Progress on animal speciation studies.

Speciation research represents our thinking and exploration about how new species are generated and maintained, and it is one of the most important parts of evolutionary biology. Revealing new species formation modes, processes of reproductive isolation establishment and their intrinsic genetic mechanisms, are not only important issues and primary tasks in the field of speciation, but also the key clues for our understandings about the species diversity in nature. Here, by focusing on animal groups, we first introduced different definitions of species concept, and then summarized present research progress and important breakthroughs made in the speciation modes and molecular mechanism of reproductive isolation. We also pointed out some limitations in current studies. Finally, we discuss the potential opportunities and new breakthroughs that can be made in the future studies of animal speciation.