Evolving ideas of legume evolution and diversity: a taxonomic perspective on the occurrence of nodulation

Legumes evolved about 60 million years ago (Ma), and nodulation 58 Ma. Nonnodulation remains common in Caesalpinioideae, with smaller numbers in Mimosoideae and Papilionoideae. The first type of infection by bacteria may have been at junctions where lateral roots emerged, followed by formation of infection threads to confine bacteria and convey them to some cells in the developing nodule, where they were generally released into symbiosomes. Infection threads were a prerequisite for root-hair infection, a process better controlled by the host, leading to a higher degree of specificity between symbionts. An alternative process, dating from the same time and persisting in about 25% of legumes, did not involve infection threads, bacteria entering a few host cells, surrounded by an undefined matrix. These cells divided repeatedly to give uniform infected tissue, with bacteria released into symbiosomes. Such legumes may have less stringent control of nodulation processes, and are found mainly in tropical and warm temperate areas. In each type of nodule, meristems may or may not be retained, leading to indeterminate or determinate forms. Nodule morphology and structure are host-determined, but the effectiveness of nitrogen fixation is largely controlled by the bacterial symbionts, which vary greatly in genotypic and phenotypic characters.     

Epialleles in plant evolution

Heritable phenotypic differences caused by epigenetic modifications, rather than DNA sequence mutations, pose a challenge to our understanding of natural variation. Here, we review what is known about plant epialleles and the role of epigenetics in evolution.     

The fucosyltransferase gene family: an amazing summary of the underlying mechanisms of gene evolution

The fucosyltransferase gene family encodes enzymes that transfer fucose in 1,2, 1,3/4 and 1,6 linkages on a large variety of glycans. The most ancient genes harbour a split coding sequence, and encode enzyme that transfer fucose at or near O- and N-peptidic sites (serine, threonine or chitobiose unit). Conversely, the more recent genes have a monoexonic coding sequence, and encode enzymes that transfer fucose at the glycan periphery. All basic mechanisms of gene evolution contribute to this amazing scenario: exon shuffling, transposition, point mutations, and duplication. As typical examples: (i) exon shuffling leads to the ancestral organization of the 1,6 fucosyltransferase gene; (ii) the ancestor of 1,2 fucosyltransferase genes is reshaped by retrotransposition at the same locus; (iii) duplication associated to point mutations leads to the most recent 1,3/4 fucosyltransferase genes.     

A brief summary of the history of the detection of creatine kinase isoenzymes

Molecular and Cellular Biochemistry -     

Speculations on carbon dioxide starvation, Late Tertiary evolution of stomatal regulation and floristic modernization

Ambient atmospheric CO₂ concentration ([CO₂]_a) has apparently declined from values above 200μmol mol⁻¹ to values below 200μmol mol⁻¹ within the last several million years. The lower end of this range is marginal for C₃ plants. I hypothesize that: (1) declining [CO₂]_a imposed a physiological strain on plants, and plant taxa evolving under declining [CO₂]_a tended to develop compensating mechanisms, including increased stomatal efficiency; (2) angiosperms were better able to adjust to declining [CO₂]_a than were gymnosperms and pteridophytes; and (3) angiosperm adjustment has been uneven. Fast-evolving taxa (e.g. grasses and herbs) have been better able to adapt to CO₂ starvation. If these propositions are true, stomatal adjustment mechanisms should show patterned variation, and a single pattern of stomatal regulation cannot be assumed.     

Bioengineering of crop plants and resistant biotype evolution in insects: Counteracting coevolution

The use, as opposed to the procurement, of transgenic crop plants is discussed in this paper. Transgenic crop plants must not be used until appropriate strategies for their use have been designed and not before crop plants with a variety of insect defenses have been developed. The use of a crop plant with a single defense will pose as strong a selection pressure as the use of a single synthetic insecticide, since insect herbivores are able to evolve effective counter-defenses. The defenses of insects in natural plant-insect associations and with regard to synthetic insecticides are described to demonstrate that there is nothing unique about insecticide resistance. It is the inevitable alternative to local extinction in response to a persistent and predictable selection pressure. Plants counteract insect defensive evolution by keeping the selection pressure as variable as possible. This leads to the conclusion that the best use of biotechnology in crop protection is to reintroduce chemical diversity into crop plants.     

A brief history of the Annual International symposium on Respiratory Psychophysiology and summary of the 1993 workshops

This article traces the history of the Annual International Symposium on Respiratory Psychophysiology from its origins in the late 1970s at St. Bartholomew's Hospital, London, U.K., to the September 1993 symposium in London, U.K. (sponsored by the Department of Medicine of the Westminster and Charing Cross Medical School), where the formation of the International Society for the Advancement of Respiratory Psychophysiology (ISARP) was announced, along with plans for a new, associated journal, Breathing Research and Therapy.The workshops, symposia, participants, and publications generated since the first formal meeting in 1981 are listed. This article also provides a summary of the 1993 workshops and a request for information concerning membership and future meetings of ISARP.     

