Radiation Of Angiosperms Research Articles

A pollinator shift explains floral divergence in an orchid species complex in South Africa.

Floral diversification driven by shifts between pollinators has been one of the key explanations for the radiation of angiosperms. According to the Grant-Stebbins model of pollinator-driven speciation, these shifts result in morphologically distinct 'ecotypes' which may eventually become recognizable as species. The current circumscription of the food-deceptive southern African orchid Eulophia parviflora encompasses a highly variable monophyletic species complex. In this study, two forms were identified within this complex that differ in distribution, floral morphology, scent chemistry and phenology, and a test was made of whether these differences represent adaptations for different pollinators. Multivariate analysis of floral and vegetative traits revealed that there are at least two discrete morphological forms in the species complex. Field observations revealed that each form is pollinated by a different insect species, and thus represent distinct ecotypes. The early-flowering coastal form which has long spurs and floral scent dominated by sesquiterpene compounds is pollinated exclusively by the long-tongued bee Amegilla fallax (Apidae, Anthophorinae), while the late-flowering inland form with short spurs and floral scent dominated by benzenoid compounds is pollinated exclusively by the beetle Cyrtothyrea marginalis (Cetoniinae; Scarabaeidae). Choice experiments in a Y-maze olfactometer showed that beetles are preferentially attracted to the scent of the short-spurred form. A spur-shortening experiment showed that long spurs are required for effective pollination of the bee-pollinated form. Although it was initially thought likely that divergence occurred across a geographical pollinator gradient, plants of the long-spurred form were effectively pollinated when transplanted to an inland locality outside the natural coastal range of this form. Thus, the underlying geographical basis for the evolution of ecotypes in the E. parviflora complex remains uncertain, although early flowering in the long-spurred form to exploit the emergence of naïve bees may restrict this form to coastal areas where there is no frost that would damage flower buds. Later flowering of the short-spurred form coincides closely with the emergence of the pollinating beetles following winter frosts. This study identifies a shift between bee and beetle pollination as the main driver of floral divergence in an orchid species complex. Floral scent and spur length appear to be key traits in mediating this evolutionary transition.

Hydraulic engineering of the angiosperm leaf: do the Baileyan trends in perforation plate evolution account for the origin of high vein density?

Hydraulic engineering of the angiosperm leaf: do the Baileyan trends in perforation plate evolution account for the origin of high vein density?

The anatomically preserved stem Zhongmingella gen. nov. from the Upper Permian of China: evaluating the early evolution and phylogeny of the Osmundales

Reinvestigation of the anatomically preserved stem Palaeosmunda plenasioides from the Lopingian (Late Permian) of China has led to the establishment of Zhongmingella gen. nov. within the extinct family Guaireaceae (Osmundales). Zhongmingella has a rhizomatous stem with heterogeneous pith and cortex comprising parenchyma and uniformly distributed secretory cells, and is dictyostelic. In order to evaluate the systematic and phylogenetic position of Zhongmingella within Guaireaceae, and Guaireaceae within Osmundales, we conducted a preliminary cladistic analysis of a broad range of Osmundales and related taxa based on 18 extinct and six extant genera and subgenera. Results do not support the traditionally defined family Thamnopteroideae (Bathypteris, Chasmatopteris, Iegosigopteris, Thamnopteris, Zalesskya) and demonstrate that Thamnopteroideae is not a subfamily of Osmundaceae as previously thought. Guaireaceae is monophyletic but in addition to its traditionally defined members (Guairea, Lunea, Donwellicaulis, Itopsidema, Shuichengella, Zhongmingella) includes the stratigraphically younger genus Osmundacaulis previously placed in Osmundaceae. Guaireaceae is sister to Osmundaceae, Millerocaulis, Ashicaulis, Palaeosmunda and Aurealcaulis in the strict consensus, but in the majority-rule consensus Palaeosmunda, Aurealcaulis, Ashicaulis and Millerocaulis form the Osmundaceae stem group, with (Aurealcaulis, (Ashicaulis + Palaeosmunda)) sister to the extant genera. Stratigraphical analysis of the selected most parsimonious tree demonstrates that Osmundales underwent primary radiation during the Pennsylvanian and Permian, terminating abruptly around the time of the end-Permian mass extinction. Radiation within Osmundaceae occurred in the Triassic–Cretaceous and stratigraphically overlaps staggered extinctions in Guaireaceae and Osmundaceae from the Late Jurassic to mid-Cretaceous alongside the earliest angiosperm radiation. Our results identify the Osmundaceae stem and sister groups for the first time, and represent an important step in unravelling the evolutionary history of Osmundales. However, reconstructed whole-plant species are imperative to improve understanding of the relationships within the clade in deep time.

