William Scott Armbruster

University of Portsmouth UK and University of Alaska Fairbanks · Biology

Field and phylogenetic studies of Collinsia previously resulted in discovery of the distinctive "metamorphica" clade from meta-morphic scree of the upper Merced River drainage on the western slope of the central Sierra Nevada, California. The three component lineages within this clade are described here as new species: C. metamorphica from the Sout...

Floral bracts (bracteoles, cataphylls) are leaf-like organs that subtend flowers or inflorescences but are of non-floral origin; they occur in a wide diversity of species, representing multiple independent origins, and exhibit great variation in form and function. Although much attention has been paid to bracts over the past 150 years, our understa...

Abstract There is good evidence that plant–pollinator interactions and flowering-plant diversification rates are often interrelated, although the actual mechanisms involved, and their relative importance, remain to be fully elucidated. In some groups, such as orchids, specialized relationships with pollinators may increase the likelihood of reprodu...

Background and Aims Morphological matching between flower and pollinator traits has been documented in diverse plant lineages. Indeed, the matching of corolla-tube length and pollinator-tongue length has been cited repeatedly as a classic case of coevolution. However, there are many possible evolutionary routes to trait matching. Our aim here is bo...

The number of angiosperms that may depend on animals for pollination has been difficult to estimate because the pollination modes of tens of thousands of species of tall trees, canopy climbers, and epiphytes, especially from the tropics, remain unknown. Ecological research over the past 50 years, however, has established a strong correlation betwee...

Essays on evolvability from the perspectives of quantitative and population genetics, evolutionary developmental biology, systems biology, macroevolution, and the philosophy of science. Evolvability—the capability of organisms to evolve—wasn't recognized as a fundamental concept in evolutionary theory until 1990. Though there is still some debate a...

Premise Linum suffruticosum shows variations in pollinator fit, pollen pickup, and local pollinators that predict pollen deposition rates. The species often coflowers with other Linum species using the same pollinators. We investigated whether L. suffruticosum trait variation could be explained by local patterns of pollinator sharing and associated...

Rapid movements by plants have been a subject of interest since Linnaeus in the 18th century. Largely lacking, however, has been a modern understanding of the adaptive significance of such movements. A recent study shows that rapid stamen movements can increase male fitness by scaring off pollinators once they have pollen placed on them.

The plant-pollinator ‘arms race’ model posits that a major driver of the evolution of elongated corollas in flowers is reciprocal selection for ‘morphological fit’ between pollinator-tongue length and access distance to nectar (usually corolla-tube length). Evidence for the pollinator-mediated selection on tube length and evolution of multiple, cor...

Understanding the causes and limits of population divergence in phenotypic traits is a fundamental aim of evolutionary biology, with the potential to yield predictions of adaptation to environmental change. Reciprocal transplant experiments and the evaluation of optimality models suggest that local adaptation is common but not universal, and some s...

Background Keel flowers are bilaterally symmetrical, pentamerous flowers with three different petal types and reproductive organs enclosed by keel petals; generally there is also connation of floral parts such as stamens and keel petals. In this study, the evolution of keel flowers within the order Fabales is explored to investigate whether the est...

Premise: Flower phenotypes evolve to attract pollinators and to ensure efficient pollen transfer to and from the bodies of pollinators or, in self-compatible bisexual flowers, between anthers and stigmas. If functionally interacting traits are genetically correlated, response to selection may be subject to genetic constraints. Genetic constraints...

During the main COVID-19 global pandemic lockdown period of 2020 an impromptu set of pollination ecologists came together via social media and personal contacts to carry out standardised surveys of the flower visits and plants in gardens. The surveys involved 67 rural, suburban and urban gardens, of various sizes, ranging from 61.18° North in Norwa...

The length of time a flower remains open and functional – floral longevity – governs important reproductive processes influencing pollination and mating and varies considerably among angiosperm species. However, little is known about large‐scale biogeographic patterns and the correlates of floral longevity. Using published data on floral longevity...

This article is a Commentary on Stewart et al. (2022), 235: 1629–1640.

Within-plant variation in seed size may merely reflect developmental instability, or it may be adaptive in facilitating diversifying bet-hedging, that is, production of phenotypically diverse offspring when future environments are unpredictable. To test the latter hypothesis, we analyzed patterns of variation in seed size in 11 populations of the p...

Although artificial-selection experiments seem well suited to testing our ability to predict evolution, the correspondence between predicted and observed responses is often ambiguous due to the lack of uncertainty estimates. We present equations for assessing prediction error in direct and indirect responses to selection that integrate uncertainty...

