Aposematism
[1] This unprofitability may consist of any defenses which make the prey difficult to kill and eat, such as toxicity, venom, foul taste or smell, sharp spines, or aggressive nature.
By mimicking similarly coloured species, the warning signal to predators is shared, causing them to learn more quickly at less of a cost.
He based the term on the Ancient Greek words ἀπό apo 'away' and σῆμα sēma 'sign', referring to signs that warn other animals away.
[3][4] The function of aposematism is to prevent attack, by warning potential predators that the prey animal has defenses such as being unpalatable or poisonous.
[7][8] This is in contrast to deimatic displays, which attempt to startle a predator with a threatening appearance but which are bluffing, unsupported by any strong defences.
Velvet ants (actually parasitic wasps) such as Dasymutilla occidentalis both have bright colours and produce audible noises when grabbed (via stridulation), which serve to reinforce the warning.
[16] Aposematism is widespread in insects, but less so in vertebrates, being mostly confined to a smaller number of reptile, amphibian, and fish species, and some foul-smelling or aggressive mammals.
[17] It has been proposed that aposematism played a role in human evolution, body odour carrying a warning to predators of large hominins able to defend themselves with weapons.
[20] Evolution of their conspicuous coloration is correlated to traits such as chemical defense, dietary specialization, acoustic diversification, and increased body mass.
[25][22] Some plants are thought to employ aposematism to warn herbivores of unpalatable chemicals or physical defences such as prickled leaves or thorns.
For example, the Spanish Dancer nudibranch (genus Hexabranchus), among the largest of tropical marine slugs, potently chemically defended, and brilliantly red and white, is nocturnal and has no known mimics.
[38] Mimicry is to be expected as Batesian mimics with weak defences can gain a measure of protection from their resemblance to aposematic species.
[35] Further, there is evidence that fish predators such as blueheads may adapt to visual cues more rapidly than do birds, making aposematism less effective.
[43] However, there is experimental evidence that pink warty sea cucumbers are aposematic, and that the chromatic and achromatic signals that they provide to predators both independently reduce the rate of attack.
[49] The mechanism of defence relies on the memory of the would-be predator; a bird that has once experienced a foul-tasting grasshopper will endeavor to avoid a repetition of the experience.
Any gaudy & conspicuous colour therefore, that would plainly distinguish them from the brown & green eatable catterpillars, would enable birds to recognise them easily as at a kind not fit for food, & thus they would escape seizure which is as bad as being eaten.
[55] In response, the entomologist John Jenner Weir conducted experiments with caterpillars and birds in his aviary, and in 1869 he provided the first experimental evidence for warning coloration in animals.
[56] The evolution of aposematism surprised 19th-century naturalists because the probability of its establishment in a population was presumed to be low, since a conspicuous signal suggested a higher chance of predation.
[4] He described the derivation of the term as follows: The second head (Sematic Colours) includes Warning Colours and Recognition Markings: the former warn an enemy off, and are therefore called Aposematic [Greek, apo, from, and sema, sign][58]Aposematism is paradoxical in evolutionary terms, as it makes individuals conspicuous to predators, so they may be killed and the trait eliminated before predators learn to avoid it.
[60] There is evidence for explanations involving dietary conservatism, in which predators avoid new prey because it is an unknown quantity;[61] this is a long-lasting effect.
[66] This suggests that Wallace's original view, that warning coloration helped to teach predators to avoid prey thus coloured, was correct.
[67] However, some birds (inexperienced starlings and domestic chicks) also innately avoid conspicuously coloured objects, as demonstrated using mealworms painted yellow and black to resemble wasps, with dull green controls.
