Cheetah (Acinonyx jubatus)- Data, Pictures & Videos

[Acinonyx sp.]

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4. How Is Olfaction Linked to Reproduction?

4.1. The Effect of Pheromones on Behaviour

Although it is true that non-chemical signals, such as hearing and visualization, the physiological state, as well as the experience the animal has had in the past, are a necessity for eliciting behavioural responses [54], it has already been stated many times that semiochemicals directly affects an animal’s behaviour [12]. This is especially behaviour related to locomotion, interactions with other animals and reproduction [11,67]. The observed effects that pheromones have on an animal’s behaviour are correlated with the animal’s endocrine status [14]. The stereotypical behaviours caused by pheromones may be an unconscious response to this particular group of odours [16].

In predator-prey relationships, prey animals will exhibit defensive behaviour and try to escape once detecting the odour of a predator [68]. The semiochemicals in the urine of a dominant animal act to suppress the physiology, as well as the reproductive behaviour (such as a decrease in the rate of marking), of the subordinate animal [14].

Pheromones involved with reproductive behaviour are used as a way of attracting the opposite sex [11] and acts as an aphrodisiac in causing the appropriate precopulatory and copulatory responses [14]. The odour of a boar increases the receptivity of a female to sexual interactions, as well as promotes lordosis in 50–60% of females in oestrus [10]. Aggressive behaviour is another known response to reproductive pheromones, although it is not always just the reproductive behaviour of an animal that is affected, but the reproductive physiology as well. Pheromones have been known to accelerate puberty [12] and stimulate the onset of oestrus [69].

4.2. Captive Breeding

Captive breeding of cheetahs occurred in response to the rapid decrease in cheetah population numbers over the past years; therefore, it initially aimed at increasing numbers, with the management of the last free-roaming cheetahs regarded as important for the species’ overall survival [37]. Unfortunately, cheetahs were found to be difficult to breed in captivity, even when there was no difference in nutrition, health, genetics, the function of the hypophysis, seminal quality in males, and anatomy of the reproductive tract in females [6,9,12,17,24,70,71].

Various behavioural methods were attempted by zoological facilities to rectify this and increase breeding success for cheetahs. Whereas some of these attempts have resulted in success, not one method was proven to work at all the various facilities. The key to success was said to be based on the knowledge of the reproductive behaviour of free-roaming cheetahs [21], as well as th cheetah’s natural social conditions, such as adhering to their solitary nature [9] and keeping breeding females separate [17]. With these management methods in place, females are observed for any behavioural signs that are indicative of oestrus [70], although this has proven to be very difficult in determining when females are actually on oestrus [6] and negatively affects the occurrence of breeding introductions [17].

Allowing each individual animal to choose their own mate is a significant part of successful breeding [72]. By using the correct housing and breeding management methods, the Ann van Dyk Cheetah Centre in South Africa (Brits, South Africa), previously known as de Wildt, has been very successful in breeding with cheetahs. It was found that the presence of male cheetahs around the females is the best method to detect when a female is on oestrus by observing her for any changes in behaviour towards the males [22]. Males are released into a walkway known as “lover’s lane” located between the female enclosures in order to smell which females are on oestrus [50]. The presence of the males has been noted to trigger the oestrous cycle in females, with interactions between the sexes resulting in a display of oestrous behaviour after the female walks towards the males in the walkway [22].

Another successful breeding method used at Wassenaar Wildlife Breeding Centre in the Netherlands (Wassenaar, The Netherlands) includes the utilization of one enclosure by the male and the female in turns. They are not allowed any direct visual or physical contact at first and are each observed according to their reaction to each other’s scent. Only after a lot of interest has been shown by both to the other’s scent, and the male starts stutter-calling or “yipping”, they are allowed visual exposure to one another. Females are observed once again for any aggression towards the male before physical introductions are allowed. If the female does not roll for the male or display oestrous behaviour then they are once again separated [73].

From the above methods, it can be speculated that semiochemicals play an important role in the initial process of breeding at Wassenaar, whereas they only seem to come into play during the last stage of the breeding process at the Ann van Dyk centre. Nevertheless, the breeding results achieved from both facilities prove that cheetahs can be bred successfully in captivity without the need for assisted reproductive techniques, as well as emphasizes the role that semiochemicals play in cheetah courtship.