Fossil Ericales from the Upper Cretaceous of New Jersey

Premise of research. Fossil flowers and other related organs of Turonian age from Cretaceous Atlantic Coastal Plain deposits in northern New Jersey are remarkable in their degree of preservation and document important events in the radiation of eudicot angiosperms relatively early in their history.Methodology. Fossils isolated from silty clays have been examined with light microscopy, TEM, SEM, and micro-CT scan to illuminate their structural details. Fossil characters were placed in data matrices that included morphological and molecular genetic characters to place them phylogenetically in order to test the hypothesis that they are extinct representatives of the modern Ericales.Pivotal results. These fossils represent a clade of three species and include flowers, inflorescences, and leaves, constituting a genus that is unique relative to existing angiosperm genera but that nonetheless shares a significant number of characters with living families placed in the broader Ericales (APG III) including Ericace...

Rise to dominance of angiosperm pioneers in European Cretaceous environments.

The majority of environments are dominated by flowering plants today, but it is uncertain how this dominance originated. This increase in angiosperm diversity happened during the Cretaceous period (ca. 145-65 Ma) and led to replacement and often extinction of gymnosperms and ferns. We propose a scenario for the rise to dominance of the angiosperms from the Barremian (ca. 130 Ma) to the Campanian (ca. 84 Ma) based on the European megafossil plant record. These megafossil data demonstrate that angiosperms migrated into new environments in three phases: (i) Barremian (ca. 130-125 Ma) freshwater lake-related wetlands; (ii) Aptian-Albian (ca. 125-100 Ma) understory floodplains (excluding levees and back swamps); and (iii) Cenomanian-Campanian (ca. 100-84 Ma) natural levees, back swamps, and coastal swamps. This scenario allows for the measured evolution of angiosperms in time and space synthesizing changes in the physical environment with concomitant changes in the biological environment. This view of angiosperm radiation in three phases reconciles previous scenarios based on the North American record. The Cretaceous plant record that can be observed in Europe is exceptional in many ways. (i) Angiosperms are well preserved from the Barremian to the Maastrichtian (ca. 65 Ma). (ii) Deposits are well constrained and dated stratigraphically. (iii) They encompass a full range of environments. (iv) European paleobotany provides many detailed studies of Cretaceous floras for analysis. These factors make a robust dataset for the study of angiosperm evolution from the Barremian to the Campanian that can be traced through various ecosystems and related to other plant groups occupying the same niches.

The Evolutionary Root of Flowering Plants

Correct rooting of the angiosperm radiation is both challenging and necessary for understanding the origins and evolution of physiological and phenotypic traits in flowering plants. The problem is known to be difficult due to the large genetic distance separating flowering plants from other seed plants and the sparse taxon sampling among basal angiosperms. Here, we provide further evidence for concern over substitution model misspecification in analyses of chloroplast DNA sequences. We show that support for Amborella as the sole representative of the most basal angiosperm lineage is founded on sequence site patterns poorly described by time-reversible substitution models. Improving the fit between sequence data and substitution model identifies Trithuria, Nymphaeaceae, and Amborella as surviving relatives of the most basal lineage of flowering plants. This finding indicates that aquatic and herbaceous species dominate the earliest extant lineage of flowering plants. [; ; ; ; ; .].

Elegance versus Speed: Examining the Competition between Conifer and Angiosperm Trees

Angiosperm radiation in the Cretaceous is thought to have profoundly diminished the success of the conifers, the other major woody plant group present at the time. However, today the conifers persist and often thrive despite their supposed inferiority in vegetative and reproductive function. By exploring this apparent conflict for global tree dominance, we seek here to reveal patterns that explain not only how the allegedly inferior conifers persist among angiosperms but also why some conifer groups became extinct in the Cretaceous. We find that despite the profound contrast between the dominant conifer families in the Southern and Northern Hemispheres, all conifers can be characterized by a common set of functional attributes that allow them to exist in an important group of niches, from high latitudes to the equator. In these environments, conifers are often highly efficient at outcompeting, outliving, or outsurviving angiosperms. Hence, we conclude that conifer success cannot be dismissed as being uniquely associated with habitats that are unfavorable for angiosperms.

