The Chemical Ecology of Elephants: 21st Century Additions to Our Understanding and Future Outlooks

Abstract

Chemical signals are the oldest and most ubiquitous means of mediating intra- and interspecific interactions. The three extant species of elephants, the Asian elephant and the two African species, savanna and forest share sociobiological patterns in which chemical signals play a vital role. Elephants emit secretions and excretions and display behaviors that reveal the importance of odors in their interactions. In this review, we begin with a brief introduction of research in elephant chemical ecology leading up to the 21st century, and then we summarize the body of work that has built upon it and occurred in the last c. 20 years. The 21st century has expanded our understanding on elephant chemical ecology, revealing their use of odors to detect potential threats and make dietary choices. Furthermore, complementary in situ and ex situ studies have allowed the careful observations of captive elephants to be extended to fieldwork involving their wild counterparts. While important advances have been made in the 21st century, further work should investigate the roles of chemical signaling in elephants and how these signals interact with other sensory modalities. All three elephant species are threatened with extinction, and we suggest that chemical ecology can be applied for targeted conservation efforts.

An odorant-binding protein in the elephant's trunk is finely tuned to sex pheromone (Z)-7-dodecenyl acetate

“…Communication between sexes in elephants has been mainly studied at the chemical and behavioural level, thanks to the long and accurate work of the late Elizabeth Rasmussen and her collaborators, who continued her research producing several interesting and unique results 2 . Two sex pheromones were first identified in the Asian elephant: ( Z )-7-dodecenyl acetate, which is released in the urine of pre-ovulatory females, and frontalin {1,5-dimethyl-6,8-dioxabicyclo[3.2.1]octane}, the main component of the male temporal gland secretion (TGS) during musth 3 – 8 .…”

Reverse chemical ecology indicates long-chain aldehydes as new potential semiochemicals for the African elephant Loxodonta africana

“…Our list also included some classes of insect pheromones, such as homologous series of longchain linear alcohols, aldehydes, esters and fatty acids, as well as γ-lactones and macrocyclic ketones. In fact, the adoption of similar or even identical chemical structures as pheromones by insects and mammals is well documented, in particular in elephants (Schulte and LaDue, 2021;Voznessenskaya et al, 2022). LafrOBP2 proved to be tuned to linear unsaturated C16-aldehydes with dissociation constants between 2.4 and 3.4 μM.…”

“…The long and detailed work of the late Elizabeth Rasmussen and her collaborators have provided a wealth of interesting and accurate information on the chemical ecology of elephants, in particular regarding chemical signals exchanged between sexes (Rasmussen et al, 1993;Rasmussen and Schulte, 1998;Schulte and LaDue, 2021). Interestingly, the discovery that (Z)-7dodecenyl acetate, a well-known component of the pheromonal blend of a large number of Lepidoptera, was also a pheromone for the elephants revealed for the first time the now well documented fact that insects and mammals often share the same volatile semiochemicals (Goodwin et al, 2006;Voznessenskaya et al, 2022).…”

“…Several volatile compounds were identified in different secretions of the elephants and their roles as pheromones or semiochemicals have been clearly established in accurate behaviour studies (Schulte and LaDue, 2021). The first compound to be identified as a pheromone was (Z)-7-dodecenyl acetate, which is found in the urine of pre-ovulatory females of the Asian elephant (Rasmussen et al, 1996(Rasmussen et al, , 1997, and elicits strong and frequent chemosensory responses, including flehmen, from male elephants in preparation to mating.…”

Sound Visualization Demonstrates Velopharyngeal Coupling and Complex Spectral Variability in Asian Elephants

“…Elephants have evolved the longest and one of the most sophisticated vocal tract elongations in mammals, the trunk [ 3 ]. Hence, this flexible muscular hydrostat plays a crucial role in their acoustic communication, apart from serving as a multipurpose tool for manipulating food and objects [ 3 , 4 , 5 ], for sensory information and for tactile, chemical, and gestural communication [ 6 , 7 , 8 , 9 ]. The three recent elephant species—the African savannah elephant ( Loxodonta africana , henceforth African elephant), African forest elephant ( Loxodonta cyclotis ) and Asian elephant ( Elephas maximus )—share 8 to 10 call types that appear to constitute a rather limited vocal repertoire at first sight but actually exhibits an impressive flexibility in within-call–type variation and the combinations of trunk and laryngeal sounds [ 10 , 11 ].…”