Realised hypothetical phenotypes and the adaptive value of Batesian mimicry

点击翻译按钮获取中文摘要

Many animals, such as venomous snakes or stinging wasps, advertise to potential predators that they are well defended by displaying bright, bold colour patterns. Other animals, known as "mimics", have evolved to deceive predators by displaying patterns similar to the dangerous "models", despite being harmless. Studying the evolution of mimicry has the potential to tell us much about how natural selection leads to adaptation in wild animals.Among mimics, we see many prominent and beautiful examples of the extreme adaptations that evolution can produce. However, some mimics, including many hoverflies that mimic wasps, only approximately resemble their model. We expect natural selection to favour the most convincing mimics, because less good ones ought to be recognised and picked off by predators: so why are some mimics inaccurate? Perhaps predators (such as birds) do not pay attention to all aspects of the prey's appearance, so the mimic does not have to be accurate in every way. Birds might avoid all prey that are roughly similar to a particularly nasty model, so beyond a certain point, further accuracy is unnecessary. Alternatively, the best chances of survival may gained by mimics which approximately resemble several nasty model species, rather than those which are perfect mimics of one particular model. To test these ideas, we need to know not only how successful existing mimics are, but also the performance of alternative mimics with different combinations of features to the existing ones. Would a more accurate mimic survive better? What if it were perfect except for its colour? This is an example of a more general problem in evolutionary biology, of predicting how non-existent, but theoretically plausible, organisms might perform in comparison to those that we observe in nature. To explore the evolutionary potential of mimics, our project brings together recently-developed technologies in a way never exploited before by biologists. First, we will photograph hoverflies and wasps from multiple angles and assemble 3D digital representations. We will then create new "morphed" images of plausible, but imaginary, intermediates between hoverflies and wasps which vary in similarity to the wasps. Thirdly, we will use 3D printing to create models of these intermediates (as well as the "real" insects) that are realistic in terms of their size, colour, pattern and shape. Lastly, we will measure the "survival" of these 3D models in a variety of experiments.We will test the response of predators by training birds to "attack" models of hoverflies, but avoid those of wasps, in order to gain food rewards. Having learnt that distinction, the birds will then be tested for how they behave towards 3D models of intermediate appearance. The longer the birds hesitate before attacking, the more effective is the mimicry, because in the wild such delays would give the insect an opportunity to escape. We will look at predator behaviour both in the wild, where natural communities of birds with varying levels of experience are foraging for food, and in the laboratory, where we can control the experiences of each individual and watch how they learn. We will also repeat the experiments using praying mantises in place of birds, to investigate whether insect predators judge mimicry differently. Our project addresses a long-standing biological question about the evolution of inaccurate mimicry, but will also provide broader insights into evolutionary processes. What is it about existing species that mean they survived when others either did not survive, or never evolved in the first place? This in turn allows us to understand how evolution produced the combinations of characteristics of existing species, and to predict the direction that evolution might take in the future. Our novel method will provide a framework for other evolutionary biologists to explore similar questions in a wide range of different organisms.