The importance of color: floral morphs, visit rates and fitness in the shrub Sarothamnus scoparius

Abstract

The study of the intraspecific variability in the flower color may help us to better understand the role of pollinators as selective agents end their effect on the local abundance of floral morphs. We studied the influence of intraspecific variation of flower color on the floral visitation rate and the fitness of Sarothamnus scoparius, a common exotic shrub in Northern Patagonia. Particularly, we determined whether the higher abundance of shrubs with yellow-flowers compared with those with red or orange flowers was consequence of a differential visitation rate of potential pollinators. We 1) measured the visitation rate to yellow flowers and their variants red and orange in natural conditions and in flowers where their color was manipulated; 2) determined whether the visitation rate to red and orange flowers depended on their distance to yellow flowers, and 3) estimated the production of fruit set and seed set in yellow and red flower morphs. We found that: 1) in both, natural and color-modified conditions, yellow flowers received 1-4 times more visits than red or orange flowers; 2) the visitation rate to red and orange flowers decreased abruptly as the distance to yellow flowers increases (7 times in only 100 cm), and 3) both fruit and seed set were ~40% higher in shrubs with yellow flowers compared with those with red flowers. These results suggest that the higher abundance of shrubs with yellow flowers is consequence of a higher visitation rate of potential pollinators, which in turn produce a higher fitness in this floral morph. This work illustrates the importance of pollinators modeling flower characteristics and the influence of floral neighborhood in such process.