Population Dynamics and the evolution of phenotypic plasticity: Experimental Adaptive Dynamics.

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The ability of an animal or plant to survive is dependent on their ability to deal with things like temperature, rainfall, predators and parasites. Some animals and plants are able to recognize changes in the habitat that they live in and change accordingly. These may include things like how active an animal is, how much they eat, how fast they grow, how many offspring they have, or even how they develop. For example, when water fleas grow up in a habitat in which fish are present they develop head and tail spines that make it harder for a fish to eat them, however these spines are not produced when fish are absent. This ability of an animal to change what they do depending upon their surroundings is called phenotypic plasticity. How plastic can an animal or plant be? In a perfect world, an organism that had unlimited plasticity could potentially live anywhere. However, this is not what we generally observe. The distribution of most plants and animals is constrained to some degree. Moreover, plants and animals that live in environments that don't change very much are generally less plastic. One reason for this could be that there are costs of being plastic as well as benefits. This work aims to examine what these costs of plasticity are. Before we can do this, we first have to define what a plastic animal is. This is not as easy as it sounds because in any animal some characteristics may be more plastic than others. For example, dragonflies that hatch late in the season reduce their body size (plastic) in order to always be able to develop as quickly as possible (not plastic). At present we have very little idea how plasticity in one characteristic is related to plasticity in others. This means that we have to measure the way that animals change many characteristics in different environments before we can compare the plasticity of one organism with another. In the first part of this project, I will compare the extent that different clones (individuals with identical genes) of a water flea change their feeding rate, growth, reproduction and survival in high and low food environments. This will enable me to (1) determine how plastic responses in different characteristics are related to each other, and (2) determine whether some clones show more overall plasticity (all characteristics) than others in response to a change in food availability. In the second part of the project, I will test the idea that being plastic is costly in some environments. Normally trying to measure how a particular characteristic of an organism influences its success in any environment is extremely difficult. The advantage of studying water fleas is that they reproduce so quickly (10 days) I can directly compete plastic and non-plastic clones against each other over many generations. In this way, the success of a particular clone in any environment can be measured as its ability to replace another clone. Using these sorts of population competition experiments I will examine whether plastic clones can replace non-plastic clones in a variable environment and whether non-plastic clones can replace plastic clones in a constant environment as would be expected if being plastic is costly.