Honest signalling through chemicals by elephants with applications for care and conservation

Chemical Conversations

Among living organisms, higher animals primarily use a combination of vocal and non-verbal cues for communication. In other species, however, chemical signaling holds a central role. The chemical and biological activity of the molecules produced by the organisms themselves and the existence of receptors/targeting sites that allow recognition of such molecules leads to various forms of responses by the producer and recipient organisms and is a fundamental principle of such communication. Chemical language can be used to coordinate processes within one species or between species. Chemical signals are thus information for other organisms, potentially inducing modification of their behavior. Additionally, this conversation is influenced by the external environment in which organisms are found. This review presents examples of chemical communication among microorganisms, between microorganisms and plants, and between microorganisms and animals. The mechanisms and physiological importance of this communication are described. Chemical interactions can be both cooperative and antagonistic. Microbial chemical signals usually ensure the formation of the most advantageous population phenotype or the disadvantage of a competitive species in the environment. Between microorganisms and plants, we find symbiotic (e.g., in the root system) and parasitic relationships. Similarly, mutually beneficial relationships are established between microorganisms and animals (e.g., gastrointestinal tract), but microorganisms also invade and disrupt the immune and nervous systems of animals.

Asian elephants distinguish sexual status and identity of unfamiliar elephants using urinary odours

Despite the ubiquity of odours in mammals, few studies have documented the natural olfactory abilities of many 'non-model' species such as the Asian elephant. As Asian elephants are endangered, we may apply odours to more effectively manage threatened populations. We implemented a habituation-discrimination paradigm for the first time in Asian elephants to test the ability of elephants to discriminate between unfamiliar male elephant urine, hypothesizing that elephants would successfully distinguish non-musth from musth urine and also distinguish identity between two closely related individuals. We conducted two bioassay series, exposing three female and three male zoo-housed elephants to the same urine sample (non-musth urine in the first series, and urine from an unfamiliar individual in the second) over 5 days. On the sixth day, we simultaneously presented each elephant with a novel sample (either musth urine or urine from a second unfamiliar individual) alongside the habituated urine sample, comparing rates of chemosensory response to each sample to indicate discrimination. All elephants successfully discriminated non-musth from musth urine, and also urine from two unfamiliar half-brothers. Our results further demonstrate the remarkable olfactory abilities of elephants with promising implications for conservation and management.

Brown bear skin-borne secretions display evidence of individuality and age-sex variation

Scent originates from excretions and secretions, and its chemical complexity in mammals translates into a diverse mode of signalling. Identifying how information is encoded can help to establish the mechanisms of olfactory communication and the use of odours as chemical signals. Building upon existing behavioural and histological literature, we examined the chemical profile of secretions used for scent marking by a solitary, non-territorial carnivore, the brown bear (Ursus arctos). We investigated the incidence, abundance, and uniqueness of volatile organic compounds (VOCs) from cutaneous glandular secretions of 12 wild brown bears collected during late and post-breeding season, and assessed whether age-sex class, body site, and individual identity explained profile variation. VOC profiles varied in the average number of compounds, compound incidence, and compound abundance by age-sex class and individual identity (when individuals were grouped by sex), but not by body site. Mature males differed from other age-sex classes, secreting fewer compounds on average with the least variance between individuals. Compound uniqueness varied by body site and age for both males and females and across individuals. Our results indicate that brown bear skin-borne secretions may facilitate age-sex class and individual recognition, which can contribute towards further understanding of mating systems and social behaviour.

The size of a smell: assessment of rival’s relative size from femoral secretions in the common wall lizards, Podarcis muralis (Laurenti, 1768)

Animal communication depends on signals conveying information to a receiver who must perceive and decode them. Signals involved in territoriality are usually complex stimuli that should be correctly interpreted to avoid unnecessary conflicts. Lacertids use both visual and chemical stimuli in modulating their aggressive response against conspecifics and the rival’s size is one of the most important information, affecting the success probability in combat. To assess the actual ability of decoding information about a rival’s size based on its chemical stimulus alone, 60 males of Podarcis muralis were tested for three consecutive days in an arena bearing a mirror (to simulate an equal-sized intruder), and the chemical cues (femoral secretions) from an unknown individual of different size. Significant differences were observed in tongue-flicks number, which grew as the size difference between the focal lizard and the secretion donor decreased. This can be interpreted as the need for the lizard to better evaluate the potential competitor’s characteristics. The size difference also affected the number of bites against the mirror. They increased when the size of the focal lizard was larger than the donor triggering the aggressive response with a higher probability of winning the contest. This confirms that the focal lizard had correctly decoded the information about the opponent’s size by chemical stimulus. Although previous studies have shown that some components of the chemical signals are potentially informative about the signaler’s size, this is the first demonstration that male P. muralis is actually able to decode and use such information.

