Macroevolution of the plant-hummingbird pollination system.

Plant-hummingbird interactions are considered a classic example of coevolution, a process in which mutually dependent species influence each other's evolution. Plants depend on hummingbirds for pollination, whereas hummingbirds rely on nectar for food. As a step towards understanding coevolution, this review focuses on the macroevolutionary consequences of plant-hummingbird interactions, a relatively underexplored area in the current literature. We synthesize prior studies, illustrating the origins and dynamics of hummingbird pollination across different angiosperm clades previously pollinated by insects (mostly bees), bats, and passerine birds. In some cases, the crown age of hummingbirds pre-dates the plants they pollinate. In other cases, plant groups transitioned to hummingbird pollination early in the establishment of this bird group in the Americas, with the build-up of both diversities coinciding temporally, and hence suggesting co-diversification. Determining what triggers shifts to and away from hummingbird pollination remains a major open challenge. The impact of hummingbirds on plant diversification is complex, with many tropical plant lineages experiencing increased diversification after acquiring flowers that attract hummingbirds, and others experiencing no change or even a decrease in diversification rates. This mixed evidence suggests that other extrinsic or intrinsic factors, such as local climate and isolation, are important covariables driving the diversification of plants adapted to hummingbird pollination. To guide future studies, we discuss the mechanisms and contexts under which hummingbirds, as a clade and as individual species (e.g. traits, foraging behaviour, degree of specialization), could influence plant evolution. We conclude by commenting on how macroevolutionary signals of the mutualism could relate to coevolution, highlighting the unbalanced focus on the plant side of the interaction, and advocating for the use of species-level interaction data in macroevolutionary studies.

Three new species of Columnea (Gesneriaceae) from the western Andean slopes of Ecuador and Colombia.

Three new species of Columnea (Gesneriaceae, tribe Gesnerieae) are described from the western Andean slopes of northern Ecuador and southern Colombia. Columneaangulata J.L. Clark & F. Tobar and Columneafloribunda F. Tobar & J.L. Clark are described from northern Ecuador. Columneatecta J.L. Clark & Clavijo is described from southern Colombia and northern Ecuador. The three new species are facultative epiphytes with dorsiventral shoots and are readily recognized by bright red tips on the abaxial and adaxial leaf surfaces. The species described here are vegetatively similar to the sympatric species Columneapicta H. Karst. and are readily differentiated by floral features that are illustrated, described and featured with digital images.

AbstractSe describen tres especies nuevas de Columnea (Gesneriaceae, tribu Gesnerieae) originarias de la vertiente occidental de los Andes de Ecuador y Colombia. Columneaangulata J.L. Clark & F. Tobar y Columneafloribunda F. Tobar & J.L. Clark se describen del norte de Ecuador; Columneatecta J.L. Clark & Clavijo se describe del sur de Colombia y norte de Ecuador. Las tres especies nuevas son epífitas facultativas con vástagos dorsiventrales, las cuales se reconocen fácilmente por las puntas de las hojas de color rojo brillante en ambas superficies; son vegetativamente similares y simpátricas con Columneapicta H. Karst., pero se pueden diferenciar por las características florales que se ilustran, describen y detallan con imágenes digitales en este artículo.

Phylogenomics of Gesneriaceae using targeted capture of nuclear genes.

Gesneriaceae (ca. 3400 species) is a pantropical plant family with a wide range of growth form and floral morphology that are associated with repeated adaptations to different environments and pollinators. Although Gesneriaceae systematics has been largely improved by the use of Sanger sequencing data, our understanding of the evolutionary history of the group is still far from complete due to the limited number of informative characters provided by this type of data. To overcome this limitation, we developed here a Gesneriaceae-specific gene capture kit targeting 830 single-copy loci (776,754 bp in total), including 279 genes from the Universal Angiosperms-353 kit. With an average of 557,600 reads and 87.8% gene recovery, our target capture was successful across the family Gesneriaceae and also in other families of Lamiales. From our bait set, we selected the most informative 418 loci to resolve phylogenetic relationships across the entire Gesneriaceae family using maximum likelihood and coalescent-based methods. Upon testing the phylogenetic performance of our baits on 78 taxa representing 20 out of 24 subtribes within the family, we showed that our data provided high support for the phylogenetic relationships among the major lineages, and were able to provide high resolution within more recent radiations. Overall, the molecular resources we developed here open new perspectives for the study of Gesneriaceae phylogeny at different taxonomical levels and the identification of the factors underlying the diversification of this plant group.

