Blog Post 9 – Automimicry Explained Further  & an Example

It is widely assumed that prey were cryptic and defended before evolving some kind of warning signal. However, focusing on the mechanisms that drove the evolution of defensive display may prevent examination of a pivotal event in the evolution of aposematism, the evolution of the secondary defence that is to be displayed (Speed et al. 2006). Secondary defences can be costly to generate and maintain so their evolution may need special consideration (Ruxton and Speed, 2005; Skelhorn and Rowe, 2007). If defences often evolve before aposematic displays in prey animals, there is a paradox: why should prey invest in costly secondary defences if they are already well-protected by crypsis? (Speed et al. 2006).

Two general explanations can resolve this issue. The first is via preadaptation. A prey species may already possess a trait that happens to provide some protection against a predator (Speed et al. 2006). For example, some chemicals may be important in intraspecific signalling, and may also deter predators (Speed et al. 2006). Similarly, locomotor behaviour and mechanical properties could have some function as a secondary defence even though they were not initially selected to (Speed et al. 2006). The second explanation is that defences evolve by genetic mutation or some other change. In chemical defence, genetic mutation may render prey tolerant of toxin-conferring food materials, or provide new secondary metabolites that are toxic to predators (Speed et al. 206). With mechanical defences mutation may cause the development of structures such as spines, or enable changes in locomotor behaviour that facilitate escape (Speed et al. 2006). In some circumstances defences could emerge without genetic change; prey may have a choice of acquiring a secondary defence by behavioural modification, for instance choosing whether to feed on certain materials or to acquire certain symbionts (Speed et al. 2006).

An interesting example of an animal that uses automimicry is the four eyed frog, Physalaemus nattereri. Endemic to South America, it has a pair of black discs on its dorsum resembling two large dark eyes that it uses as a bluff (Barbosa et al. 2015). These 'decoy eyes' act as the first line of defence acting as important visual warning features to intimidate potential predators. They are also the second line of defence as they constitute as the major source of a toxic secretion capable of inflicting disturbing physiological consequences on numerous vertebrates like regurgitating, gut contractions and diarrhea (Barbosa et al. 2015). 

The four eyed frog, Physalaemus nattereri. Image by Arystene Nicodemo. Source: https://hiveminer.com/Tags/physalaemus/Recent  Retrieved on: 15/05/2019 

This image shows the "decoy eyes" that secrete a powerful toxin. Image by Michelle Martin. Source: https://www.igoterra.com/photo_info.asp?photoid=211330  Retrieved on: 15/05/2019

Here is the Physalaemus nattereri in defence mode, puffed up and lifting its rear to reveal its false eyes, pretty cool right! Source: https://upload.wikimedia.org/wikipedia/commons/b/b5/Physalaemus_nattereri_in_deimatic_behavior.jpg  Retrieved on: 15/05/2019


References


Barbosa, E.A., Iembo, T., Martins, G.R., Silva, L.P., Prates, M.V., Andrade, A.C. and Bloch Jr, C., 2015. Skin secretion peptides: the molecular facet of the deimatic behavior of the four‐eyed frog, Physalaemus nattereri (Anura, Leptodactylidae). Rapid Communications in Mass Spectrometry, 29(21), pp.2061-2068.

Ruxton, G.D. and Speed, M.P., 2005. How can automimicry persist when predators can preferentially consume undefended mimics?. Proceedings of the Royal Society B: Biological Sciences, 273(1584), pp.373-378.

Skelhorn, J. and Rowe, C., 2007. Automimic frequency influences the foraging decisions of avian predators on aposematic prey. Animal Behaviour, 74(5), pp.1563-1572.

Speed, M.P., Ruxton, G.D. and Broom, M., 2006. Automimicry and the evolution of discrete prey defences. Biological Journal of the Linnean Society, 87(3), pp.393-402.
 
 

Comments

  1. Tasmin14 May 2019 at 20:32

    That frog is pretty cool! Do you know if these frogs suffer lower predation rates that other frogs in the same area that are only chemically defended?

    ReplyDelete

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