Increased understanding of metabolism of secondary plant products frequently generates sketchy and incorrect statements concerning their evolution and function

Secondary plant products perform important functions within the complex interactions between plants and their environment, e.g. as protective agents against pathogens and herbivores, or as attractants for potential pollinators. We are all aware that the enormous diversity of these natural products resulted from evolutionary processes driven by the selection of advantageous properties. However, when these nexuses are mentioned, very often we incline to formulate ‘Plants have acquired the ability to synthesize secondary plant products in order to …’ without realising that such a statement contradicts the Darwinian principles of evolution and corresponds to a Lamarckian view of teleological evolution. One of the major reasons for these automatic and unconscious misapprehensions is because of the ambiguous usage of the term ‘biological function’, which is very often thought to comprise an intention or a special purpose.     

A hypothesis for the evolution of sex

Summary Sex is one of the most creative of the major transitions in Evolution and its existence allows faster and wider mobility of species in the ‘History of Life’. We postulate that sex evolved from prokaryotes in the tail of the fitness distribution curve for a given environment. Once sex was established we have the potential for the evolution of species and the rich flowering of organisms in a relatively short period of time.     

Non-random pre-transcriptional evolution in HIV-1. A refutation of the foundational conditions for neutral evolution

The complete base sequence of HIV-1 virus and GP120 ENV gene were analyzed to establish their distance to the expected neutral random sequence. An especial methodology was devised to achieve this aim. Analyses included: a) proportion of dinucleotides (signatures); b) homogeneity in the distribution of dinucleotides and bases (isochores) by dividing both segments in ten and three sub-segments, respectively; c) probability of runs of bases and No-bases according to the Bose-Einstein distribution. The analyses showed a huge deviation from the random distribution expected from neutral evolution and neutral-neighbor influence of nucleotide sites. The most significant result is the tremendous lack of CG dinucleotides (p < 10(-50) ), a selective trait of eukaryote and not of single stranded RNA virus genomes. Results not only refute neutral evolution and neutral neighbor influence, but also strongly indicate that any base at any nucleotide site correlates with all the viral genome or sub-segments. These results suggest that evolution of HIV-1 is pan-selective rather than neutral or nearly neutral.     

The mitochondrial genome of the moss Physcomitrella patens sheds new light on mitochondrial evolution in land plants

The phylogenetic positions of bryophytes and charophytes, together with their genome features, are important for understanding early land plant evolution. Here we report the complete nucleotide sequence (105,340 bp) of the circular-mapping mitochondrial DNA of the moss Physcomitrella patens. Available evidence suggests that the multipartite structure of the mitochondrial genome in flowering plants does not occur in Physcomitrella. It contains genes for 3 rRNAs (rnl, rns, and rrn5), 24 tRNAs, and 42 conserved mitochondrial proteins (14 ribosomal proteins, 4 ccm proteins, 9 nicotinamide adenine dinucleotide dehydrogenase subunits, 5 ATPase subunits, 2 succinate dehydrogenase subunits, apocytochrome b, 3 cytochrome oxidase subunits, and 4 other proteins). We estimate that 5 tRNA genes are missing that might be encoded by the nuclear genome. The overall mitochondrial genome structure is similar in Physcomitrella, Chara vulgaris, Chaetosphaeridium globosum, and Marchantia polymorpha, with easily identifiable inversions and translocations. Significant synteny with angiosperm and chlorophyte mitochondrial genomes was not detected. Phylogenetic analysis of 18 conserved proteins suggests that the moss-liverwort clade is sister to angiosperms, which is consistent with a previous analysis of chloroplast genes but is not consistent with some analyses using mitochondrial sequences. In Physcomitrella, 27 introns are present within 16 genes. Nine of its intron positions are shared with angiosperms and 4 with Marchantia, which in turn shares only one intron position with angiosperms. The phylogenetic analysis as well as the syntenic structure suggest that the mitochondrial genomes of Physcomitrella and Marchantia retain prototype features among land plant mitochondrial genomes.     

