Fig I.

Two equilibrium cases exist for the linkage disequilibrium (LD), a proxy for differentiation into two distinct “species” in this proof-of-concept model, that can be maintained between two loci that are under disruptive selection and determine assortative mating. With little initial LD, the one-species equilibrium is likely to be reached even when the intensity of assortment is high. When LD in the traits is initially large, as can be the case if there is initially divergence in allopatry, the two-species equilibrium can be reached instead. Modified from (Kirkpatrick & Ravigné 2002).