期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：11
页码：3433-3438
DOI：10.1073/pnas.1419522112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceBy using structural characteristics, such as long tubular flowers, plants are known to achieve selective visitation by certain pollinator species. These morphological traits typically arise over evolutionary timescales. We show for the first time, to our knowledge, that at least one plant has also evolved the capacity to recognize pollinator species immediately after visitation, thereby increasing the likelihood that a flower visitor has delivered high-quality pollen. This novel responsiveness by the plant leads to functional specialization in an apparently generalized tropical plant-pollinator network. Such specialized linkages likely facilitate coevolution but also, render pollination mutualisms more vulnerable to environmental change. Understanding the mechanisms enabling coevolution in complex mutualistic networks remains a central challenge in evolutionary biology. We show for the first time, to our knowledge, that a tropical plant species has the capacity to discriminate among floral visitors, investing in reproduction differentially across the pollinator community. After we standardized pollen quality in 223 aviary experiments, successful pollination of Heliconia tortuosa (measured as pollen tube abundance) occurred frequently when plants were visited by long-distance traplining hummingbird species with specialized bills ([IMG]f1.gif" ALT="Formula" BORDER="0"> pollen tubes = 1.21 {+/-} 0.12 SE) but was reduced 5.7 times when visited by straight-billed territorial birds ([IMG]f1.gif" ALT="Formula" BORDER="0"> pollen tubes = 0.20 {+/-} 0.074 SE) or insects. Our subsequent experiments revealed that plants use the nectar extraction capacity of tropical hummingbirds, a positive function of bill length, as a cue to turn on reproductively. Furthermore, we show that hummingbirds with long bills and high nectar extraction efficiency engaged in daily movements at broad spatial scales ([~]1 km), but that territorial species moved only short distances (<100 m). Such pollinator recognition may therefore affect mate selection and maximize receipt of high-quality pollen from multiple parents. Although a diffuse pollinator network is implied, because all six species of hummingbirds carry pollen of H. tortuosa, only two species with specialized bills contribute meaningfully to its reproduction. We hypothesize that this pollinator filtering behavior constitutes a crucial mechanism facilitating coevolution in multispecies plant-pollinator networks. However, pollinator recognition also greatly reduces the number of realized pollinators, thereby rendering mutualistic networks more vulnerable to environmental change.
