Anas superspecies complex can form complex multi-species introgressions within the complex.
Genetic Introgression results in reproduction between two different, but related species (a.k.a. Hybridization). The advantage to introgression is that it has the potential to introduce novel genes into a population, and these genes may be adaptive. Likewise, introgression may be a source of speciation.
Examples[]
Mallard superspecies (Anas) and eight species of gulls (Larus genus) both form complex introgression amongst themselves respectively.
Literature[]
Rheindt, F.E. and S.V. Edwards. 2011. Genetic introgression: an integral but neglected component of speciation in birds.