ContentSnapshots

Plant−pollinator interactions along the pathway to paternity (Review)

Annals of Botany 123: 225–245, 2019

doi: 10.1093/aob/mcy167

Animal-mediated pollen transfer has led to the evolution of an astounding array of reproductive strategies to lure pollinators and facilitate pollen placement on their bodies. Once placed, pollen grains undertake a complex pollinator-mediated journey to reach potential mates. Minnaar et al. discuss male reproductive strategies which may increase siring success along this journey. In particular, they describe the bodies of pollinators as arenas for pollen competition where rival males constantly cover or displace competitor pollen. This review provides an exciting new direction and perspective on the impact of male reproductive strategies on floral evolution.

Authors: Corneile Minnaar, Bruce Anderson, Marinus L. de Jager, and Jeffrey D. Karron

Evolutionary ecology of nectar (Review)

Annals of Botany 123: 247–261, 2019

doi: 10.1093/aob/mcy132

Floral nectar is a key evolutionary innovation in the interactions between plants and their pollinators. While macro-evolutionary processes of nectar evolution are well-characterised, less work has been done on micro-evolutionary processes. Parachnowitsch et al. bring together current knowledge on the evolutionary ecology of floral nectar, including phenotypic variation, heritability and natural selection. They also explore how pollinators, antagonists and abiotic factors influence evolution of nectar traits. With this review they aim to inspire future work on the evolutionary ecology of nectar to help fill in major gaps for this important trait.

Authors: Amy L. Parachnowitsch, Jessamyn S. Manson, and Nina Sletvold

Functional significance and optical properties of floral visual signals (Review)

Annals of Botany 123: 263–276, 2019

doi: 10.1093/aob/mcy119

Many plants produce colourful flowers that play a role in pollinator attraction. These floral visual signals may have distinct optical properties that differ in biological relevance. In this review, van der Kooi et al. discuss the optical properties and functional significance of common and uncommon aspects of floral visual signals. Drawing on a large body of literature covering the ecology, optics and anatomy of flowers, as well as studies on the behaviour and visual systems of pollinators, they explain how different visual effects come about, their relevance for signalling to pollinators, and highlight fruitful avenues for future research.

Authors: Casper J. van der Kooi, Adrian G. Dyer, Peter G. Kevan, and Klaus Lunau

Dominant pollinators drive flower colour patterns in daisy communities

Annals of Botany 123: 277–288, 2019

doi: 10.1093/aob/mcy126

As most plants rely on pollination for persistence in communities, pollination interactions should be important for plant community assembly. Kemp et al. investigate the structuring of complex flower colour patterns, as perceived by pollinators, in daisy (Asteraceae) communities of South Africa. They find that co-occurring species frequently share flower colour patterns, and that these over-represented patterns are favoured by the dominant fly pollinators in communities. This suggests that pollinators are an important determinant of community assembly, but that this is not the outcome of competitive interactions. Instead, in some contexts the benefits of pollinator sharing outweigh the costs, resulting in clustered floral trait assembly.

Authors: Jurene E. Kemp, Nicola G. Bergh, Muri Soares, and Allan G. Ellis

Floral scent of insect- vs. wind-pollinated flowers

Annals of Botany 123: 289–301, 2019

doi: 10.1093/aob/mcy131

Floral scent plays a critical role in pollinator attraction, contributing to enhanced seed and fruit production. Thalictrum (Ranunculaceae), with its multiple transitions from insect- to wind-pollination, offers a unique opportunity to test interspecific changes in floral fragrance and their impact on pollinator response. In this study, Wang et al. integrate pollination mode, floral scent and insect physiology within a phylogenetic context. Floral volatile organic compounds from insect-pollinated Thalictrum elicited a larger antennal response from a potential pollinator than those from wind-pollinated congeners, suggesting that an ancestral ability of floral fragrance to elicit an insect response was lost during multiple evolutionary transitions to wind pollination.

Authors: Theresa N. Wang, Marie R. Clifford, Jesús Martínez-Gómez, Jens C. Johnson, Jeffrey A. Riffell, and Verónica S. Di Stilio

Pollination quantity and purity

Annals of Botany 123: 303–310, 2019

doi: 10.1093/aob/mcy120

If two plant species flower together and share pollinators, they may affect each other by influencing both visitation rates and the species purity of pollen loads. One species may draw visitors away from the other, exerting a negative, harmful effect. Alternatively, a less attractive species might receive more visitation in the vicinity of a more attractive one, simply because pollinators are recruited to the area by the attractive species and then visit the less attractive species. Thomson et al. report experiments allowing bumblebees to forage on arrays of artificial flowers. They demonstrate that pollinator-mediated interactions between plant species depend on both pollination quantity and purity, which can vary with spatial intermingling.

