NEOTROPICAL ANT GARDENS .1. CHEMICAL-CONSTITUENTS

In ant gardens of lowland Amazonia, parabiotic ant species Camponotus femoratus and Crematogaster cf. limata parabiotica cultivate a taxonomically diverse group of epiphytic plants, whose establishment is restricted to arboreal carton ant nests. Epiphyte seeds are collected by workers of Ca. femoratus, the larger of the two ants, and stored unharmed in brood chambers where they subsequently germinate. Although seeds of some ant-garden epiphytes bear nutritional rewards, previous studies have shown that these rewards are not sufficient to explain the pattern of ant attraction to seeds. Five aromatic compounds occur frequently in and on the seeds of most ant-garden epiphytes and may be chemical cues by which ants recognize propagules of their symbiotic plants. The most widely distributed of these is methyl 6-methylsalicylate [6-MMS]1, previously reported as a major mandibular gland product in related Camponotus species and present in trace quantities in Ca. femoratus males. (-)-Citronellol 6 (previously unreported in Camponotus) was the principal volatile constituent in extracts of male heads, and (-)-mellein 7 was present in small quantities. Discovery of 6-MMS inside the mandibular glands of male Ca. femoratus (and its presence in analogous glands of related ants) offers preliminary support for Ule's (1906) hypothesis that seeds attract ants by mimicking ant brood. In addition, the likely fungistatic activity of seed compounds suggests that they could retard microbial pathogens of ants and plants in the organic detritus of nest gardens. While the presence of identical seed compounds in so many unrelated plant lineages might represent a remarkable case of convergent evolution, other interpretations are possible. © 1990 Plenum Publishing Corporation.