LSM1303 Animal Behaviour

Always thought starfish were cute and harmless? Pretty and dainty?

WELL, THINK AGAIN.

Not quite what you had in mind? Introducing the Crown-of-Thorns Starfish (Acanthaster planci L.), commonly found throughout the Pacific and Indian oceans. Its monstrous appearance does not belie its appetite, which is equally as ferocious. EACH Crown-of-Thorns starfish destroys up to 20 square kilometres of precious coral reef every year! The atrocity!

Watch the culprits here.

Before we move on, here are some cold hard facts about sea stars:

• Starfish, (or rather, sea stars) are marine bottom-dwelling invertebrates (Echinoderms) characterized by their hard, calcified skin. Their relatives include sea urchins ( Echinoidea) and sea cucumbers ( Holothuroidea).

• Sea stars can be circular, pentagonal or star-shaped, with several radiating arms.  Under each arm are tiny tube feet which the creature uses for walking.

• Sea stars have two stomachs, no brains and no blood. (Betcha didn’t know that!)

• Sea stars can live up to 35 years!

• Although sea stars in reality do not have heads, each does has eyes and a mouth. The mouth of the sea star is found on the ventral surface; the underside. More amazingly, their microscopic eyes are found at the end of each arm, which can view movement as well as differentiate between light and dark. So a 5-armed sea star has 5 eyes, while a 14-armed ‘comrade’ has… (wait for it) …FOURTEEN EYES. (How unfair, I say.)

• Sea stars are most famous for their ability to grow new arms in place of unfortunately severed ones. In some cases, a whole new sea star can grow from one severed arm.

• Most sea stars (more than 99%) are separate in sexes despite the common misperception that they reproduce by asexual methods such as binary fission. SO, sea stars produce eggs and sperms too, which are externally fertilized in the water during spawning time.

• If you’re wondering how sea stars consume their prey – and you SHOULD wonder – they use their suction-cupped puny feet to pry open shellfish, while their sack-like cardiac stomach emerges from their mouth and oozes inside the shell. The stomach then envelops the prey to digest it, and finally withdraws back into the body.

Going back to our thorny issue at hand, it should be noted that despite causing severe damage to coral reef due to their immense appetite, the Crown-of-Thorns Starfish actually help to increase diversity of the coral reef ecosystem when their populations do not reach explosive numbers. AND, they don’t just chomp their way through all corals; in fact they do have feeding preferences. How so? I will spare you the scientific jargon here and plunge into layman terms for simplicity’s sake. De’ath and Moran (1998) categorize these feeding preferences into a hierarchical order: our thorny friends prefer corals with higher energy and protein levels, and also those whose tissues they can absorb with ease. This is referred to as the Optimal Diet Theory.

Keesing (1990) holds a contrasting hypothesis: he hypothesized that “feeding preference may be more dependent on the suitability of the food (e.g., surface area complexity, biomass, nutritional value and abundance)”. This was also proven in De’ath and Moran’s 1998 study, where the Crown-of-Thorns starfish “exhibited a strong hierarchy of preference for particular forms”: corals with tabular morphologies were preferred 4 to 5 times as much as branching, submassive and foliaceous forms; 9 times as much as encrusting forms and 36 times as much as massive forms. The rationale behind this?  De’ath and Moran conclude that “the preference of starfish for particular forms of coral may be due in part to the surface complexity of the coral”.

These Crown-of-Thorns starfish can base their feeding preferences on both coral genus and coral form. Brainless sea stars? Hardly, in my opinion. Makes you wonder how they ‘process’ information about coral genus and form, does it not?

