The steps of vascular plant and land ecosystem evolution

Basal steps of higher plant evolution are reconstructed by the structure of their conducting tissues. Historically, transport networks are derivatives of buffer zones for symbiotic exchange between prokaryotic pro-cursers. Two symbiogenetic acts (prochlorophytes + protists → higher algae; marine algae + fungi → higher land plants) are fixed in plant body by two networks for water transport. Descending phloem arises in phylogenesis from the membrane capsule of cyanobacteria. Fungi mycelium is a source of rising xylem exudates. The diversity of plant life forms is considered as a sequence of adaptive evolution of algo-myco-bacterial complex. Relationship to global chronical of climate events is shown by the specificities of Paleogene thermal floras and Neogene cold floras. The trends of plant genome size evolution are discussed.     

The tomato genome: implications for plant breeding, genomics and evolution

ABSTRACT: The genome sequence of tomato (Solanum lycopersicum), one of the most important vegetable crops, has recently been decoded. We address implications of the tomato genome for plant breeding, genomics and evolutionary studies, and its potential to fuel future crop biology research.     

Ecophysiological and bioclimatic foundations for a global plant functional classification

Question: What plant properties might define plant functional types (PFTs) for the analysis of global vegetation responses to climate change, and what aspects of the physical environment might be expected to predict the distributions of PFTs? Methods: We review principles to explain the distribution of key plant traits as a function of bioclimatic variables. We focus on those whole‐plant and leaf traits that are commonly used to define biomes and PFTs in global maps and models. Results: Raunkiær's plant life forms (underlying most later classifications) describe different adaptive strategies for surviving low temperature or drought, while satisfying requirements for reproduction and growth. Simple conceptual models and published observations are used to quantify the adaptive significance of leaf size for temperature regulation, leaf consistency for maintaining transpiration under drought, and phenology for the optimization of annual carbon balance. A new compilation of experimental data supports the functional definition of tropical, warm‐temperate, temperate and boreal phanerophytes based on mechanisms for withstanding low temperature extremes. Chilling requirements are less well quantified, but are a necessary adjunct to cold tolerance. Functional traits generally confer both advantages and restrictions; the existence of trade‐offs contributes to the diversity of plants along bioclimatic gradients. Conclusions: Quantitative analysis of plant trait distributions against bioclimatic variables is becoming possible; this opens up new opportunities for PFT classification. A PFT classification based on bioclimatic responses will need to be enhanced by information on traits related to competition, successional dynamics and disturbance.     

Pollen starch reserves in tomato relatives: Ecophysiological implications

The presence or absence of starch in microspore development and in pollen grains was recorded in eleven wild tomato species (Solanum sect. Lycopersicon) and two close relatives (S. lycopersicoides and S. sitiens). In all the species starch started to accumulate in the early microspore bicellular stage and continued until the cytoplasm was filled. At flower anthesis, pollen grains were mostly starchless in the wild tomatoes, except in S. pennellii, which had starchy pollen. Starchy pollen is also present in the two related species. The latter two species had larger pollen grains and grow in drier environments than the other species. The heterogeneity of pollen starch content among all these species, supposed to have the same pollination mechanism, is a new finding supporting the idea that starch content and pollination mechanism do not necessarily influence each other. The presence of starchy pollen in the self‐incompatible species, which grow in the driest environments, raises questions regarding the relationship between carbohydrates content and pollen survival.     

孑遗植物水杉种子萌发的生理生态特性研究

从种子活力和抗氧化酶活性两个方面研究了温度和光照对孑遗植物水杉 (Metasequoiaglyptostroboides)种子萌发的生理生态特性的影响。实验结果表明 ,萌发温度对水杉种子的活力和抗氧化酶活性有较大影响 ,在 19-2 8℃范围内 ,种子的发芽率、发芽速率、活力指数、脱氢酶及超氧化物歧化酶 (SOD)、过氧化物酶 (POD)和过氧化氢酶 (CAT)等抗氧化酶活性均较高 ,其中在 2 4℃条件下最高 ;当温度低于 15℃或者高于 32℃时 ,种子活力很低 ;10℃条件下种子几乎不萌发。可以认为 ,水杉种子萌发的适宜温度范围为 19- 2 8℃ ,最适温度为 2 4℃。光照萌发试验表明 ,6 5 μmol·m-2 ·s-1(12h/d)光照对水杉种子的萌发有较大的抑制作用 ,黑暗条件更适于水杉种子的萌发。自然状态下水杉种子质量很差 ,空瘪率超过 90 % ,加之产地春季温度不适于水杉种子的萌发 ,这两者可能是限制水杉种群更新的重要因素。这也许是水杉种群中缺乏幼苗和幼树的原因之一。     

