New perspectives on the evolution of plant mating systems

BACKGROUND: The remarkable diversity of mating patterns and sexual systems in flowering plants has fascinated evolutionary biologists for more than a century. Enduring questions about this topic include why sexual polymorphisms have evolved independently in over 100 plant families, and why proportions of self- and cross-fertilization often vary dramatically within and among populations. Important new insights concerning the evolutionary dynamics of plant mating systems have built upon a strong foundation of theoretical models and innovative field and laboratory experiments. However, as the pace of advancement in this field has accelerated, it has become increasingly difficult for researchers to follow developments outside their primary area of research expertise. SCOPE: In this Viewpoint paper we highlight three important themes that span and integrate different subdisciplines: the changes in morphology, phenology, and physiology that accompany the transition to selfing; the evolutionary consequences of pollen pool diversity in flowering plants; and the evolutionary dynamics of sexual polymorphisms. We also highlight recent developments in molecular techniques that will facilitate more efficient and cost-effective study of mating patterns in large natural populations, research on the dynamics of pollen transport, and investigations on the genetic basis of sexual polymorphisms. This Viewpoint also serves as the introduction to a Special Issue on the Evolution of Plant Mating Systems. The 15 papers in this special issue provide inspiring examples of recent discoveries, and glimpses of exciting developments yet to come.     

New perspectives on the origin and evolution of new world domesticated plants: Introduction

The symposium “New perspectives on the origin and evolution of New World domesticated plants” includes nine papers that all deal with the systematic relationships, center(s) of origin, and genetic diversity of particular New World crops. Recent molecular analyses and fieldwork in remote regions have supplied much new biosystematic evidence bearing on these topics. This new evidence, as well as the further integration of plant breeding, systematic/evolutionary, ethnobotanical, and archaeobotanical research, has done much to clarify New World crop origins and evolution.     

Mitogenomic perspectives into sciaenid fishes' phylogeny and evolution origin in the New World

Sciaenid fishes are widely distributed throughout the coastal waters and estuaries of the world. A total of 23 genera of this family are endemic to the Old World. However, evolutionary relationships among Old World sciaenid fishes and their origin have remained unresolved despite their diversity and importance. Besides, hypotheses that explain the origin and biogeographical distribution of sciaenid fishes are controversial. In this study, the complete mitochondrial genome sequences of seven representative sciaenid species were determined and a well-resolved tree was recovered. This new timescale demonstrated that the sciaenid originated during the late Jurassic to early Cretaceous Period. The estimated origin time of sciaenid fish is 208 Mya, and the origin of Old World sciaenid is estimated at 126 Mya. Reconstruction of ancestral distributions indicated a plesiomorphic distribution and center of origin in the New World, with at least one lineage subsequently dispersed to the Old World. Moreover, we conclude that the common ancestors of Old World sciaenid fishes were derived from species of New World.     

