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Mating success of flowering plants depends strongly on the efficiencies of pollen removal from flowers and its subsequent dispersal to conspecific stigmas. We characterized the economy of pollen dispersal in flowering plants by analysing pollen fates and their correlates for 228 species. The mean percentage of pollen removed from flowers (removal efficiency) varied almost twofold according to the type of pollen-dispersal unit, from less than 45% for orchids and milkweeds with solid pollinia, to greater than 80% for species with granular monads or sectile (segmented) pollinia. The mean percentage of removed pollen reaching stigmas (pollen transfer efficiency, PTE) varied from 2.4% for species with separate monads to 27.0% for orchids with solid pollinia. These values tended to be higher in plants with single pollinator species and in those with non-grooming pollinators. Nectar production increased removal efficiency, but did not influence PTE. Among types of pollen-dispersal units, the net percentage of produced pollen that was dispersed to stigmas varied negatively with removal efficiency and positively with PTE, indicating the relative importance of the latter for overall pollen economy. These findings confirm the key importance of floral traits, particularly pollen packaging, for pollen dispersal outcomes and highlight the under-appreciated pollination efficiency of non-grooming pollinators. [ABSTRACT FROM AUTHOR]

Why are some traits and trait combinations exceptionally common across the tree of life, whereas others are vanishingly rare? The distribution of trait diversity across a clade at any time depends on the ancestral state of the clade, the rate at which new phenotypes evolve, the differences in speciation and extinction rates across lineages, and whether an equilibrium has been reached. Here we examine the role of transition rates, differential diversification (speciation minus extinction) and non-equilibrium dynamics on the evolutionary history of angiosperms, a clade well known for the abundance of some trait combinations and the rarity of others. Our analysis reveals that three character states (corolla present, bilateral symmetry, reduced stamen number) act synergistically as a key innovation, doubling diversification rates for lineages in which this combination occurs. However, this combination is currently less common than predicted at equilibrium because the individual characters evolve infrequently. Simulations suggest that angiosperms will remain far from the equilibrium frequencies of character states well into the future. Such non-equilibrium dynamics may be common when major innovations evolve rarely, allowing lineages with ancestral forms to persist, and even outnumber those with diversification-enhancing states, for tens of millions of years. [ABSTRACT FROM AUTHOR]

To communicate with animals, plants use signals that are distinct from their surroundings. Animals generally learn to use these signals through associative conditioning; however, signals are most effective when they elicit innate behavioural responses. Many plant species have flowers specialized for pollination by ground-dwelling mammals, but the signals used to attract these pollinators have not been elucidated. Here, we demonstrate the chemical basis for attraction of mammal pollinators to flowers of the dioecious parasitic plant Cytinus visseri (Cytinaceae). Two aliphatic ketones dominate the scent of this species; 3-hexanone, which elicits strong innate attraction in rodents, and 1-hexen-3-one, which repels them in isolation, but not in combination with 3-hexanone. The aliphatic ketone-dominated scent of C. visseri contrasts with those of insect-pollinated plants, which are typically dominated by terpenoids, aromatic or non-ketone aliphatic compounds. 3-hexanone is also known from some bat-pollinated species, suggesting independent evolution of plant signals in derived, highly specialized mammal-pollination systems. [ABSTRACT FROM AUTHOR]

Pollen limitation (PL) of seed production creates unique conditions for reproductive adaptation by angiosperms, in part because, unlike under ovule or resource limitation, floral interactions with pollen vectors can contribute to variation in female success. Although the ecological and conservation consequences of PL have received considerable attention in recent times, its evolutionary implications are poorly appreciated. To identify general influences of PL on reproductive adaptation compared with those under other seed-production limits and their implications for evolution in altered environments, we derive a model that incorporates pollination and post-pollination aspects of PL. Because PL always favours increased ovule fertilization, even when population dynamics are not seed limited, it should pervasively influence selection on reproductive traits. Significantly, under PL the intensity of inbreeding does not determine whether outcrossing or autonomous selfing can evolve, although it can affect which response is most likely. Because the causes of PL are multifaceted in both natural and anthropogenically altered environments, the possible outcrossing solutions are diverse and context dependent, which may contribute to the extensive variety of angiosperm reproductive characteristics. Finally, the increased adaptive options available under PL may be responsible for positive global associations between it and angiosperm diversity. [ABSTRACT FROM AUTHOR]