) were selected from each population to determine damage patterns and measure seed production. Two of the predictions of the reserve meristem hypothesis were clearly supported. The proportion of fruits damaged on the main stalk of branched plants was significantly greater than unbranched plants, and branched plants produced significantly more seeds. Hence, the reserve meristem hypothesis is supported as an adaptive interpretation of apical dominance in this species. This study is a potential example of overcompensation following granivory in the field.