How chemical signals integrate Asian elephant society: The known and the unknown

The importance of chemical senses to elephants was recognized in anecdotal observations by ancient humans. Modern scientific tools, such as molecular biological techniques, highly sensitive gas chromatographic/mass spectrometric instrumentation, and statistically valid ethological methods, have allowed the study of real events of chemical communication between elephants. Such communication encompasses long- and short-range navigation, relationship recognition, and inter- and intra-sexual exchange of reproductive condition, metabolic state, and social status. Asian elephants emit large amounts of complex chemical mixtures in breath and urine, and in secretions from the temporal gland, inter-digital glands, and ears. Some emitted chemicals originate in blood and may be metabolic products; others are secretory products, at times apparently under hormonal control. The wide variety of emitted compounds includes hormones, proteins, and volatile compounds; selected volatile ketones and an acetate ((Z)-7-dodecenyl acetate) function as chemical signals and a pheromone, respectively. Some of these specific chemicals identified in emissions from Asian elephants dwelling in the United States have been found to be present in exudates from elephants in India. This similarity is demonstrable for three metabolic conditions: pregnancy in females and pre- and post-musth in males. Future chemical communication studies on male elephants should focus on musth and its relevance to reproduction and male social structures. Such investigations should include hormones, metabolites, brain chemistry, and possible primer pheromones. For females, the factors influencing possible estrous synchrony, what role primer pheromones play in female reproduction, how chemical signals influence social behavior, and whether luteinizing hormone influences pheromone production are among remaining fundamental questions. Zoo Biol 19:405–423, 2000. © 2000 Wiley-Liss, Inc.