Saturday, April 11, 2009
Visual adaptations
On page 55 Sean Carroll suggests that the white rump of certain pigeons distracts predators when executing an arial dive significantly enough to escape the diving path of the falcons. What are some other visual evolutionary adaptations that have allowed organisms in danger of predation to escape. Of these adaptations, other than distraction, how do these visual adaptations facilitate escape? (ex. Batesian mimicry)
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Batesian mimicry is the form of mimicry in which a palatable species changes its apperance so that it is able to resemble an unpalatable species in order to repel potential predators. One example of this type of mimicry occurs in larva of hawkmoth, which puffs up its head and thorax whenever it feels threatened by a predator. This allows it to resemble the head of a small poisonous snake, thereby scaring off any organism looking to harm it, as the predator determines that the costs of attaining the prey would in some capacity outweigh any potential rewards of acquiring the organsism. In fact, the Dendrobates leucomelas (Yellow-banded Poison Dart Frog)helps this process along by doing push-ups, which demonstrates to the predator that pursuing it would not energetically profitable.
ReplyDeleteBatesian mimicry, or just mimicry in general, is part of the "evolutionary arms race", which refers to the evolutionary struggle between two species involved in a predator-prey relationship, as it pertains to this topic of Batesian mimicry. In response to this evasion tactics, predators use agressive mimicry, a type of mimicry that involves the predator tricking its prey into believing that it is harmless. This allows them to evade being correctly identified as harmful, thus preventing Batesian mimicry from ever occurring.
The trade-off between predator and prey, agressive and defensive mimicry, both contribute to the evolutionary arms race, a race that has been going on between organisms forever; a race that will continue forever.
http://en.wikipedia.org/wiki/Aggressive_mimicry
ReplyDeletehttp://en.wikipedia.org/wiki/Batesian_mimicry
http://en.wikipedia.org/wiki/Dendrobates_leucomelas
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1762363
Many organisms adapt to their environment and change their physiological appearance over time to create easier stalking attempts, while at the same time creating an effective protective barrier to try to fool the predator. In Batesian mimicry the mimic shares signals similar to the model, but does not have the attribute that makes it unprofitable to predators . In other words, a Batesian mimic is a sheep in wolf's clothing. One organism copies the look of a dangerous organism, so it looks like a dangerous species and nobody will bother it. However, if that mimicing speices is attacked; it has no defense like the speices it is mimicing. An example of Batesian mimicry is The False Cobra is a mildly venomous but harmless colubrid snake which mimics the characteristic "hood" of an Indian cobra's threat display. The Eastern Hognose Snake similarly mimics the threat display of venomous snakes.
ReplyDeleteAnother type of visual defense, is another type of mimicry, Mullierian mimicry. Müllerian mimicry describes a situation where two or more species have very similar warning or aposematic signals and both share genuine anti-predation attributes. If two species were confused with one another by a common predator, individuals in both would be more likely to survive. This type of mimcry could also be used to explain mutualism because they are both increasing their numbers of scare and are both helping each other out. Many different tiger moths make ultrasonic clicking calls to warn bats that they are unpalatable. Presumably a bat may learn to avoid any signalling moths, which would make this an example of Müllerian mimicry.
Another great ability of some species is their ability to camoflauge in with their surroundigns if need to escape a predator. A great example of camofluage is the chameleon. Some, but not all, chameleon species are able to change their skin colors. Different chameleon species are able to change different colorrs which can include pink, blue, red, orange, green, black, brown, yellow and turquoise. Recent research indicates that they do not just change their color for reasons of camouflage, but also use colour changes as a method of communication, including to make themselves more attractive to potential mates. This method of communication to work together and enhances their ability to work together and increase the chances of survival for the entire population.
http://en.wikipedia.org/wiki/Chameleon
http://www.geocities.com/brisbane_insects/Mimicry.htm
http://rainforests.mongabay.com/0306.htm
As both Mitchell and Varad mentioned, Batesian mimicry is the evolution by one species to resemble the coloration, body shape, or behavior of another species that is protected from predators by a venomous stinger, bad taste, or some other defensive adaptation. These organisms are essentially really good actors. They pretend to be something that they are not in order to avoid predation and therefore increase their chances of surviving and reproducing. This kind of mimicry is often observed in butterflies and moths, but another example is the coral snake and the milk and king snakes. The coral snake is venomous and therefore dangerous and avoided by predators. Its coloration goes in the order red, yellow, and then black. The milk and king snakes are of no danger whatsoever, but they also have this red, yellow and black coloration which causes predators to recognize them as dangerous as they are associated with the coral snake. There is, however, a slight difference between the two: the king and milk snakes have the colors in the order of red, black, and then yellow. This is where the old scout saying, “red against yellow, kill a fellow; red against black, friend to Jack,” originated from. It is important to remember, though, that due to mutations and such, this rule is not always true.
ReplyDeleteAnother type of mimicry mentioned by Mitchell is Mullerian mimicry. This type of mimicry is when two or more organisms of different species resemble each other. This is different from Batesian mimicry because in this case both organisms are actually dangerous or unpalatable. The advantage of this kind of mimicry is that there is a greater number of organisms that look similar and that have the same effects on predators – whether it is they taste bad or cause the predator to be sick – which means that predators will learn faster to avoid organisms that look specific ways more quickly as they encounter these organisms more frequently. It also means that a smaller percentage of each population of these mimics will be killed by predators when the predators are still learning to avoid them. Mullerian mimicry is observed in the monarch and viceroy butterflies. Both species can be recognized by their dark orange and black coloration and taste bad to predators. Another example is poison arrow frogs. They all come in very bright colors such as red, blue, yellow, and green against black markings. The bright colors with the black are a signal to predators that the frog is highly poisonous.
