Brighter is Better!

If you have asked to approach two animals; one with bright colour and other with dull colour, which one would you choose to approach? What these colours signify to other animals in the surrounding? For a predator, the choice would be a dull colour individual. This is a survival strategy among many species, where prey (an animal being fed on) show bright colour as a warning signal – a troubling sign to the predator (an animal being fed). This means prey is not suitable for a potential predator. The predator must make a precise decision or experience bad taste, poison or even death. This mechanism of warning signals by prey is called Aposematism; a common example is black and orange Monarchs butterfly.




Monarchs butterfly (Danaus plexippus): the black and orange colour pattern is easily detectable to predators


The bright colour is a sign of danger, don’t peruse them. But don’t you think being brighter is more conspicuous to prey upon? Yes, it is indeed, but at the same time, brighter colour conveys a warning signal as a primary defense to a potential predator.


Warning signals could be a bright colouration, a foul odour or a contrast colour pattern in animals. Warning signals work best when they are easily detectable by predators at a distance and therefore facilitates the learning and avoidance behaviour in predators. For example; Swinhoe’s tree lizards and the weevils, despite inhabiting the same tree the lizard rarely attacks the weevil due to its conspicuous colour. In addition to primary defense prey always has a secondary defense mechanism (e.g. toxic chemical) if attacked by predators - a backup plan.





Swinhoe’s tree lizards (Japalura swinhonis) often inhabit the same trees with pachyrhynchid weevils, but they rarely attack weevils (Tseng et al., 2014)


Many of you are wondering why to become conspicuous and invite trouble rather just be cryptic or camouflage. Being hidden is a good idea but once spotted and attacked by predators such animals unlike aposematic species does not have any secondary defense mechanisms or backup defense, fight or become a meal. Therefore playing conspicuous without a backup defense is not worthy. Conspicuous with strong secondary defense works best for certain prey.


Rößler et al. 2018 showed that red soles (a warning signal) individuals of Harlequin toad population has high detection rate (reduce predation) by a predator than individuals lacking them. Hence proving the brighter is better!




Point estimates of detection risk for non-red footed, red footed and brown models in Harlequin toads (Rößler et al., 2018)


Although playing conspicuous without secondary defense is not a good strategy, certain species do play conspicuous but are palatable and pose no harm to predators. This type of behaviour is called mimicry; in this case a Batesian mimicry. Batesian mimicry is a special case where certain species mimic the potentially toxic and unpalatable species but originally are palatable. This is a clear case of cheating! A species take advantage of warning signals of true aposematic species – an honest signaler. Such species do not possess any secondary defense mechanism and totally rely on the warning signals as they mimic the honest signaler. For example, scarlet snakes mimic the several species of venomous coral snake.


Brighter is better! Either it is a true signaler or a mimic, both can reduce the risk of predation ultimately increase the survival rate – the eventual goal of all living organisms.



Reference


Mappes, J., Marples, N., Endler, J.A., 2005. The complex business of survival by aposematism. Trends Ecol. Evol. 20, 598–603. https://doi.org/10.1016/j.tree.2005.07.011


Rößler, D.C., Lötters, S., Mappes, J., Valkonen, J.K., Menin, M., Lima, A.P., Pröhl, H., 2019. Sole coloration as an unusual aposematic signal in a Neotropical toad. Sci. Rep. 9, 1–11. https://doi.org/10.1038/s41598-019-55021-0


Skelhorn, J., Halpin, C.G., Rowe, C., 2016. Learning about aposematic prey. Behav. Ecol. 27, 955–964. https://doi.org/10.1093/beheco/arw009


Tseng, H.Y., Lin, C.P., Hsu, J.Y., Pike, D.A., Huang, W.S., 2014. The functional significance of aposematic signals: Geographic variation in the responses of widespread lizard predators to colourful invertebrate prey. PLoS One 9. https://doi.org/10.1371/journal.pone.0091777



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