Male African Elephant (Loxodonta africana) Behavioral Responses to Estrous Call Playbacks May Inform Conservation Management Tools

Simple Summary

During annual periods of heightened sexual activity (musth), male African elephants expend a significant amount of energy communicating their reproductive status, as well as searching and competing for potential mates. To locate females, musth males may risk venturing outside protected areas and into landscapes shared with humans where conflict between wildlife and people can occur. Adverse interactions between elephants and people can be detrimental to human livelihoods, resulting in negative attitudes towards elephants and, in some cases, retaliatory killings. Interactions with aggressive musth males can also be life-threatening to community members who attempt to confront them. Mitigation strategies that effectively target the reproductive motivations of musth males may offer solutions as the human–elephant interface continues to expand. In this study, we build on earlier research showing that playbacks of female elephant reproductive calls, (i.e., estrous rumbles) can change the movement trajectory and behavior of male elephants in Etosha National Park, Namibia. Individuals belonging to three male groups were opportunistically subjected to playback experiments and evaluated based on their reaction intensity. Our results demonstrate that mature musth adults are more likely to change directions and approach the source of a female’s estrous call than mature, sexually-inactive adult elephants. We also show that post-dispersal young males that were not in musth also respond strongly to the stimulus. These findings support further exploration of mitigation solutions that incorporate elephant behavior, reproductive status, and context-specific vocalizations.

Abstract

Driven by reproductive motives, male African elephants (Loxodonta africana) in musth often expand their home ranges to locate estrous females. This extended range, coupled with heightened aggression often observed in musth males, can be particularly problematic in regions where human-modified landscapes and elephant territories increasingly overlap. Several mitigation tools have been tested to resolve a wide range of human–elephant conflicts with varying degrees of success due to geographical disparities and habituation. We present findings on the potential application of estrous call playbacks in manipulating the behavior and movement of male elephants non-invasively, particularly mature musth adults and younger post-dispersal males, in Etosha National Park. Estrous vocalizations were presented across 26 experimental trials to mature musth adults (n = 5), mature non-musth adults (n = 6), and non-musth males belonging to younger, post-dispersal age classes (n = 8), with behavioral responses scored on a gradient scale from 0–1. Both mature musth adults and younger non-musth elephants were significantly more likely to respond with the highest intensity by approaching the acoustic source compared to mature non-musth adults that avoided the call. However, younger males tested in the presence of an older, higher-ranking male tended to react with a lower intensity than those tested alone. This result likely demonstrates the influence of social hierarchy and associations on male elephant behavior. We also observed a significant increase in physiological response, measured by defecation rate, across all male groups in response to the estrous call playbacks. Our findings suggest that using estrous calls as acoustic deterrents may effectively and non-invasively aid in reducing tension at the human–elephant interface, depending on the age, social context, and reproductive status of the male elephant.

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

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.

Chemical signals in terrestrial vertebrates: search for design features

We review current information on intraspecific chemical signals and search for patterns in signal chemistry among modern terrestrial vertebrates (Amniota), including tortoises, squamate reptiles (amphisbaenians, lizards, and snakes), birds, and mammals.

Analytical methods for chemical and sensory characterization of scent-markings in large wild mammals: a review

In conjoining the disciplines of "ethology" and "chemistry" the field of "Ethochemistry" has been instituted. Ethochemistry is an effective tool in conservation efforts of endangered species and the understanding of behavioral patterns across all species. Chemical constituents of scent-markings have an important, yet poorly understood function in territoriality, reproduction, dominance, and impact on evolutionary biology, especially in large mammals. Particular attention has recently been focused on scent-marking analysis of great cats (Kalahari leopards (Panthera pardus), puma (Puma concolor) snow leopard (Panthera uncia), African lions (Panthera leo), cheetahs (Acinonyx jubatus), and tigers (Panthera tigris)) for the purpose of conservation. Sensory analyses of scent-markings could address knowledge gaps in ethochemistry. The objective of this review is to summarize the current state-of-the art of both the chemical and sensory analyses of scent-markings in wild mammals. Specific focus is placed on sampling and sample preparation, chemical analysis, sensory analysis, and simultaneous chemical and sensory analyses. Constituents of exocrine and endocrine secretions have been most commonly studied with chromatography-based analytical separations. Odor analysis of scent-markings provides an insight into the animal's sensory perception. A limited number of articles have been published in the area of sensory characterization of scent marks. Simultaneous chemical and sensory analyses with chromatography-olfactometry hyphenation could potentially aid conservation efforts by linking perceived odor, compounds responsible for odor, and resulting behavior.

