LSM1303 Animal Behaviour

  The Hyena is a mammalian family of order Carnivora.  Hyenas are native to both African and Asian continents.  They consist of four living species, the Striped Hyena and Brown Hyena (genus Hyaena), the Spotted Hyena (genus Crocuta), and the Aardwolf (genus Proteles).  Hyenas generally live in packs which are led by a matriarch.  In hyena society, the females are the dominant gender.  This trait is shared by all four sub-species.  The spotted hyena goes one step further, with females being larger in size than males.  This article, by analyzing two studies on hyenas, aims to show that both nature and nurture play important roles in contributing to this unique gender dominance in spotted hyena society.

            In a study which made it to the international science journal Nature, Michigan State University zoology professor Kay Holekamp, her former graduate student Stephanie Dloniak and Jeffrey French from the University of Nebraska, reported that high-ranking, dominant spotted hyena mothers pass to their offspring high levels of certain hormones that make cubs more aggressive and sexually vigorous.[1]  This allowed cubs to have a better chance of surviving to adulthood and reproducing.  The study found higher levels of androgen during the final stages of pregnancy in the more dominant females as compared to the lower-ranking group members.[2]  These hormones played a significant influence on the behaviour and appearance of the offspring.  “What this means is that there are gifts a mom can give to her baby. She can manipulate her offspring’s behaviour and help her kids to survive and reproduce successfully by transferring status-related traits via prenatal hormone exposure,” said Holekamp.[3]  In addition, the maculinizing effects of androgens causes females to gain greater muscle mass, aggressive behaviour and dominance. More aggressive females are better able to compete for food when hyenas squabble over kills.[4]  This study supports the nature theory.

            The second study published in the scientific journal Behavioral Ecology suggests that dominance is more a case of nurture, and that hyenas inherit their social status.  An international team of scientists from the Leibniz Institute for Zoo and Wildlife Research (IZW) in Berlin, Germany, and the University of Sheffield, UK, used observations during the last 20 years of rare cases of adoption among hyenas in the Serengeti and Ngorongoro Crater in Tanzania in combination with the latest molecular techniques to identify genetic mothers to demonstrate that hyena mothers pass on their social status by supporting their young during social interactions with other group members.[5]  In spotted hyena society, social status is highly important.  It determines access to resources, survival and reproductive success.  As a result, parents may attempt to pass on their status to their offspring. “In spotted hyenas, surrogate mothers adopt young cubs soon after their birth. The adopted cubs obtained a rank at adulthood that was similar to and just below the rank of their surrogate mother. In contrast, the rank of adopted offspring was unrelated to the rank of their genetic mother” says Dr Marion East from the IZW. “This is consistent with the idea that maternal behavioural support determines rank inheritance.”[6]

            The results of the second study however throw into doubt two existing hypotheses explaining dominance in spotted hyenas.  The first being that mothers might transfer genes that cause their offspring to be as competitive as themselves; and the second being, maternal status might determine the concentration of maternal androgens that a foetus is exposed to, and this exposure in turn might make offspring become as competitive as their mother. “These hypotheses would predict a relationship between the rank of adopted offspring and that of their genetic mother, but we found no evidence of such a relationship” explains Dr Oliver Höner from the IZW.[7]  The study suggests that hyena young learn as they grow which group members they can dominate when their mother helps them win contests against group members that are subordinate to the mother.  As they grow older and reach adulthood, they continue to defend the privilege passed down to them.[8]

            To conclude, it is my believe that it is impossible to split the cause of hyena dominance to either simply nature, or nurture alone.  They both play apart in contributing to hyena dominance.  Perhaps maybe more so in hyena society as compared to any other species, hyenas need the heavy mixture of both nature and nurture to attain their aggressiveness and dominance to continue surviving and reproducing.

A giant Ichneumon wasp

We have watched movies of aliens taking over human bodies and turning them into mutants, but how many of us know that similar horror movies are occurring closer to home?

A parasitic wasp, the Ichneumon wasp, is capable of taking over its host’s behaviour and manipulates it to its own advantage. It is this wasp that caused Charles Darwin to question natural theology, as the Ichneumon wasps’ method of ‘torturing’ other insects seems incompatible with the notion that the study of nature demonstrates God’s benevolence.