Spatiotemporal variation in natural selection is expected, but difficult to estimate. Pollinator‐mediated selection on floral traits provides a good system for understanding and linking variation in selection to differences in ecological context. We studied pollinator‐mediated selection in five populations of Dalechampia scandens (Euphorbiaceae) in...

This is a field guide of Dalechampia from Brazil.

Abstract—In an account of 13 taxa (12 species and one variety) of Dalechampia occurring inMadagascar, ten species were lectotypified, two weresynonymized, and one species was reestablished. Information about typifications aswell as maps of distribution for each species are provided herein.Illustrations and a key for identifying species of Dalechamp...

Plants sometimes suffer mechanical injury. The nonlethal collapse of a flowering stalk, for example, can greatly reduce plant fitness if it leads to ‘incorrect’ floral orientation and thus reduced visitation or poor pollination. When floral orientation is important for accurate pollination, as has been suggested for bilaterally symmetrical flowers,...

Aim Intraspecific trait variation (ITV) within natural plant communities can be large, influencing local ecological processes and dynamics. Here, we shed light on how ITV in vegetative and floral traits responds to large‐scale abiotic and biotic gradients (i.e., climate and species richness). Specifically, we tested whether associations of ITV with...

Available at https://authors.elsevier.com/c/1abk21JWF1qLF8

Abstract—A new species of Dalechampia from southeastern Brazil, belonging to Dalechampia sect. Dioscoreifoliae, is described and illustrated here. Dalechampia margarethiae is a twining vine occurring exclusively in Esp´ırito Santo state. Its pseudanthia are similar to those of D. peckoltiana and D. pentaphylla, but D. margarethiae differs in a set...

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Angiosperm flowers have diversified in adaptation to pollinators, but are also shaped by developmental and genetic histories. The relative importance of these factors in structuring floral diversity remains unknown. We assess the effects of development, function and evolutionary history by testing competing hypotheses on floral modularity and shape...

Greater pollination intensity can enhance maternal plant fitness by increasing seed set and seed quality as a result of more intense pollen competition or enhanced genetic sampling. We tested experimentally these effects by varying the pollen load from a single pollen donor on stigmas of female flowers of Dalechampia scandens (Euphorbiaceae) and me...

For the ongoing revision of Dalechampia sect. Dioscoreifoliae, we proceed with the lectotypification of D. juruana, D. luetzelburgii, D. schottii and D. schottii var. trifoliolata.

Background: To predict the evolutionary consequences of pollinator declines, we need to understand the evolution of delayed autonomous self-pollination, which is expected to evolve as a mechanism of reproductive assurance when cross-pollination becomes unreliable. This involves estimating the costs of increased levels of selfing as well as those a...

Co‐flowering plants may commonly experience interspecific pollination. It remains unknown, however, whether interspecific pollination is a largely stochastic process or consistent enough over years to exert selection for traits that can reduce interspecific pollination or ameliorate its deleterious effects on reproduction. To assess the likelihood...

Seed dormancy is considered to be an adaptive strategy in seasonal and/or unpredictable environments because it prevents germination during climatically favorable periods that are too short for seedling establishment. Tropical dry forests are seasonal environments where seed dormancy may play an important role in plant resilience and resistance to...

Pollination syndromes describe recurring adaptation to selection imposed by distinct pollina-tors. We tested for pollination syndromes in Merianieae (Melastomataceae), which contain bee-(buzz-), hummingbird-, flowerpiercer-, passerine-, bat-and rodent-pollinated species. Further, we explored trait changes correlated with the repeated shifts away fr...

Premise of the study: Turnover in biotic communities across heterogeneous landscapes is expected to lead to variation in interactions among plants, their mutualists, and their antagonists. Across a fragmented landscape in northern Costa Rica, populations of the euphorb vine Dalechampia scandens vary widely in mating systems and associated blossom...

Fig. S1 Nectar‐producing Meriania species with known pollinators grouped into the ‘mixed‐vertebrate’ pollination syndrome. Fig. S2 Ranking of all 61 floral traits by decrease in Gini index using random forest (RF) analyses. Fig. S3 Structural properties of petals and stamens in Merianieae. Fig. S4 Stochastic character mapping of pollination synd...

Background and aims: The Berg hypothesis proposes that specialized-flower traits experience stronger stabilizing selection than non-floral structures and predicts that variation in specialized-flower traits will be mostly uncorrelated with variation in non-floral traits. Similarly, adaptive-accuracy theory predicts lower variation (as a proportion...

