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Tropical Biology Section

Vary, Laura B. [1], Schlessman, Mark A. [1], Lowry II, Porter P. [3], Munzinger, Jérôme [2].

Sexual Dimorphism in the Native Flora of New Caledonia.

Sexual dimorphism (dioecy, gynodioecy, androdioecy, etc.) is rare among angiosperms. Dioecy is the most common form of sexual dimorphism, and recent estimates suggest that only 6% of angiosperms are dioecious. Higher than expected frequencies of dioecy on certain oceanic islands, particularly Hawaii and New Zealand, have been important in formulations of theories about the evolution of dioecy. The distinctive flora of New Caledonia is much richer and more diverse than those of Hawaii and New Zealand. It includes descendants of both Gondwanan relicts and more recent long-distance colonizers. Seventy-eight percent of the species are endemic, and approximately 28% occur in the unique maquis vegetation on ultramafic soils. We used the literature, herbarium specimens, and field observations to determine the sexual systems of 97.8% of the described native species of angiosperms. Of those, 20.8% are sexually dimorphic (20.2% dioecious, 0.4% androdioecious, 0.2% gynodioecious). Dioecy occurs in 46 of the 163 families represented, while androdioecy and gynodioecy are each restricted to only two families. Dioecy is over-represented in endemic species, woody species, and species found in dense evergreen rainforest. Sexual dimorphism is under-represented in wetlands and disturbed vegetation. New Caledonia has the highest incidence of sexual dimorphism of any island flora. Given that 75% of the native flora is woody and 45% of the species can occur in dense evergreen forests, it is likely that the widely recognized associations of dioecy with woodiness and with tropical forest habitats have contributed to the very high incidence of sexual dimorphism. The depauperate bee fauna may also be a contributing factor. We are now evaluating the relative contributions of 1) relictual versus colonizing lineages and 2) autochthonous origins versus introductions in the evolution of sexual dimorphism on New Caledonia.

1 - Vassar College, Department of Biology, Vassar College Box 187, 124 Raymond Ave., Poughkeepsie, New York, 112604-0187, U.S.A.
2 - Institute de Recherche pour le Dévelopement, B.P. A5, 98848, Nouméa Cedex, , Nouvelle-Calé:donie
3 - Missouri Botanical Garden, PO Box 299, St. Louis, Missouri, 63166-0299, USA

New Caledonia
sexual dimorphism
sexual systems.

Presentation Type: Paper
Session: 8-7
Location: Peruvian (Cliff Lodge)
Date: Monday, August 2nd, 2004
Time: 10:15 AM
Abstract ID:499

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