Fantastic Feigners of Injury and Death

The critically endangered St. Helenian Plover

(Charadrius sanctaehelenae) feigning injury 

(Source: Flickr. Image by Burns)

Two weeks ago my boyfriend’s parents came back from a trip away to the remote island of St. Helena Island off the coast of South Africa where they stumbled upon a bird called the wirebird or St. Helenian plover (Charadrius sanctaehelenae) and came back telling me stories of their find. They were able to watch how a nesting pair they found tried to protect their eggs. I was told that one (they were unsure whether it was the male or the female) sat on the nest and refused to budge while the other moved about around the nest and pretended to be injured in the hope that the predator (in this case my boyfriend’s parents) would get distracted by this display and not go after the eggs anymore but instead go after the ‘injured’ parent.

This in known as ‘injury-feigning’ and is relatively common among birds. Many species of doves and plovers have been observed feigning injury (Swrath, 1935) as well as the Florida nighthawk (Ckhordeiles minor chapmani) (Tompkins, 1942) among others. I have even been lucky enough to witness this in a family of Willy Wagtails (Rhipidura leucophrys) in my back yard back in Innisfail. 

Initially, the reason behind this display was thought to be the birds mixed emotions between wanting to flee the nest to get away from a predator and its attachment to its young causing a muscular inhibition and an inability to fly (Friedmann 1934; Tompkins, 1934). Further observations have lead scientists to believe that this behaviour is in fact a device used voluntarily to lure predators away from young. This would prove to be an advantageous behaviour to adopt because the parent is obviously better able to escape the predator than the chicks in the nest (and definitely the eggs if they are unhatched). By acting injured, the predator is alerted of the existence of a larger and more filling meal being available for only a little more work than it would take to get the chicks or eggs. Weighing the cost over the benefits, the predator is then more likely to attempt to attack the ‘injured’ parent. Hopefully, the injured parent will be able to get away at the last moment and the predator will give up on this meal.

Animals are also known to go one step further. Many animals are able to feign death in order to trick their predators into discarding them. This is called letisimilation or thanatosis (Gregory, et al., 2007) and is widespread among the animal kingdom from insects, amphibians and reptiles to birds and mammals (Gregory, et al., 2007). Some examples of the animals that demonstrate this behaviour are the red flour beetle (Tribolium castaneum) (Miyatake, et al., 2008), ant-lions (of the family Myrmeleontidae) (Turner, 1915), some crickets (eg Gryllus bimaculatus), grass snakes (Natrix natrix) (Gregory, et al., 2007) and rough earth snakes (Virginia striatula) among others (Thomas & Hendricks, 1976) to name a few. 

Western hog-nosed snake (Heterodon nasicus) 

feigning death to escape predation

(Source: Arkive. Image by Visuals Unlimited)

The strategy of feigning death is usually used as a last resort when an animal has been captured by a predator and all its other attempts to avoid predation (eg. toxicity, crypsis, group living, predator confusion, pursuit deterrent signals etc.) have failed. Simulated death may be achieved by rolling over onto their back and opening their mouth like the Western hog-nosed snake (Heterodon nasicus), or by releasing chemicals through their skin threat smell as tough they have been dead for a while and slowing their heart rate. By acting as if they are dead they will either confuse the predator for a split second allowing it to escape or the predator will believe the deception and moves on. Either way, feigning death makes them less likely to be eaten by the predator and more likely to reach their goal of passing their genes onto the next generation (Gregory, et al., 2007).

References

Friedmann, H., 1934. The Instinctive Emotional Life of Birds. The Psychoanalytic Review, 21(3 - 4), pp. 1-57.

Gregory, P. T., Isaac, L. A. & Griffiths, R. A., 2007. Death feigning by grass snakes (Natrix natrix) in response to handling by human "predators.". Journal of Comparative Psychology, 121(2), pp. 123-129..

Miyatake, T. et al., 2008. Pleiotropic antipredator strategies, fleeing and feigning death, correlated with dopamine levels in Tribolium castaneum. Animal Behaviour, 75(1), pp. 113 - 121.

Swrath, H. S., 1935. Injury-Feigning in Nesting Birds. The Auk, 52(3), pp. 352 - 354.

Thomas , R. A. & Hendricks, F. S., 1976. Letisimulation in Virginia striatula (Linnaeus). The Southwestern Naturalist , 21(1), pp. 123-124.

Tompkins, I. R., 1942. The "Injury-Feigning" Behavior of the Florida Nighthawk. The Wilson Bulletin, 54(1), pp. 43 - 49.