Evolutionary Voyage of Angiosperm Vessel Structure-Function and Its Significance for Early Angiosperm Success

A hypothesized advantage of the building block of the angiosperm vascular network, the vessel, is often cited as a critical innovation that elevated the competitive abilities of early angiosperms above nonangiosperms during the Cretaceous. Here we synthesize recent discoveries on the hydraulic functions of living basal angiosperm lineages with evidence from the fossil record to trace the early evolutionary significance of vessels in the early ecophysiological radiation of angiosperms. Evidence from extant comparative biology and the Early Cretaceous fossil record of leaves and wood do not support the hypotheses that vessels improved drought tolerance of angiosperms, increased angiosperm’s photosynthetic abilities, or provided an immediate leap in hydraulic capacity. Instead, later tuning of vessel structure for increased flow efficiency—in particular, by the evolution of simple perforation plates—enabled major increases in xylem hydraulic efficiency.

Evolution of Double Positive Autoregulatory Feedback Loops in CYCLOIDEA2 Clade Genes Is Associated with the Origin of Floral Zygomorphy

Members of the CYCLOIDEA2 (CYC2) clade of the TEOSINTE BRANCHED1, CYCLOIDEA, and PCF transcription factor genes are widely involved in controlling floral zygomorphy, a key innovation in angiosperm evolution, depending on their persistently asymmetric expression in the corresponding floral domains. However, it is unclear how this asymmetric expression is maintained throughout floral development. Selecting Primulina heterotricha as a model, we examined the expression and function of two CYC2 genes, CYC1C and CYC1D. We analyzed the role of their promoters in protein-DNA interactions and transcription activation using electrophoresis mobility shift assays, chromatin immunoprecipitation, and transient gene expression assays. We find that CYC1C and CYC1D positively autoregulate themselves and cross-regulate each other. Our results reveal a double positive autoregulatory feedback loop, evolved for a pair of CYC2 genes to maintain their expression in developing flowers. Further comparative genome analyses, together with the available expression and function data of CYC2 genes in the core eudicots, suggest that this mechanism might have led to the independent origins of floral zygomorphy, which are associated with plant-insect coevolution and the adaptive radiation of angiosperms.

Mesozoic mass extinctions and angiosperm radiation: does the molecular clock tell something new?

Mesozoic mass extinctions and angiosperm radiation: does the molecular clock tell something new?Angiosperms evolved rapidly in the late Mesozoic. Data from the genetic-based approach called ‘molecular clock’ permit an evaluation of the radiation of flowering plants through geological time and of the possible influences of Mesozoic mass extinctions. A total of 261 divergence ages of angiosperm families are considered. The radiation of flowering plants peaked in the Albian, early Campanian, and Maastrichtian. From the three late Mesozoic mass extinctions (Jurassic/Cretaceous, Cenomanian/Turonian, and Cretaceous/Palaeogene), only the Cretaceous/Palaeogene event coincided with a significant, abrupt, and long-term decline in angiosperm radiation. If their link will be further proven, this means that global-scale environmental perturbation precluded from many innovations in the development of plants. This decline was, however, not unprecedented in the history of the angiosperms. The implication of data from the molecular clock for evolutionary reconstructions is limited, primarily because this approach deals with only extant lineages.

Accelerated evolution and coevolution drove the evolutionary history of AGPase sub-units during angiosperm radiation.

