Tradeoff-Induced Fitness Landscapes with Diminishing Returns Epistasis

The Tradeoff-Induced Landscapes (TIL) model uses tradeoff between the costs and benefits of mutations to describe an environment-dependent fitness landscape through a parameterized function. This model has been successful in generating highly rugged and highly accessible landscapes, which are key features observed in a growing body of experimental results. Recent experimental data was analyzed in this context, and found to strongly encode diminishing returns epistasis in the parameters of the fitness function, namely the mutation cost and resistance proxies. While fitness itself showed a dominant positive epistasis trend. In an attempt to model the results, the TIL model framework was used to introduce diminishing returns epistasis into the parameters of fitness which allowed the emergence of a positive epistasis trend in fitness, this new model will be called the TILME model. The evolutionary dynamics and the landscape properties of the TILME model have been studied in two simplified cases. The violations of accessibility as defined by the TIL model were identified. This study also provides insight into the landscape ruggedness, where it was found that the number of potential peaks in a landscape decreases with increasing levels of epistatic interactions.