But that shall constitute another blog post another day, when more research has been done. (:

References

BBC – Science and Nature. (n.d.) Animal Fact Files: Crown of thorns starfish (Acanthaster planci). Retrieved April 13, 2009, from http://www.bbc.co.uk/nature/blueplanet/factfiles/starfish_urchins/crown_of_thorns_bg.shtml

De’ath, G. and Moran, P. J. (1998). Factors affecting the behaviour of crown-of-thorns starfish (Acanthaster planci L.) on the Great Barrier Reef:: 2: Feeding preferences. Journal of Experimental Marine Biology and Ecology, 220(1), 107-126. Retrieved April 13, 2009, from http://www.sciencedirect.com.libproxy1.nus.edu.sg/science?_ob=ArticleURL&_udi=B6T8F-3S2BN1X-7&_user=111989&_coverDate=01%2F31%2F1998&_rdoc=1&_fmt=full&_orig=search&_cdi=5085&_sort=d&_docanchor=&view=c&_acct=C000008700&_version=1&_urlVersion=0&_userid=111989&md5=3a5fdfce58d44e376db4c1c2d4d98406#bb9 . doi:10.1016/S0022-0981(97)00100-7

Keesing, J.K. (1990). Feeding biology of the crown-of-thorns starfish, Acanthaser planci, (Linnaeus). Ph.D. thesis, James Cook University of North Queensland, Townsville.

Lad, K. (2008). Interesting Facts About Starfish. Buzzle.com – Intelligent Life on the Web. Retrieved April 13, 2009, from http://www.buzzle.com/articles/interesting-facts-about-starfish.html

Microdocs. (2009). Crown-of-Thorns. Retrieved April 13, 2009, from http://www.stanford.edu/group/microdocs/crownofthorns.html

National Geographic. (2009). Starfish (Sea Star) (Asteroidea). Retrieved April 13, 2009, from http://animals.nationalgeographic.com/animals/invertebrates/starfish.html

You’d think mosquitoes are out to annoy you with their buzzing, but research shows that “the familiar buzz of flying mosquitoes is an important mating signal, with the fundamental frequency of the female’s flight tone signaling her presence” (Cator, Arthur, Harrington & Hoy, 8 Jan 2009).

Watch here! (Morgan, 8 Jan 2009)

For a long time, the buzzing of the mosquitoes was seen as an unintentional effect of their flapping wings. In addition, what sounded like a steady buzz to humans could range up to 2,000 hertz to the mosquitoes, exceeding their previously established hearing limit, whereby male mosquitoes could hear between 300-800Hz, while females were thought to be deaf.

However, this research has proven otherwise. With live Aedes aegypti mosquitoes tethered to the end of insect pins, tones made by both male and female mosquitoes were recorded to show that their fundamental tones – 400Hz for females and 600Hz for males – reached a synchronised note at 1,200Hz when brought within a few centimeters from each other, signifying a mating match.

According to Ron Hoy (in Bland, 8 Jan 2009), co-author of the study at Cornell University, “We think that females could use harmonic matching as a fitness measure for the males”. It begins with the female flying through the air and producing a complex sound including its fundamental tone and harmonics (multiples of the basic tone), which is an irresistable mating song to the males. However, the male must modulate his own sound to match the female’s, because only when she is satisfied with his love song will she mate with him.

Aedes aegypti is the mosquito that transmits diseases such as yellow fever and dengue fever, which has been exceptionally rampant in Singapore (National Environment Agency, 2009). By understanding their mating process, it may inspire better ideas to more effectively curb the breeding of these dangerous mosquitoes. Some of the ideas include creating sterile or genetically engineered males that cannot transmit dengue virus and tricking the females into mating with them, which will bear them no offspring or harmless ones (Morgan, 8 Jan 2009). In theory, the population of mosquitoes would then decline. However, there are still many obstacles to overcome, one such as the female’s ability to tell if a male has been altered, reducing their interest. Nevertheless, this research has opened up new areas to explore for the solution. As Professor Harrington, one of the co-authors of the study, rightly asserts (in Morgan, 8 Jan 2009), “If you eliminate the vector, you eliminate the disease.”

Now that the source of the problem has been determined, all we need is a solution.

