Diversification and hybridization in Malagasy baobabs

Madagascar is the world’s fourth largest island, and is renowned for its species diversity and endemism. Due to the wide diversity of climatic and ecological conditions on the island, the native biota provides a fascinating context for the study of speciation and plant radiation. On Madagascar, the trees of the genus Adansonia (Bombacoideae, Malvaceae), the baobabs, are prominent in the dry deciduous forests and thickets of the western half of the island. Baobab trees may live for more than 1000 years and are characterized by outcrossing breeding systems with self-incompatibility.

Adansonia (Bombacoideae) comprises nine species, six of which are endemic to Madagascar and genetic relationships within these remain unresolved due to conflicting results between nuclear and plastid DNA variation. A recent paper in Annals of Botany analyses nuclear microsatellite variation using Bayesian clustering programs and find a clear interspecific differentiation. They identify early-generation hybrids in contact areas between the species showing overlapping flowering periods and sharing the same pollinators. The results reveal a new, stabilized differentiated entity originating from hybridization in the current absence of the parental species, suggesting a potential role of hybridization in the recent diversification history of the Malagasy baobabs.

Tsy, J. M. L. P., Lumaret, R., Flaven-Noguier, E., Sauve, M., Dubois, M. P., & Danthu, P. (2013) Nuclear microsatellite variation in Malagasy baobabs (Adansonia, Bombacoideae, Malvaceae) reveals past hybridization and introgression. Annals of botany, 112(9), 1759-1773