Speciation on a round planet: phylogeography of the goatfish genus Mulloidichthys
The goatfish genus Mulloidichthys is abundant on reefs throughout the tropics. Characteristic of this genus is a long larval and pelagic juvenile phase, which could potentially confer large dispersal capacity. We sampled its mitochondrial DNA to answer the following questions: What speciation events have led to the formation of the extant species? How do they correlate with geological and oceanographic events? Are M. dentatus and M. martinicus geminate species formed by the rise of the Isthmus of Panama? Is there genetic structure between conspecific populations?
All tropical oceans.
We constructed a phylogeny of Mulloidichthys, based on the ATPase-8 and ATPase-6 genes and the control region. We estimated degree of genetic structuring in four species.
The phylogeny revealed that the Indo-Pacific M. pflugeri diverged first, followed by M. flavolineatus, also from the Indo-Pacific, followed by the central Pacific M. mimicus. The most recent splitting event resulted in a tritomy composed of the Atlantic M. martinicus, the eastern Pacific M. dentatus and the Indo-Pacific M. vanicolensis. The differentiation between M. martinicus and M. dentatus was substantially smaller than divergence in the same DNA fragments in eight other fish genera likely to have been split by the rise of the Isthmus of Panama. Low genetic structuring was found between conspecific populations of Mulloidichthys, even across the entire Indo-Pacific. Only populations at Clipperton Atoll and at Ascension Island in the Atlantic were genetically isolated from other conspecific populations.
The oldest extant species of Mulloidichthys are found in the Indo-Pacific. Younger species probably maintained genetic contact between the Atlantic and the Indo-Pacific until the late Pleistocene. The low degree of genetic structuring and the unusual recent connections around the globe are likely to be the result of the large, highly mobile, and long-lived juvenile phase in this genus.