Even though parasitic stories may seem rather commonplace in the animal and insect kingdom, the Ichneumon wasp goes a step further in ‘possessing’ the host’s body. In a particular study, this wasp invades an orb-weaving spider’s body and lays an egg on the tip of the spider’s abdomen. It seems to go on unnoticed as the spider goes about its usual web-spinning routine, while the growing larva slowly sucks juices out of the spider’s belly.

The interesting part comes on the night before the larva kills the spider – it somehow induces the spider to spin a totally different kind of web just for it. It is almost as if the spider is possessed, as it spins two sturdy silk cables conduce for the wasp larva to spin its cocoon on, before it is killed.

The mystery lies in how the wasp larva manages to shape the spider’s web-spinning behaviour. Scientists can only assume that it manipulates a particular subroutine in the spider’s web-building programme, but how it achieves that is still a question.

References:

Our creature of interest: The Spitting Cobra

Source: http://dsc.discovery.com/news/2009/01/21/cobra-venom.html

Recently, a curious creature that has come into interest is the cobra. Its name has often been borrowed to name military programmes. We have in Singapore the Cobra Division, Exercise Cobra and the AH-1W Cobra Helicopter. We say imitation is the best form of flattery. Just look at the Cobra Division Badge Patch Design(below); it’s pretty telling.

It gives accolodes to the cobra’s deadly strike and swift immobilising power. But within cobras, some species have evolved this unique mechanism that’s patent-worthy. The spitting cobra has this unusual ability to jet venom out into the eyes of a would-be predator/attacker. This defence mechanism works in very simple steps: Enter the potential predator. Cobra engages its head and neck muscles. Muscle contractions squeeze the cobra’s venom gland, forcing venom to stream out of the snale’s fangs. There is enough fluid pressure to spray venom beyond six feet (ScienceDaily).

When we explore the dynamics involved in this unique artillery, there’re more reasons to feel awed by this creature. Firstly, the venom does not spray out randomly. The venom streams out in complex geometric patterns which’re actively controlled by the cobra. Secondly, the potency of this weaponry is how it maximises the chances of striking the eyes. There’re no points won for hitting other parts of the body, deterrence only occurs when the accoster is hit in the eyes. If we check out the spitting cobra’s scoreboard, we may feel fascinated or mortified(for those of us who’ve never hit the bull’s eye in dart-throwing or archery); cobras hit their targets with alarming frequency; nearly 100% accuracy from 60 centimetres away (tad bit disconcerting huh)! Like every master archer, it fixates its gaze on its target; the eyes. And its target maximising strategy works like this: It rotates its head rapidly when squirting the toxin, increasing the spatial distribution of venom and creating a higher chances of striking bull’s eye! Dr Westhoff, a member of the research team which derived for us these findings, states “Rather like we do when we wish to use a garden hosepipe to water the flowers of an entire flowerbed.” To think about it, this technique is almost state-of-the-art.

But this unique morphology is only exclusive among a few species of cobras. Through a narrow channel in their fangs, the cobras spew venom out when pressure is exerted via muscular contractions(ScienceDaily). When we think about it, it’s almost like the make-up of our water pistols, just with more finesse. Not all spitting cobras are equal in their marksmenship though (nature does endow us unfairly). The black-necked spitting cobra (below) hits its goal in only 80% of target practice. The red mozambique(below), however, achieves a 100% full score.

The Black-necked Spitting Cobra

Scoreboard: 8/10

Source: http://www.conservationsafaris.com/Pictures/Black-necked_spitting_cobra.jpg

Red Mozambique Spitting Cobra

Scoreboard: 10/10

Source: http://i.livescience.com/images/h_spitting_cobra_02.jpg

That’s a powerful weapon to have in your arsenal, no doubt, but it must have high energetic costs too. Which is why spitting cobras do not eject venom randomly. The sprewing action is released by an external stimulus; moving objects. A study conducted by the University of Bonn revealed that the spitting action can be triggered by a moving human face or a moving human photo( Westhoff et al,2005). Stationary objects do not stimulate any action. Furthermore, the cobra does not spit blindly, it can differentiate between human faces and hands(since the ultimate target are the eyes)! The spitting cobra does not waste its venom if you wave your hands before it just to give you a free show.

