Are floral traits and their phenotypic variability related to plants with generalized or specialized pollination systems? A community perspective

Abstract

Flower traits under selection by specialized pollinators may experience a decrease in their phenotypic variation. Another viewpoint suggests that flower traits of plants under selection by generalized pollinators could display comparable variability to that of plant species with a specialized pollination system. We evaluated the following alternatives: (a) species with specialized pollination system (zygomorphic flowers, long corolla tube and higher amount of nectar, and visited by only one group of pollinators) will present higher natural fruit set and less floral phenotypic variation in comparison with species with generalized pollination system (actinomorphic flowers with short corolla tube and comparatively lower amount of nectar, and visited by a wide spectrum of taxonomically diverse pollinator species); (b) alternatively, if species with generalized pollination system show similar reproductive success to that of with specialized pollination system, comparable phenotypic variation in flower traits will be expected between them. Natural fruit set, corolla tube length, amount of nectar per flower, nectar sugar composition, and variability of these floral traits were measured in 43 biotically-pollinated species growing in a Chaco Serrano community from central Argentina. Plants were classified as specialists or generalists based on focal observations made to record their pollinators. Correlations and General Linear Models were used to compare fruit set and flower traits between plant species with generalized and specialized pollination system. Plants with specialized pollination system display flowers with higher amounts of nectar than plants with generalized pollination system. Nevertheless, species with generalized and specialized pollination system showed similar fruit set and floral phenotypic variation (except for the percentage of sucrose). The trends observed in species with generalized or specialized pollination systems from the Chaco forests suggest that pollinators could be an effective evolutionary force in selecting primary and secondary floral traits for both types of plant species.