Turner, C. H., 1915. Notes on the Behavior of the Ant-Lion with Emphasis on the Feeding Activities and Letisimulation. Biological Bulletin, 29(5), pp. 277 - 307.

University of Bath, 2010. The critically endangered St. Helenian Plover feigning injury, photograph, viewed 27 May 2014

< http://farm4.staticflickr.com/3820/12087002524_78b072d4ac_z.jpg>

Visuals Unlimited, n.d., Western hog-nosed snake (Heterodon nasicus) feigning death to escape predation, photograph, viewed 27 May 2014

< http://cdn2.arkive.org/media/C1/C10548AF-A87F-4314-8C1D-8A039B127130/Presentation.Large/western-hog-nosed-snake-ssp-kennerlyi-feigning-death.jpg>

An alluring meal or a luring trap? More deceptive tricks animals use to get an easy meal

Continuing on for last week, here are a few more animals that have devised ways to trick their prey into coming to them so they can sit back, relax and enjoy the meal.

Striated Heron (Butorides striata) using a dragonfly to lure fish

(Source: Biodiversity Explorer. Image by DeWet)

Herons

While there are many animals that have specialised appendages in order to lure their prey in, not all are so lucky. Some species of heron have not let this discourage them. Green Herons (Butorides virescens), Squacco Herons (Ardeola ralloides), Striated Herons (Butorides striata) and Goliath Herons (Ardea goliath) have all learnt that if they place a flower, a feather, a stick an insect or some other item in the water, that that they can trick fish into coming toward what they think is a food item and get an easy feed (Gavin and Solomon, 2009; Ruxton and Hansell, 2011). This method is thought to have evolved from ‘passive bait fishing’ where birds take advantage of fish being attracted to intimate objects floating by in the water (Ruxton & Hansell, 2011).

Assassin bug Stenolemus bituberus

(Source: Die Raubwanzen der Welt. Image by Jestis)

Assassin Bugs

The assassin bug (Stenolemus bituberus) has a dangerous choice of food; spiders. To get a meal they risk facing a counter attack by the spider that could possibly kill them resulting in the assassin bug becoming the prey. To lower the chances of being attacked, assassin bugs have devised a way to seize spiders when they least expect it; when they are lining up for their dinner. The assassin bug will go up to the edge of a spider’s web and shake it. The spider, thinking an insect has gotten itself caught in the sticky web, comes down to eat it but instead gets attacked by the assassin bug. The assassin bug attacks by piercing its rostrum into the animal and injecting it with its venom, paralysing it. The assassin bug then proceeds to suck the juices out of the insect (Wignall & Taylor, 2009).

Even when not hunting spiders, the assassin bug can still be deceptive. When the assassin bug stalking its prey, as it gets close it alters its footsteps to an uneven pattern so that it blends in with the background noise of the wind moving the plants (Wignall & Taylor, 2009). The poor animal never knew what hit it!

Capable of pulling the face made famous by a particular boot wearing

cat in the movie ‘Shrek 2’, you would never have expected that the 

Margay was capable of dishonesty and deception.

(Source: Fotopedia. Image by unknown)

Margays

While Dr. Fabiano Calleia was studying tamarin monkeys in Brazilian rainforest, he heard the sound of a distressed tamarin pup in the distance. This greatly disturbed the other tamarin monkeys in the troop he was following and they went off to find the defenceless pup. To his astonishment, Dr. Calleia saw that it was not actually a tamarin pup but a margay (Leopardus wiedii) mimicking the sound of a distressed pup to lure the other tamarin monkeys closer (Angier, 2010). Luckily, the tamarin monkeys realised this was the case and a sentinel money screamed and the troop escaped unharmed. While vocal mimicry has been observed in bottlenose dolphins (Tursiops truncatus), harbour seals (Phoca vitulina), killer whales (Orcinus orca), orangutans (Pongo spp.) and African savannah elephants (Loxodonta africana) (Kelley & Healy, 2011), to date, this is the only confirmed case of vocal mimicry used to attract prey.

References

Angier, N., 2010. Why copycats have nine lives; Aping your prey is just one of many surviving-by-disguising strategies in the animal kingdom. Edmonton Journal, p. E.2.

