Introduction to Müllerian Mimicry

Along with Batesian mimicry, Müllerian mimicry is the other major form of defensive mimicry. In contrast to Batesian mimicry, Müllerian mimicry does not involve any deception, as all species involved are unpalatable. Müllerian mimicry is defined as two or more unpalatable prey species sharing a similar appearance (eg: colours, patterns, etc) (Huheey, 1976).

In practise however, the difference between Batesian and Müllerian mimicry isn't black and white; there's actually a sliding scale of (un)palatability among mimetic species (ie: a mimetic species might be entirely harmless, just as dangerous as their model, or somewhere in-between) (Huheey, 1976).

An example of Müllerian mimicry is found in the Viceroy (Limenitis archippus) and Monarch (Danaus plexippus) butterflies shown in Figure 1, where both species are unpalatable. Until recently, the Viceroy was believed to be palatable - which would have made this relationship an example of Batesian mimicry (Ritland and Brower, 1991).

Figure 1: Similarities between Viceroy (top) and Monarch (bottom) butterflies.

While Batesian mimicry could be considered a form of antagonistic symbiosis (one species benefits at the expense of others), Müllerian mimicry is a mutualistic relationship between species. This is because mimic and model alike benefit from the shared 'advertisement' as it makes it easier for predators to recognize (and avoid) certain colourations/patterns in unpalatable prey species (Huheey, 1976); which, as it happens, also benefits the predator species .... Good guy Müllerian mimicry? 

- Huheey, J. E. 1976, 'Studies in Warning Coloration and Mimicry. VII. Evolutionary Consequences of a Batesian-Müllerian Spectrum: A Model for Müllerian Mimicry', Evolution, vol. 30, no. 1, pp. 86-93.

- Ritland, D. B. and Brower, L. P. 1991, 'The viceroy butterfly is not a batesian mimic', Nature, vol. 350, pp. 497-498.

- Figure 1: http://upload.wikimedia.org/wikipedia/commons/6/63/BatesMimButter.JPG, Photographer(s): D. Gordon, E. Robertson and Derek Ramsey, retrieved: 29/03/14

Mimic Spotlight: Orchid Mantis (Hymenopus coronatus)

I find the Malaysian Orchid Mantis (Hymenopus coronatus) fascinating. Not only is it a beautiful and just generally cool looking insect, but it also expresses both mimicry and mimesis throughout its life-cycle. 

I mentioned in my first post that mimicry and camouflage are different from one another. Camouflage is used by animals to make themselves less visible - via body colouration, patterns, or morphological structures (Stevens and Merilaita, 2008) to blend into the background. This is distinct from mimicry, where animals are still perfectly visible. Mimesis is an area of overlap between the two, where an organism resembles a specific object, such as a leaf or bird dropping (Pasteur, 1982).

Figure 1: A juvenile Orchid Mantis

Hymenopus coronatus, shown in Figure 1, expresses (aggressive) mimesis in its juvenile and adult forms, where it mimics parts of the flower of a orchid. The colours and shapes of the orchid mantis act as visual cues to pollinators (prey of the orchid mantis), attracting them (O'hanlon et al., 2013). The mantis' four walking legs look like petals, whilst the two front limbs are used to grasp any prey unfortunate enough to get too close. 

Figure 2: An adult Orchid Mantis

Adult orchid mantises (as shown in Figure 2) do not resemble orchid flowers to the same extent that juveniles do. However, they still retain femoral lobes and a similar white colouration, both of which could still be attractive to pollinators (O'hanlon et al., 2013). It is also entirely possible that the orchid mantis' resemblance to an orchid flower in the juvenile stage helps it hide from predators; therefore, as individuals mature and are better able to defend themselves, there may be less need to be such a convincing mimic.

Figure 3: Orchid Mantis nymph

Whilst the older Orchid Mantises mimics orchid flowers (mimesis), the first stage nymphs (shown in Figure 3) mimic members of the Reduviidae family (mimicry). This is a form of Batesian mimicry, as the model insect tastes pretty awful and also has a powerful bite (Gurney, 1951) and therefore, by resembling the model, the nymph can deter potential predators. 

- Gurney, A. 1951 'Praying mantids of the U.S, native and introduced', Annual Report of the Board of Regents of the Smithsonian Institution, vol. 105, no. 1, pp. 344-345.
- O'hanlon, J., Li, D. and Norma-Rashid, Y. 2013, 'Coloration and Morphology of the Orchid Mantis Hymenopus coronatus', Journal of Orthoptera Research, vol. 22, no. 1, pp. 35-44.
- Pasteur, G. 1982, 'A Classificatory Review of Mimicry Systems', Annual Review of Ecology and Systematics, vol. 13, no. 1, pp. 169-199.
- Stevens, M. and Merilaita, S. 2008, 'Animal camouflage: current issues and new perspectives', Philosophical Transactions of The Royal Society, vol. 364, no. 1, pp. 423-437.

