Drivers of genetic diversity across the marine tree of life

Why do some species have more genetic diversity than others? This question is one of the greatest remaining mysteries in evolutionary biology, and is particularly urgent in marine species, which are experiencing catastrophic anthropogenic impacts. We address this critical gap by estimating genetic diversity for 93 marine species sampled over 9,000 localities. For each species, we aggregate biotic traits and abiotic geographic data for their ranges. We show that diversity increases with range extent and planktonic dispersal. We hypothesize that these traits increase a species' ability to avoid or recover from bottlenecks, thereby maintaining diversity. Our findings provide insights into the factors interacting to shape genomic variation in the ocean, and offer a predictive framework for understanding marine biodiversity in the face of global change.