Authors: James D. Thomson, Hannah F. Fung, and Jane E. Ogilvie

The diversity and evolution of pollination systems in the Apocynaceae

Annals of Botany 123: 311–325, 2019

doi: 10.1093/aob/mcy127

Interactions between flowering plants and their pollinators are known to be responsible for part of the tremendous diversity of the angiosperms, currently thought to number at least 350,000 species. Using a new database of pollinators of the large, globally distributed family Apocynaceae (>5300 species) Ollerton et al. explore how different types of pollination system (bird, bee, moth, fly, etc.) are distributed across the evolutionary tree of the family; how those pollination systems have evolved over time; and how they vary biogeographically. Earlier diverging clades are characterized by a narrower range of pollination systems. Transitions from one type of pollination system to another are evolutionarily constrained, and there is significant convergent evolution of pollination systems by geographically and phylogenetically distinct clades.

Authors: Jeff Ollerton, Sigrid Liede-Schumann, Mary E. Endress, Ulrich Meve, André Rech et al.

Evolution of plant mating systems drives pollen limitation

Annals of Botany 123: 327–336, 2019

doi: 10.1093/aob/mcy181

Seed production of plants is rarely maximized, because it is limited by pollen receipt. Previous theories have shown that ecological mechanisms can drive the evolution of pollen limitation. Devaux et al.’s model shows that pollen limitation can also evolve as a by-product of the evolution of the mating system. At evolutionarily stable equilibria, plants are pollen limited because they produce (i) too many flowers and pay the cost of inbreeding depression due to self-fertilization among simultaneously open flowers or (ii) too few flowers and pay the cost of too few pollinator visits. How ecological and evolutionary mechanisms of pollen limitation interact remains unknown.

Authors: Céline Devaux, Emmanuelle Porcher, and Russell Lande

Does self-fertilization rescue populations or increase the risk of extinction? (Viewpoint)

Annals of Botany 123: 337–345, 2019

doi: 10.1093/aob/mcy144

The evolution of plant mating systems is a major evolutionary transition in seed plants. Whether evolution of selfing rescues or fails to rescue populations has, however, rarely been investigated. Cheptou reviews empirical studies reporting the consequences of selfing on population or lineage viability. Empirical studies reveal that short-term or long-term evolution have contrasting effects on population extinction, suggesting the role of direct (e.g. increased seed set) or indirect effects (e.g. genomic consequences) of selfing. Moreover, a simple model shows that either rescue or extinction can occur through evolution of self-fertilization. This emphasizes the need for studies of the demographic consequences of self-fertilization.

Author: P.-O. Cheptou

Stabilizing selection in deceptive orchids

Annals of Botany 123: 347–354, 2019

doi: 10.1093/aob/mcy083

Sexually deceptive orchids produce odours that match the sex pheromones of female insects. This incredible case of mimicry allows them to attract male insects that pollinate their flowers through attempted mating. Whether they also match their male pollinators in size to ensure successful pollen transfer remains unknown. Using the Australian orchid Chiloglottis trapeziformis (Orchidaceae), de Jager and Peakall employ experimental manipulations that extend the natural range of floral trait sizes to show that both larger and smaller flowers elicit less intense mating behaviour from pollinators. Phenotypic selection analysis in natural populations reveals that these changes in pollinator behaviour can negatively affect plant fitness.

Authors: Marinus L. de Jager and Rod Peakall

Intra-floral modularity increases pollination accuracy of triggerplant flowers

Annals of Botany 123: 355–372, 2019

doi: 10.1093/aob/mcy184

Most triggerplant (Stylidium, Stylidiaceae) flowers actively and repeatedly place pollen on, and later retrieve it from, pollinators. Both actions involve a central, finger-like column (fused staminate and pistillate tissues) and occur rapidly (10–15 milliseconds). The paper by Armbruster and Wege poses the hypothesis that selection for precise pollen placement and stigma contact with pollinators has led to less random variation in column traits than in other floral parts, a pattern termed intra-floral modularity. A novel combination of statistical analysis, including allometric analysis, revealed strong patterns of intra-floral modularity and reduced variation in the column length in a sample of 10 Australian triggerplant species.