Capable of pulling the face made famous by a particular boot wearing cat in the movie ‘Shrek 2’, you would never have expected that the Margay was capable of dishonesty and deception, n.d., photograph, viewed 20 May 2014

<http://de.fotopedia.com/items/flickr-771396288> 

DeWet, C, n.d., Striated Heron (Butorides striata) using a dragonfly to lure fish, photograph, viewed 20 May 2014
<http://www.biodiversityexplorer.org/birds/ardeidae/butorides_striatus.htm>

Jestis, D, n.d., Assassin bug (Stenolemus bituberus), photograph, viewed 20 May 2014
<http://www.reduviidae.de/systematik/emesinae/stenolemus.html>

Gavin, M. C. & Solomon, J. N., 2009. Active and Passive Bait-Fishing by Black-Crowned Night Herons. The Wilson Journal of Ornithology, 121(4), pp. 844 - 845.

Kelley, L. A. & Healy, S. D., 2011. Vocal mimicry. Current Biology, 21(1), pp. R9- R10.

Ruxton, G. D. & Hansell, M. H., 2011. Fishing with a Bait or Lure: A Brief Review of the Cognitive Issues. Ethology, 117(1), pp. 1 - 9.

Wignall, A. E. & Taylor, P. W., 2009. Alternative predatory tactics of an araneophagic assassin bug (Stenolemus bituberus). Acta Ethologica, 12(1), pp. 23 - 27.

An alluring meal or a luring trap? Ways animals deceive and entice their prey

If pizza didn’t cost extra to get delivered, I doubt anyone would ever make all that effort to drive ALL the way to the store, wait around cos it still isn’t finished and then drive ALL the way home again. We would much rather our meals came to us. The same goes for animals.

There are many deceptive animals out there that will do anything to get out of having go and hunt for their food. Many have to chase their prey and this often requires a lot of energy. In some cases, the predator may even risk their life in the pursuit of their prey. Obviously, it is much more beneficial for the animal to save this energy if it can, so what is the logical course of action to take? Lure your prey in!

Cantil snake (Agkistrodon bilineatus taylori) displaying its tail

(Source: The Gardens of Eden. Image by Kerr)

Cantil

Found in northern Mexico and Central America (ref), the highly poisonous Cantil snakes (Agkistrodon bilineatus taylori) are rather stocky snakes and for that reason are pretty hopeless at moving at any great speed (Parkinson, et al., 2000). To obtain their prey they use the tip of their tail. The tip of their tail is thin and often yellow or off white in contrast to their thick dark coloured bodies and resembles a wriggling worm; the prey of many of the Cantil snakes favourite food. A little critter will then come along, see a delightful treat and end up becoming the treat for the Cantil snake instead.

Alligator Snapping Turtle (Macrochelys temminckii) displaying its tongue

(Source: 8tracks, Image by unknown)

Snapping turtle

Alligator snapping turtles are slow moving and rather good at looking like a rock. In order to catch their prey they sit at the bottom of the water with their mouth open wiggling their tongue in the current to make it look like a little worm and wait (East, et al., 2013). Eventually an intrigued fish will come along and the alligator snapping turtle will bear down on the unsuspecting fish with the second strongest jaw pressure bite of any other animal in the world!

Tasselled Wobbegong Shark (Eucrossorhinus dasypogon)

(Source: svdelos.blogspot.com. Image by unknown)

Wobbegong

Wobbegong sharks are found predominantly in Australia and their name means “shaggy beard” in one of the many indigenous languages. Wobbegongs use their frilly appendage to break up their outline to better camouflage them selves but it serves another purpose. Their “shaggy beard” also lures in small fish for them to feast on (Motta & Wilga, 2001).

While there are 12 species of shark which are commonly referred to as wobbegongs, one stands out above the rest for its deceptive abilities. The tasselled wobbegong shark (Eucrossorhinus dasypogon) employs another, more effective, technique to obtain a hearty meal. It also moves its tail about like a small fish. The tasselled wobbegong shark tail is even somewhat forked tipped and in some cases they even have a fake eye making their deception even more convincing.

A female Photuris versicolour eats a male Photinus ignightus

(Source: Cornell Chronicle. Image by Eisner)

Photuris firefly

The Photuris firefly is especially skilled at gaining from their use of deceitful actions. A Photuris firefly preys upon male Photinus fireflies. The poor Photinus fireflies go about regular firefly courtship routine and emit flashes of light at a frequency unique to their species. Males fly above the ground while the females, who’s wings are too small to fly, rest on the ground watching their potential suitors fly overhead (Eisner, et al., 1997). Meanwhile, the conniving Photuris firefly sits and studies other female fireflies in order to mimic their flashing patterns. When a male sees this copied pattern he thinks it is a female of his own species and descends prepared to mate with the lovely maiden below. The result of this encounter is not procreation but ingestion of the male Photinus firefly by the Photuris firefly (Eisner, et al., 1997).

