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The pollinator-driven ecological speciation model has frequently been invoked to explain plant richness in biodiversity hotspots. Here, by focusing on Gladiolus (260 species), a flagship example of a clade with diverse pollination biology, we test the hypothesis that high species diversity in southern Africa, one of the world's most floristically rich regions, has primarily been driven by ecological shifts in pollination systems.We use phylogenetic methods to estimate rates of transition between the seven highly specialized pollination strategies in Gladiolus. We find that pollination systems have evolved multiple times and that some pollination strategies arose by a variety of evolutionary pathways. Pollination shifts account for up to one-third of all lineage splitting events in the genus, providing partial support for the pollinator-driven speciation model. Transitions from the ancestral pollination mode to derived systems have also resulted in increased rates of diversification, suggesting that certain pollination systems may speed up speciation processes, independently of pollination shifts per se. This study suggests that frequent pollination shifts have played a role in driving high phenotypic and species diversity but indicates that additional factors need to be invoked to account for the spectacular diversification in southern African Gladiolus. [ABSTRACT FROM AUTHOR]

Many plant species have been introduced from their native ranges to new continents, but few have become naturalized or, ultimately, invasive. It has been predicted that species that do not require the presence of compatible mates and the services of pollinators for reproduction will be favored in establishment after longdistance dispersal. We tested whether this hypothesis, generally referred to as Baker's law, holds for South African species of Iridaceae (iris family) that have been introduced in other regions for horticultural purposes. Fruit and seed production of flowers from which pollinators had been experimentally excluded was assessed for 10 pairs of species from nine different genera or subgenera. Each species pair comprised one naturalized and one nonnaturalized species, all of which are used in international horticulture. On average, species of Iridaceae that have become naturalized outside their native ranges showed a higher capacity for autonomous fruit and seed production than congeneric species that have not become naturalized. This was especially true for the naturalized species that are considered to be invasive weeds. These results provide strong evidence for the role of autonomous seed production in increasing potential invasiveness in plants. [ABSTRACT FROM AUTHOR]

Floral morphology and observations on insect and avian visitors to species of the southern African and largely Western Cape genus Tritoniopsis indicate that short-tubed pink flowers, ancestral in the genus, are pollinated by anthophorine bees forging for nectar; Multiple shifts to more specialized pollination systems have occurred in the genus during its evolution. Four species with elongate floral tubes and a pink to red bilabiate perianth are pollinated either by sunbirds (Nectarinia) alone or by sunbirds and the satyrid butterfly Aeropetes tulbaghia. Another red-flowered species with an actinomorphic flower is inferred to be pollinated only by Aeropetes, while two species with pale pink flowers with red markings are pollinated by long-proboscid flies in the genus Prosoeca (Nemestrinidae). Tritoniopsis parviflora is unique in the African Iridaceae in producing floral oils as a reward to the short-tongued bee Rediviva gigas (Melittidae), as well as conventional sugar nectar Tritoniopsis nervosa has white, sweetly scented, long-tubed flowers and is assumed to be pollinated by night-flying moths. Although relationships within Tritoniopsis are poorly understood, it is clear that at least five shifts in pollination strategy have occurred in this genus of just 24 species. Studies also show that bimodal pollination systems using two different pollinator groups occur in several species, using sunbirds and Aeropetes, anthophorine bees and nemestrinid flies, or oil-collecting Rediviva and nectarivorous bees. Such bimodal systems are probably important for the successful reproduction of these plants. [ABSTRACT FROM AUTHOR]