Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 106, Issue 50, Pages 21236-21241Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0907926106
Keywords
diversification; Formicidae; Rhizobiales; symbiosis; trophic level
Categories
Funding
- Baker Fund
- Tides Foundation
- Harvard University Center for the Environment
- Green Memorial Fund of Harvard University
- Putnam Expeditionary Fund of the Museum of Comparative Zoology
- National Science Foundation Social and Economic Sciences [0750480]
- Green Memorial Fund
- National Science Foundation Postdoctoral Fellowship in Microbiology
- Department of Organismic and Evolutionary Biology at Harvard
- Miller Institute for Basic Research in Science
- University of California Berkeley
- Department of Zoology
- Field Museum of Natural History
- Singapore Ministry of Education [R-154 000-270-112]
- Divn Of Social and Economic Sciences
- Direct For Social, Behav & Economic Scie [0750480] Funding Source: National Science Foundation
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Ants are a dominant feature of terrestrial ecosystems, yet we know little about the forces that drive their evolution. Recent findings illustrate that their diets range from herbivorous to predaceous, with herbivores'' feeding primarily on exudates from plants and sap-feeding insects. Persistence on these nitrogen-poor food sources raises the question of how ants obtain sufficient nutrition. To investigate the potential role of symbiotic microbes, we have surveyed 283 species from 18 of the 21 ant subfamilies using molecular techniques. Our findings uncovered a wealth of bacteria from across the ants. Notable among the surveyed hosts were herbivorous turtle ants'' from the related genera Cephalotes and Procryptocerus (tribe Cephalotini). These commonly harbored bacteria from ant-specific clades within the Burkholderiales, Pseudomonadales, Rhizobiales, Verrucomicrobiales, and Xanthomonadales, and studies of lab-reared Cephalotes varians characterized these microbes as symbiotic residents of ant guts. Although most of these symbionts were confined to turtle ants, bacteria from an ant-specific clade of Rhizobiales were more broadly distributed. Statistical analyses revealed a strong relationship between herbivory and the prevalence of Rhizobiales gut symbionts within ant genera. Furthermore, a consideration of the ant phylogeny identified at least five independent origins of symbioses between herbivorous ants and related Rhizobiales. Combined with previous findings and the potential for symbiotic nitrogen fixation, our results strongly support the hypothesis that bacteria have facilitated convergent evolution of herbivory across the ants, further implicating symbiosis as a major force in ant evolution.
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