The Adaptedness of Corolla-Color Variants in Experimental and Natural Populations of Phlox drummondii

The adaptedness of corolla-color variants was investigated in experimental and natural populations of Phlox drummondii. A population of a polymorphic cultivar was established in the garden, with lavender, red pink, pale pink, white, maroon, coral, and red "plants" present in equal proportions. Pollinator exploitation was judged from seed and capsule sets per flower and from pollen loads on stigmas. The variants have similar penchants for crossing and do not differ in floral morphology. They are pollinated by lepidopterans. Major differences in capsule and seed sets and pollen loads were observed, suggesting that pollinators were attracted more to some colors than others. Mean number of capsules per flower varied from 0.79 in maroon to 0.56 in red. The mean number of seeds per flower ranged from 1.95 in lavender to 1.39 in red in the following order: lavender > maroon > white > red pink > coral > pale pink > red. Mean pollen loads ranged from 124 in lavender to 83 in coral in the following order: lavender > white > red pink > pale pink > red > coral. There is no significant association between pollen load and seed-set rankings. A pair of native P. drummondii subspecies with different flower colors and interdigitating ranges offers an opportunity to study the effect of corolla color on pollinator exploitation by populations. Subspecies drummondii is red flowered, while subspecies goldsmithii is pink flowered. Both taxa are restricted to east-central Texas, where they grow in similar habitats, have similar ecological associates, and have similar crossabilities. Subspecies goldsmithii received much more pollinator service than its congener. Mean number of capsules per flower in subspecies goldsmithii was 0.76 as compared with 0.55 in subspecies drummondii. Mean seeds per flower in the former was 2.23 as compared with 1.57 in the latter. It is clear that some corolla variants can exploit the pollinator fauna better than others. This is true at the individual as well as the population level. Correlatively, pollinators may act as strong selective agents upon corolla color. In P. drummondii, the variants which reflected strongly in the blue and orange red portions of the spectrum generally were the most attractive.