Steven D Johnson

..We present several hypotheses for the association between nectar properties and specificity in bird pollination systems...

..These findings provide empirical support both for Darwin's contention that pollinarium bending is an anti-selfing mechanism in orchids and for the idea that floral deception serves to maximize the efficiency of pollen export...

..Positive directional selection on tube length was found to occur in both morphs...

..Despite technical advances, phylogenies remain limited in their power to distinguish among various pollinator-driven evolutionary processes...

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..Thus, rarer and nonrewarding species in the guild are forced to keep pace with the coevolutionary race between common rewarding flowers and flies...

..This suggests that mutations affecting the production of particular scent compounds could precipitate shifts between pollinators, independently of floral morphology, colour or nectar properties...

..Flower color and location of E. zeyheriana plants relative to rewarding magnet patches are therefore key components of the exploitation by this orchid of the relationship between W. cuspidata and Lipotriches bee pollinators...

..Pollination rates and levels of self-pollination were high compared with those in other deceptive orchids and it is therefore unlikely that this mimicry system evolved to promote outcrossing...

..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...

..These results show that a transition from wind pollination to insect pollination occurred in sedges and shed new light on the function of traits involved in this important transition...

..These findings provide support for the idea that floral deception serves to reduce pollinator-mediated self-pollination...

..These results support Baker's law, and we recommend that screening protocols for predicting invasiveness of species considered for introduction should include assessment of their breeding system...

..Our results confirm that the markings on L. oreogena flowers serve as nectar guides and suggest that they are under strong selective maintenance through both male and female fitness components in this pollination system...

..I thus also consider the evidence that disturbance provokes pollination failure in some southern African plants with specialized pollination systems...

..We conclude that ecological speciation is likely to have been important for radiation of the Cape flora, but there is no evidence as yet for special "Cape" patterns of ecological speciation...

..Reconfiguration times were also consistently longer than pollinator visit times. These results provide strong support for Darwin's idea that this mechanism promotes cross-pollination...

..We conclude that coevolution is a compelling explanation for the geographical covariation in flower depth and fly proboscis length...

..Here an unusual mechanism--anther cap retention--that appears to prevent self-pollination in the South African orchid Eulophia foliosa is examined...

..3-hexanone is also known from some bat-pollinated species, suggesting independent evolution of plant signals in derived, highly specialized mammal-pollination systems...

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..We propose that changes in pollinator flight behaviour, rather than pollinator conditioning, are likely to account for negative frequency-dependent reproductive success in deceptive orchids...

..Thus the dark phenolic component of the nectar appears to function as a floral filter by attracting some animals visually and deterring others by its taste...

..Here it is shown that a functional stigma has evolved secondarily from modified tepals in some Albuca species (Hyacinthaceae)...

..The plants, however, gain clear benefit from the interaction, as verified by the removal and insertion of pollinia in flowers exposed solely to visits by pompilid wasps...

..Intramorph pollination does not result in fertilization, because of an effective heteromorphic incompatibility system...

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..The probability that seeds will be fertilized from self- versus cross-pollen depends strongly on whether plants have self-incompatibility systems, and how these systems influence the fate of pollen tubes...

..This phenotype by environment interaction demonstrates that the flower colour shift in D. ferruginea is adaptive and driven by local colour preference in its pollinator...

..The apparent constitutive emission of isothiocyanates raises interesting new questions about their functional role in flowers...

..Much of the extensive variation in floral form in G. diffusa therefore appears to have arisen without evolutionary shifts between pollinator types...

..In contrast, there is no significant association between pollination system shifts and edaphic shifts for allopatric sister species. These results are interpreted as evidence for reinforcement...

..Neither of these possibilities are mutually exclusive. Recent studies have provided experimental evidence for the first two hypotheses, and we suggest promising avenues for future research into this little-known floral trait...

..Our results show that P. roupelliae is largely dependent on birds for pollination, and thus confirm the utility of floral syndromes for generating hypotheses about the ecology of pollination systems...

..The research has shown that there is still much to be learned about plant-pollinator interactions in areas of high plant diversity such as South Africa...

..This study demonstrates that selection may occur among plants with natural phenotypic variation in flower-tube length, and supports Darwin's model of pollinator-mediated selection...