Gender and sexual behavior modulate the composition of serum lipocalins in Nile tilapia (Oreochromis niloticus)

In tilapia species, plasma lipoproteins with high electrophoretic mobility function in intra- and intergender communication. Blood samples taken at onset and peak of daily sexual activity from dominant and subordinate Oreochromis niloticus males and females were fractionated by native gel electrophoresis and the fast-migrating proteins were subjected to mass spectrometry. Mining the sequence data of the Cichlid Genome Consortium, we identified 11 proteins from the lipocalin super-family and characterized their genes' structures. Phylogenetic and structural analyses subdivided these genes into two classes: (I) 3-coding-exon apolipoproteins and (II) more complex 6-coding-exon sulfide-bond-containing lipocalins. Five apolipoproteins and PTGDSL1, TBTBP, and MSP proteins were modulated by gender and sexual behavior. PTGDSL1 protein was only observed in the plasma serum of dominant males. However, the cysteine residue in the position that is crucial for synthetase activity in mammalian prostaglandin D synthetases was not conserved in PTGDSL1 or PTGDSL2 proteins. In line with previous reports suggesting their involvement in male functions as pheromone transporters, TBTBP and MSP proteins were not detected in females at the onset of daily activity. Their increasing amount in males was concordant with the increase in apolipoproteins AFP4L, APOA4a, APOA4b, APO14kD and APOC2, which were detected exclusively in dominant males, indicating a possible role in mobilization of the energy required to maintain their social hierarchy.

Why do African elephants (Loxodonta africana) simulate oestrus? An analysis of longitudinal data

Female African elephants signal oestrus via chemicals in their urine, but they also exhibit characteristic changes to their posture, gait and behaviour when sexually receptive. Free-ranging females visually signal receptivity by holding their heads and tails high, walking with an exaggerated gait, and displaying increased tactile behaviour towards males. Parous females occasionally exhibit these visual signals at times when they are thought not to be cycling and without attracting interest from musth males. Using demographic and behavioural records spanning a continuous 28-year period, we investigated the occurrence of this “simulated” oestrus behaviour. We show that parous females in the Amboseli elephant population do simulate receptive oestrus behaviours, and this false oestrus occurs disproportionately in the presence of naïve female kin who are observed coming into oestrus for the first time. We compare several alternative hypotheses for the occurrence of this simulation: 1) false oestrus has no functional purpose (e.g., it merely results from abnormal hormonal changes); 2) false oestrus increases the reproductive success of the simulating female, by inducing sexual receptivity; and 3) false oestrus increases the inclusive fitness of the simulating female, either by increasing the access of related females to suitable males, or by encouraging appropriate oestrus behaviours from female relatives who are not responding correctly to males. Although the observed data do not fully conform to the predictions of any of these hypotheses, we rule out the first two, and tentatively suggest that parous females most likely exhibit false oestrus behaviours in order to demonstrate to naïve relatives at whom to direct their behaviour.

Age and seasonal changes in the semiochemicals of the sternal gland secretions of male koalas (Phascolarctos cinereus)

Male koalas communicate with conspecifics using scent markings from their sternal scent gland. We examined age and seasonal changes in the profile of organic compounds produced by koala sternal glands. Scent exudates from 12 male koalas were collected over a one-year period and analysed by direct-injection gas chromatography–mass spectrometry (GC–MS) of the methanol extract. Carboxylic acids, aldehydes, ketones, and alcohols were found to dominate the scent mixture. Thirty-seven compounds were identified by comparison of their spectra with those in the Wiley 138K library. The identity, complexity and relative concentrations of these compounds were found to vary both seasonally and by age of the individuals, with the most odorous and complex mixtures occurring during the mating season. We suggest that seasonal and age differences in the complexity of the chemical composition of the koala scent gland exudate provides evidence that olfactory communication probably has important ramifications for male reproductive success in the wild.