Genetic diversity and biogeography of the boab Adansonia gregorii (Malvaceae: Bombacoideae)

The Kimberley region of Western Australia is recognised for its high biodiversity and many endemic species, includingthecharismaticboabtree,AdansoniagregoriiF.Muell.(Malvaceae:Bombacoideae).Inordertoassesstheeffects ofbiogeographicbarriersonA.gregorii,weexaminedthegeneticdiversityandpopulationstructureofthetreespeciesacross itsrangeintheKimberleyandadjacentareastotheeast.Geneticvariationatsixmicrosatellitelociin220individualsfromthe entire species range was examined. Five weakly divergent populations, separated by west-east and coast-inland divides, were distinguished using spatial principal components analysis. However, the predominant pattern was low geographic structure and high gene flow. Coalescent analysis detected a population bottleneck and significant gene flow across these inferred biogeographic divides. Climate cycles and coastline changes following the last glacial maximum are implicated in decreasesinancientA.gregoriipopulationsize.Ofallthepotentialgene flowvectors,variousmacropodspeciesandhumans are the most likely.