The xeric scrublands of southern Madagascar support a number of charismatic and intriguing plant species, more than 90% of which exist nowhere else on earth. The proposed research will focus on the endemic genus Megistostegium and will utilize field and laboratory methods to clarify the evolutionary mechanisms at play in the group's diversification. Prior work has shown that Megistostegium is related to members of the genus Hibiscus that have radiated in arid regions of the island. Megistostegium contains three bird-pollinated species that are morphologically distinct from their close relatives (which appear to be either bird or insect pollinated). A particularly interesting situation occurs at the most southern tip of Madagascar, where all three currently recognized species occur in close physical proximity to each other yet remain morphologically distinct (M. Koopman, pers. obs.). This is intriguing given the fact that these species have overlapping flowering seasons and share the same, single pollinator, a small, green sunbird. There is also one undescribed species of Megistostegium in a remote valley 100 miles to the northeast, which is differentiated by an asymmetrical flower (M. Koopman, pers. obs). The aim of the proposed research will be to explore the genetic relationships, evolution and pollination ecology of Megistostegium. Fieldwork will determine the role of ecological barriers to pollen flow and seek evidence of reproductive barriers after pollination. Leaf tissue will be collected for molecular analyses and sequences for multiple nuclear genes will be produced to elucidate the extent of gene flow between the three forms and whether all three warrant species status (e.g., Is one a hybrid between the other two?).
This study will not only enhance basic systematic knowledge of an important group of species in a region threatened by anthropogenic habitat disturbance but has the potential to elucidate the ecological and genetic mechanisms that allow the coexistence of closely related species. Pollination biology at the species and population level has been shown to be of particular importance for the management and conservation of ecosystems. The pollination ecology of a vast majority of African plant taxa remains unexplored and this is especially true on the island of Madagascar. This project will document the pollination ecology of Megistostegium, which will help in planning community level sustainable management of pollinators and the forests they live in. Fieldwork will be conducted with one Malagasy student from the University of Antananarivo, Madagascar and will, thus, facilitate international scientific exchange.
