Dominik R Laetsch

1 Introduction Wolbachia is a genus of Alphaproteobacteria that lives as intracellular endosymbiont of arthropods and nematodes, and is primarily transmitted vertically through the egg cytoplasm. Although the taxonomy of the genus is unclear, Wolbachia is classified into distinct genetic clades or ‘supergroups’ (Lo et al. 2007); whether such supergroups constitute distinct species is a matter of debate (Ellegaard et al. 2013).

Abstract Many closely related species continue to hybridise after millions of generations of divergence. However, the extent to which current patterning in hybrid zones connects back to the speciation process remains unclear: does evidence for current multilocus barriers support the hypothesis of speciation due to multilocus divergence?

Abstract The allopatric model of speciation has dominated our understanding of speciation biology and biogeography since the Modern Synthesis. It is uncontroversial because the cessation of gene flow during allopatry will allow reproductive isolation to readily emerge as a by-product of evolutionary divergence. However, whether allopatric speciation is common has rarely been systematically tested across a continuum of closely-related species.