Koopman, Margaret M. , Raveloarison, Tahiry A. , Baum, David A. .
Reproductive isolation among sympatric species of Megistostegium (Malvaceae) in southern Madagascar.
Megistostegium is traditionally circumscribed to include three Malagasy endemic species within a large, exclusively Malagasy clade of Hibiscus s.l.. Two of the species have a broad distribution in Southern Madagascar: Megistostegium microphyllum with small leaves and flowers, a straight staminal column, and broadly overlapping petals and M. nodulosum with larger leaves and flowers, a curved staminal column, and narrow petals. The third species, M. perrieri, is restricted to windswept limestone pavements and cliffs at the southern tip of Madagascar and is characterized by large tomentose leaves, enormous pendent flowers, broad petals, and a straight style. We have found all three species in sympatry at Cap Sainte Marie, with M. microphyllum often growing side by side with the other species. All three species were flowering at the same time and appeared adapted to pollination by the single resident species of sunbird. A few individuals with an intermediate morphology between M. microphyllum and either M. perrieri or M. nodulosum were found. Additionally, nuclear gene sequence data suggested gene flow between M. nodulosum and M. perrieri. Nonetheless, the three forms remain very distinct and the number of putative hybrids is low considering. Therefore, we sought to document pollination biology and to explore the potential for reproductive isolation mediated by pollen-stigma interactions through seed maturation. Bagged, emasculated flowers were pollinated with homo- or heterospecific pollen. Some styles were collected for observation of pollen tube growth, whereas others were allowed to develop as fruit to determine an index of crossability. For M. microphyllum and M. perrieri we also conducted experiments to assess self-compatibility, apomixis, day versus night pollination, and pollen flow between species. These data are relevant to our understanding of how plant taxonomic species can remain morphologically distinct in sympatry despite overlapping flowering and similar pollination systems.
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1 - University of Wisconsin Madison, Department of Botany, Birge Hall, 430 Lincoln Drive, Madison, Wisconsin, 53706-1381, USA
2 - University of Antananarivo, Biologie et Ecologie Végétale, Faculté des Sciences, Antananarivo, 101, Madagascar
Presentation Type: Oral Paper:Papers for Topics
Location: Lake Ontario/Hilton
Date: Tuesday, July 10th, 2007
Time: 8:15 AM