Solutions to Challenge Data Sets:
- genetrees_W.tre = M1 [Speciation intervals are 2.0 coalescent units]
- genetrees_X.tre = M3 [B is a hybrid taxon with 30-70% parental contributions]
- genetrees_Y.tre = M4 [B is a hybrid taxon with 50-50% parental contributions]
- genetrees_Z.tre = M2 [Speciation intervals are 0.5 coalescent units]
In all cases the model tree is ((((A,B)C),D),(E,F)); when
hybridization occurs, it is between taxa A and C to produce hybrid
species B.