Elsa Youngsteadt, Satoshi Nojima, and Coby Schal. Department of Entomology, North Carolina State University, Charlotte, NC
Seed dispersal by ants occurs in more than 80 plant families worldwide. Typical ant dispersal, or myrmecochory, is a diffuse multi-species interaction driven by seed-borne nutritional rewards. This study addresses a unique and unexplained case of obligate, species-specific myrmecochory that is independent of nutrition: the Neotropical ant-gardens (AGs). In this mutualism, AG ants collect seeds of ten plant species and cultivate them in nutrient-rich arboreal nests, forming abundant hanging gardens throughout lowland Amazonia. The interaction between the AG ants and seeds is mediated by chemical cues, but the origin, identity, and evolutionary context of these chemicals is unknown. To characterize behavioral cues on AG seeds, solvent extracts of three species (Anthurium gracile, Codonanthe uleana, and Peperomia macrostachya) were subjected to chromatographic fractionation. To test behavioral activity, each fraction was applied to other seeds that ants ordinarily ignore. Treated seeds were paired with solvent blanks and presented to foraging AG ants. Solvent blanks were ignored, but at least one fraction of each seed extract elicited retrieval behavior in the AG ant Camponotus femoratus. The active fractions of the three species differed in polarity, and are being further analyzed by gas chromatograph-electroantennography, gas chromatography-mass spectrometry, and derivatization to identify individual components that will be tested for behavioral activity. While all AG seed species share a common interaction with ants, the results suggest that each seed species elicits the interaction with a different class of chemical attractants.
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