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 spectromet ric instrumentation, and statistically valid ethological methods, have allo wed the study of real events of chemical communication between elephants. S uch communication encompasses long- and short-range navigation, relationshi p recognition, and inter- and intra-sexual exchange of reproductive conditi on, metabolic state, and social status. Asian elephants emit large amounts of complex chemical mixtures in breath and urine, and in secretions from th e temporal gland, inter-digital glands, and ears. Some emitted chemicals or iginate in blood and may be metabolic products; others are secretory produc ts, ar times apparently under hormonal control. The wide variety of emitted compounds includes hormones, proteins, and volatile compounds; selected vo latile ketones and an acetate (Z)-7-dodecenyl acetate) function as chemical signals and a pheromone, respectively. Some of these specific chemicals id entified in emissions from Asian elephants dwelling in the United States ha ve been found to be present in exudates from elephants in India. This simil arity 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, metabo lites, brain chemistry, and possible primer pheromones. For females, the fa ctors influencing possible estrous synchrony, what role primer pheromones p lay 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. (C) 2000 Wiley- Liss, Inc.