Pollination syndromes describe recurring adaptation to selection imposed by distinct pollinators. We tested for pollination syndromes in Merianieae (Melastomataceae), which contain bee‐ (buzz‐), hummingbird‐, flowerpiercer‐, passerine‐, bat‐ and rodent‐pollinated species. Further, we explored trait changes correlated with the repeated shifts away f...

Significance Intersexual conflict over maternal resource allocation to offspring can lead to the evolution of imprinted genes with parent-of-origin–specific expression. However, the precise mechanism involved in the evolution of such imprinted genes is less well understood, and few clear predictions have been presented. We resolve this issue, and,...

Revisionary studies of Dalechampia sect. Dalechampia have revealed the need to lectotypify D. colorata and that it represents a distinct species rather than a synonym of D. tiliifolia. Dalechampia karsteniana is interpreted to be a synonym of D. colorata.

Beringia (eastern Asia, Alaska, northwest Canada) has been a land-bridge dispersal route between Asia and North America intermittently since the Mesozoic Era. The Quaternary, the most recent period of exchange, is characterized by large, geologically rapid climate fluctuations and sea-level changes that alternately expose and inundate the land-brid...

Premise of the study: Heterostyly, the reciprocal positioning of stigmas and anthers in different floral morphs, has long been thought to promote intermorph pollination. However, extensive intramorph pollination occurs commonly in heterostylous species, leading to recurrent questions about the functional and evolutionary significance of heterostyl...

Background and aims: Although there has been much experimental work on leaf colour change associated with selection generated by abiotic environmental factors and antagonists, the role of leaf colour change in pollinator attraction has been largely ignored. We tested whether whitening of the apical leaves subtending the inflorescences of Saururus...

In the face of climate change, populations have two survival options - they can remain in situ and tolerate the new climatic conditions ("stay"), or they can move to track their climatic niches ("go"). For sessile and small-stature organisms like alpine plants, staying requires broad climatic tolerances, realized niche shifts due to changing biotic...

Floral nectar usually functions as a pollinator reward, yet it may also attract herbivores. However, the effects of herbivore consumption of nectar or nectaries on pollination have rarely been tested. We investigated Iris bulleyana, an alpine plant that has showy tepals and abundant nectar, in the Hengduan Mountains of SW China. In this region, flo...

The goal of biological measurement is to capture underlying biological phenomena in numerical form. The reciprocity index applied to heterostylous flowers is meant to measure the degree of correspondence between fertile parts of opposite sex on complementary (inter‐compatible) morphs, reflecting the correspondence of locations of pollen placement o...

Accurate estimates of trait evolvabilities are central to predicting the short-term evolutionary potential of populations, and hence their ability to adapt to changing environments. We quantify and evaluate the evolvability of herkogamy, the spatial separation of male and female structures in flowers, a key floral trait associated with variation in...

There is good evidence that plant–pollinator interactions and plant diversification rates are interrelated, although the actual mechanisms involved, and their relative importance, remain to be fully elucidated. In some groups, such as orchids, specialized relationships with pollinators may increase the likelihood of reproductive isolation between s...

The reproductive-assurance hypothesis predicts that mating-system traits will evolve towards increased autonomous self-pollination in plant populations experiencing unreliable pollinator service. We tested this long-standing hypothesis by assessing geographic covariation among pollinator reliability, outcrossing rates, heterozygosity and relevant f...

Euglossine bees (Apidae: Euglossini) have long been hypothesized to act as long‐distance pollinators of many low‐density tropical plants. We tested this hypothesis by the analysis of gene flow and genetic structure within and among populations of the euglossine bee‐pollinated vine Dalechampia scandens . Using microsatellite markers, we assessed his...

We developed novel microsatellite markers for D alechampia scandens L. (Euphorbiaceae). The target plants belong to a distinct, but undescribed, species in the D . scandens species complex, characterized by small resin-producing glands. In total, 110 alleles over 36 novel markers were identified across 39 individuals from three populations. The num...

Specialization in plant–pollinator relationships is a core concept in discussions of plant evolution and ecology; it is central to our thinking, not just about the ecology of plant–pollinator interactions and pollinator services, but also about reproductive isolation, speciation, extinction and assembly of communities. However, as reviewed here, th...

Premise of research. Selfing rates in mixed-mating plant species are often found to fluctuate greatly across time and space. Environmentally induced changes in floral traits may mediate changes in selfing rates through several mechanisms, including direct effects via changes in traits influencing autofertility rates and indirect effects via changes...

Backgrounds and aims: Floral traits that attract pollinators may also attract seed predators, which, in turn, may generate conflicting natural selection on such traits. Although such selection trade-offs are expected to vary geographically, few studies have investigated selection mediated by pollinators and seed predators across a geographic mosai...

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 whe...

