LSM1303 Animal Behaviour

The phenomenon of switching back and forth being male and female is not a new phenomenon. It has been observed in certain types of animals such as fishes, shrimps, worms and snails. Male fishes have the ability to develop female traits by growing new sexual organs and producing eggs – due to anti-androgens in waters that contribute to this feminization of the fish (by blocking the actions of male hormones). (Sohn, 4 March 2009) However, this is the first study that observes how corals can change their sex in either direction (Sohn, 30 March 2009).

This study on mushroom corals was undertaken by Yossi Loya (a zoologist at Tel Aviv University) and her colleagues on a patch reef near Japan’s Okinawa which is home to tens of thousands of mushroom corals. In July 2004, the collected mushroom corals for observation and research purposes released sperms and eggs which were then analyzed under the microscope. These gamete explosions produce larvae that drift off to become new corals in the ocean when in their natural habitats. (Sohn, 30 March 2009)

The results: Each coral produced either sperm or eggs since they do not belong to corals which were hermaphroditic (having both male and female reproductive parts).

The coral reef scientists repeated the same experiment in 2006 and 2007 respectively with the same corals and new corals.

The results in 2006: approximately 25% of one species and 50% of the other species had changed sex since they’d been tagged two years earlier

The results in 2007: approximately 80% percent of the corals had changed sex from 2006, with 25% reverting back to the sex in 2004.

“We know in detail the reproductive patterns of more than 500 coral species, but no one reported before on the fact that some coral species may change sex… I believe this was quite a big surprise to all coral reef scientists…” – Yossi Loya (2009)

“We never realized in our wildest dreams that these corals can undergo sex changes. This is really exciting.” – Robert van Woesik, a marine biologist at the Florida Institute of Technology in Melbourne (2009)

Understanding why and when these mushroom corals switch from male to female or vice versa may be contributing to the world of biological evolution of these corals and imperative in understanding how the changing environment  affects them and in helping efforts to conserve these corals. From an evolutionary perspective, Loya and van Woesik said that it made sense for young mushroom corals to be male since it requires less energy to produce sperm than to produce eggs but as these corals grow, it is more advantageous to be female. But the switching back and forth sexes may be an indication of stress such as climate changes and water pollution. The danger of this phenomenon is that when a majority of these mushroom corals tend towards becoming male or female – leading to an unbalanced sex ration – these corals could well become extinct. (Sohn, 30 March 2009)

This is an especially important discover to the scientific community since a recent Australian Institute of Marine Science (AIMS) field expedition researching on a coral community near Miall Island on the southern Great Barrier Reef concluded that corals can adjust to the higher sea surface temperatures and the higher acidity of the waters. (Jacquot, 22 March 2008) According to the study:

“The corals there have managed to do so by switching out their old zooxanthellae, symbiotic algae that provide them with a constant source of nutrition, in favor of newer, more heat-resistant ones. This phenomenon, observed in coral communities that underwent mass bleaching events in 2006, has been dubbed ‘symbiont shuffling’; the researchers found that the corals now were much more likely to have two strains of thermally-resistant zooxanthellae than they were prior to the bleaching events.”

Bringing the argument of the need to heighten environmental consciousness to another level, Charles Tyler, an ecotoxicologist at the University of Exeter in England warns that:

“At the end of the day, wildlife are fantastic sentinels for potential human impacts… If it happens in fish, it can happen in humans.” (Sohn, 4 March 2009)

To read more about the feminization of species and the sexual disruption in wild fish populations, you can read more about how exposure to steroid estrogens  or chemically-induced endocrine affect the sex of fishes and other wildlife animals, you can read more in:

Jobling, S., Williams, R., Johnson, A., Taylor, A. Gross-Sorokin, M. Nolan, M. Tyler, C. R., van Aerle, R., Santos, E. and Brighty, G. 2006. ‘Predicted Exposures to Steroid Estrogens in U.K. Rivers Correlate with Widespread Sexual Disruption in Wild Fish Populations’. Environmental Health Perspective. Vol. 114(Suppl. 1). Pp. 32-39.

Jobling, S. and Tyler, C. R. 2006. “Introduction: The Ecological Relevance of Chemically Induced Endocrine Disruption in Wildlife”. Environmental Health Perspective. Vol. 114(Suppl 1). Pp. 7-8.