ADP-glucose pyrophosphorylase (AGPase) is a key enzyme of starch biosynthesis. In the green plant lineage, it is composed of two large (LSU) and two small (SSU) sub-units encoded by paralogous genes, as a consequence of several rounds of duplication. First, our aim was to detect specific patterns of molecular evolution following duplication events and the divergence between monocotyledons and dicotyledons. Secondly, we investigated coevolution between amino acids both within and between sub-units. A phylogeny of each AGPase sub-unit was built using all gymnosperm and angiosperm sequences available in databases. Accelerated evolution along specific branches was tested using the ratio of the non-synonymous to the synonymous substitution rate. Coevolution between amino acids was investigated taking into account compensatory changes between co-substitutions. We showed that SSU paralogues evolved under high functional constraints during angiosperm radiation, with a significant level of coevolution between amino acids that participate in SSU major functions. In contrast, in the LSU paralogues, we identified residues under positive selection (1) following the first LSU duplication that gave rise to two paralogues mainly expressed in angiosperm source and sink tissues, respectively; and (2) following the emergence of grass-specific paralogues expressed in the endosperm. Finally, we found coevolution between residues that belong to the interaction domains of both sub-units. Our results support the view that coevolution among amino acid residues, especially those lying in the interaction domain of each sub-unit, played an important role in AGPase evolution. First, within SSU, coevolution allowed compensating mutations in a highly constrained context. Secondly, the LSU paralogues probably acquired tissue-specific expression and regulatory properties via the coevolution between sub-unit interacting domains. Finally, the pattern we observed during LSU evolution is consistent with repeated sub-functionalization under 'Escape from Adaptive Conflict', a model rarely illustrated in the literature.

A critical transition in leaf evolution facilitated the Cretaceous angiosperm revolution.

The revolutionary rise of broad-leaved (flowering) angiosperm plant species during the Cretaceous initiated a global ecological transformation towards modern biodiversity. Still, the mechanisms involved in this angiosperm radiation remain enigmatic. Here we show that the period of rapid angiosperm evolution initiated after the leaf interior (post venous) transport path length for water was reduced beyond the leaf interior transport path length for CO2 at a critical leaf vein density of 2.5–5 mm mm−2. Data and our modelling approaches indicate that surpassing this critical vein density was a pivotal moment in leaf evolution that enabled evolving angiosperms to profit from developing leaves with more and smaller stomata in terms of higher carbon returns from equal water loss. Surpassing the critical vein density may therefore have facilitated evolving angiosperms to develop leaves with higher gas exchange capacities required to adapt to the Cretaceous CO2 decline and outcompete previously dominant coniferous species in the upper canopy.

Corolla Monosymmetry: Evolution of a Morphological Novelty in the Brassicaceae Family

Evolution of floral monosymmetry is thought to be a major driving force of angiosperm radiation, making angiosperms the most successful land plant group in terms of species richness. Monosymmetry evolved from a polysymmetric ancestor repeatedly in different angiosperm lineages, where it likely facilitated diversification through the interaction with insects. Most monosymmetric taxa are thus dominated by monosymmetric members. However, in the Brassicaceae, only few members develop a monosymmetric corolla with two petal pairs of unequal size, making them an ideal system to study the evolution of molecular mechanisms enhancing flower complexity. Monosymmetry is controlled by the TCP transcription factors that belong to the CYC2 clade in distantly related taxa. In Iberis amara, the first crucifer analyzed in terms of monosymmetry development, unequal corolla formation is due to a stronger CYC2 clade gene expression in the smaller adaxial petals compared with the larger abaxial ones. Phylogenetic reconstruction of the crucifer family reveals that the monosymmetric genera Iberis, Calepina, and Teesdalia belong to one major crucifer lineage. Monosymmetry is most pronounced in Iberis and less so in Calepina and Teesdalia, with a positive dosage-dependent correlation between the strength of a CYC2 expression difference and the extent of monosymmetry formation. An early adaxial CYC2 expression in floral meristems, observed in many distantly related taxa, might have facilitated the repeated evolution of CYC2-controlled monosymmetry. Comparison of early and late CYC2 expression in monosymmetric and polysymmetric crucifers representative for the four major crucifer lineages reveals that an adaxial CYC2 expression in floral meristems is likely ancestral for the Brassicaceae. However, it got lost in all analyzed monosymmetric members and is, as such, not a prerequisite for the establishment of corolla monosymmetry in crucifers. Here, monosymmetry evolved via a heterochronic CYC2 expression shift from an ancestral early adaxial expression in floral meristems to an adaxial CYC2 transcript accumulation later in petal development. This study emphasizes the potential of regulatory changes in the evolution of morphological novelties, like corolla monosymmetry in the Brassicaceae. In combination with a corymboid inflorescence, monosymmetry might have served as a key invention driving diversification in the genus Iberis comprising more than 20 monosymmetric species.

