Parallel speciation, despeciation and respeciation: implications for species definition

" Can the same species arise more than once in different places or at different times? Can a species go extinct by hybridization? If so, can it reappear afterwards? Biologists are used to thinking about species as historical events. They arise once (speciation), exist for a certain time (undergoing stasis or anagenetic change) and then disappear (extinction). Some people even like to think of them as ‘individuals’, although, whether the use of the technical philosophical definition of this word is helpful to many biologists, is perhaps debatable. By and large, our observations of real animal species are not at all incompatible with these ideas. But, recent studies on fishes are suggesting that we may need to rethink our views of the life of a species to include the concepts of parallel speciation, despeciation and respeciation.The ideas I discuss in this paper are not necessarily new, but many fish biologists, like myself, may not have found any particular reason to consider them until recently. There is a very large literature on species concepts, and in a short opinion piece, I could scarcely attempt to do justice to the breadth of the debate or the complexity of the arguments raised. I will focus on issues relating to practical implications of species concepts that have to come to my attention as a fish biologist working on evolutionary questions "