Dispersal evolution in temporally variable environments: implications for plant range dynamics

Dispersal—the movement of an individual from the site of birth to a different site for reproduction—is an ecological and evolutionary driver of species ranges that shapes patterns of colonization, connectivity, gene flow, and adaptation. In plants, the traits that influence dispersal often vary within and among species, are heritable, and evolve in response to the fitness consequences of moving through heterogeneous landscapes. Spatial and temporal variation in the quality and quantity of habitat are important sources of selection on dispersal strategies across species ranges. While recent reviews have evaluated the interactions between spatial variation in habitat and dispersal dynamics, the extent to which geographic variation in temporal variability can also shape range-wide patterns in dispersal traits has not been synthesized. In this paper, we summarize key predictions from metapopulation models that evaluate how dispersal evolves in response to spatial and temporal habitat variability. Next, we compile empirical data that quantify temporal variability in plant demography and patterns of dispersal trait variation across species ranges to evaluate the hypothesis that higher temporal variability favors increased dispersal at plant range limits. We found some suggestive evidence supporting this hypothesis while more generally identifying a major gap in empirical work evaluating plant metapopulation dynamics across species ranges and geographic variation in dispersal traits. To address this gap, we propose several future research directions that would advance our understanding of the interplay between spatiotemporal variability and dispersal trait variation in shaping the dynamics of current and future species ranges.     

Ecophysiological adaptation of green roof plant Sedum lineare to temperature variation

以屋顶生长的佛甲草为材料,通过光照培养箱进行不同温度条件处理,分别测量了叶片的CO2交换、叶绿素含量、叶绿素荧光参数以及植株不同部位的碳同位素比率变化(δ13 C).结果表明:持续高温/低温、较大的昼夜温差和叶表面风力的条件下,佛甲草为适应环境变化,光合会由C3代谢途径转变成景天酸代谢途径(CAM),是兼性CAM植物.短期降温会使叶片光系统Ⅱ(PSⅡ)发生不可逆失活,光合能力下降;复水后有助于PSⅡ的恢复和重建,而干旱天气会减缓恢复过程;在不利温度环境中生长的佛甲草老叶掉落较多,剩余叶片的叶绿素含量和Fv/Fm值增高,光合能力提高.δ13C测定结果显示,高温使嫩叶气孔导度降低,对成熟叶片气孔导度影响小,佛甲草茎杆虽然含有叶绿素,但没有明显的光合作用.     

屋顶绿化植物佛甲草对温度梯度的生理生态适应

以屋顶生长的佛甲草为材料,通过光照培养箱进行不同温度条件处理,分别测量了叶片的CO2交换、叶绿素含量、叶绿素荧光参数以及植株不同部位的碳同位素比率变化(δ13C)。结果表明:持续高温/低温、较大的昼夜温差和叶表面风力的条件下,佛甲草为适应环境变化,光合会由C3代谢途径转变成景天酸代谢途径(CAM),是兼性CAM植物。短期降温会使叶片光系统Ⅱ(PSⅡ)发生不可逆失活,光合能力下降;复水后有助于PSⅡ的恢复和重建,而干旱天气会减缓恢复过程;在不利温度环境中生长的佛甲草老叶掉落较多,剩余叶片的叶绿素含量和Fv/Fm值增高,光合能力提高。δ13C测定结果显示,高温使嫩叶气孔导度降低,对成熟叶片气孔导度影响小,佛甲草茎杆虽然含有叶绿素,但没有明显的光合作用。     

Ecophysiological differentiation between life stages in filmy ferns (Hymenophyllaceae)

Journal of Plant Research - Desiccation tolerance was a key trait that allowed plants to colonize land. However, little is known about the transition from desiccation tolerant non-vascular plants...     