- Figure 1: http://www.themagazine.ca/cms/wp-content/uploads/2011/03/Malaysian-orchid-mantis.jpg By Unknown photographer, retrieved: 22/03/14
- Figure 2: http://upload.wikimedia.org/wikipedia/commons/3/36/Insect_camouflage_PP08338.png Photographer: Philipp Psurek, retrieved: 22/03/14
- Figure 3: http://www.nature-china.net/home/attachment/201102/28/195028_1298915776QH1R.jpg Unknown photographer, retrieved 22/03/14

Introduction to Batesian Mimicry

Prey species use a huge variety of defense mechanisms to avoid being eaten; some species spray formic acid, some species confuse their attacker by suddenly jumping into the air, and some species simply run away as fast as they can. Other species leave a bad taste, or sometimes make their attacker ill, when eaten. Whilst this usually doesn't help the individual being eaten (rest in many pieces, little guy), predators learn to avoid that particular species - resulting in protection for a whole population of that prey species. 

Often, prey will announce how dangerous or bad-tasting they are by having distinct markings, or colours. Enter center stage, the Batesian Mimic (who, spoiler alert, lies). Batesian mimicry is a type of defensive mimicry which involves a non-harmful species looking like a harmful species (called a 'model') to avoid being eaten (Allen and Cooper, 1995).

Figure 1: Mimetic Scarlet King Snake and its model, the Eastern Coral Snake

Logic dictates that Batesian mimicry would be frequency-dependant (ie: the number of mimetic individuals would be limited by the number of model individuals), and this has been shown to be the case is the majority of mimetic species such as the Scarlet King Snake shown in Figure 1, where the frequency of predation on the mimic species decreased with increased relative abundance of the model species (Pfennig et al., 2001). 

This is not always the case, however, as hoverflies are more abundant than their wasp model species (Dittrich et al., 1993). In cases such as this, the model species is usually so dangerous that it is thought that predators will avoid any prey which looks like the model, even if the chance of catching a harmless mimic is much higher than catching the actual dangerous species; "better safe than sorry" springs to mind.

Interestingly, it has been suggested that mimicking a species that can easily escape a predator can be just as an effective method to avoid predation as mimicking a harmful species. It is suspected that a certain predator could associate markings/colours of a very agile prey species as being a "waste of energy" and will not try to catch said species. As such, a less agile species (that would otherwise be easy to catch and eat) could mimic the "waste of energy" model and hence, predators would not bother trying to eat it (Gibson, 1974).

- Allen, J. A. and Cooper, J. M. 1995, ‘Mimicry’, Journal of Biological Education, vol. 29, no. 1, pp. 23-26
- Dittrich, W., Gilbert, F., Green, P., McGregor, P. and Grewcock, D. 1993, 'Imperfect mimicry: a pigeon's perspective', Proceedings of the Royal Society of London, vol. 251, no. 1332, pp. 195-200.
- Gibson, D. O. 1974, 'Batesian mimicry without distastefulness?', Nature, vol. 250, no. 1, pp. 77-79.
- Pfennig, D. W., Harcombe, W. R. and Pfennig, K. S. 2001, 'Frequency-dependent Batesian mimicry', Nature, vol. 410, no. 1, pp. 323.

- Figure 1: https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEitNsKjhlsSlWcgdJytSdJiVK6ez4yB3Z_-aMSUENLRV6ONjT-eIP-dGLRN6qe3bKocz3bxaYlrgl4hQSWz7I_pO0cDIDlkYUoBUN6M5VHiLNuTK4570r5BIWzKZR9Cv_ud-qmpkvwv5xGq/s1600/Coral_snake_mimics.gif

Introduction to Mimicry in Animals

To get the ball rolling, what exactly is ‘mimicry in animals’? A mimetic organism (An organism which displays mimicry) is one which resembles another organism, in order to deceive a third organism (and benefit from said deception) (Allen and Cooper, 1995).

Mimicry occurs in many different forms, for example behavioral or morphological, and can largely be divided into 2 categories; ‘aggressive’ or ‘defensive’ mimicry. Aggressive mimicry is an adaption which allows an organism to appear less dangerous than it really is, to allow it to approach prey more easily. Defensive mimicry is an adaptation which allows an organism to appear more dangerous than it is, in order to deter a potential predator (Allen and Cooper, 1995). It is important to note that camouflage, whilst also being a form of passive defense, is not a form of mimicry.

Over the course of this semester I’ll explain why animals mimic other animals, outline some of the many forms of mimicry, as well as look in detail at some particularly interesting examples of mimetic animals.     

Allen, J. A. and Cooper, J. M. 1995, ‘Mimicry’, Journal of Biological Education, vol. 29, no. 1, pp. 23-26