Wednesday, April 7, 2010

An ever evolving struggle

In Coyne’s harrowing tale of the Asian giant hornet he describes a specific prey adaptation of the Japanese bee in order to combat the hornet upon an invasion of their hive (112). He also gives one other example of a predator/parasite-prey evolutionary relationship with the example of a roundworm infecting an ant in Central America but this point for evolution is rather scarcely covered with examples. What other examples are there of complex and specific predator (or parasite) to prey relationships where the predator is well adapted to hunt its prey and the prey has evolved specific defenses as a reaction to these recurrent attacks? Also is it not also true that, in time, predators would begin to adapt to the strategies used by their prey to fight them off? Provide another example for this case where the predator is adapting alongside its prey.


  1. There are many examples of prey antipredator adaptations, with their purposes usually falling under one of three categories: avoiding detection, avoiding attack, and avoiding capture.
    Adaptations like camoulflage and nocturnal behavior fall into the first category. By changing the distribution of pigment in an organism's skin or changing an organism's sleeping patterns, they become harder to spot by predators and thus are not targeted as frequently for predation. An example of a relationship in which prey have adapted a certain trait to avoid detection by a predator highly attuned to its surroundings is that of the snowshoe hare and its predator the gray fox. During changing seasons, the snowshoe hare's coat actually changes color to meet the specific time of year. During winter, for example, the coat becomes snow-white. In addition to this chromatic change to suit the surroundings based on season, the hare has also developed a defensive behavior in which it stops in its tracks at the first sight of a predator. As explained on the website Animal Diversity “Presumably, they are attempting to escape notice by being cryptic. Given the hare's background-matching coloration, this strategy is quite effective.” ( )
    Thus, the snowshoe hare becomes even harder to spot with this 'freezing' behavior, and increase their chances of survival and reproduction.
    ( )
    The second method of anti-predator adaptation does not attempt to avoid detection by predators but rather warns them to think twice about attacking. Natural poisons or bright colors to warn predators as well as mimicry of other organisms using those defenses (Mullerian if the organism also has those traits or Batesian if it is harmless and merely mimicking) fall under this category. Another example of this is behavior that indicates fitness to a predator that prefers weaker or unfit prey less likely to resist, such as the stot of the gazelle when faced with the threat of a predatory lion. Lions prefer to target individuals less able to resist their attacks as this allows them to conserve more energy in the acquisition of food, and as Richard Dawkins explains in The Selfish Gene, the stot “is an attempt at advertising an animal's health”. Even though such behavior may seem maladaptive at first glance (wasting energy and potentially singling the individual out for predation), it is actually a form of boasting or taunting to predators, encouraging them to call off the chase in favor of a less resistent meal.
    ( )
    The third method of anti-predator adaptation involves avoiding capture by predators. This kicks into action after a predator has decided to single out a prey for consumption, taking the form of increased speed and sensitivity in predator detection to maximize the potential distance between the predator and prey during the chase, eating and moving collectively as a herd to avoid singling out by a predator, and adaptations like claws and horns to fight back. An example of this third form is the mobbing “divebomb” behavior of crows upon eagles seeking easy prey. The sharp talons and beaks of eagles have made them highly attuned to targeting and killing individuals, but this mobbing behavior (similar to that of the bees mentioned by Coyne) prevents these predators from gaining a lock on a single attacker. By repeatedly attacking the eagle on all sides, the crows minimize the potential damage caused by eagles 'picking off' many crows one by one.
    ( )

  2. Of course, if predators did not adapt to meet the needs of such defensive mechanisms, they would not survive and reproduce to be alive today. As Coyne notes on page 115, “everywhere we look in nature, we see animals that seem beautifully designed to fit their environment, whether that environment be the physical circumstances of life, like temperature and humidity, or other organisms [like] competitors, predators, and prey”. As the evolutionary pressures to obtain food alter, so too must the predator to continue survival and reproduction, leading to a sort of evolutionary arms race between predator and prey.
    An example of a specific predator-prey 'arms race' is that of the kestral and the vole. The vole, a type of small rodent, faces many predatory threats, such as owls, foxes, and kestrals. To increase their chances of survival and reproduction, they make their home underground with less of a chance of predatory detection. At the first sight of a predator, they immediately leap into their burrows and wait for the threat to leave. However, the kestral has developed an interesting response to this defense mechanism: the ability to 'see' “vole scent marks visible in ultraviolet light” ( ). While with normal vision the predator would be hard pressed to spot the homes of the vole, the ability to see vole scent marks in their urine and feces allows the kestral to zero in on these burrows, thus somewhat negating the vole's defensive mechanism.