5. Semiochemicals
Semiochemicals are defined as chemical substances released by a life form that instigates a physiological or behavioural reaction from another living organism [74,75]. The earliest and most studies on semiochemicals have been on insects [14]. Semiochemicals have since been classified according to the relationship between the individual that released the chemical signal and the individual that received the signal [14], thus resulting in changes to the behaviour and/or physiology of the receiver. Semiochemicals that act as chemical signals between individuals of the same species (intraspecific) are classified as pheromones, whereas chemical signals acting between members of two different species (interspecific) are classified as allelochemicals [12].
Pheromones can be both odorous, thus originating from volatile chemical compounds, or non-odorous, which are from non-volatile chemical compounds [11]. Pheromones are divided into two categories based on the response to the chemical signal, namely releasers and primers. Releasers are pheromones that result in an immediate response in the behaviour of the receiver [11] and are otherwise known as signalling pheromones involved in communication [11,12]. Primers act along with the nervous system of an animal and generate a physiological response after a longer period of time [11]; therefore, primers affect mainly the endocrine system [14].

5.1. Complex vs. Single Compounds

There has been very little evidence to support the theory that a chemical signal is reliant on a number of chemical compounds [52] and it has been shown that a single chemical compound is as efficient as a mixture of compounds in evoking a behavioural response [76]. The fact that multiple chemical compounds, with each coding for the same or similar chemical signal/behavioural response, are released in scent markings is because the interaction of the chemical compounds increases detection of the signal, memorization, and learning of different chemical signals released by different species, such as those released by predators, as well as discrimination between different chemical signals [77].

5.2. Semiochemicals in Communication

Semiochemicals that are involved in communication act between animals/organisms that have more advanced olfactory systems, with which they rely on more than they do with hearing or vision [11,12]. Scent-marking releases a large amount of volatile and non-volatile chemical compounds that are usually present at low concentrations. The different concentrations of chemical compounds could be important with reference to the message that is sent [78]; and could release specific characteristic odours, although exactly what compounds are inhaled and how they are analysed by the animal has not yet been fully discovered [11].

Territorial marking, identification of neighbours, detection of larger predators and food/prey, signalling of alarm and attraction of members of the opposite sex are all functions of scent-marking [12,14,19,54]. Scent marks, in fact, also provide information on the animal’s sex, age and the reproductive state of females [14,19], which is also an indication of whether or not she is sexually receptive [79]. Genetic relatedness and compatibility of future mates can also be assessed from scent marks [54].

5.3. Identification of Individuals through Semiochemicals

Determining whether individuals have their own specific body odour, or ‘biochemical fingerprint’ or not, has become a topic of increasing interest since the identification of individuals through semiochemicals is of great significance [54]. Soso, [11] stated that semiochemicals in exocrine secretions (scent marks), which can be complex or simple mixtures, code for individuality based on the amount and the presence of particular chemical compounds. This has also been confirmed in humans where volatile compounds, identified from the sweat, urine and saliva, were shown to be both individual and gender-specific [80]. It has also been demonstrated that dogs could discriminate between the body odours of several different humans. This study showed that the dogs were able to differentiate the body odours of not only individuals of the same family, but between a set of twins as well [81]. In previous studies done with lions, over 50 volatile chemical compounds were identified in the marking fluid, with each individual having a different chemical composition [82]. Seven chemical compounds were found in the marking fluid of almost all the lions, and therefore, it is possible that some, or all of these compounds, are involved in species identification, either individually or in a combination [78].

5.4. Semiochemicals in Cheetahs

Although many studies have proved the importance of semiochemicals in domestic and wild felids [11,14,54,62,63,64,78,83], very little is known about their role in cheetahs.

Unfortunately, cheetah urine itself has not acquired much interest from scientists, probably due to the very little amount of odour it emits [26]. As reported by Visser [12], who analysed the urine of three males and two females, and Burger et al. [26], who analysed the urine of six males and one female, there was a much wider variety of volatile constituents identified in female urine than male urine. The constituents that were common in the males from both studies included that of 2-butanone, phenol, hexanal, octanal, nonanal, benzaldehyde, 2-pentanone, 2-hexanone, 2-heptanone, 3-pentanone, 4-heptanone, 3-hexanone, acetophenone, cyclohexanone, 3-methylcyclopentanone, ethyl propyl ether, butyl ethyl ether, butyl propyl ether, dimethyl disulfide, dimethyl sulfone, sulfur S6, sulfur S8 and urea. Of these compounds, only a few are known to be involved in certain behaviours in various species such as 2-butanone, phenol, octanal, nonanal, benzaldehyde, 2-pentanone, 4-heptanone, acetophenone, cyclohexanone, 3-methylcyclopentanone and dimethyl disulfide [10,11,51,67]. Many of the abovementioned compounds have been identified in the marking fluid/urine of various other feline species as well. These compounds, together with the animals in which they have been found and the behaviour they elicit are listed in Table 1.

