Evolution: No fish is an island

The distribution of marine animals around islands is determined by different processes from those that influence population dynamics of land-based animals, suggests a paper published online in Nature this week. Investigations of island biogeography ― the study of the distribution of species on islands over time ― have focused on the terrestrial residents. This new analysis sheds light on the factors that affect species diversity of marine communities.

To learn more about the processes that shape the aquatic environments of islands, Hudson Pinheiro and colleagues studied the evolutionary history of 10 reef fish species in a chain of volcanic seamounts and islands off the coast of Brazil. Sea-level changes are found to have had an effect on marine speciation, which is also seen in terrestrial species. However, the authors note that the fishes are better at dispersing than land-based organisms, filling most of niches by immigration and preventing in situ diversification, unlike what happens to their terrestrial counterparts. Speciation of marine organisms then increases with the random accumulation of species with low dispersal ability over time. Thus, despite some similarities, island geography, geological history and sea-level fluctuations influence the diversification of marine organisms in different ways than they affect land-based organisms, the authors conclude.