COMPRENDO (Comparative Research on Endocrine Disrupters). 2004. Ecological Relevance of Chemically-Induced Endocrine Disruption in Wildlife. Available at http://www.comprendo-project.org/_files/AbstractsExeter2004.pdf [accessed 13 April 2009].

References:

Sohn, E . 2009. “Stressed female mushroom corals become male”. Discovery News. 30 March 2009

Sohn, E . 2009. “Worldwide she-male fish mystery widens”. Discovery News. 4 March 2009.

Jacquot, J. E. 2008. “New research indicates some corals are taking the heat and surviving”.  Science and Technology. 22 March 2008.

Elephants are the largest land animals and among the strongest mammals on Earth. However, they are often depicted in fiction as sensitive and gentle animals, perhaps due to the fact they are herbivores. The most famous of these depictions is, of course, Dumbo.

In the Disney movie Dumbo, a baby elephant named Jumbo Jr. (nicknamed Dumbo) is ostracised in a circus due to his abnormally large ears; his only friend being a mouse named Timothy. The relationship between Dumbo and Timothy plays on the stereotypical myth that elephants are afraid of mice and that the two animals are generally hostile to each other.

Depictions of the relationship between mice and elephants in popular culture are common – in Indian folklore mice and elephants are described as being the best of friends because of two incidents where elephants saved the lives of mice, and vice versa. These diverse urban legends which are contradictory in their portrayal of the relationship between elephants and mice raise an intriguing question – are elephants really afraid of mice?

An experiment conducted by Adam Savage and Jamie Hyneman from the Discovery Channel programmeMythbusters see the two hosts put the urban legend to test. After conducting their experiment, they concluded that the myth that elephants are afraid of mice appears to be plausible; though it is inconclusive whether elephants are afraid of mice, they certainly seem to avoid them.

Mythbusters – Are Elephants Afraid of Mice?

The Mythbusters’ conclusions lend credence to suggestions that elephants’ behaviour in relation to mice are a result of an instinctive reaction to movements they cannot see or hear, such as that of mice scurrying underfoot. Several studies have been conducted, however, that conclude that domesticated elephants are not affected by the presence of mice at all and indeed co-exist with them with little fanfare. Few studies have been conducted on this, perhaps because the reaction of elephants to mice have been mixed. In addition, as demonstrated by the Mythbusters experiment, the reaction of elephants to mice is minimal. As a result, a deeper understanding of this behavioural kink among elephants has not been deemed scientifically worthy.

That does not mean, however, that the behaviour of elephants in relation to other animals have not been studied. In recent years, it has been discovered that elephants are afraid of bees – according to scientists, the sound of disturbed bees buzzing led to groups of elephants moving away from the source of the sound within seconds. This revelation has led to scientists postulating a harmless, cost-effective way of controlling elephants in the wild. By placing loudspeakers in strategic areas, elephants (which can be dangerous and riotous, contrary to Disney’s depictions!) can be diverted from encroaching upon farms and villages. Scientists have gone on to characterise bees – not mice – as the elephants’ worst fears.

Yet, rather than use this as mere fodder for cartoons, this behavioural characteristic of elephants has been harnessed to tangible and positive programmes targetted at improving the relationship between elephants and human populations. Indeed, humans and animals can co-exist as long as humans endeavour to attain a deepened understanding of animal behaviours; the elephants’ worst fear gives hope to that!

Citations:

“Bee Buzz Scares Off Elephants.” National Geographic News, October 9, 2007. http://news.nationalgeographic.com/news/2007/10/071009-elephants-bees.html (accessed April 13, 2009).

“It’s bees, not mice, that send elephants into a panic.” Daily Mail Online, October 8, 2007. http://www.dailymail.co.uk/news/article-486468/Its-bees-mice-send-elephants-panic.html (accessed April 13, 2009).

“Elephant vs. Mouse.” Chimaera: The Bestiary Blog. http://bestiary.ca/chimaera/48 (accessed April 13, 2009).

“The Mice and the Elephant, a Tale from India.” Stories for Children in Crisis. http://www.healingstory.org/crisis/mice/mice_and_elephant.html (accessed April 13, 2009).

