The pattern of sexual resource allocation in the yellow monkey flower,Mimulus guttatus

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Abstract
The allocation of biomass to female, male and attractive structures was measured in Mimulus guttatus. Four populations of contrasting ecologies were compared. From each population, two plants were assigned to each of three treatments. In one treatment, all flowers were pollinated, allowing total seed production to be measured. In the second, all flowers were removed, preventing any post-anthesis investment (Post-AI). In the third, the daily pattern of investment in capsules was measured by reaping capsules a random number of days after fertilization. This showed that post-AI was complete within fourteen days of fertilization, and competed directly with investment in pollen and attractive structures. The investment in primary female structures exceeds investment in anthers, and the mass of seeds is greater still. Significant between population variation in post-AI is found, with the population with an annual life history and small flowers having the greatest valuies. The mass of the corolla is a good predictor of ovary and capsule mass, and it is argued that the cumulative corolla mass can thus be used as an indirect mesure of parental investment. By using this measure, and including attractive structures as part of the male function of a plant, the sex ratio (male:male+female) of this species is between 34 and 42%. The relationship of these findings to sexual resource allocation theory is discussed.