Research study:

Cator, L. J., Arthur, B. J., Harrington, L. C. & Hoy, R. R., 8 Jan 2009. Harmonic Convergence in the Love Songs of the Dengue Vector Mosquito [On-line]. Science Magazine, 323 (5917): 1077 – 1079.

References:

National Environment Agency, 2009. Campaign Against Dengue. Accessed 14 April 2009.

“Mosquito Buzz Actually a Love Song,” by Eric Bland. Discovery News, 8 Jan 2009.

“Mosquitoes make sweet love music,” by James Morgan. BBC News, 8 Jan 2009.

“Love Song of the Dengue Vector Mosquito,” by Laura Sanders. Science News, 31 Jan 2009.

Ireton, R., 27 Jun 2007. “A Capital Offence.” Photo. Flickr.com Accessed 14 April 2009.

The California ground squirrel, otherwise known as Spermophilus beecheyi, have taken one step closer to avoiding one of their biggest predators – the rattlesnake – by chewing the shed skin of their predators and licking themselves all over. Yes, you heard me right. They use their predators skin as chewing gum and then lick themselves all over when they are done with it to imprint the scent of the rattlesnake onto their own bodies.

“That doesn’t mean it tastes good…”

These species of squirrels already have a variety of amazing  techniques in their arsenal to avoid being prey. For instance, they are able to super heat their 15cm tails by a few degrees, up to 28 degrees Celsius, and then swish them around vigorously to give an impression of a bigger prey that’s very swift. The rattlesnakes which rely on their pit organ, which detects infra-red, to hunt, will be deterred and search for easier prey. However, this mechanism will not work against gopher snakes, another worthy adversary, as the latter lack heat seekers. How do they know what type of snake they are up against you say? They have an amazing ability to distinguish rattlesnakes from their other predators by the scent of the rattlesnake. Even more astounding is their ability to tell the size of the rattlesnake by the sound of the rattle! Either way, if all else fails, these squirrels are able to fall back on their evolved anti-venom. Unfortuntately, behavioral biologist Aaron Rundus of the University of Nebraska–Lincoln School of Biological Sciences says that these techniques are not really effective to squirrel pups, purported to form 70% of the rattlesnake diet. However, with Eau De Rattlesnakes, these pups can avoid sleepless nights!

“Chemical defences are ubiquitous among invertebrates, and several invertebrate and vertebrate species sequester the chemicals used in defence. However, no vertebrate has clearly been demonstrated to use a self-applied chemical from a foreign source in predator defence,” writes Clucas. Normally they just “ingest such foreign substances and sequester them in their integument.” Ownings says that “the squirrels are not limited to the use of shed snake skins. They also pick up snake odor from soil and other surfaces on which snakes have been resting, and use that to apply scent”

Don’t jump to conclusions that predator scent application is only an anti-predator behavior across all animals though. It doesn’t only serve a single function. It could also be used as an ectoparasite defence, that is, to reduce the amount of ectoparasites on them by repelling them or by masking their odour cues . Alternatively, conspecific deterrence could be a possibility. A scented animal might gain “a competitive advantage by distracting a conspecific adversary during an aggressive interaction”.

You can check out the common waxbill who uses of olfactory camouflage to protect their nests and other related articles about the california squirrel’s behavior from UC Davis, National Geographic, and Wikipedia. Clucas, Rowe and Ownings also have another study to affirm the behavoir described in this post here.

