REPRODUCTIVE ISOLATION MECHANISMS AMONG 4 CLOSELY-RELATED SPECIES OF CONOSPERMUM (PROTEACEAE)

The effectiveness of geographical isolation, ecological isolation, tem poral isolation, mechanical isolation, ethological isolation, cross-in compatibility, hybrid inviability, hybrid sterility and hybrid breakdo wn as practical barriers to gene flow in the field between Conospermum taxifolium, C. ericifolium, C. ellipticum and C. longifolium has been quantified. The barriers to gene flow between C. ericifolium and C. e llipticum are completely effective, owing to their allopatric distribu tions. The barriers to gene flow between C. taxifolium and these two s pecies are only partially effective, as their ecological separation br eaks down in intermediate habitats, and partially-fertile F1 plants ca n grow in the areas of overlap. The barriers to gene flow between C. l ongifolium and the other three species are almost completely effective , as cross-incompatibility is very high and the F1 plants are female-s terile.