Molecular phylogeny of the plant bugs (Heteroptera: Miridae) and the evolution of feeding habits.

The first comprehensive cladistic analysis of Miridae, the plant bugs, is presented based on analysis of 3935 base pairs of mitochondrial (16S, COI) and nuclear (18S, 28SD3) DNA for 91 taxa in seven subfamilies. Data were analysed using maximum likelihood (ML), parsimony and Bayesian inference (BI) phylogenetic frameworks. The phylogenetic results are compared with previous hypotheses of higher relationships in the family using alternative hypothesis tests. A Bayesian relaxed molecular clock is used to examine divergence times, and ancestral feeding habits are reconstructed using parsimony and a Bayesian approach. Clades recovered in all analyses are as follows: Cimicomorpha, Miroidea and Miridae; Bryocorinae: Bryocorini; Stenodemini; Mirinae; Deraeocorinae (Clevinemini + Deraeocorini); Cylapinae; Isometopinae; Bryocorinae: Dicyphini; Orthotylini; Phylinae (Phylini + Pilophorini), and Phylinae as sister group to all the remaining mirid taxa. These results are largely congruent with former hypotheses based on morphological data with respect to the monophyly of various subfamilies and tribes; however, our results indicate that the subfamily Bryocorinae is not monophyletic, as the two tribes, Dicypini and Bryocorini, were separated in the phylogenetic results. Divergence time estimates indicate that the radiation of the Miridae began in the Permian; most genus-level radiations within subfamilies began in the late Cretaceous, probably in response to the angiosperm radiation. Ancestral feeding state reconstructions based on Bayesian and parsimony inference were largely congruent and both reconstructed phytophagy as the ancestral state of the Miridae. Furthermore, the feeding habits of the common ancestors of Mirinae + Deraeocorinae, Bryocorinae + Cylapinae + Isometopinae + Orthotylinae, and the remaining taxa excluding Phylinae, were inferred as phytophagous. Therefore, at least three shifts from phytophagy or polyphagy to predation occurred within the Miridae. Additionally, based on the mirid host-plant records, we discovered several trends, such as a strong relationship between host-plant ranges and a facultative feeding habit. © The Willi Hennig Society 2011.

Leaf evolution in Southern Hemisphere conifers tracks the angiosperm ecological radiation.

The angiosperm radiation has been linked to sharp declines in gymnosperm diversity and the virtual elimination of conifers from the tropics. The conifer family Podocarpaceae stands as an exception with highest species diversity in wet equatorial forests. It has been hypothesized that efficient light harvesting by the highly flattened leaves of several podocarp genera facilitates persistence with canopy-forming angiosperms, and the angiosperm ecological radiation may have preferentially favoured the diversification of these lineages. To test these ideas, we develop a molecular phylogeny for Podocarpaceae using Bayesian-relaxed clock methods incorporating fossil time constraints. We find several independent origins of flattened foliage types, and that these lineages have diversified predominantly through the Cenozoic and therefore among canopy-forming angiosperms. The onset of sustained foliage flattening podocarp diversification is coincident with a declining diversification rate of scale/needle-leaved lineages and also with ecological and climatic transformations linked to angiosperm foliar evolution. We demonstrate that climatic range evolution is contingent on the underlying state for leaf morphology. Taken together, our findings imply that as angiosperms came to dominate most terrestrial ecosystems, competitive interactions at the foliar level have profoundly shaped podocarp geography and as a consequence, rates of lineage diversification.

Could Land Plant Evolution Have Fed the Marine Revolution?

Abstract. The advent of flowering plants on land has been suggested previously as a potential trigger for Cretaceous innovations in the marine realm by providing a greater energetic base for marine ecosystems through a more nutrient-rich terrestrial runoff. The scope of the angiosperm radiation certainly was unprecedented—flowering plants came to represent the large majority of species in all terrestrial floras in a geologically short span of time—and angiosperms possess much higher photosynthetic and hydraulic capacities than all other plants. Angiosperm evolution could have affected both the organic and inorganic content of terrestrial runoff, but the magnitude of these changes is in question. Angiosperms are more productive than other plants, suggesting an increase in organic matter runoff, but that quantity is small in comparison to native marine photosynthesis even in the modern angiosperm-dominated world. Changing the inorganic nutrient content of terrestrial runoff requires changing weathering rate...