Accosting a spitting cobra

Source: http://www.wildlifeextra.com/images/large-brown-spitting.jpg

All that military jargon would no doubt have us thinking that the spitting cobra is a rather gladiatorial, hawk-like creature. But that ain’t true; there’s no need to feel overly threatened by this creature. It only attacks when threatened. And a further boon: It hunts in the same manner as other snakes; by biting its prey with its fangs. Which means it doesn’t depend on this for its bread and butter. Consider having such a formidable auxiliary weapon in your arsenal! This gives it an additional edge over ordinary cobras against its traditional arch-rival and nemesis, the mongoose. Intuitively speaking, the evolving of unusual defence functions are usually in response to real world challenges and constraints.Some scientists theorize that the development of the spitting mechanisms were the result of these cobra species cohabitating with numerous antelop species. They believe that the primary function of the fangs are to prevent being trampled on by hooves. By spewing venom when necessary and deter the onslaught of hooves(Tigerhomes Sanctury website).

It has a drawback though; it is useless against oncoming vehicles!But it comes into mind every time we’re aiming at the dartboard or in a watermelon spitting contest. Before you go, do take a look at the following video depicting the confrontation between the spitting cobra and lion. It shows our centerstage creature triumphing against the grunting, huffing lion, who then scampers away. Follow the slow-motion trajectory of the venom stream and notice that it’s jets out in double, not single streams which run almost parallel to each other. On this, researchers found that spitting cobras don’t spray as a stream, mist or cloud. The venom sprays out in distinctive patterns, typically paired ovals (Discovery News) When I described the venom spray as “state-of-the-art” earlier, I meant it.

Video: Spitting Cobra Vs Lion (http://www.youtube.com/watch?v=_5dtpMj9Ehs)

References:

Westhoff, G, Tzschatzsch. K, Bleckmann H. (2005). Journal of Comparative Physiology A: Neuroethology, Sensory, Neural and Behavioral Physiology. Vol 191(10). pp 873-881.

Science Daily (Jan 26, 2009). Here’s venom in your eye: Spitting Cobras Hit Their Mark. From http://www.sciencedaily.com/releases/2009/01/090122152709.htm. Accessed on April 13, 2009.

Science Daily(Feb 17, 2005). When Cobras Spit, There’s Not A Dry Eye In The House. From http://www.sciencedaily.com/releases/2005/02/050212194818.htm. Accessed on April 13,2009.

Tigerhomes.org Animal Sanctuary. Spitting Cobra-Fangs, Captive Breeding, Pictures, Baby Spitting Cobras. From http://www.tigerhomes.org/animal/spitting-cobra.cfm. Accessed on April 13,2009.

Jennifer Viegas, Discovery News. (2009). Spitting Cobra’s Sharp-Shooting Secrets. From http://dsc.discovery.com/news/2009/01/21/cobra-venom.html. Accessed on April 13, 2009.

The humble dung beetle , destined for a lifetime of shit has now expanded its diet to include chomping on live millipedes!

Scientists from Peru have recently discovered a particular species of dung beetle (Coleoptera: Scarabaeidae), Deltochilum valgum, which is the first of its kind to display predatory behaviour, using its modified head and sharper “teeth” to decapitate live millipedes and slice up ther rest of the body for feeding.

Using infrared cameras, the research team led by Dr. Trond Larsen were able to catch live footage of the nocturnal dung beetles in action. Dung beetle heads are normally flat and shovel-like, useful for burrowing in a dung pile. However, D. valgum has a much narrower and pointy head, adapted to get inside the millipede’s body and feed on its insides. The sharper ‘teeth’ they posses are also useful in severing the head of the millipedeand cutting up the body into smaller pieces.

Talk about ferocious!

watch?v=VjLfcHTwr6E
Supplementary material video accompanying Biology Letters article ‘From coprophagy to predation: a dung beetle that kills millipedes’.
Such behaviour intrigues scientists as there is a huge jump from coprophagy (dung feeding) to carnivory. They hypothesise that this unusual evolutionary transition was driven by the high levels competition for food.

This extraordinary behaviour of carnivorous dung beetles is certainly one which will change the way we view the humble dung beetle!
For more information:

Larsen, T., Lopera, A., Forsyth, A. & Genier, F. 2009. From coprophagy to predation: a dung beetle that kills millipedes. Biol. Lett. 5 : 152-155

BBC News “Little dung beetle is big chopper”. Accessed 8th April 2009. (http://news.bbc.co.uk/2/hi/science/nature/7840404.stm)