The Photuris firefly gets a many benefits out of this tactic. Obviously, he gains a meal helping him to increase fitness and ability to produce offspring. Furthermore, by eliminating his rivals he lessens the competition he has to face with other fireflies for resources. These things considered, perhaps the most devious outcome is one of toxicity. While Photuris fireflies are not toxic when they are born, by consuming naturally toxic Photinus fireflies they assume their chemical defence (chemical compounds called lucibufagins) (Eisner, et al., 1997).

References

Alligator Snapping Turtle (Macrochelys temminckii) displaying its tongue, n.d., photograph, viewed 13 may 2014
<http://i.imgur.com/9koX3GL.jpg>

East, M. B., Fillmore, B. M. & Ligon, D. B., 2013. Feeding Behavior of Captive-Reared Juvenile Alligator Snapping Turtles (Macrochelys temminckii). Southeastern Naturalist, 12(4), pp. 692 - 702.

Eisner, T., 1997, A female Photuris versicolour eats a male Photinus ignightus, photograph, viewed 13 May 2014
<http://www.news.cornell.edu/sites/chronicle.cornell/files/fireflyeatingmale.72.JPEG>

Eisner, T. et al., 1997. Firefly "femmes fatales" acquire defensive steroids (lucibufagins) from their firefly prey. Proceedings of the National Academy of Sciences of the United States of America, 94(18), pp. 9723 - 9728.

Kerr, M. D., 2011, Cantil snake (Agkistrodon bilineatus taylori) displaying its tail, photograph, viewed 13 May 2014
<http://www.thegardensofeden.org/p169755082/h3B5F7EE#h3b5f7ee>

Motta, P. J. & Wilga, C. D., 2001. Advances in the Study of Feeding Behaviors, Mechanisms, and Mechanics of Sharks. Environmental Biology of Fishes, 60(1), pp. 131 - 156.

Parkinson, C. L., Zamudio, K. R. & Greene, H. W., 2000. Phylogeography of the pitviper clade Agkistrodon: historical ecology, species status, and conservation of cantils. Molecular ecology, 9(4), pp. 411-420.

Tasselled Wobbegong Shark (Eucrossorhinus dasypogon), 2013, photograph, viewed 13 May 2014

<http://lh4.ggpht.com/-f4N-NS_73Mc/UnMxLxD5kLI/AAAAAAAAKT4/He3EFu7_bjA/%2525281%252529_thumb%25255B1%25255D.jpg?imgmax=800>

Liar, liar, pants on fire!

Lying. We all do it (some of us better than others), but why?

Liar (Source: Glen the Great. Image by unknown)

Did you ever play the game in primary school Two truths and a Lie? The aim of the game is to have a person tell 2 truths and 1 lie and the other person has to work out which one is the lie. Here goes…

1. My boyfriend’s Father was born in Sweden and his mother was born in Uganda

2. I went to Canada on a high school band camp

3. Every one of my mother’s 5 siblings have owned a small business at some point in their lives

So which one do you think is the lie?

Despite the little games we play, lying is an important part of human existence. Because of our ability to lie, an individual has the opportunity secure itself more food, more mates and perhaps most importantly, good social standing with their peers. All of these things are not guaranteed though. The individual needs to be able to lie well and escape detection from the people they are lying to. Equally, they need to be able to detect liars so they themselves are not duped.

Learning to lie and detect liars takes a lot of time to develop. We start lying at a surprisingly young age. 6 months according to Gray (2007). You have probably seen this yourself. A baby sits crying in their crib. Their bawling is interrupted by a short pause where he/she looks around to see if anyone is coming to give them attention and if no one is there they resume their wailing. 3 years later and she is lying to mum about who really broke her little sister’s toy horse. By 15 she is telling mum she is going over her friends place to study after school (wink wink). By the time she is an adult she will most likely tell an average of 3 lies in a 10 minute conversation (Meyer, 2011).

Some people are so advanced at lying that they can actually lie to themselves. This is known as self-deception (Bayne & Fernandez, 2009). This occurs when a person holds two pieces of contradicting information in their mind but only pays attention to one. This is often the case for pathological liars. According to Mele (1983), when pathologiacal liars tell a lie is possible for them to believe wholeheartedly that what they are saying is the truth. That is not all though.