Authors: W. Scott Armbruster and Juliet A. Wege

Nectar supplementation changes pollinator behaviour and pollination mode in Pedicularis dichotoma

Annals of Botany 123: 373–380, 2019

doi: 10.1093/aob/mcy102

Gain or loss of floral nectar is a key innovation that has occurred in diverse lineages of flowering plants. Phylogenetic studies show that gains of floral nectar frequently occur in the species-rich genus Pedicularis (Orobanchaceae), but the adaptive significance of this strategy remains unclear. P. dichotoma produces very little nectar and is visited primarily by pollen-collecting bumblebees. Tong et al. experimentally added nectar to flowers of this species, and observed a marked behavioural shift in the foraging posture of bees as they foraged for nectar instead of pollen. Their findings suggest that the evolutionary gain of nectar may be associated with enhanced pollinator attraction in unpredictable pollination environments.

Authors: Ze-Yu Tong, Xiang-Ping Wang, Ling-Yun Wu, and Shuang-Quan Huang

Sterile flowers increase fitness at low frequency in Viburnum

Annals of Botany 123: 381–390, 2019

doi: 10.1093/aob/mcy117

Darwin hypothesized that sterile accessory flowers function to increase reproductive success by promoting insect visitation, citing Viburnum as an example. Although several studies have supported Darwin’s hypothesis, none has specifically examined the benefits of sterile flowers in a context that reflects their first appearance in a population. In this study, Park et al. find that plants of Viburnum lantanoides (Adoxaceae) with intact sterile marginal flowers (SMFs) received more insect visits and produced more fruit than did plants from which SMFs were experimentally removed. This was true even when intact plants were in low frequency within a population of plants with their SMFs removed.

Authors: Brian Park, Miranda Sinnott-Armstrong, Caroline Schlutius, Juan-Carlos Penagos Zuluaga, Elizabeth Spriggs, Raymond G. Simpson, Edgar Benavides, Michael J. Landis, Patrick W. Sweeney, Deren A. R. Eaton, and Michael J. Donoghue

Sexuality and apomixis in Hieracium are tightly associated with ploidy

Annals of Botany 123: 391–403, 2019

doi: 10.1093/aob/mcy137

Asexual reproduction via seeds (apomixis) is an important speciation mechanism in angiosperms, but its frequency is largely unknown. Mráz and Zdvořák used flow cytometric seed screening to unravel reproductive pathways in more than 50 Hieracium s.str. taxa (Asteraceae) sampled across Europe. They found that diploid taxa produced their seeds solely after double fertilization, i.e. sexually, whereas polyploid taxa reproduced strictly apomictically. However, very rare sexual reproduction was also recorded in certain polyploids. This is the first evidence of functional sexuality in polyploid members of the genus. While strict apomixis can enhance colonization abilities through increased reproductive assurance, residual sexuality increases genetic variation in otherwise asexual polyploids.

Authors: Patrik Mráz and Pavel Zdvořák

Novel adaptation to hawkmoth pollination is not sufficient to prevent gene flow

Annals of Botany 123: 405–413, 2019

doi: 10.1093/aob/mcy143

Clarkia breweri (Onagraceae) has evolved many new floral traits to use nocturnal hawkmoths like Hyles lineata (Sphingidae) for pollination, including large size, pale colour, and a spicy sweet scent. Kay et al. test whether these traits prevent cross-pollination with sister species C. concinna, by presenting mixed floral bouquets to hawkmoths. Although hawkmoths do not visit C. concinna when isolated, they will visit in mixed bouquets, resulting in some cross-pollination. Kay et al. conclude that floral isolation is not sufficient to prevent gene flow but works in concert with spatial isolation.

Authors: Kathleen Kay, Aubrey Zepeda, and Robert Raguso

Does a supergeneralist plant locally specialize on the most effective pollinators?

Annals of Botany 123: 415–428, 2019

doi: 10.1093/aob/mcy140

Plant-pollinator relationships are an important driver of angiosperm evolution. However, most studies focus on relatively specialized plants and evolution of pollination niches, and drivers of floral divergence of generalist plant species are largely unknown. In three populations located along a 700 km transect, Zych et al. explore whether a ‘supergeneralist’ Angelica sylvestris (Apiaceae) could locally specialize on the most effective pollinators. Recording variation in pollinator assemblages and floral phenotypes, and performing field experiments, they show that despite taxonomic diversity of floral visitors, the plant is pollinated by functionally equivalent pollinator morphogroups, and that surveyed populations do not represent distinct pollination ecotypes. Zych et al. conclude that the observed variation in nectar and scent characters can likely be interpreted as ‘adaptive wandering’.

Authors: Marcin Zych, Robert R. Junker, Massimo Nepi, Malgorzata Stpiczyńska, Barbara Stolarska and Katarzyna Roguz