Figure 7.

Patterns of gene flow among the three species in the northern oriole group estimated using IMa2. Circle sizes reflect relative N_e estimates. Relative rates of gene introgression are indicated by the width of solid arrows. Dashed arrows indicate little or no introgression. (a) The full three-population analysis inferred gene flow only between the hybridizing Icterus galbula and I. bullockii, whereas (b) two-population analyses also indicated a low level of introgression (highlighted in red) from I. abeillei into I. galbula. The introgression between these highly allopatric species is best ascribed to ancestral polymorphisms shared between I. abeillei and I. bullockii introduced to I. galbula across the I. galbula–I. bullockii hybrid zone. This study clearly illustrates how introgression from other taxa not included in the analysis (in this case I. bullockii) can bias gene flow estimation if not accounted for.