Two distinct mechanisms generate biological diversity. Evolutionary adaptation proceeds by Darwinian selection favouring certain genotypes over others, changing the genetic composition of populations over subsequent generations. Phenotypic plasticity, the ability to express different phenotypes without changes in DNA sequence, allows much faster adjustment to the environment. Plastic responses are ubiquitous in nature and greatly influence individual performance and ecological interactions. Yet, the role of plasticity in species formation and persistence is disputed: it is believed to promote as well as hinder diversification. This limits our understanding of biodiversity dynamics in a changing world.
We address this problem using a model system which is famous for both phenotypic plasticity and species diversity: the cichlid fish family. We focus on visual plasticity, because the visual system has a relatively simple genetic basis, exhibits environmental plasticity, mediates many biological functions and is often associated with species divergence. We investigate the macro-evolutionary consequences of plasticity - by characterising visual plasticity across the cichlid family and determining its relationship to species diversity; and explore the underlying mechanisms - by testing experimentally how visual plasticity influences individual behaviour and fitness.
Together, these approaches provide a quantitative test of the hypothesis that phenotypic plasticity promotes niche expansion and species divergence. Results will improve our ability to predict how organisms respond to environmental change, either from natural causes or human-induced. Our findings will also help to improve aquaculture practices, as fish visual properties influence growth and survival in artificial light regimes.