Grey and White Brain Matter

(Source: Medical News Digest. Image By Unknown)

Studies conducted by Yang et. al. (2005) showed that pathological liars had significantly different brain structure compared to normal people. They found that the prefrontal cortex of liars had around 25% more white matter (the part of the brain that connects everything together) and 14% less grey matter (the part of the brain that processes information) when compared to normal controls (Yang , et al., 2005). This essentially means that pathological liars have a heightened ability to make connections in their brain and therefore keep track of all the information due to the increased white matter. The trade-off is in the reduced amount of grey matter which correlates to our ability to think critically about (in this case) the implications of the lie being told.

As we all grow older we learn how to lie, who is good at detecting our lies and what lies we can get away with (McCann, 1998). So how advanced are you? Which of the 3 options given earlier did you think was the lie? Do you think it is unlikely that my boyfriend has such a diverse heritage? Do you doubt that a small high school in Innisfail would take their band all the way to Canada? Or do you think it is beyond belief that my mothers 4 sisters and 1 brother have ALL owned small business in their lifetime? If you guessed option 2 “I went to Canada on a school band camp” you are correct. My boyfriend’s father is Swedish and his mother was born in Uganda (to English parents though), and my aunties and uncles do all have businesses (most in farming), but I have actually never left the country (although just for your information, I do know that quite a while ago my high school did actually send their band over to Innisfail, Canada on a band camp but it was before I was born.)

References

Bayne, T. & Fernandez, J., 2009. Delusion and Self-Deception. New York: Psychology Press.

Gray, R., 2007. Babies not as innocent as they pretend. The Telegraph, 1 July.

Grey and White Brain Matter, n.d., photograph, viwed 5 may 2014

<http://www.medinewsdigest.com/wp-content/uploads/2011/12/Brain_Cortex_Harvard-e1323835780229.png>

Liar, n.d., photograph, viewed 5 May 2014

<http://glennthegreat.com/wp-content/uploads/2012/05/liar.jpg>

McCann, J. T., 1998. Malingering and Deception in Adolescents: Assessing Credibility in Clinical and Forensic Settings. Washington, DC: American Psychological Press.

Mele, A. R., 1983. Self-Deception. The Philosophical Quarterly, 33(133), pp. 365-377.

Meyer, P., 2011. How to spot a liar. Video recording: TED.

Yang , Y. et al., 2005. Prefrontal white matter in pathological liars. The British Journal of Psychiatry, Volume 187, pp. 320-325.

A Biology Lesson From Winnie-the-Pooh: Crypsis and Masquerade

'It's like this,' [Pooh] said. 'When you go after honey with a balloon, the great thing is not to let the bees know you're coming. Now, if you have a green balloon, they might think you were only part of the tree, and not notice you, and if you have a blue balloon, they might think you were only part of the sky, and not notice you, and the question is: Which is most likely?'

‘Wouldn't they notice you underneath the balloon?' [Christopher Robin] asked.

'They might or they might not,' said Winnie-the-Pooh. 'You never can tell with bees.' He thought for a moment and said: I shall try to look like a small black cloud. That will deceive them'

'Then you had better have the blue balloon' [Christopher Robin] said: and so it was decided…

…Winnie-the-Pooh went to a very muddy place that he knew of, and rolled and rolled until he was black all over; and then, when the balloon was blown up as big as big, and you and Pooh were both holding on to the string, you let go suddenly, and Pooh Bear floated gracefully up into the sky'

(Milne, 1926)

Still from The Many Adventrures of Winnie-the-Pooh

(Source: Disney Image by Disney)

What Winnie-the-Pooh (or the author A. A Milne I assume) probably did not realise was that Pooh was using two different types of mimicry when he made his feeble attempts to approach the bees nest and steal their honey unnoticed. In having his balloon blend in with the surroundings (the blue sky) he used crypsis. By covering himself in mud to try and look like an intimate object that would normally be in a sky (a dark cloud) he used masquerade. Unfortunately for Pooh, his skills at mimicry left quite a bit to be desired! In the animal kingdom, this is far from the case.

Animals that use crypsis don’t always have it as easy as Pooh did. In Pooh’s case, the sky was one colour and all he had to do was match that colour. A similar case would be of a green aphid blending into its background of a green leaf or a polar bear blending into the snow and ice. Not all environments are that uniform though. Animals can live in habitats that vary greatly in colour and can also vary from season to season proving crypsis to be difficult. An example pointed out by Allen and Cooper (1985) is the common meadow grasshopper Chorthippus parallelus found in grasslands in Europe. There are many morphs of this species that all appear to represent different sections of the background environment (pictured below) (Allen & Cooper, 1985).

