Can phenotypic plasticity and DNA methylation promote adaptive radiation?

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How do living things adapt to a new environment? In the long-run this will need genetic (or occasionally cultural) changes, but biologists are beginning to take seriously the idea that the genome has evolved to allow an organism's development to be responsive to the environment. This process may operate at a fundamental level, with chemical changes to the structure of the DNA itself in the form of 'epigenetic' marks which can enhance or inhibit the expression of individual genes. Mostly, these are short-term changes that vary among tissues and life-stages in an individual organism as part of the normal process of development, but it is now known that sometimes they can be induced by the environment and occasionally even persist across generations. Can this type of epigenetic change help organisms cope with new environmental challenges or even lead to them evolving into new species through later genetic changes, a process called 'genetic assimilation'? These are important questions for understanding the origins of biodiversity and its maintenance in a changing world. We aim to investigate these questions focussing on a small fish- the Eastern Happy- which belongs to one of the most spectacular examples of explosive evolutionary diversification, the African Great Lakes cichlid fishes, which have evolved into thousands of species in a few million years. Cichlid fishes have a second set of (pharyngeal) jaws in their throats that they use for processing their food, while the external (oral) jaws are specialised for capturing prey. Many closely-related cichlid species have subtly different jaw structures allowing them to feed on different things. This helps populations adapt to different environments, and allows different species to live together, exploiting different resources. We plan to look at three closely-related pairs of populations of the Eastern Happy: in each pair one population feeds mostly on soft food- plankton or plant material, but the other includes hard-shelled prey such snails in its diet, and this is reflected in their more powerful jaws. We aim to see how much of these difference in jaw structures can be explained by environmentally-induced flexibility and how much is genetic. We will test live fish in aquaria to see whether the anatomical differences among populations really do improve how they capture and process different kinds of prey. We will see whether genetic differences cause anatomical variation in the same direction as the environmentally-induced changes. We will investigate the structure of the genomes to see whether epigenetic changes are associated with divergent diets and structures, and try to determine if different population pairs are diverging in similar ways. We aim to test if the activities of key genes in the jaws are associated with epigenetic changes. These experiments will be based around investigations of fish reared in research aquaria, fed on different diets to mimic the hard and soft-diets they experience in the wild. This allows us to feed fish from soft-diet populations on hard diets and vice versa. Particularly good insights will come from splitting a single brood of fish after 6th months and rearing one half on hard diet and the other half on a soft diet, thus controlling for the effects of genetics. By rearing several generations in this way, we will be able to see whether epigenetic changes to the genome can persist over several generations. This study has the potential to reveal exciting new insights at the most fundamental level into how organisms adapt rapidly to their environments. The findings and techniques will have applications across a range of species and situations and perhaps cast light on how species will respond to the challenges of the environmental changes being caused by humans, through climate change, pollution and the introduction of alien species.