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

Abstract

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.

Extreme expansion of the olfactory receptor gene repertoire in African elephants and evolutionary dynamics of orthologous gene groups in 13 placental mammals

“…The African elephant genome contained ;2000 functional genes and >2200 pseudogenes, which is by far the largest OR gene repertoire among the genomes examined. The large repertoire of elephant OR genes might be attributed to elephants' heavy reliance on olfaction in various contexts, including foraging, social communication, and reproduction (Langbauer 2000;Rasmussen and Krishnamurthy 2000). In fact, the Asian elephant (Elephas maximus) is among the few mammalian species for which a sex pheromone has been chemically identified (Rasmussen et al 1996(Rasmussen et al , 1997.…”

Asian Elephants (Elephas maximus) Discriminate Between Familiar and Unfamiliar Human Visual and Olfactory Cues

“…The results for the frequency of trunk reaches support previous studies on Asian and African elephants' olfactory abilities. Previous studies on Asian elephants have shown that they can discriminate between odors with similar chemical structures (Arvidsson et al, 2012) and have long-term odor memory (Rasmussen & Krishnamurthy, 2000). African elephants have also been shown to be capable of detecting human scent on cloths a distance of 10 m away (Bates et al, 2007).…”

Elephant cognition in primate perspective

“…Sources of odours used in chemical communication between elephants include urine, faeces, saliva and secretions from the temporal gland, a large multi-lobed sac with an orifice mid-way between the ear and eye (Langbauer, 2000;Rasmussen & Krishnamurthy, 2000). Elephants can frequently be seen to raise their trunks up in the air to smell, or use the tips of their trunks to explore the ground, for urine spots and faecal matter, as well as the genitals, temporal glands, or mouths of other elephants (Rasmussen & Krishnamurthy, 2000).…”

“…Elephants can frequently be seen to raise their trunks up in the air to smell, or use the tips of their trunks to explore the ground, for urine spots and faecal matter, as well as the genitals, temporal glands, or mouths of other elephants (Rasmussen & Krishnamurthy, 2000).…”