Sources:

• “Ground Squirrels Chew Snakeskins to Mask Their Scent” by Henry Fountain. New York Times, 5 February 2008.
• “Squirrel has hot tail to tell snakes” by JR Minkel. Scientific American, 14 August 2007.
• Clucas B, Rowe MP & Ownings DH (2008) Snake scent application in ground squirrels, Spermophillus spp.: a novel form of antipredator behavior? Animal Behavior, 75: 299-307.
• Schuetz J.G. (2005) Common Waxbills use carnivore scat to reduce the risk of nest predation. Behavorial Ecology, 16: 133-137.
• B. Clucas, D. H Owings, and M. P Rowe (2008). Donning your enemy’s cloak: ground squirrels exploit rattlesnake scent to reduce predation risk. Proceedings of the Royal Society B, April 7, 2008; 275(1636): 847 – 852

Photos from flickr.com

• Main Photo
• Squirrel with tongue sticking out

We all know that reptilian romances, like most Hollywood romances (Hello Jennifer Aniston and Brad Pitt!), do not last beyond  a single mating season. In fact, reptiles have the tendency to seek out various mating partners within a season (Madsen et al. 1992; Olsson 1995; Olsson and Madsen 1995). This points to a polygynous mating system in which the male mates with several females.

But unlike the serial-womanisers in Hollywood (Yes, I’m talking to you, Jude Law) who simply cannot keep their hands to themselves, polygyny within the reptilian community is linked to territoriality. Bull (2000) states the following:

In many lizard species males are also more active in the mating season because they are defending a territory. Dominant males can hold territories that contain the home ranges of several females…leading to a territorial polygynous mating system.

However, do not even for one second think that the ladies are then relegated to the passive role of being a member of the men’s harem. Female reptiles like the sand lizard (Lacerta agilis) are also known to mate with several males within a mating season (Olson and Madsen, 1995). The act of mating with several males is to ensure enhanced genetic variabilty among their offspring which will greatly improve reproductive successes.

So…is there “true love” in the reptilian kingdom?

I caught an episode of David Attenborough’s Life in Cold Blood series which documents the monogamous relationship between two Shingleback lizards (Tiliqua rugosa). The documentary prompted a quick search online for the Shingleback lizard and I came across Michael Bull’s article titled “Monogamy in Lizards” (2000), which also led me to Bull et al.’s article titled “Social monogamy and extra-pair fertilization in an Australian lizard, Tiliqua rugosa” (1998).

Before moving on to the discussion proper, here are some unknown facts of the Shingleback lizard. Below is an excerpt from Wikipedia:

Tiliqua rugosa is a short tailed and slow moving species of blue-tongued skink found in Australia. It has a heavily armored body and can be found in various colors, ranging from dark brown to cream. It is often seen sunning itself on roadsides or other paved areas.The skink is known by a variety of common names such as bobtail, shingleback or stump-tailed skink, bogeyes, and the Pinecone or Australian sleepy lizard. They have short, wide stumpy tails that resemble their head, and may confuse predators. The tail also contains fat reserves, which are drawn upon during hibernation in winter. The shingleback skink is an omnivore that eat snails and plants and spends much of its time browsing through vegetation for food.

Shingleback lizard

Knowing that prosmicuity is widespread within the reptilian community, it is even more shocking to know that Shingleback lizards are generally monogamous. I say “generally” because Bull et al. (1998) found that there exist certain cases of extra-pair copulation i.e. it was found that 79% of the females were with the same male partners while the remaining were found to be with different male partners. Still, I doubt the anomalous cases take anything away from how amazingly monogamous these creatures are. Bull (2000) describes the following:

Adult males and females of this species form monogamous pairs for an extended period before mating each spring, and they select the same partner in successive years.

If the mating pair gets separated, the male Shingleback lizard will attempt to track down the female by following her scent trail. When the male has finally located its mate, it was observed to nudge the female flank or back leg with its nose, and to tongue flick the female’s flank (Bull et al., 1993). In fact, Bull documents a story that took place in 1997 in which a male Shingleback lizard was found lying next to the carcass of a female Shingleback lizard who had died after being stuck in wired fence.

Bull proposed the following reasons for the monogamous bond between Shingleback lizards:

1. Having a single partner is advantageous because familiarity with the partner will improve one’s chances of feeding and detecting predators. (I figure that it’s somewhat like developing a certain chemistry with your significant other, one wouldn’t want to shop around for other mates if your current mate makes you happy. Seriously, why would you want to look for someone else if your current partner makes excellent spaghetti or helps you hold off the insane crowds during the Great Singapore Sale?)