Chemical Basis of Floral Color Signals in Gesneriaceae: The Effect of Alternative Anthocyanin Pathways.

Changes in floral pigmentation can have dramatic effects on angiosperm evolution by making flowers either attractive or inconspicuous to different pollinator groups. Flower color largely depends on the type and abundance of pigments produced in the petals, but it is still unclear whether similar color signals rely on same biosynthetic pathways and to which extent the activation of certain pathways influences the course of floral color evolution. To address these questions, we investigated the physical and chemical aspects of floral color in the Neotropical Gesnerioideae (ca. 1,200 spp.), in which two types of anthocyanins, hydroxyanthocyanins, and deoxyanthocyanins, have been recorded as floral pigments. Using spectrophotometry, we measured flower reflectance for over 150 species representing different clades and pollination syndromes. We analyzed these reflectance data to estimate how the Gesnerioideae flowers are perceived by bees and hummingbirds using the visual system models of these pollinators. Floral anthocyanins were further identified using high performance liquid chromatography coupled to mass spectrometry. We found that orange/red floral colors in Gesnerioideae are produced either by deoxyanthocyanins (e.g., apigenidin, luteolinidin) or hydroxyanthocyanins (e.g., pelargonidin). The presence of deoxyanthocyanins in several lineages suggests that the activation of the deoxyanthocyanin pathway has evolved multiple times in the Gesnerioideae. The hydroxyanthocyanin-producing flowers span a wide range of colors, which enables them to be discriminated by hummingbirds or bees. By contrast, color diversity among the deoxyanthocyanin-producing species is lower and mainly represented at longer wavelengths, which is in line with the hue discrimination optima for hummingbirds. These results indicate that Gesnerioideae have evolved two different biochemical mechanisms to generate orange/red flowers, which is associated with hummingbird pollination. Our findings also suggest that the activation of the deoxyanthocyanin pathway has restricted flower color diversification to orange/red hues, supporting the potential constraining role of this alternative biosynthetic pathway on the evolutionary outcome of phenotypical and ecological diversification.

Targeted Capture of Hundreds of Nuclear Genes Unravels Phylogenetic Relationships of the Diverse Neotropical Palm Tribe Geonomateae.

The tribe Geonomateae is a widely distributed group of 103 species of Neotropical palms which contains six ecologically important understory or subcanopy genera. Although it has been the focus of many studies, our understanding of the evolutionary history of this group, and in particular of the taxonomically complex genus Geonoma, is far from complete due to a lack of molecular data. Specifically, the previous Sanger sequencing-based studies used a few informative characters and partial sampling. To overcome these limitations, we used a recently developed Arecaceae-specific target capture bait set to undertake a phylogenomic analysis of the tribe Geonomateae. We sequenced 3,988 genomic regions for 85% of the species of the tribe, including 84% of the species of the largest genus, Geonoma. Phylogenetic relationships were inferred using both concatenation and coalescent methods. Overall, our phylogenetic tree is highly supported and congruent with taxonomic delimitations although several morphological taxa were revealed to be non-monophyletic. It is the first time that such a large genomic dataset is provided for an entire tribe within the Arecaceae. Our study lays the groundwork not only for detailed macro- and micro-evolutionary studies within the group, but also sets a workflow for understanding other species complexes across the tree of life.

Hummingbird pollination and the diversification of angiosperms: an old and successful association in Gesneriaceae.

The effects of specific functional groups of pollinators in the diversification of angiosperms are still to be elucidated. We investigated whether the pollination shifts or the specific association with hummingbirds affected the diversification of a highly diverse angiosperm lineage in the Neotropics. We reconstructed a phylogeny of 583 species from the Gesneriaceae family and detected diversification shifts through time, inferred the timing and amount of transitions among pollinator functional groups, and tested the association between hummingbird pollination and speciation and extinction rates. We identified a high frequency of pollinator transitions, including reversals to insect pollination. Diversification rates of the group increased through time since 25 Ma, coinciding with the evolution of hummingbird-adapted flowers and the arrival of hummingbirds in South America. We showed that plants pollinated by hummingbirds have a twofold higher speciation rate compared with plants pollinated by insects, and that transitions among functional groups of pollinators had little impact on the diversification process. We demonstrated that floral specialization on hummingbirds for pollination has triggered rapid diversification in the Gesneriaceae family since the Early Miocene, and that it represents one of the oldest identified plant-hummingbird associations. Biotic drivers of plant diversification in the Neotropics could be more related to this specific type of pollinator (hummingbirds) than to shifts among different functional groups of pollinators.