A final type of mimicry is self mimicry. Self mimicry is a term for animals that have one body part that mimics another to increase survival during an attack. For example, many butterfly, moth, and fish species have markings that resemble eyes called eyespots. These large dark spots, when flashed, may startle a predator and give the prey a little extra time in which to escape. It may also serve as a false target for predators. The owl butterfly, for example, has a large eyespot on the back edge of its wing. A predator is more likely to aim for the eyespot over any other part of the butterfly’s body because it is so distinct. This is advantageous for the butterfly as it is more likely to survive an attack to its wing than an attack to its head.
Perhaps the most well-known form of defense displayed by animals involving their physical appearance, as mentioned by Mitchell, is camouflage. Camouflage is observed in animals that seek to look inanimate or inedible to avoid detection by predators. These organisms are extremely good at blending in with their surroundings so that they are difficult to see. Katydids are a nocturnal insect that are virtually impossible to spot during the day when they are inactive because of their amazing camouflage. They are able to remain completely still and look exactly like a leaf. They have evolved to resemble not only normal leaves, but half-eaten leaves, dying leaves, and even leaves with bird droppings on them. Camouflage is a perfect example of the interaction with the environment theme of biology. These organisms have evolved along with their environments in a way that allows them to hide from predators and therefore increase their chances of survival and allows them a greater opportunity to reproduce.
Sources:
http://highered.mcgraw-hill.com/sites/0070294267/student_view0/glossary_a-d.html
http://rainforests.mongabay.com/0306.htm
http://www.thefreedictionary.com/Mullerian+mimicry
http://www.geocities.com/brisbane_insects/SelfMimicry.htm
In addition to Batesian mimicry, camouflage is commonly used to help organisms to escape from predators. Camouflage is a method of cryptic or concealing coloration that allows an otherwise visible organism or object to remain indiscernible from the surrounding environment through deception. Many animals, such as deer, squirrels, and the peppered moths Carroll describes on pages 52 and 53, use “earthy” tones to blend in amongst the trees in their woody habitats. Sharks and dolphins have a dark dorsal side to blend in with the darker waters below when viewed from above and a lighter underbelly to blend with the light reflecting from the ocean surface when viewed from below. The Artic fox has a brown coat in summer to blend with vegetation and a white coat in winter to blend in with the snow. These coloring examples make the organism less visible to predators and prey, allowing them to escape detection.
ReplyDeleteA zebra’s stripes, while they do not help them to blend in with their surroundings, break up the outline of the animal, called the Craik-O'Brien-Cornsweet illusion. Since the zebra’s main predator, the lion, is color blind, the contrast helps the zebra herd to look like one large mass instead of individuals, making it harder to pick out one zebra to focus on.
http://en.wikipedia.org/wiki/Camouflage
http://www.howstuffworks.com/animal-camouflage.htm
http://conservationreport.com/tag/can-you-see-me-animal-camouflage/
Saturday, April 11, 2009
ReplyDeleteVisual adaptations
On page 55 Sean Carroll suggests that the white rump of certain pigeons distracts predators when executing an arial dive significantly enough to escape the diving path of the falcons. What are some other visual evolutionary adaptations that have allowed organisms in danger of predation to escape. Of these adaptations, other than distraction, how do these visual adaptations facilitate escape? (ex. Batesian mimicry)
Answer:
The process of evading a predator is a very interesting thing. There are many kinds of visual evolutionary adaptations that help organisms evade danger. Many organisms use their environment or habitat to help them go unnoticed by predators. One way to evade danger is Batesian mimicry, as mentioned by Matt. Batesian mimicry is a very effective adaption to enhance escaping prey and therefore survival and reproduction. In Batesian mimicry, a harmless species mimics a harmful model. An example is the larva of the hawkmoth puffs up its head and thorax when disturbed, looking like the head of a poisonous snake. These prey evolved this “copycat” adaptation to gain significant protection by looking like dangerous organisms so that predators would get confused and leave them alone.
Similar to Batesian mimicry, in Mullerian mimicry, two or more unpalatable species resemble each other. Each species gains an advantage because the larger numbers of dangerous organisms that look a like will cause predators to learn more quickly that prey with a particular appearance is dangerous and that they should avoid them. An example of this is the cuckoo bee and the yellow jacket wasp. They both have stingers that release toxins but they both benefit from looking like each other.
Another defense mechanism against predators is aposematic coloration. Animals with effective chemical defenses are often brightly colored as a warning to predators such as the poison-arrow frog. This warning coloration is adaptive. There is evidence that predators are more cautious in dealing with bright colored prey. This is a warning signal that is beneficial for actually both the predators and the prey because they both avoid harm. This defense helps animals escape predators because it correlates them directly with death, because of the fatal poisons or toxins they have, so the predators learn to stay away from them.
Another way animals can defend themselves against predators is cryptic coloration, or camouflage. This has evolved repeatedly among animals and is a passive defense that makes potential prey difficult to spot against its background. An example is a canyon tree frog or more famously, a chameleon. These animals can also evade prey by “hiding” against their background.
http://en.wikipedia.org/wiki/Aposematism
http://beheco.oxfordjournals.org/cgi/content/abstract/arl046v1
http://rainforests.mongabay.com/0306.htm