Inbreeding depression is assumed to be a central factor contributing to the stability of plant mating systems. Predicting the fitness consequence of inbreeding in natural populations is complicated, however, because it may be affected by the mating histories of populations generating variation in the amount of purging of deleterious alleles. Furthe...

Abstract Aim Previous research on how climatic niches vary across species ranges has focused on a limited number of species, mostly invasive, and has not, to date, been very conclusive. Here we assess the degree of niche conservatism between distant populations of native alpine plant species that have been separated for thousands of years. Locatio...

Premise of the study: Competition among pollen grains from a single donor is expected to increase the quality of the offspring produced because of the recessive deleterious alleles expressed during pollen-tube growth. However, evidence for such an effect is inconclusive; a large number of studies suffer from confounding variation in pollen competi...

Flowers fertilized by multiple fathers may be expected to produce heavier seeds than those fertilized by a single father. However, the adaptive mechanisms leading to such differences remain unclear, and the evidence inconsistent. Here, we first review the different hypotheses predicting an increase in seed mass when multiple paternity occurs. We sh...

Background: Small-scale topographic complexity is a characteristic feature of alpine landscapes, with important effects on alpine plant distribution. Aims: We investigated the links between small-scale topographic complexity and resultant microclimatic heterogeneity, vascular-plant species richness and beta diversity, and realised niche width and...

Sexual conflicts and their evolutionary outcomes may be influenced by population-specific features such as mating system and ecological context; however, very few studies have investigated the link between sexual conflict and mating system. The self-compatible, mixed-mating hermaphrodite Collinsia heterophylla (Plantaginaceae) is thought to exhibit...

We tested the hypothesis that greening of the floral (involucral) bracts of Dalechampia scandens blossoms after pollination (when bracts are white) increases carbon assimilation and provides photosynthate to developing seeds. We investigated the importance of the involucral bracts for the process of seed development in two ways. First, we removed o...

Floral morphology often directly influences interactions with pollinators, but less is known about the role of extrafloral structures. We studied the relationship between bract motility, floral structural specialization and pollination in Dalechampia aff. bernieri, an endemic Madagascan species with floral structures indicating specialized buzz-pol...

Recent debate on whether the climatic niche of species is conserved or not in a context of climate change has generally focused either solely on invasive species or on a relatively limited number of native species. However, invasive species may not be optimal for assessing the likelihood of niche conservatism because the time since geographical sep...

In this Special feature, we assemble studies that illustrate phylogenetic approaches to studying salient questions regarding the effect of specialization on lineage diversification. The studies use an array of techniques involving a wide-ranging collection of biological systems (plants, butterflies, fish and amphibians are all represented). Their r...

Aim To use a variety of data sources to infer how northern boreal trees recovered their range upon deglaciation and/or Holocene warming. Location Scandinavia, Alaska/north-west Canada (eastern Beringia). Methods Mapped fossil occurrences for Picea (spruce) were assessed against available palaeoenvironmental and phylogeographic information. Results...

Plant specialization on soils derived from unusual parent materials is an important contributor to regional biodiversity. These stressful substrates include serpentine, gabbro, and other ultramafic rocks rich in heavy metals. The effect of substrate on plant diversity is illustrated by serpentine soils in California: they comprise less than 1% of t...

If genetic constraints are important, then rates and direction of evolution should be related to trait evolvability. Here we use recently developed measures of evolvability to test the genetic constraint hypothesis with quantitative genetic data on floral morphology from the Neotropical vine Dalechampia scandens (Euphorbiaceae). These measures were...

Integration and modularity refer to the patterns and processes of trait interaction and independence. Both terms have complex histories with respect to both conceptualization and quantification, resulting in a plethora of integration indices in use. We review briefly the divergent definitions, uses and measures of integration and modularity and mak...

See also the Commentary by Selosse

Plant reproduction by means of flowers has long been thought to promote the success and diversification of angiosperms. It remains unclear, however, how this success has come about. Do flowers, and their capacity to have specialized functions, increase speciation rates or decrease extinction rates? Is floral specialization fundamental or incidental...

Background and AimsSpatial (herkogamy) and temporal (dichogamy) separation of pollen presentation and stigma receptivity have been interpreted as reducing interference between male and female functions in hermaphroditic flowers. However, spatial separation leads to a potential conflict: reduced pollination accuracy, where pollen may be placed in a...

Background and AimsInterest in pollinator-mediated evolutionary divergence of flower phenotype and speciation in plants has been at the core of plant evolutionary studies since Darwin. Specialized pollination is predicted to lead to reproductive isolation and promote speciation among sympatric species by promoting partitioning of (1) the species of...