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5.5. Current Uses of Synthetic Scent to Influence Behaviour and Its Potential Use in Cheetahs

Providing enrichment for captive animals aims mainly to improve the welfare of the animals [89] by decreasing stress and improving natural and, therefore, reproductive behaviour as well [90]. Pheromones are used quite frequently in captive facilities as a form of olfactory enrichment by introducing new scents or objects that have been scented to an animal’s enclosure [91]. Felids display cheek rubbing behaviour as a result of the use of novel scents (e.g., perfume for behavioural enrichment in zoological parks) [92]; lions respond to olfactory enrichment by behaving more socially and displaying an increase in the activity and frequency of various behaviours [76]. Besides enrichment, semiochemicals have also been specifically used for reproductive purposes in some species. For instance, synthetic boar pheromone is used to identify when a sow is on oestrus. These pheromones are already produced and sold on a commercial level in aerosol cans [51]. A synthetic scent known as Feliway® has proven useful in lowering the level of corticosteroid metabolites in the faeces of tigers after artificial insemination operation procedures [67].

With regards to cheetahs, since the presence/odour of a male cheetah has been noted to trigger the oestrous cycle in the females [22,73] and the scent is known to play an important role in reproduction with cheetahs as well as other felids [21,39,62,63,70,73,88,93], there is an opportunity to further investigate the role of semiochemicals in cheetahs and their possible use to improve oestrus behaviours for successful mating. For instance, it could be possible to use a synthetic or natural scent in cheetahs as well in order to increase the frequency of oestrus behaviours displayed in younger females to ensure successful mating when the females are introduced to the males.

6. Conclusions
The overall cheetah population is currently listed as vulnerable, with a decreasing population trend [2]. The management of the last free-roaming cheetahs is therefore regarded as important for the species’ overall survival [37]. Captive breeding of cheetahs occurred in response to the rapid decrease in numbers in the past and therefore is aimed at increasing cheetah population numbers with a higher genetic variety when compared to their wild counterparts. This would lead to the creation of a sustainable, healthy population of cheetahs that would be able to survive after possible reintroduction [8,9,37]. Despite the fact that reproduction in wild cheetahs is not an issue, cheetahs were found to be difficult to breed in captivity [6,7,9,12,17,23,24,71,94].
The key to success is based on the knowledge of the reproductive behaviour of free-roaming cheetahs [21] and, therefore, managing individuals according to their natural social conditions [71]. This would include keeping males and females in separate enclosures and only introducing pairs during mating [9] and keeping breeding females separate since even small amounts of social aggression acts to suppress the oestrous cycle [17]. Using male cheetahs to detect when a female is on oestrus [22] and allowing each individual animal to choose their own mate also played a significant part in ensuring successful breeding [72].
Since female cheetahs are susceptible to the effects of asymmetric reproductive aging (ARP), it would be necessary for them to breed when they are still young adults in order to prevent this aging process [8], such as after reaching sexual maturity at 20–24 months of age [1]. Unfortunately, females younger than the age of four years display a significantly lower frequency of characteristic oestrous behaviour than females older than the age of six years [9], this means that even though a male is still able to detect a female on oestrus by her scent, if she does not display oestrus behaviour, he will not be able to find her [50] and the chance of mating is severely reduced.
Intraspecific semiochemicals [12] that are involved with reproductive behaviour are used as a way of attracting the opposite sex [11] and acts as an “aphrodisiac” in causing the appropriate precopulatory and copulatory responses [14]. These semiochemicals are synthesized by an animal [54] and released as exocrine secretions to create a ‘scent-mark’ [11], such as urine and marking fluid [67].
Since the presence/odour of a male cheetah has been noted to trigger the oestrous cycle in the females [22,73] and the scent is known to play an important role in reproduction with cheetahs as well as other felids [7,21,39,62,63,73,88,93], if one were to analyse the chemical compounds in the marking fluid of male cheetahs (with a specific focus on high impact odorants), it could lead to the identification of a single compound (or a limited number of compounds in a mixture) that would be able to increase the frequency of reproductive behaviour displayed by the females in the hopes that intercourse and pregnancy would occur at a higher rate.

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