Transcriptomic resources for an endemic Neotropical plant lineage (Gesneriaceae).

PREMISE OF THE STUDY: Despite the extensive phenotypic variation that characterizes the Gesneriaceae family, there is a lack of genomic resources to investigate the molecular basis of their diversity. We developed and compared the transcriptomes for two species of the Neotropical lineage of the Gesneriaceae. METHODS AND RESULTS: Illumina sequencing and de novo assembly of floral and leaf samples were used to generate multigene sequence data for Sinningia eumorpha and S. magnifica, two species endemic to the Brazilian Atlantic Forest. A total of 300 million reads were used to assemble the transcriptomes, with an average of 92,038 transcripts and 43,506 genes per species. The transcriptomes showed good quality metrics, with the presence of all eukaryotic core genes, and an equal representation of clusters of orthologous groups (COG) classifications between species. The orthologous search produced 8602 groups, with 15-20% of them annotated using BLAST tools. DISCUSSION: This study provides the first step toward a comprehensive multispecies transcriptome characterization of the Gesneriaceae family. These resources are the basis for comparative analyses in this species-rich Neotropical plant group; they will also allow the investigation of the evolutionary importance of multiple metabolic pathways and phenotypic diversity, as well as developmental programs in these nonmodel species.

Decoupled evolution of floral traits and climatic preferences in a clade of Neotropical Gesneriaceae.

BACKGROUND: Major factors influencing the phenotypic diversity of a lineage can be recognized by characterizing the extent and mode of trait evolution between related species. Here, we compared the evolutionary dynamics of traits associated with floral morphology and climatic preferences in a clade composed of the genera Codonanthopsis, Codonanthe and Nematanthus (Gesneriaceae). To test the mode and specific components that lead to phenotypic diversity in this group, we performed a Bayesian phylogenetic analysis of combined nuclear and plastid DNA sequences and modeled the evolution of quantitative traits related to flower shape and size and to climatic preferences. We propose an alternative approach to display graphically the complex dynamics of trait evolution along a phylogenetic tree using a wide range of evolutionary scenarios. RESULTS: Our results demonstrated heterogeneous trait evolution. Floral shapes displaced into separate regimes selected by the different pollinator types (hummingbirds versus insects), while floral size underwent a clade-specific evolution. Rates of evolution were higher for the clade that is hummingbird pollinated and experienced flower resupination, compared with species pollinated by bees, suggesting a relevant role of plant-pollinator interactions in lowland rainforest. The evolution of temperature preferences is best explained by a model with distinct selective regimes between the Brazilian Atlantic Forest and the other biomes, whereas differentiation along the precipitation axis was characterized by higher rates, compared with temperature, and no regime or clade-specific patterns. CONCLUSIONS: Our study shows different selective regimes and clade-specific patterns in the evolution of morphological and climatic components during the diversification of Neotropical species. Our new graphical visualization tool allows the representation of trait trajectories under parameter-rich models, thus contributing to a better understanding of complex evolutionary dynamics.

The geographical pattern of speciation and floral diversification in the neotropics: the tribe sinningieae (gesneriaceae) as a case study.

The geographical pattern of speciation and the relationship between floral variation and species ranges were investigated in the tribe Sinningieae (Gesneriaceae), which is found mainly in the Atlantic forests of Brazil. Geographical distribution data recorded on a grid system of 0.5 x 0.5 degree intervals and a near-complete species-level phylogenetic tree of Sinningieae inferred from a simultaneous analysis of seven DNA regions were used to address the role of geographical isolation in speciation. Geographical range overlaps between sister lineages were measured across all nodes in the phylogenetic tree and analyzed in relation to relative ages estimated from branch lengths. Although there are several cases of species sympatry in Sinningieae, patterns of sympatry between sister taxa support the predominance of allopatric speciation. The pattern of sympatry between sister taxa is consistent with range shifts following allopatric speciation, except in one clade, in which the overlapping distribution of recent sister species indicates speciation within a restricted geographical area and involving changes in pollinators and habitats. The relationship between floral divergence and regional sympatry was also examined by analyzing floral contrasts, phenological overlap, and the degree of sympatry between sister clades. Morphological contrast between flowers is not increased in sympatry and phenological divergence is more apparent between allopatric clades than between sympatric clades. Therefore, our results failed to indicate a tendency for sympatric taxa to minimize morphological and phenological overlap (geographic exclusion and/or character displacement hypotheses). Instead, they point toward adaptation in phenology to local conditions and buildup of sympatries at random with respect to flower morphology. Additional studies at a lower geographical scale are needed to identify truely coexisting species and the components of their reproductive isolation.