(A)          Purple morph of the meadow grasshopper Chorthippus parallelus

(Source: Adur Nature Notes 2005. Image by Unknown)

(B)          Brown morph of the meadow grasshopper Chorthippus parallelus

(Source: naturephoto-cz.com. Image by Krasensky)

(C)          Purple, green and brown morph of the meadow grasshopper Chorthippus parallelus

(Source: Wyre Forest Blog. Image by Unknown)

(D)          Green morph of the meadow grasshopper Chorthippus parallelus

(Source: Natural History Museum. Image by Palmer)

(E)           Green and white morph of the meadow grasshopper Chorthippus parallelus

(Source: Lound Bird Club. Image by Warne)

An alternative to crypsis is masquerade. In masquerade, organisms copy an object that would be of no interest to their predator (or their prey) despite being obvious to them. This, unlike crypsis, counts on the fact that the predator (or prey) actually sees the individual but mistakes it for something else. Some examples of prey escaping detection are butterflies that look like dead leaves, or caterpillars that resemble bird droppings (Allen & Cooper, 1985). My personal favourite example of a predator hiding in order to capture is the carnivorous caterpillars of Hawaii (Eupithecia orichloris) which imitate sticks and wait for an unsuspecting fly (or similar sized insect) to venture onto the “branch” and become their next meal (Montgomery, 1982). This strategy is also used by prey avoiding predation (Allen & Cooper, 1985).

Anaea archidonia butterfly

(Source: Personal Documents. Image by Summers)

Papilio demoleus caterpillar

(Source: Wildlife Junior Journal. Image by Payne)

In some cases it is hard to determine whether an organism is being masquerading or being cryptic. If the object that the organism is masquerading as is abundant enough it may be considered to be cryptic. Returning to A.A Milne’s example, how many little black clouds would there need to be before our little friend Pooh goes from masquerading as a cloud to blending into a background of clouds and being cryptic? Or else, how many stones would there need to be in an area before stone grasshoppers (pictured below) are being cryptic?

Stone Grasshopper from Namibia

(Source: What’s That Bug? Image by Grimfoot)

References

Allen, J. A. & Cooper, J. M., 1985. Crypsis and masquerade. Journal of Biological Education, 19(4), pp. 268-270.

Disney, n.d., Still from The Many Adventrures of Winnie-the-Pooh, photograph, viewed 22 April 2014

<http://video.disney.com/watch/climb-a-tree-4bb39d8294da5a8833003b15>

Grimfoot, 2009, Stone Grasshopper from Namibia, photograph, viewed 22 April 2014

< http://www.whatsthatbug.com/2009/11/30/stone-grasshopper-from-namibia/>

Krasensky P, n.d., Brown morph of the meadow grasshopper Chorthippus parallelus, photograph, viewed 22 April 2014

< http://www.naturephoto-cz.com/chorthippus-parallelus-photo_lat-4538.html>

Milne, A. A., 1926. Winnie-the-Pooh. 1st ed. London: Methuen & Co. Ltd..

Montgomery, S. L., 1982. Biogeography of the Moth Genus Eupithecia in Oceania and the evolution of ambush predation in Hawaiian caterpillars. Entomologia Generalis, 8(1), pp. 27-34.

Palmer, G, n.d., Green morph of the meadow grasshopper Chorthippus parallelus, photograph, viewed 22 April 2014

< http://www.nhm.ac.uk/nature-online/species-of-the-day/biodiversity/climate-change/chorthippus-parallelus/>

Payne, JA, n.d., Papilio demoleus caterpillar, photograph, viewed 22 April 2014

< http://www.nhptv.org/wild/karnereasterntigerswallowtail.asp>

Purple, green and brown morph of the meadow grasshopper Chorthippus parallelus, 2013, photograph, viewed 22 April 2014

< http://www.wyreforest.net/wyreblog/2013/08/10/meadow-grasshopper-chorthippus-parallelus/_mg_2693-chorthippus-parallelus-meadow-grasshopper-franks-clearing-dowles/>

Purple morph of the meadow grasshopper Chorthippus parallelus, 2005, photograph. Viewed 22 April 2014

< http://www.glaucus.org.uk/July2005.html>

Summers, KM, 2014, Anaea archidonia butterfly, photograph, viewed 22 April 2014.

Warne, M, 2011, Green and white morph of the meadow grasshopper Chorthippus parallelus, photograph, viewed 22 April 2014

< http://www.loundbirdclub.com/wildlifesightings2011.htm>

The History of Müllerian Mimicry Part 2: How far we have come

If I have seen further it is by

standing on the shoulders of giants.

