Speciation in the Brachionus plicatilis species complex

The Brachionus plicatilis species complex is the best-studied example among rotifers where the use of integrative taxonomy, coupling morphology, ecology, physiology, cross-mating experiments, and DNA taxonomy helps disentangling the biological reality of the different species in the complex. Here we review the theoretical and empirical approaches in species definition applied to the B. plicatilis complex, we outline the history of the discovery of the complex, and we explore the evidence in support of the currently accepted presence of 15 species. We review the evidence for long-distance dispersal and for co-occurrence of the species in the complex, including the processes favoring the co-occurrence (e.g., niche differentiation). We discuss evolutionary explanations for the morphological similarity of the species in the complex. Finally, by reviewing studies on intraspecific population differentiation and mate recognition, we identify putative factors acting on speciation in the complex.