Abstract:
Flower color is often viewed as a trait that signals rewards to pollinators, such that the relationship between flower color and plant fitness might result from its association with another trait. We used experimental manipulations of flower color and nectar reward to dissociate the natural character correlations present in a hybrid zone between Ipomopsis aggregata and Ipomopsis tenuituba. Isozyme markers were used to follow the male and female reproductive success of these engineered phenotypes. One field experiment compared fitnesses of I. aggregata plants that varied only in flower color. Plants with flowers painted red received more hummingbird visits and sired more seeds than did plants with flowers painted pink or white to match those of hybrids and I. tenuituba. Our second held experiment compared fitnesses of I. aggregata, I. tenuituba, and hybrid plants in an unmanipulated array and in a second array where all flowers were painted red. In the unmanipulated array, I. aggregata received more hummingbird visits, set more seeds per flower, and sired more seeds per flower. These fitness differences largely disappeared when the color differences were eliminated. The higher male fitness of I. aggregata was due to its very high success at siring seeds on conspecific recipients. On both I. tenuituba and hybrid recipients, hybrid plants sired the most seeds, despite showing lower pollen fertility than I. aggregata in mixed donor pollinations in the greenhouse. Ipomopsis tenuituba had a fitness of only 13% relative to I. aggregata when traits varied naturally, compared to a fitness of 36% for white relative to red flowers when other traits were held constant.

Author Keywords:
flower color, hybrid zone, Ipomopsis, male fitness, pollinator visitation, selection, trait manipulation

KeyWords Plus:
RADISH RAPHANUS-RAPHANISTRUM, WILD RADISH, EXPERIMENTAL POPULATIONS, POLLINATION SUCCESS, POLEMONIUM-VISCOSUM, DELPHINIUM-NELSONII, NATURAL-SELECTION, FLORAL ISOLATION, SEED PRODUCTION, PINYON PINE

Addresses:
Melendez-Ackerman E, Inst Trop Ecosyst Studies, POB 363682, San Juan, PR 00936 USA
Univ Calif Irvine, Dept Ecol & Evolutionary Biol, Irvine, CA 92697 USA
Rocky Mt Biol Labs, Crested Butte, CO 81224 USA

Publisher:
SOC STUDY EVOLUTION, 810 E 10TH STREET, LAWRENCE, KS 66044 USA

IDS Number:
137RZ

ISSN:
0014-3820