Abstract
In lowland Amazonian rainforests, specific ants collect seeds of several plant species and cultivate them in arboreal carton nests, forming species-specific symbioses called ant-gardens (AGs). In this obligate mutualism, ants depend on the plants for nest stability and the plants depend on ant nests for substrate and nutrients. AG ants and plants are abundant, dominant members of lowland Amazonian ecosystems, but the cues ants use to recognize the seeds are poorly understood. To address the chemical basis of the ant-seed interaction, we surveyed seed chemistry in nine AG species and eight non-AG congeners. We detected seven phenolic and terpenoid volatiles common to seeds of all or most of the AG species, but a blend of the shared compounds was not attractive to the AG ant Camponotus femoratus. We also analyzed seeds of three AG species (Anthurium gracile, Codonanthe uleana, and Peperomia macrostachya) using behavior-guided fractionation. At least one chromatographic fraction of each seed extract elicited retrieval behavior in C. femoratus, but the active fractions of the three plant species differed in polarity and chemical composition, indicating that shared compounds alone did not explain seed-carrying behavior. We suggest that the various AG seed species must elicit seed-carrying with different chemical cues.
Highlights
In the ant-garden (AG) mutualism, arboreal ants collect seeds of specific epiphytic plants and cultivate them in nutrient-rich carton nests
In lowland Amazonia, foraging territories of AG ants can occupy more than one third of forest area, depending on habitat type, and AG ants are the most frequently encountered and numerically abundant species in arboreal ant samples [1,6,7]
In the case of AG ants, this independence is inseparably linked to the epiphytic mutualism, because the longterm structural integrity of the large carton nests depends on AG plants, which dry the nest by transpiration and provide shelter from heavy rains [8,9]
Summary
In the ant-garden (AG) mutualism, arboreal ants collect seeds of specific epiphytic plants and cultivate them in nutrient-rich carton nests. Further studies of P. macrostachya indicated that a blend of terpenoid and phenolic volatiles, including 6-MMS but not the other previously identified compounds, elicited olfactory attraction but not seed-carrying in C. femoratus [5]. Behavior-guided extraction and fractionation Seed extracts of three AG plant species, A. gracile, C. uleana, and
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