Phylogenetic position and generic differentiation of Epithemateae (Gesneriaceae) inferred from plastid DNA sequence data.

The systematic position and generic differentiation of the morphologically and geographically outstanding tribe Epithemateae (Gesneriaceae) was analyzed using the rbcL/atpB-spacer and trnL-F intron-spacer regions of chloroplast DNA. In our analysis Epithemateae forms a strongly supported monophyletic clade (bootstrap [BS] = 100%; jackknife [JK] = 100%; decay index [DI] = 12) and appears as sister to the rest of the paleotropical Gesneriaceae (= subfamily Cyrtandroideae). The paleotropical Gesneriaceae form a monophyletic group (BS = 88%; JK = 85%; DI = 3) that is sister to the neotropical Gesneriaceae (subfamily Gesnerioideae) plus Austral Gesneriaceae (subfamily Coronantheroideae) (BS = 99%; JK = 98%; DI = 10). Within Epithemateae Rhynchoglossum is sister to the remaining Epithemateae (BS = 97%; JK = 96%; DI = 12), in which Epithema is sister to a clade of two genera: Loxonia/Stauranthera (BS = 68%; JK = 64%; DI = 1), which form, together with Epithema, a sister clade (BS = 85%; JK = 83%; DI = 2) to Whytockia and Monophyllaea. While the support for Loxonia and Stauranthera is moderate, the relationship of Whytockia and Monophyllaea is very strongly supported (BS = 100%; JK = 100%; DI = 13). Apart from the somewhat surprising (but well-substantiated) isolated position of Rhynchoglossum, the results are in perfect accordance with the relationships worked out earlier on grounds of architectural and floral characters. Especially remarkable is the predicted coherence between the morphologically and geographically different genera Whytockia and Monophyllaea.

Systematics and evolution of tribe Sinningieae (Gesneriaceae): evidence from phylogenetic analyses of six plastid DNA regions and nuclear ncpGS.

For nearly all species in the three genera of tribe Sinningieae (Gesneriaceae), Sinningia, Paliavana, and Vanhouttea (mostly in southeastern Brazil) plus 10 outgroups, we have sequenced six non-coding DNA regions (i.e., plastid intergenic spacers trnT-trnL, trnL-trnF, trnS-trnG, atpB-rbcL, and introns in the trnL and rpl16 genes) and four introns in nuclear plastid-expressed glutamine synthetase gene (ncpGS). Separate and combined analyses of these data sets using maximum parsimony supported the monophyly of Sinningieae, but the genera Paliavana and Vanhouttea were found embedded within Sinningia; therefore a new infrageneric classification is here proposed. Mapping of pollination syndromes on the DNA-based trees supported multiple origins of hummingbird and bee syndromes and derivation of moth and bat syndromes from hummingbird flowers. Perennial tubers were derived from perennial stems in non-tuberous plants.

Nectar Sugar Composition in Relation to Pollination Syndromes in Sinningieae (Gesneriaceae).

A putative correlation between nectar sugar composition and pollination syndrome was evaluated in the tribe Sinningieae (Neotropical Gesneriaceae). Sucrose, fructose and glucose were quantified in the nectar of 45 species using high performance anion-exchange chromatography. Representative species of the hummingbird, bee, bat and moth pollination syndromes were sampled in relation to their numeric importance in the tribe. In hummingbird and bee flowers, which represent 95% of the species in Sinningieae, nectar was sucrose-dominant (ratio [sucrose]/[hexose] > 1). Sugar ratios below one were only found in the nectar of three species with moth and bat syndromes. Sugar concentration averaged 23.9 ± 10.6% (wt/total wt) in hummingbird flowers and 28.7 ± 10.6% in bee flowers, whereas diluted nectar (7.1 ± 3.4%) was restricted to bat flowers. Similarities in the nectar of hummingbird and bee flowers contrast with the presence of specific morphological traits associated with these two syndromes, indicating that plant-pollinator relationships rely on flower display rather than on nectar characteristics. By contrast, distinct nectar chemistry is correlated with the bat syndrome in which a particularly low sucrose production is responsible for hexose dominance.