Zoology

When Animals Communicate with each other why don’t they always Communicate Truthful Information



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Communication between animals can be thought about through signals they send to each other. A signal occurs when the action of one animal leads another to change its behaviour voluntarily (because of the action of the first). Untruthful communication usually occurs when the signallers and receivers interests conflict, such as rivals competing for a mate, an example; a bird displaying it is stronger than it actually is to make the other retreat, so the first will get the mate, or when defending territory. Other common situations include, offspring-parent relationships, mate-to-mate relationships, competition for resources, and predator prey relationships. Mimicry and Crypsis play important roles especially in the latter.




I will discuss how through the evolutionary stable strategy and common sense, truthful information is usually given, and how de-valuing of false signals aids this. The driving force for all behaviour is to increase ones Darwinian fitness, to leave the greatest number of one's own genes in the next generation.




Truth Vs Lie




Evolutionary stable strategies (ESS) show that there are natural equilibriums between, liars and honest animals, usually the liars being in the minority. If the liars become the majority the lie will become devalued, all would learn that it is a lie and won't respond, in this situation the non-liars would be at an advantage (Lecture notes). Also the signal is likely to be costly in energy terms because the receiver would need to be convinced, again lying can be disadvantageous.




Physical constraints may mean lying can't occur (Lecture notes). House finches feather colours result from the type of food they eat. The females know by seeing a variety of bright vivid colours that a male is good at finding food, meaning he is fit and will find plenty of food for their offspring.




In some cases when the disadvantage to the receiver is slight enough, the ESS is not affected and the liar effectively "gets away with it". There is a constant, arms race between signallers and receivers, signallers as manipulators, and receivers as mind readers.



















Evolution of signals




There are two perspective for the evolution of signals, the efficacy based theory which entails that due to selection pressures the signaller has evolved to induce a response at all times as efficiently as possible. The strategic theory contrastingly, describes how selection pressures on receivers mean that displays evolve so that they are difficult to be corrupted by deceit. Both serve as good answers in different situations, though the efficacy based theory to date has been more successful, in more situations. (Book 2 Pg 173)






Batesian mimicry




When a harmless edible species adopts the warning signs of another species (the model) which is not eaten by predators, because it may be dangerous distasteful, or for some other good truthful reason, it is called Batesian mimicry. The warning signs of the model species tells the predator not to eat them. The warning signs used by models are often bold contrasting colours such as yellow and black, these warnings are called Aposematism, Wasps are Aposematic.




Batesian resemblances are evolutionarily unstable, because the model will try to change, so it can be identified by the prey, meaning it will survive better. The original copied signs would be doing the job of keeping predators informed so the evolution of change of these signs is slowed. Obviously the mimic would benefit if the prey can't distinguish them. (Book 5 Pg 374)




Moths are masters of mimicry, some mimic wasps/bees. The tropical lo moth, supports the eyes spots which appear on so many of it's relatives wings as well, it will open out the wings when threatened, appearing to be a much larger animal.

Their aposematism and mimicry doesn't stop there. It is possible state Blest Collett and Pye (book 3 Pg 86) that the ultra sonic sound produced by certain moths when they are around bats, may be to conceal the moth from the bats. As the frequency of the ultra sound produced by the moths are in echo-sound range used by bats to locate their prey. The other and more likely possibility is that the sound are Aposematic or Batesian mimicry depending on the species. Dunning (1968) found that moths, mainly arctiids
and ctenuchids which emit these sounds where eaten less, by bats in a cage, than the control group which didn't emit the sounds. He concluded for these species the sounds where genuinely Aposematic and that Pyrrharctia a species which is edible, made these sounds as well showing it is using Batesian mimicry.




The Xylophanes caterpillar has such tiny eyes that you would need a hand lens to see them. The red markings appearing as eyes and pointed "stinger" on it's body are both fake.




The sphingid moth Leucorampha orntus, caterpillar acts like a snake. Its large thorax and fake shiny eye spots mimic the head of a snake; to make the display as believable as possible it sways its body snake-like, this is thought to discourage predators. (Book 5)




Crypsis




Another type of mimicry is crypsis, the mimicking of plants and other inedible objects. The classic example of this would be the stick insect, as it's name implies it resembles a stick. Members of this family also resemble leaves. A Gravid Katydid blends amazingly well, their wings mimic the mottling of the surrounding leaves, they even hold the long antennae still and mimicking such fine detail as the vein of the leaf. Resembling a partly dead leaf it blends in with the surroundings for a longer period of time (from the fresh leaves to the dead and dying ones in autumn)




In the rain forest of the Peruvian Amazon, a "bird dropping" on a leaf turns out to be a caterpillar. (Web site)

Crypsis can be behaved as well as anatomical. The Pauraque uses both, to stay hidden whilst nesting, on the ground. Its cryptic behaviour consists of keeping its eyes partly closed, remaining immobile, and being as flat as possible. (Web site)




A Lonomia moth resembles a dead leaf on the forest floor, the detail to which this mimicry is followed is remarkable, there is a simulated leaf vein running from wingtip to wingtip. (Web site)




When predators mimic and lie




Camouflage can work from the predators point-of-view as well, being termed aggressive mimicry . The zone-tailed hawk, Buteo albonotatus, has plumage which resembles harmless vultures. Gliding with these birds, when spotting prey it breaks free and goes for the kill, the unsuspecting prey has little or no time to react. The family Mantidae, sometimes appear as gorgeous colourful nectar bearing flowers; attracting nectar seeking insects (Book 5).




