Within-Population Variation in Sexual Resource Allocation in Mimulus guttatus

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Abstract
1. The theory of sexual resource allocation in plants assumes (a) that trade-offs occur between the resources allocated to male, female and attractive structures, and (b) that genetic variation occurs, or has occurred, within populations upon which natural selection could act to optimize the relative investment in each structure. These assumptions were tested in a study of 10 clones of Mimulus guttatus isolated from a natural population, which varied in the proportion of viable pollen they produced. The experiment was designed to investigate whether plants which invest less in viable pollen can reallocate the resources released to other functions within the same or subsequent flowers or fruits. 2. This study has failed to find any significant difference in other floral characters associated with the variation in pollen quality. Plants producing less pollen do not produce bigger or more numerous flowers, do not invest more in female function (ovaries or fruits), and do not differ in the rate at which flowers and floral components decline in size as the plants age. 3. These results suggest therefore that trade-offs between male and female function do not occur, or at least are not inevitable. There is evidence for a trade-off between primary sexual characters and attractive structures, and between the size of flowers and the rate at which flowers declined in size with time. This indicates that early investment in large flowers may be costly. 4. Pollen-ovule ratios decline with time and size of flower. Most of the floral characters studied were significantly correlated with flower size, but even when this correlation was removed by analysis of covariance, significant genetic variation could still be detected for most characters. This indicates that selection could act to alter the relative contribution of the different components of the flower if it should be advantageous.

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