Abstract

The co-occurrence of elaborate fl owers visited by specific groups of pollinators and capacity for autonomous selfi ng in the same plant species has puzzled evolutionary biologists since the time of Charles Darwin. To examine whether autonomous selfi ng and fl oral specialization evolved in association, we quantifi ed the autofertility level (AFI) in nine Schizanthus species characterized by a wide range of pollination specialization, revealing AFI values of 0.02 to complete selfi ng. An independent contrasts analysis conducted on AFIs and number of functional pollinator groups showed that autonomous selfi ng evolved from an ancestral outcrossing system as plants became increasingly specialized ( r =-0.82). To assess whether autonomous selfi ng together with specialization acts as a reproductive assurance mechanism, we estimated spatial and interannual variation in fruit set due to pollinator failure in two closely related high Andean Schizanthus species differing in their specialization levels. Variation in pollinator failure rate was more pronounced and autonomous selfi ng increased fruit production over biotically assisted pollination in the more specialized species. Our study suggests that specialized pollination deems species more vulnerable to pollinator fl uctuation thus promoting the evolution of delayed autonomous selfi ng.