The scorpion fish, rests immobile on a coral reef, 60 feet below the surface, camouflaged against the colourful embroidery of the reef. Using its crypsis to keep it hidden from smaller fish which may become a meal if they come in range. (Web site)




Even more remarkably some predators mimic their preys prey. Alligator snapping turtles and angler fish, can wriggle fleshy outgrowth's near their mouth's attracting small fish, who think it is a tasty meal, when in fact they are the tasty meal! A species of smaller carnivorous fish feed on larger fish. These fish, the Aspidontus taeniatus mimic another small species of fish, a wrasse, which feed on parasites and damaged tissue of larger fish aiding their recovery. The model fish is characterised by its shape, brilliant blue and black stripes, and its distinctive swimming behaviour, the mimic, copies all these qualities. The larger fish which require the services of the wrasse, let the mimic approach thinking it is going to be of use to them, when Aspidontus taeniatus, get up close behind the larger fish it sinks its sharp teeth in the unsuspecting fish biting huge chunks off. (Book 5 Pg 383)




Other creatures' use bioluminescence to attract prey. Some of the female firefly attract mates by flashing, the genus, Photuris , exploits this by mimicking these flashes, having attracted a male it devours him. The p. versicolor can go one step further it can change the pattern of its flashes in response to passing males, it can mimic two or three prey species. (book 5, pg 383) In the deep oceans where little or no light gets through, predatory fish have glowing bulbs dangling above there mouths, other fish attracted to the light swim to it and are eaten.




Parasitic and deceitful birds




Beau gesta "broken wing mimicry"

The ringed Plover which nests on pebbly beaches, has eggs which are camouflaged to resemble the pebbles. If the bird is approached by a predator it will run from the predator, pretending to have a broken wing, the predator thinking it will easily get a larger meal, as the bird appears to be injured. Having taken the predator well away from its eggs it flies off. The eggs being camouflaged are very difficult to find, the bird would have saved her eggs. If this is done too often the predator would learn that the bird is faking and wouldn't go after the bird, the behaviour would be de-valued.

(lec notes )




Another example of deceitful distracting, is the Tasmanian native Hen. It runs fast in a zigzag pattern, across the open ground looking like a small mammal, such as a bandicoot or rabbit. The predator is distracted and goes after the hen. (book 5 Pg 382)




The Cuckoo bird is a very deceitful bird. The adults lay their eggs in nests of other birds, the eggs are similar to the host eggs, and then departs leaving the host bird to care for the cuckoos offspring. The deceit does not stop there, when the fledgling hatches, it will beg harder for food, lying about how hungry it is. Consequently it will receive more food from its foster parents (Book 2). The parasite chicks also look like the hosts chicks.




In other types of these brood parasitic birds, the resemblance's with the host chicks are exceptionally detailed. The melba finch Pytilia melba chicks have species-specific mouth patterns of black spots on their tongues, palate and lower mandible. Their parasites
Isteganura paradisaea have exactly the same gape patterns and vocalizations. The vocals of the honeyguide go one step further, its offspring can sound like a full brood of bee eater nestlings (the host), it can even elicit feeding from neighbouring bee eaters! (BOOK 5, Pg 383)






Conclusion




Evolutionary stable strategies evolve between truth and lie, through de-valuing of false signal and physical constraint most signals evolve to be honest signals. Batesian mimicry and Crypsis both of which miss-lead the receiver, play important roles for predators and prey. Courtship, rivalry and prey-predator relationships are often subject to deceit, as the signallers and receivers interests conflict. Untruthful communication between animals occurs because each individual wants to increase their own Darwinian fitness. This is done by increasing ones own and its' offspring's survival. Having plenty of food, living a for a long time, having fit and large number of offspring all increase survival and ultimately Darwinian fitness, all this is bought about which ever tactics are the best whether truthful or not.






Bibliography




Books

1) Ridley M, Animal Behaviour, Blackwell Scientific Publications, USA

2) Krebs and Davies, Behavioural ecology, Blackwell Scientific Ltd, GB

3)Sales and Pyes, Ultrasonic communication by animal, Chapman and Hall, GB

4)McFarland, D, Animal Behaviour, Longman, Singapore

5) Smith, The behaviour of communicating, Harvard University Press, USA

6) Halliday and Slater, Animal Behaviour Communication,
Blackwell Scientific Publications, GB

7)Readers Digest, Nature's Masterpieces, Readers Digest Association Ltd, Barcelona




Website

1) http://www.dimijianimages.com/Crypsis-mimicry-page1/Crypsis-and-mimicry-page1.htm




Lecture Notes

Dr Chevins, module Bisc-109 lecture 3,4,5 (Keele University)

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