The Origin of Mimicry Deception or merely coincidence Bram Wiggers, s2485834, [email protected], Supervisor: Dr. Harmen de Weerd Abstract: One of the most remarkable phenomena in nature is mimicry, the ability of one species (mimics) to imitate the phenotype of another species (models). Several reasons for the origin of mimicry have been proposed, but no definitive conclusion has been found yet. In this paper, different hypotheses will be tested by an agent based co-evolution model. We consider an adaptive plane with a camouflage and toxic gradient. Animal populations can move over this adaptive plane by evolving. Two options will be compared: (1) Deception, which assumes that mimics evolve to take advantage of the warning color of the models. (2) Coincidence, where models evolve a warning color that coincidentally benefits the mimics. We found that both the hypotheses are a plausible reason for the origin of mimicry, but that deception takes place in the coincidence environment as well. When the model loses its camouflage, the mimics do not move toward the model, but stay in their own place, which supports the idea of coincidence. 1 Introduction (Rabosky, Cox, Rabosky, Title, Holmes, Feldman, and McGuire, 2016) and other animals (Maan and One of the most remarkable phenomena in nature Cummings, 2011). Various research has been done is mimicry, the ability of animals (mimics) to mimic (Mallet and Joron, 1999), but no clear answer has the phenotype of other animals (models). Typically, been found for the origin of mimicry. the effect is called mimicry when the mimic imitates a phenotype of a model which can be dangerous We distinguish Batesian mimicry and M¨ullerian for a predator. For the mimic, mimicry has a pos- mimicry. In Batesian mimicry the mimic is not itive effect on the chance of survival, since it gets toxic, which is disadvantageous for the model. The confused for the dangerous model. For the models, mimic will be eaten or tasted by the predator and it might be beneficial (M¨ullerian,M¨uller(1879)) found to be harmless, giving a positive feedback or disadvantageous (Batesian, Bates (1862)). Sev- stimulus to the predator since the mimic is not poi- eral reasons have been proposed for the origin sonous. This results in models being eaten more, of mimicry, but no definitive conclusion has been since the predators have found positive feedback found as yet. on eating these colored animals. Hence, the more The first one to discover mimicry was Bates mimics exist in the habitat of the model, the lower (1862). Bates found there are animals that are poi- the survival chance of the model. This results in a sonous with very bright colors, and camouflaged an- negative or parasitical effect on the model. imals which were not poisonous. The effect of hav- ing a bright color to scare off predators is known as M¨ullerianmimicry on the other hand, considers aposematism. This effect became more remarkable two animals that are both toxic to a certain de- when Bates found animals that had similar colors gree, and therefore enhance each others aposema- and shapes as the toxic animals, but were not toxic tism. This will be explained by taking animals A at all. and B, which both are toxic and have a similar phe- This type of mimicry has been called Batesian notype. Each animal which starts to look more like mimicry, the effect where non-toxic animals imi- the other one will be better remembered, and there- tate the toxic animals. This effect can be found fore have a better chance of survival. As a result an in butterflies (Bates, 1862; M¨uller,1879), snakes evolutionary co-operation mechanism is created. 1 1.1 Camouflage and toxicity in their evolutionary progress. Not all animals get eaten when predators learn of their toxicity. Preda- In mimicry we can distinguish between preys and tors tend to taste their prey first, before consum- predators, where the predators are hunting the ing them whole. Therefore preys do not have to die preys. The preys have two defense mechanisms when they are tasted, but it is not beneficial for against the predators: (1) camouflage and (2) tox- their health either. The evolution of toxicity is also icity. explained by kin selection. When a species is more toxic, the group as a whole will be eaten less and 1.1.1 Camouflage have a benefit. As an individual it is less beneficial The camouflage of a prey can be beneficial to avoid to be toxic, but since the group has a benefit when detection of the prey. To stay undetected the an- developing toxic, toxicity still evolves. imal needs a good camouflage color, which makes them undetectable for the predators. This causes 1.2 Hypotheses: Deception & Coin- animals with a higher camouflage to be eaten less cidence (Stevens