Artificial neural networks in models of specialization, guild evolution and sympatric speciation

Sympatric speciation can arise as a result of disruptive selection with assortative mating as a pleiotropic by-product. Studies on host choice, employing artificial neural networks as models for the host recognition system in exploiters, illustrate how disruptive selection on host choice coupled with assortative mating can arise as a consequence of selection for specialization. Our studies demonstrate that a generalist exploiter population can evolve into a guild of specialists with an 'ideal free' frequency distribution across hosts. The ideal free distribution arises from variability in host suitability and density-dependent exploiter fitness on different host species. Specialists are less subject to inter-phenotypic competition than generalists and to harmful mutations that are common in generalists exploiting multiple hosts.When host signals used as cues by exploiters coevolve with exploiter recognition systems, our studies show that evolutionary changes may be continuous and cyclic. Selection changes back and forth between specialization and generalization in the exploiters, and weak and strong mimicry in the hosts, where non-defended hosts use the host investing in defence as a model. Thus, host signals and exploiter responses are engaged in a red-queen mimicry process that is ultimately cyclic rather then directional. In one phase, evolving signals of exploitable hosts mimic those of hosts less suitable for exploitation (i.e. the model). Signals in the model hosts also evolve through selection to escape the mimic and its exploiters. Response saturation constraints in the model hosts lead to the mimic hosts finally perfecting its mimicry, after which specialization in the exploiter guild is lost. This loss of exploiter specialization provides an opportunity for the model hosts to escape their mimics. Therefore, this cycle then repeats.We suggest that a species can readily evolve sympatrically when disruptive selection for specialization on hosts is the first step. In a sexual reproduction setting, partial reproductive isolation may first evolve by mate choice being confined to individuals on the same host. Secondly, this disruptive selection will favour assortative mate choice on genotype, thereby leading to increased reproductive isolation.     

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.     

The evolution of adult height in Europe: A brief note

This paper presents new evidence on the evolution of adult height in 10 European countries for cohorts born between 1950 and 1980 using the European Community Household Panel (ECHP), which collects height data from Austria, Belgium, Denmark, Finland, Greece, Ireland, Italy, Portugal, Spain, and Sweden. Our findings show a gradual increase in adult height across all countries. However, countries from Southern Europe (Greece, Italy, Portugal, and Spain) experienced greater gains in stature than those located in Northern Europe (Austria, Belgium, Denmark, Finland, Ireland, and Sweden).     

A brief history of the investigations on photosynthesis in Bulgaria

The effect of temperature, O₂ and Mg⁺⁺ on the kinetic characteristics of the slow inactivation (fallover) of Rubisco isolated from spinach (Spinacia oleracea L.) was determined. Comparing 25 and 45 °C, the rate of activity decline of Rubisco increased by 20-fold, but the final ratio of steady state to initial activity increased from 0.38 to 0.62, respectively. Low CO₂ increased the extent of fallover but only caused a marginal increase in fallover rate in agreement with results reported previously. In contrast, increased O₂ during catalysis significantly increased only the fallover rate. Low Mg⁺⁺ greatly increased the fallover of Rubisco both in rate and extent. Rubisco carbamylation was assayed using a new separation technique and it revealed that a loss of carbamylation largely accounted for the increased fallover observed with low Mg⁺⁺. In conclusion, Rubisco fallover is facilitated by high temperature, low concentration of CO₂ or Mg⁺⁺, and high O₂. The physiological importance of these factors in affecting Rubisco fallover and contributing to photosynthetic inhibition at high temperatures in planta are discussed.*Mention of a trademark, proprietary product or vendor does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products or vendors that may also be suitable.     

Recruitment trade-offs and the evolution of dispersal mechanisms in plants

In this study we place seed size vs. seed number trade-offs in the context of plant dispersal ability. The objective was to suggest explanations for the evolution of different seed dispersal mechanisms, in particular fleshy fruits, wind dispersal and the maintenance of unassisted dispersal. We suggest that selection for improved dispersal may act either by increasing the intercept of a dispersal curve (log seed number vs. distance) or by flattening the slope of the curve. 'Improved dispersal' is defined as a marginal increase in the number of recruits sited at some (arbitrary) distance away from the parent plant. Increasing the intercept of the dispersal curve, i.e. producing more seeds, is associated with a reduction in seed size, which in turn affects the recruitment ability, provided that this ability is related to seed size. If recruitment is related to seed size there will be a recruitment cost of evolving increased seed production. On the other hand, a flattening of the slope by evolving dispersal attributes is likely to be associated with a fecundity cost. An exception is wind dispersal where smaller (and hence more numerous) seeds may lead to more efficient dispersal. We derive two main predictions: If recruitment is strongly related to seed size, selection for improved dispersal acts on the slope of the dispersal curve, i.e. by favouring evolution of dispersal attributes on seeds or fruits. If, on the other hand, recruitment is only weakly related to seed size (or not related, or negatively related), selection for improved dispersal favours increased seed production. Despite its simplicity, the model suggests explanations for (i) why so many plant species lack special seed dispersal attributes, (ii) differences in dispersal spectra among plant communities, and (iii) adaptive radiation in seed size and dispersal attributes during angiosperm evolution. This revised version was published online in July 2006 with corrections to the Cover Date.