APOSEMATISM - DEATH IS COLORFUL

Aposematism is an evolutionary trait developed by animals as a warning sign to its potential predators that it is not worth attacking or eating. This unprofitability may consist of any defences which make the prey difficult to kill and eat, such as toxicity, venom, foul taste or smell, sharp spines, or aggressive nature. Aposematism always involves advertising signals, which may take the form of conspicuous coloration, sounds, odours or other perceivable characteristics. These signals are beneficial to both predator and prey, since both avoid potential harm. The term was coined by Edward Bagnall Poulton for Alfred Russel Wallace’s concept of warning coloration. Aposematism is exploited in Müllerian mimicry, where species with strong defences evolve to resemble one another. By mimicking similarly coloured species, the warning signal to predators is shared, causing them to learn more quickly at less of a cost to each of the species. Despite this, 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. If warning coloration puts the firstindividuals at such strong disadvantage, it should never last in the species long enough to become beneficial.

The most common and effective colours are red, yellow, black and white because they provide strong contrast with green foliage, resist changes in shadow and are highly chromatic. Some forms of warning coloration provide distance dependent camouflage by having an effective pattern that does not allow for easy detection by a predator from afar, but are warning-like from close distance, allowing for an advantageous balance between camouflage and aposematism. Visible signals may be accompanied by odours, sounds or behaviour to provide a multi-modal signal which is more effectively detected by predators.

In frogs the characteristic is present within the family Dendrobatidae, also known as poison dart frogs, to warn their predators that they are in fact poisonous. In their case is the mucus that they secrete when in danger to be deadly. The most toxic of this excretions (Batrachotoxin) could kill between 10 and 20 people but there are no records of someone’s death caused by them. Nevertheless it is one of the most toxic poisons existing and it originates from a shift in diet to alkaloid-rich arthropods.*

* Jump to pg. 22 for more on Batrachotoxin.