~ Isaac Newton ~

Since Friz Müller first attempted to explain the phenomenon of two poisonous or unpalatable species mimic each other there has been a considerable amount of research into the topic. As scientists have explored the relationships that mimics have with each other and their predators, they have been able to build on Müller’s ideas. Unfortunately, Müller has also been found to be wrong in some cases (which is understandable considering he made these claims 135 years ago!). Never the less, his contributions to the topic have not gone unnoticed and this phenomenon is still commonly referred to as Müllerian mimicry.

Last week, I posted a general explanation of Müller’s model he put forward. In his model he assumed that animals need to learn to avoid unpalatable species and that, in learning to avoid them, they eat a fixed amount of them before being turned off them all together. Let’s see how far research has come since then.

Do predators really need to learn to avoid prey? 

Müller’s first proposition was that animals need to learn to avoid prey that tastes bad. This is usually the case but not always. In studies concerning some very poisonous prey items (eg. Snakes), predators seem to innately avoid these species (Cladwell & Rubinoff, 1983).  Apart from these few cases, the majority of predators researched have demonstrated that they need to learn by their mistakes before they will avoid an unpalatable prey species. Examples include young birds learning to avoid noxious insects and butterflies in studies by Mostler in 1935 and Chai in 1996 (Cited in Sherratt, 2008) as well as inexperienced lizards attacking unpalatable butterflies before learning to avoid them (Boyden, 1976).

Do predators take a fixed number of prey regardless (independent) of the abundance? 

Müller’s second assumption was that there was a fixed number (n) of individuals a predator would take from a population before it had learnt to avoid it. In Müller’s theory he supposed that the number of individuals taken from two species not mimicking each other would be the same regardless of the size of the population. For example, if there were 100 individuals of one species and 900 individuals from another species that looked different from each other, Müller predicted that both species would have an equal absolute number taken from each population and resulting in the rarer population having a far greater proportion of the total population eaten relative to the more abundant population. Unfortunately for Müller, there has been no research to date showing that a “fixed n” exists (Sherratt, 2008).

Contrary to Müller’s hypothesis, an experimental study by Greenwood et. al. (1989) found that when birds were left to forage for unpalatable prey of two different appearances and in different abundances that the absolute number taken from the two different appearances were different. Greenwood et. al. (1989) randomly placed pieces of pastry flavoured with quinine hemi-sulphate (proven to be unpalatable to the birds) on grid in a ratio of yellow to red of 1:9 and repeated with a ratio of 9:1. Of all the trials conducted, the more common form had a larger absolute number of pieces of pastry eaten by the birds compared to the rarer form. This disproves Müller and confirms that there is not a ‘fixed n’. Never the less, the proportion of rarer forms eaten was larger than the proportion of abundant forms taken and therefore proves it would still be beneficial if these two forms were a mimic of each other. In a way, Müller was right, this development only means that there is no ‘fixed n’ and that the amount of benefit gained by mimicry is less than what Müller originally anticipated (Greenwood, et al., 1989).

Building on Müller’s Ideas: Research into other factors influencing mimicry

As well as the influences of abundance on predation on unpalatable food, there have been many studies that have found or proposed other factors could influence the number of unpalatable prey that will be eaten. Greenwood et. al. (1989) suggested that hungrier birds may be more likely to eat unpalatable if they assessed the cost of eating a bad tasting individual to outweigh the benefit of acquiring food (for instance, I don’t like beetroot and usually avoid it. But if I hadn’t have eaten for a few days, I’m sure I would jump at the chance if I had no other choices). Other possible influences on predation of mimetic species include predators’ ability to distinguish between mimetic species, differences in defences of species that mimic each other (eg having different toxins that make them them unpalatable) which may cause one predator to view both species as distasteful but another predator to view only one of the species as distasteful, and the intensity of unpalatability of the two mimetic species to name a few.

References

Fritz Müller in Brazil, n.d., photograph,  viewed 6 April 2014,
<http://en.wikipedia.org/wiki/File:Fritz-muller-1821-1897.jpg>

Boyden, T. C., 1976. Butterfly palatability and mimicry - experiments with Amevia lizards. Evolution, 30(73-81), pp. 1992-1998.

Cladwell, G. S. & Rubinoff, R. W., 1983. Avoidance of venomous sea snakes by naive herrons and egrets. The Auk, 100(1), pp. 185-198.

