Phenotypic Dimorphism and Populational Fitness in Phlox

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Abstract
Populations of P. pilosa typically display a pink corolla phase in high frequency. An alternative corolla phase, white, prevails only in areas of immediate contact with P. glaberrima in whose presence it is selectively advantageous. Consideration was given to the relative adaptedness of pink and white monomorphic, and dimorphic populations in the absence of P. glaberrima. The adaptive component measured was fertility, which is a manifestation of pollinator attractiveness, or mating success. The fertility of populations was strongly dependent upon phase proportions, the correlation coefficient of proportions vs. fertility being .89. Populations in which white was the sole morph or in which pink was rare had a collective mean fertility of 45% as compared to 65% in monomorphic pink populations. Even the presence of P. glaberrima failed to alter the phase differential, although it did depress fertility. The fertility differential observed at the extremes of the phase spectrum was lacking within populations. Surprisingly, white fertility was higher in most dimorphic populations. Thus within populations the white phase has a slight advantage which was more than counterbalanced at the populational level. Phlox pilosa is competing with other genera for lepidopteran pollinators. Monomorphic pink populations more efficiently exploit this resource than white or dimorphic populations, and accordingly are considered highly adapted. Presumably pollinators spend proportionally greater periods of time foraging upon other genera as the white phase becomes more prevalent.

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