RSS1 regulates the cell cycle and maintains meristematic activity under stress conditions in rice

Plant growth and development are sustained by continuous cell division in the meristems, which is perturbed by various environmental stresses. For the maintenance of meristematic functions, it is essential that cell division be coordinated with cell differentiation. However, it is unknown how the proliferative activities of the meristems and the coordination between cell division and differentiation are maintained under stressful conditions. Here we show that a rice protein, RSS1, whose stability is controlled by cell cycle phases, contributes to the vigour of meristematic cells and viability under salinity conditions. These effects of RSS1 are exerted by regulating the G1–S transition, possibly through an interaction of RSS1 with protein phosphatase 1, and are mediated by the phytohormone, cytokinin. RSS1 is conserved widely in plant lineages, except eudicots, suggesting that RSS1-dependent mechanisms might have been adopted in specific lineages during the evolutionary radiation of angiosperms.

The Cretaceous – The 'Golden Age' of Insect Evolution

It is my great pleasure to introduce this new subject issue of Insect Systematics & Evolution which focuses on Cretaceous insects. Th e Cretaceous (approximately 145–65 million years ago) marks the ‘golden age’ of insect evolution as it was during this geological period that most Recent insect groups fi rst appeared. Major events of the Cretaceous, such as the origin and radiation of angiosperms and the fragmentation of Gondwana had immense impact on insect evolution. Studies of fossils from this period do not only allow unique insights into the past insect diversity but also help understand their complex evolutionary history. Th e current issue of Insect Systematics & Evolution comprises nine original research papers in which signifi cant new fossils from eight diff erent orders are described, analyzed and phylogenetically interpreted. Ten species are newly described and a number of higher taxa proposed including eight new genera, a new subfamily, two new families, and even a new order. Th e latter is highlighted on the front cover of this issue. I sincerely thank all contributors and reviewers for making this subject issue possible.

The Pollination of Mid Mesozoic Seed Plants and the Early History of Long-proboscid Insects1,2,3

Abstract A defining event for Mesozoic plant-pollinator interactions is the angiosperm radiation, which extended the reach of pollinating insects during the Early Cretaceous in a brief interval of geologic time. Recent evidence indicates that events beginning in the Early Permian and increasing during the Middle Jurassic provided repeated opportunities for insect feeding on pollen, pollination drops, and reproductive tissues of extinct gymnosperm lineages. Pollination was an associated development. Studies on the detailed mouthpart structure of several fluid-feeding insect lineages indicate targeting of certain tubular features of gymnosperm ovulate organs that previously were considered anomalous and difficult to interpret. One mouthpart type, the long-proboscid condition, consists of elongate, tubular (siphonate) proboscises that accessed surface fluids powered by a cibarial pump, often assisted with a distal proboscis sponging organ. These proboscises were received in ovulate organs through often intri...

Angiosperms Helped Put the Rain in the Rainforests: The Impact of Plant Physiological Evolution on Tropical Biodiversity1

The recycling of transpired water is well known to be an important source of rainfall, particularly in the tropics, and angiosperms have transpiration capacities higher than any other plants throughout evolutionary history. Thus, the evolution and rise to ecological dominance of flowering plants are proposed to have strongly altered climate. Transpiration capacity is closely correlated with leaf vein density, and the average vein density of angiosperm leaves is four times greater than that of all other plants, living or extinct. A rapid transition to high vein densities occurred separately in three or more flowering plant lineages about 100 million years ago. Climate modeling of the impact of this physiological revolution indicates that the tropics would be hotter, drier, and more seasonal in the absence of the angiosperms, and the overall area of tropical rainforest would decline substantially. Because angiosperm diversity is influenced by rainforest area and by precipitation abundance and evenness, the high diversity of angiosperms is partially a product of a positive feedback loop with the climate modifications initiated by the angiosperms themselves. Lineage diversifications among vertebrate and invertebrate animals and nonangiospermous plants in the wake of the angiosperm radiation may be tied to the unprecedented impact of angiosperms on climate.