Greenwood, J. D., Cotton, P. A. & Wilson, M. D., 1989. Frequency-dependent selection on aposematic prey - some experiments. Biological Journal of the Linnean Society, 36(1-2), pp. 213-226.

Müller, F., 1879. Ituna and Thyridia; a remarkable case of mimicry in butterflies. Transactions of the Entomological Society of London, pp. xx-xxix.

Sherratt, T. N., 2008. The Evolution of Müllerian Mimicry. Naturwissenschaften, 95(8), pp. 681-695.

The History of Müllerian Mimicry

Attempts to explain what is now known as Müllerian mimicry were first made 135 years ago by German biologist Johann Friedrich Theodor (Fritz) Müller. Müller (1879) provided an evolutionary explanation to describe the phenomenon where two unpalatable species exhibit a similar appearance to each other. He was also the first person to present a “formal mathematical model to support an evolutionary hypothesis” (Sherratt, 2008, p. 682).

Müller (1879) hypothesised that if predators were required to learn from experience which prey items were distasteful, that two similarly distasteful prey items would benefit if they displayed similar appearances because this would reduce the number of individuals that die during the process where inexperienced predators ‘learn’ which prey items are distasteful. More specifically, Müller (1897) was saying a predator would only eat a given number of what they thought were a single distasteful species before they learned that they were distasteful regardless of whether it was in fact a single species or two species that mimicked each other (Sherratt, 2008).

Müller's formula explaining how it is beneficial for two poisonous species to have similar appearances (Source: Transactions of the Entomological Society of London. Image: Müller)

Using his proposed formula (pictured right) Müller (1879) put forward an explanation using two theoretical species in a community (Species A and Species B) and a theoretical number of individuals of a particular appearance must be eaten in the population before the predator species learns not to eat them. To put it simply, let’s pretend we are an animal who feeds on butterflies. When you are born you have absolutely no knowledge of what butterflies are good or bad tasting; all you know is that you have to eat butterflies. You eat a few butterflies but then you catch one that tastes revolting. You keep feeding, possibly thinking that it was just a dodgy butterfly. But then it happens again! This is another disgusting tasting butterfly that looks suspiciously similar to the last one that tasted bad.... For arguments sake, let’s say it takes you 5 attempts at eating that type of butterfly before you decide you will never eat a butterfly that looks like that again.

If there are two completely different species of bad tasting butterflies and one (Species A) is pretty small (eg. 2000 individuals) and the other (Species B) is relatively large (eg 10,000 individuals), 1 predator taking the same number of individuals out of both populations will make a larger difference in the smaller population than the larger one. For Species A, if we take into account for the entire population of predators and assume that there are 240 juveniles in the population each taking 5 individuals from a species, that is 1200 members of butterfly Species A that get eaten in one season. That equates to 60% of the population! If we compare that to Species B with 10,000 individuals, the predators still only take 1200 butterflies but it only equates to about 12% of the total population (See Figure 1).

Figure 1. Proportions of individuals eaten from two unpalatable
species that look different (Image: Summers)

Obviously, the larger population has the advantage here, but what if these two species looked similar? If a predator cannot tell the difference between them visually, they only need to remember one type of markings. If they eat one from Species A they will remember it and when they eat one from Species B they will see, what looks like to them, the same animal and avoid it also. This way, one predator only needs to eat five individuals from Species A or Species B and not five individuals from Species A and Species B. That equates to 1200 individuals from Species A or Species B and not 2,400 individuals from Species A and Species B combined.


Müller (1879) goes on to explain that when the predator takes individuals from species A and B thinking they are the same species, that the number of individuals eaten is dependent upon the number of individuals in each species and therefore the proportion taken from each species is e qual. In other words, the predator species will eat 200 individuals from Species A and 1,000 individuals B; 10% of each species’ initial population 

Figure 2. Proportions of individuals eaten from two unpalatable
species that look the same (Image: Summers)

References
Müller, F., 1879. Ituna and Thyridia; a remarkable case of mimicry in butterflies. Transactions of the Entomological Society  of London, pp. xx-xxix.

Sherratt, T. N., 2008. The Evolution of Müllerian Mimicry. Naturwissenschaften, 95(8), pp. 681-695.

Summers, K. M., 2014. Figure 1. Proportions of individuals eaten from two unpalatable species that look different photograph, viewed 31 March 2014.

Summers, K. M., 2014. Figure 2. Proportions of individuals eaten from two unpalatable species that look the same, photograph, viewed 31 March 2014.