Epigenetics and plant evolution

A fundamental precept of evolutionary biology is that natural selection acts on phenotypes determined by DNA sequence variation within natural populations. Recent advances in our understanding of gene regulation, however, have elucidated a spectrum of epigenetic molecular phenomena capable of altering the temporal, spatial, and abundance patterns of gene expression. These modifications may have morphological, physiological, and ecological consequences, and are heritable across generations, suggesting they are important in evolution. A corollary is that genetic variation per se is not always a prerequisite to evolutionary change. Here, we provide an introduction to epigenetic mechanisms in plants, and highlight some of the empirical studies illustrative of the possible connections between evolution and epigenetically mediated alterations in gene expression and morphology.     

Nasal aperture area and body mass in felids: Ecophysiological implications and paleobiological inferences

In order to study the adaptive significance of the nasal chamber in felids (Mammalia, Carnivora), we measured the nasal aperture area and used it as an indirect estimate of the nasal chamber volume. We assume that this measurement relates to the metabolic demands for oxygen by animals, which in turn would depend on their mass, hunting techniques and/or the environment inhabited. The proven relationship between nasal aperture area and body size among living felids was used to estimate the mass and different aspects of the paleobiology of nine extinct felids from the New and Old World, six of the subfamily Machairodontinae and three of the subfamily Felinae. Results obtained confirm that the North American lion and the Eurasian cave lion were both comparable in size, with a body about 25% heavier than in today's lions. The large nasal apertures of smilodontines suggest that, compared to extant felids with skulls of similar length, these ambushing saber-tooth cats had a more robust body and thus greater oxygen demands. In contrast, coursing homotherines had longer skulls, narrower palates and a more lightened body than other saber-tooth cats.     

Polyploidy in differentiation and evolution

Somatic and generative (germ-line) polyploidy are more widely spread phenomena among living organisms than generally thought. The occurrence of polyploidization and related events in normal and pathological differentiation, their recognized main functions, as well as the structural specificities of polyploid nuclei are reviewed, and the relationship between ontogenetic and phylogenetic events is discussed. The mechanisms leading to the polyploid state, as well as other processes resulting in a genomic condition different from the diploid one (such as DNA under-replication, gene amplification, and chromatin elimination), are briefly sketched. The various changes in chromosomal DNA described are, in conclusion, seen as evidence supporting the paradigm of a "fluid" or dynamic organization of the eukaryotic genome, as being part of a cybernetic feedback regulation system of gene expression. A model is proposed that unifies the aspects of DNA variation, chromatin structure, and diversification in ontogenesis and phylogenesis.     

High regional genetic differentiation of an endangered relict plant Craigia yunnanensis and implications for its conservation

Of the genus Craigia, widespread in the Tertiary, only two relict species survived to modern times. One species is now possibly extinct and the other one, Craigia yunnanensis, is severely endangered. Extensive surveys have located six C. yunnanensis populations in Yunnan province, southwest China. Using fluorescent amplified fragment length polymorphism (AFLP), the genetic diversity and population structure of these populations were examined. It was found that genetic diversity of C. yunnanensis was moderate at the species level, but low at regional and population levels. Analysis of population structure showed significant genetic differentiation between Wenshan and Dehong regions, apparently representing two geographically isolated for long time refuges. There are also clear indications of isolation between populations, which, together with anthropogenically caused decline of population size, will lead to general loss of the species genetic variation with subsequent loss of adaptive potential. To conserve the genetic integrity of C. yunnanensis, we recommend that ex-situ conservation should include representative samples from every population of the two differentiated regions (e.g. Wenshan and Dehong). The crosses between individuals originated from different regions should be avoided because of a high risk of outbreeding depression. As all the extant populations of C. yunnanensis are in unprotected areas with strong anthropogenic impact, there is no alternative to reintroduction of C. yunnanensis into suitable protected locations.     

Foraging strategies of insects for gathering nectar and pollen, and implications for plant ecology and evolution

The majority of species of flowering plants rely on pollination by insects, so that their reproductive success and in part their population structure are determined by insect behaviour. The foraging behaviour of insect pollinators is flexible and complex, because efficient collection of nectar or pollen is no simple matter. Each flower provides a variable but generally small reward that is often hidden, flowers are patchily distributed in time and space, and are erratically depleted of rewards by other foragers. Insects that specialise in visiting flowers have evolved an array of foraging strategies that act to improve their efficiency, which in turn determine the reproductive success of the plants that they visit. This review attempts a synthesis of the recent literature on selectivity in pollinator foraging behaviour, in terms of the species, patch and individual flowers that they choose to visit.