2. The reason for “sticking” to a partner for years may be due to genetic compatibility. (This reminds me of the “Sweaty T-Shirts” video shown in class.)

3. Long term monogamy is also helpful in preventing the spread of parasites and diseases. An individual lizard would want to stay with a partner for many more years to come if it does not contract any diseases from that partner the first time round. (If you’ve been with a partner for years without contracting any sort of disease, chances are, you’d stay around him or her instead of actively searching for other partners who may have some forms of diseases . Then again, I should not give too much credit to humans, seeing how fickle we can be.)

So, is the monogamous partnership motivated by biological needs and concerns, or is there something more to it? You decide.

References:

Bull, C.M., Bedford, G.S. and Schulz, B.A., 1993. How do sleepy lizards find each other?. Herpetologica 49: 294–300.

Bull, C. Michael. Cooper, Steven J.B. Baghurst, Ben C. (1998). Social monogamy and extra-pair fertilization in an Australian lizard, Tiliqua rugosaBehav Ecol Sociobiol 44: 63-72

Bull, C. Michael. (2000). Monogamy in Lizards. Behavioural Processes 51 (1-3): 7-20

Madsen T, Shine R, Loman J, Hakansson T (1992). Why do female adders copulate so frequently? Nature 355:440-441

Olsson M (1995) Territoriality in Lake Eyre dragons Ctenophorus maculosus: are males “superterritorial”? Ethology 101:222-227

Olsson M, Madsen T (1995) Female choice on male quantitative traits in lizards – why is it so rare? Behav Ecol Sociobiol 36:179-184

Wikipedia.org

We are well familiar with the Eiffel Tower, Sydney Opera House and even the Great Wall of China. But as impressive as these human architectures are, we have equally (or some would say, even better) awesome architects in nature: the Termites.

Certain species of Macrotermes and Amitermes build huge mound nests which are more than 10m in height. Amitermes are also known as magnetic termites due to the way they orientate their flat and broad protruding mounds which are along the north and south axis of the Earth. Unlike us, in which we can employ the help of heavy machinery and tools to aid in construction today, the termites built their enormous mounds solely relying only on their own strength. Bit by bit, each worker places a “brick” of building material, consisting of nothing but the soil in their vicinity, probably mixed with a bit of their saliva for cementing purposes.

Why the high and conspicuous mound you might ask. The reason is ventilation. Nests like these house large colonies of termites, some reaching a population of a million strong. With such numbers in an enclosed place, it can get truly hot. Acting as a chimney, the protrusion draws away heat and exchanges it with cooler fresh air. In addition to a chimney, these mound nests are fully equipped with a “well’ at the bottom in which the termites draw precious water.

The designs of these mounds serve several functional purposes like thermoregulation, ventilation and hydration. Moulded and fine-tuned overtime through evolution, they stand the trial of time. It is indeed fascinating to see such elaborate structures constructed by these little creatures working in great unison with such efficiency. But exactly how it is they communicate to each other to achieve such cooperation to the most minute of details, we don’t yet know.

 BBC Home Making: Termites

Termite World – Life in the Undergrowth – BBC Attenborough

References

Korb, J. and Linsenmair, K. E., 2000. Thermoregulation of termite mounds: what role does ambient temperature and metabolism of the colony play? Insectes Sociaux, 47:357-363.

Korb, J., 2003. The shape of compass termite mounds and its biological significance. Insectes Sociaux, 50: 218-221.

BBC Home Making: Termites. Accessed 9 April 2009.

http://www.youtube.com/watch?v=ld07xdqnytk

BBC – Life in the Undergrowth: Episode 3. Accessed 9 April 2009

http://www.youtube.com/watch?v=xGaT0B__2DM