Relative High Fitness and Genome-wide Diversity May Facilitate Plastic and Active Foragers' Diversification

Explaining the variation in diversification rates across the Tree of Life is an important challenge for evolutionary biologists. Growing evidence suggests that key innovations or historical contingency give rise to high diversification rates, but the genetic mechanisms through which this process may occur remain poorly investigated. Based on fitness landscapes, a high diversification is predicted to result from local adaptation as species traverse along genotype space. To test this prediction, we conducted a comparative analysis of 997 reptile species that vary in their locomotion while foraging. The species ranged from those that travel long distances to acquire food to those that barely move and acquire food in nearby sites or those that adopt a plastic strategy. We found that plastic foragers and active foragers not only have high diversification rates but may also have higher fitness compared to sit-and-wait foragers. While traversing among heterogeneous environments, plastic foragers and active foragers could accelerate the pace of evolution by exposing cryptic genetic variation to selection. This is possible in plastic foragers because their larger genomes potentially facilitate variation in gene expression. By contrast, higher genome-wide nucleotide diversity among active foragers could make up for the small size of their genomes, allowing natural selection to operate effectively to the point where divergence by ecological speciation could occur. We used emerging genomic data and macroevolutionary observations supported by microevolutionary processes to provide key insights into mechanisms of diversification.