The variable nature of floral resources necessitate foraging behaviour based upon flexible learning, so that foragers can respond to the pattern of rewards that they encounter. Fidelity to particular species allows foragers to learn appropriate handling skills and so reduce handling times, but may also be favoured by use of a search image to detect flowers. The rewards received are also used to determine the spatial patterns of searches; distance and direction of flights are adjusted so that foragers tend to remain within rewarding patches and depart swiftly from unrewarding ones. The distribution of foragers among patchy resources generally conforms to the expectations of two simple optimal foraging models, the ideal free distribution and the marginal value theorem.

Insects are able to learn to discriminate among flowers of their preferred species on the basis of subtle differences in floral morphology. They may discriminate upon the basis of flower size, age, sex or symmetry and so choose the more rewarding flowers. Some insects are also able to distinguish and reject depleted flowers on the basis of ephemeral odours left by previous visitors. These odours have recently been implicated as a mechanism involved in interspecific interactions between foragers.

From the point of view of a plant reliant upon insect pollination, the behaviour of its pollinators (and hence its reproductive success) is likely to vary according to the rewards offered, the size and complexity of floral displays used to advertise their location, the distribution of conspecific and of rewards offered by other plant species, and the abundance and behaviour of other flower visitors.     

Trends and patterns in the evolution of vascular plants: macroevolutionary implications of a multilevel taxonomic analysis

Cascales‐Miñana, B., Muñoz‐Bertomeu, J., Ros, R., Segura, J. 2010: Trends and patterns in the evolution of vascular plants: macroevolutionary implications of a multilevel taxonomic analysis. Lethaia, 10.1111/j.1502‐3931.2009.00212.x Studying the macroevolutionary patterns of vascular plants from the Silurian to the present‐day provides a global record of plant life history. Evolutionary rates (origination, extinction and diversification) for families, orders, classes and divisions were analysed, as was abundance and richness for 21 time intervals. An accumulative analysis, based on the total plant fossil record, the accumulated extinctions and relative diversity, was also carried out. The diversification rate shows a uniquely constant and progressive reduction from the end of the Carboniferous to the Permian when the lowest values are registered. Very small peaks seem to reflect Cretaceous extinction for families. At family level, only two time intervals present higher extinctions, than originations. Richness and accumulative analyses reveal that only 32% of the families analysed became extinct, and that approximately 90% of them disappeared at the end of the Palaeozoic. Our results indicate that plants did not undergo mass extinction events in the ‘big five’ sense, but rather, mass ecological reorganization the absence of important extinction events or evolutionary innovations producing diversification patterns without abrupt changes. □Diversification, evolutionary, extinction, fossil record, innovations, radiation, vascular plants.     

c-mos variation in songbirds: molecular evolution, phylogenetic implications, and comparisons with mitochondrial differentiation

Nucleotide sequences from the c-mos proto-oncogene have previously been used to reconstruct the phylogenetic relationships between distantly related vertebrate taxa. To explore c-mos variation at shallower levels of avian divergence, we compared c-mos sequences from representative passerine taxa that span a range of evolutionary differentiation, from basal passerine lineages to closely allied genera. Phylogenetic reconstructions based on these c-mos sequences recovered topologies congruent with previous DNA-DNA hybridization-based reconstructions, with many nodes receiving high support, as indicated by bootstrap and reliability values. One exception was the relationship of Acanthisitta to the remaining passerines, where the c-mos-based searches indicated a three-way polytomy involving the Acanthisitta lineage and the suboscine and oscine passerine clades. We also compared levels of c-mos and mitochondrial differentiation across eight oscine passerine taxa and found that c-mos nucleotide substitutions accumulate at a rate similar to that of transversion substitutions in mitochondrial protein-coding genes. These comparisons suggest that nuclear-encoded loci such as c-mos provide a temporal window of phylogenetic resolution that overlaps the temporal range where mitochondrial protein-coding sequences have their greatest utility and that c-mos substitutions and mtDNA transversions can serve as complementary, informative, and independent phylogenetic markers for the study of avian relationships.