  3. There are many other types of predator prey relationships. For instance, the plant milkweed, which is the food source for the monarch butterfly, is constantly under attack from hungry caterpillars. "Milkweeds use three primary defenses to limit damage caused by caterpillars: hairs on the leaves, cardenolid toxins, and latex fluids". The most interesting adaptation is the toxicity that the plant has built up over the course of evolution. This toxicity threatens animals such as caterpillars away from eating its leaves, its site of food production: photosynthesis. However, due to this increase in toxicity, the monarch butterfly (the caterpillar from before) has coevolved with its meal, and developed an immunity to the toxin. This explains the monarch's orange color, which is a clue to many other predators that it is toxic and dangerous to eat. To combat this development, scientists have discovered that "recently evolved milkweed species utilize less of these preventative strategies, but grow faster than older species; potentially regrowing faster than caterpillars can consume them". This is a very long battle of side by side evolution that has no foreseeable end in the future.
    Another sweet defense adaptation is some lizard's ability to: "When attacked, many lizards jettison the wriggling appendage and flee. The predator often feasts on the tail while the lucky lizard scurries to safety. Later, the lizard simply grows a new tail."
    This is an evolutionary dead end, it seems, though, because both predator and prey benefit from this defense maneuver. The lizard lives to see another day, and the predator has a tasty snack.

    Ramanujan, Krishna (Winter 2008). "Discoveries: Milkweed evolves to shrug off predation". Northern Woodlands (Center for Northern Woodlands Education) 15 (4): 56.

  4. One of more interesting predator-prey relationships is found between the poison arrow frog (Phyllobates terribilis), and the liophis snake (Leimadophis). The poison arrow frog (as the name implies), developed a toxin so powerful, that it is deadly to an adult if held in the hand. This is obviously very beneficial to the organism, because the toxin deters many creatures from trying to eat it. However, there is one known predator of the poison arrow frog, the liophis, and it has evolved its own resistance to the frog's poison. The poison arrow frog's toxin is so powerful that the snake is not entirely immune to the toxin, but only partially resistant.(1)

    Predators MUST evolve to adapt to the strategies used by the prey to fight them off because otherwise, the predator would be unable to consume the prey. For example, if a zebra evolves to run faster, the group of lions that hunts that zebra must either chase it down faster, or they will lose this specific ecological niche. Natural selection will proliferate the genes that will increase the lions speed, lest the lion lose a food source. (2)

    More broadly, selective pressures drive all evolutionary change. If a prey changes to better avoid the predator, he must in effect change to better catch his prey. Like an arms race, if you are stuck with last-generation weapons, you are much more vulnerable to attack. Thus, natural selection will drive beneficial change (Coyne, P.120) in all organisms, to better their chances for survival and reproduction.


  5. When we think of a predator prey relationship, we tend to automatically think of a relationship between two animals or organisms. For example, between a lion and a zebra or an anteater and an ant. What we do not always realize is that this predator prey relationship also applies to plants. This is why I was intrigued when I found this juicy little tidbit- yes I did say juicy little tidbit- on The Galapagos islands are teeming with life, and one predator-prey relationship on the islands is between Geochelone nigra (Galapagos tortoise) and the Opuntia cactus, which is more commonly known as the Paddle Cactus due to its ball-and-paddle toy shape. The Galapagos tortoise depends upon the sap from the cactus as a source of moisture.* In order to avoid the tortoise’s predation, the Paddle Cacti have evolved to have branches higher from the ground so that the tortoise’s can not reach them. Consequently, the Galapagos tortoises have co-evolved with the cacti to have longer necks to reach the higher branches. This is why the islands with cacti that have branches lower to the ground also have tortoises with shorter necks and islands with branches higher from the ground have tortoises with longer necks. Therefore, the predator and the prey co-evolve to adapt to their changing environments.

    In order to defend themselves, prey become faster and stronger, used camouflage and produces toxins Another example where the predator adapts alongside its prey is between Taricha granulosa, a rough-skinned newt, and its only known predator garter snakes (Thamnophis sirtalis). For defense, the newt’s skin produces the toxin tetrodotoxin. Tetrodotoxin binds to the sodium channels in nerve cells which can result in paralysis or death. Garter snakes have a protein which prevents the toxin from binding to the ion channels allowing them to consume the newts without being harmed. This is an example of coevolution because as the potency of the newt’s toxin increases, the garter snakes resistance increases as well.

    *Tortoises have th ability to survive for over a year without taking in liquids. They have evolved to break down their body fat which creates water as a by product.