Venomous Knowledge: April 2014

Slow lorises are the only venomous primates. They do not have venom glands; instead, their saliver mixes with the secretion of their brachial glands on their arms to produce the venomous fluid. Their anterior incisors, or tooth comb, are normally used for feeding and grooming, but are also an effective venom delivery system. When threatened, the slow loris raises its arms above its head, allowing it to move its mouth to its glands to combine fluids if need be. The fluid is either applied to the top of the head for defence, or kept in the mouth to bite the threat (Nekaris, et al., 2013).

Slow loris bites are intensely painful and the wound can retain fluid, fester and heal very slowly. There is also a high chance the wound will scar. Due to the illegal pet trade in Asia, people are often bitten by slow lorises. There have been two cases where owners have almost died because they were bitten by their pet lorises. These people, who were allergic to cats, went into anaphylactic shock because the loris' gland extract shares a high degree of sequence similarity with cat allergens (Nekaris, et al., 2013).

A slow loris (Image 1).

A slow loris' brachial gland and mouth which makes up its venom system (Image 2).

A slow loris in its defensive position (Image 3).

There are many potential reasons why slow lorises use their venom. It was thought that the lorises used venom to subdue their prey; however, the lorises consume their prey very rapidly and do not appear to need venom to paralyse them. Lorises have been seen using their venom to defend against predators. Female lorises will cover their offspring with their fluid before 'parking' them for a few hours whilst they forage. The venom has also repelled cats, sun bears and civets, which are some of the slow loris' predators. Whilst the loris is going through a period of torpor, it decreases its social behaviour. Venom could provide an essential line of defence against ectoparasites during this time, as the loris is not grooming itself. Lorises may also use the venom as a seasonal, offensive weapon during the breeding season. This could explain why venom is only sometimes potent. During the few days which mating can occur, there is intense competition and feeding between males and females (Nekaris, et al., 2013).

One theory about slow lorises is that they evoled to mimic the spectacled cobra. Many animals possess protective colouration that deceives predators, but it is extremely rare in mammals. Multiple researchers have pointed out that lorises have snake-like characteristics in regards to their defensive postures and serpentine gait. Their grunt that they make during aggressive encounters also resembles the hiss of a cobra during threatening displays. Lorises also have facial markings similar to the eyespots and stripes of the spectacled cobra, and their dorsal stripes closely resembles the body of the cobra, particularly when viewed from above. It is thought that this mimicry evolved during a period of co-existance between these two species, at a time when environmental pressures would have favoured its selection. Ten million years ago, when the spectacled cobra and slow loris were moving into Asia, the climate underwent a number of fluctuations, causing a band of drier woodland to run from the Malay Peninsula down to Java, replacing the tropical forests. This change in habitat may have benefited some animals, as it made migrations easier. Being arboreal, slow lorises dislike travelling on the ground, as it increases the risk of predation. The drying out of the land forced the lorises to travel on the ground. They experienced a change in predation pressure, which caused them to develop these mimicking features to put off aerial predators (Nekaris, et al., 2013).

Potential mimicry of specatacled cobras in slow lorises (Image 4).

References

Nekaris, K., et al. (2013). Mad, bad and dangerous to know: the biochemistry, ecology and evolution of slow loris venom. Journal of Venomous Animals and Toxins including Tropical Diseases , 19 (21).

Images

Image 1 - http://ichef.bbci.co.uk/naturelibrary/images/ic/credit/640x395/s/sl/slow_loris/slow_loris_1.jpg. Accessed on 29/4/14.

Image 2 -https://taxo4254.wikispaces.com/file/view/brachial%20gland%20and%20incisors.jpg/384315024/brachial%20gland%20and%20incisors.jpg. Accessed on 29/4/14.

Image 3 - http://www.nocturama.org/wp-content/uploads/2012/03/Nekaris_c.jpg. Accessed on 29/4/14.

Image 4 - Retrieved from Nekaris, K. et al. (2013) on 29/4/14.

Monotremes are egg-laying mammals that are only found in Australia and New Guinea. The only extant monotremes are the platypus and the four species of echidnas. Playtpi live in fresh water rivers and streams along the East Coast of Australia. They have a spur on their hind legs that delivers the venom. Both males and females are born with these spurs, but females lose them during development. Male platypi use their spurs (and venom) to fight with one another to compete for females. Whilst fighting, the males puncture one another with their spurs and inject each other with venom. During the mating season, the crural glands and testicles increase in size, and the crural glands become highly active, producing venom to be delivered by the spur. Platypus envenomation was first recorded in the early 1800s. Envenomation results in immediate and acute pain and swelling. The only effective treatment is localised anaesthetic, but even then symptoms can last from two weeks to several months. In the venom, there are 88 venom genes, many of which are similar to the venom genes of reptiles, insectivores, fish and invertebrates. The peptides in the venom affect the blood pressure and disrupt ion transport pathways of the victim (Ligabue-Braun, Verli, & Carlini, 2012).

A platypus (Image 1).

A diagram of the venom system of a platypus (Image 2).

Echidnas have a very similar system, but they do not use it in the same way that the platypus does. Both male and females have degenerate spurs, like the female platypus. During the mating season, the male glands undergo change consistent with their levels of sexual hormones. The poor mechanism for locking the spur the the tibia during an attack suggests that the spur is not used as a weapon. Instead, it is thought that glands produce a scent that the male echidnas use to attract a mate (Ligabue-Braun, Verli, & Carlini, 2012).