The National Geographic’s profile of the male deep-sea angler fish mentions that he is peculiar not only because of his minute size – he is dwarf that is a fraction the size of the female – but because of his behaviour when he meets a female. The male angler fish attaches himself to the female and then literally merges with the female’s body such that their blood systems fuse and he becomes totally dependent on the female for nutrients and oxygen. The extent of this dependence is quite remarkable, for the males actually do not need organ systems such as their eyes, teeth and digestive systems because they parasitically exist off the female’s body. As a result, his body “degenerates into essentially a pair of sperm-producing testicles”( http://waynesword.palomar.edu/ww0701.htm) because he exists solely to fertilise the female’s eggs.

Angler fish on Youtube

Why has such drastic sexual dimorphism and parasitic behaviour come about? The answer lies in the harsh environment of the angler fish. They exist in the deep fathoms of the sea and the National Geographic in fact, terms this to be “easily Earth’s most inhospitable environment” (http://animals.nationalgeographic.com/animals/fish/anglerfish.html) due to the lack of light and scarcity of other living creatures. Living lives of intense solitude, these tiny males don’t know when they might ever encounter a mate, and therefore seize the day with a vengeance, attaching themselves irrevocably to the first female they meet. This brings an entirely literal meaning to the phrase ‘co-dependence’…

The male angle fish’s determination to not take any chances is what the scientific journal Nature suggests this to be an instance of correlative adaptation, wherein changes in morphology are made due to new habits. Nature goes on to state that “the actions and reactions of the animals themselves result in modifications to structure which become hereditary” ( http://www.nature.com.libproxy1.nus.edu.sg/nature/journal/v125/n3159/pdf/125747a0.pdf). This is thus an example of sexual selection that has arisen out of necessary responses to the angle fish’s environment.

References:

“Anglerfish“. National Geographic.

Armstrong, W.P., 1998. Sexual Suicide. Wayne’s World, 7(1). <http://waynesword.palomar.edu/ww0701.htm#Angler>

Regan C. T., 1930.  Angler-fishes. Nature, 125 (3159): 747-50. <http://www.nature.com.libproxy1.nus.edu.sg/nature/journal/v125/n3159/pdf/125747a0.pdf>

Mind control is a word that is not usually associated with the real world. What comes to mind when this word is mentioned are images from horror movies. However, in actual fact, the manipulation of the mind for the benefit of self is not that far fetched after all! There have been recorded instances of animals that appeared to have the ability to control the behaviour of others through parasitism.

Parasitism refers to a type of relationship between two organisms, in which one receives benefit from the other at the expense of the other organism. Some examples of well known parasites are the tapeworms and fleas.

Tapeworm

While some parasites induce pain, spread diseases and cause general deterioration of the host’s health, there are some parasites that do far more than merely affecting the physical being of the host.

wasp eggs deposited on caterpillar

The trematode parasite, Microphallus sp. was found to affect the behaviour of infected snails radically. The snails are the intermediate host for the parasite while birds are the eventual host. It was found that snails that were infected by the parasite were more prone to linger in open areas, where they were more noticeable by its predators. This bizzare behaviour greatly increases the possibility of the snails being spotted and consumed by birds. Once the parasitized snail is consumed by a bird, the parasite is then able to complete its developmental cycle in the bird’s body. Hence, through the modification of the behaviour of the snail, the parasite significantly increased its chances of completing its development (Levri, 1999).

Another example of such mind control actions of parasites include how wasps affect the behaviour of orb weaving spiders. The wasp Hymenoepimecis argyraphaga parasitizes on its host, the orb-weaving spider Plesiometa argyra by laying eggs on the abdomen of the spider. The spider is then able to carry out its normal daily function and appeared unaffected by the infection while the larva of the wasp feeds on the spider through small holes made on the spider’s abdomen. However, on the night before the larva kills off its host, the spider is induced to make a cocoon web that is able to support the cocoon of the larva, instead of its usual orb shaped web. Upon completion of this task, the spider is then killed and becomes food for the growing larva (Eberhard, 2001).

Normal orbweb vs Web spun by parasitized spider

Researchers are currently looking into the mechanism behind such phenomenon and if successful, this could translate into highly effective pest control measures.

References

Eberhard, W.G. (2001). Under the influence: Webs and building behaviour of Plesiometa argyra (Araneae: Tetragnathidae) when parasitized by Hymenoepimecis argyraphaga (Hymenoptera: Ichneumonidae). Journal of Arachnology 29, 354-366.

Levri, E.P. (1999). Parasite-induced change in host behaviour of a freshwater snail: parasitic manipulation or byproduct of infection? Behavioural Ecology 10, 234-241.