Marine fishes exhibit a striking latitudinal diversity gradient (LDG), with far more species occurring in the tropics than in extratropical regions. Speciation rates are substantially elevated in polar and high-latitude temperate regions relative to the tropics, suggesting that faster tropical speciation cannot explain the LDG in marine fish diversity. However, we do not yet understand the role of lineage dispersal over macroevolutionary timescales in generating and maintaining the LDG. The "out of the tropics" model posits that tropical taxa expand their ranges and disperse out, thereby enriching high latitude regions. However, extratropical diversification and environmental niche conservatism might be expected to influence the strength of the gradient as well as the movement of species from polar-temperate to tropical regions. We assessed latitudinal source-sink dynamics in marine fishes by estimating biogeographic transition rates and dispersals between tropical, temperate and polar regions while distinguishing between taxa with predominately shallow versus deep-water distributions.
Results/Conclusions
We find a strong contrast in rates between the northern and southern high latitudes, with dispersal rates associated with the Arctic being the greatest, and relatively low dispersal rates associated with the Southern Ocean, thus reflecting the Arctic’s history as an area of biotic interchange between the north Pacific and north Atlantic oceans. We also find a strong pattern of greater movement of deep-water lineages than shallow-water lineages both towards and away from the tropics, suggesting that environmental conservatism and the depth distribution of biogeographic corridors likely play important roles in shaping global patterns of marine fish diversity.