and Merilaita, 2009). However, when an aposematism is established, a prey that is camou- In our research we want to get a closer understand- flaged will signal the predators that the prey is safe ing of the origin of mimicry and the course of evo- to eat. Hence, when the camouflaged animals are lution in the preys and predators. A common as- found, the chance that a predator decides to eat sumption in the literature is that the preys delib- them is very big. erately deceive the predators (Holmgren and En- The warning color, or low camouflage, can be quist, 1999; Rabosky et al., 2016). However, this beneficial since it scares off predators. However, a assumption can be argued by the idea of coinci- warning signal can be hard to establish since the dence, which argues that mimics had the phenotype prey has to deviate from its camouflaged color, all along, and the toxic animals coincidentally got which makes it more vulnerable to predator at- the same phenotype. These two hypotheses will be tacks. When aposematism is created, the warning tested by a co-evolution model. We will elaborate colors can be useful. However, aposematism is hard on the hypotheses in the next two sections. This feature to establish. In our research, we represent will be done by two defenitions: speciation and the camouflage as an optical characteristic, but it can adaptive plane be applied to odor, sound, and taste as well. Speciation is the term we use for populations which evolve in different sub-populations. For ex- 1.1.2 Toxicity ample, an animal population which is all camou- flaged can split into one group which stays the Similarly, synthesizing toxic compounds can be same, and another which gets bright colors and be- beneficial when they serve their purpose, namely, comes a mimic of another population. scaring away predators. However, the first preys to The adaptive plane is used to explain the evolu- explore this peak in the adaptive plane will still be tion of the preys. The plane has a camouflage and eaten by the predators since these have not learned toxic dimension over which the populations move. which preys are toxic. A move is described as a change in features for a The synthesis of toxic has a small negative in- population. When the mean toxicity and camou- fluence on the fitness. The reason for this decrease flage changes, we say the population moves over in fitness is that these toxic acids or proteins have the adaptive plane. to be synthesized in the animal, which takes an adaptive cost. However, examples of animals can be 1.3 Deception by the preys found that feed on toxic flora, and use the residues to keep their toxicity intact. An example of this In deception, the preys have a dominant role in the is the Zygaena (Holzkamp and Nahrstedt, 1994), evolution of mimicry. As seen from the perspective which feeds on toxic plants and uses the residues of the preys, the mimicry group will need to be as for its own protection. Therefore, the content of similar to the phenotype of the toxic group as pos- toxic in the animals can be a very low cost adaption sible, to make sure the predators do not mistake 2 Figure 1.1: In deception, the mimic and camou- Figure 1.2: In coincidence, the toxic and camou- flaged animals will start with the same charac- flaged animals will start with the same charac- teristics. The hypothesis states that the mimicry teristics. The mimicry group is already in place. group will move toward the place without toxic The toxic population now gets more toxic, and and without camouflage: the mimicry place, consequently moves toward the lesser camou- since this place is best if the animals do not get flaged site. Our hypothesis is that the mimicry eaten. group will move towards the toxic group first, after which it moves back with the toxic group. them for a camouflaged animal. Therefore, when the toxic group is less camouflaged, the mimicry group will have to evolve to have a similar pheno- type to maintain the mimicry, as can be seen in group moving to the less camouflaged part of the Figure 1.1. adaptive plane, to create a better distinction be- Deception can also be explained in terms of spe- tween them and camouflaged animals. The mimicry ciation. When all the preys are starting as a big group can stay at the brightly colored place, since population, this is first divided in an camouflage the predators take them for toxic animals. non-toxic population and a non-camouflaged toxic population. This is the starting position for this hypothesis. After this the hypothesis is that the How does mimicry evolve out of this? One ex- mimicry population is a sub-population of the cam- planation is the recognition of poisonous colors in ouflaged population, by lowering their camouflage.