New perspectives on bacterial ferredoxin evolution

Summary Recent evidence indicates that a gene transposition event occurred during the evolution of the bacterial ferredoxins subsequent to the ancestral intrasequence gene duplication. In light of this new information, the relationships among the bacterial ferredoxins were reexamined and an evolutionary tree consistent with this new understanding was derived. The bacterial ferredoxins can be divided into several groups based on their sequence properties; these include the clostridial-type ferredoxins, theAzotobacter-type ferredoxins, and a group containing the ferredoxins from the anaerobic, green, and purple sulfur bacteria. Based on sequence comparison, it was concluded that the amino-terminal domain of theAzotobacter-type ferredoxins, which contains the novel 3Fe3S cluster binding site, is homologous with the carboxyl-terminal domain of the ferredoxins from the anaerobic photosynthetic bacteria.A number of ferredoxin sequences do not fit into any of the groups described above. Based on sequence properties, these sequences can be separated into three groups: a group containingMethanosarcina barkeri ferredoxin andDesulfovibrio desulfuricans ferredoxin II, a group containingDesulfovibrio gigas ferredoxin andClostridium thermoaceticum ferredoxin, and a group containingDesulfovibrio africanus ferredoxin I andBacillus stearothermophilus ferredoxin. The last two groups differ from all of the other bacterial ferredoxins in that they bind only one FeS cluster per polypeptide, whereas the others bind two. Sequence examination indicates that the second binding site has been either partially or completely lost from these ferredoxins.Methanosarcina barkeri ferredoxin andDesulfovibrio desulfuricans ferredoxin II are of interest because, of all the ferredoxins whose sequences are presently known, they show the strongest evidence of internal gene duplication. However, the derived evolutionary tree indicates that they diverged from theAzotobacter-type ferredoxins well after the ancestral internal gene duplication. This apparent discrepancy is explained by postulating a duplication of one halfchain sequence and a deletion of the other halfchain. TheClostridium thermoaceticum andBacillus stearothermophilus groups diverged from this line and subsequently lost one of the FeS binding sites.It has recently become apparent that gene duplication is ubiquitous among the ferredoxins. Several organisms are now known to have a variety of ferredoxins with widely divergent properties. Unfortunately, in only one case are the sequences of more than one ferredoxin from the same organism known. Thus, although the major features of the bacterial ferredoxin tree are now understood, a complete bacterial phylogeny cannot be inferred until more sequence information is available.     

The evolution of fidelity in sensory systems

We investigate the effect that noise has on the evolution of measurement strategies and competition in populations of organisms with sensory systems of differing fidelities. We address two questions motivated by experimental and theoretical work on sensory systems in noisy environments: (1) How complex must a sensory system be in order to face the need to develop adaptive measurement strategies that change depending on the noise level? (2) Does the principle of competitive exclusion for sensory systems force one population to win out over all others? We find that the answer to the first question is that even very simple sensory systems will need to change measurement strategies depending on the amount of noise in the environment. Interestingly, the answer to the second question is that, in general, at most two populations with different fidelity sensory systems may co-exist within a single environment.     

New perspectives on spinal motor systems

The production and control of complex motor functions are usually attributed to central brain structures such as cortex, basal ganglia and cerebellum. In traditional schemes the spinal cord is assigned a subservient function during the production of movement, playing a predominantly passive role by relaying the commands dictated to it by supraspinal systems. This review challenges this idea by presenting evidence that the spinal motor system is an active participant in several aspects of the production of movement, contributing to functions normally ascribed to 'higher' brain regions.     

New thoughts on the evolution of hormone-receptor systems

A possible pathway of the evolution of hormone-receptor systems has been discussed in light of the genomic potential hypothesis. Unlike the Darwinian system which is based on uninvestigatable chance events, the genomic potential hypothesis offers predictions based upon chemical determinism (boundary determinism). Accordingly, the production of highly specific protein-protein interactions between receptors and hormones, for example, are based upon the development of interacting components before the primordial chemistry was segregated by membranes. It is proposed that in addition to the primary structure (coding activity) a higher level of information exists in the genome which caused genomic products to function in a complementary fashion in living systems. The first steps in that direction have already been taken via experiments on sense and antisense peptides which may have specific relationships to each other. It is clear that I have not given an answer but I hope that I have touched upon certain aspects of a problem that can be illuminated better by a new and different approach to evolution. The hormone-receptor development was probably a powerful formative force in the development of macroorganisms, and its baffling complexity can only begin to find an explanation on the basis of structure/function relationships of the encoding material and its products.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ecological constraints on the evolution of avian brains

Birds have brains that are comparable in size to those of mammals. However, variation in relative avian brain size is greater in birds. Thus, birds are ideal subjects for comparative studies on the ecological and behavioral influences on the evolution of the brain and its components. Previous studies of ecological or behavioral correlates in relative brain size were mainly based on gross comparisons between higher taxa or focussed on the relationships between the sizes of specific brain structures and the complexity of different tasks. Here we examine variation in dimensions of the braincase, relative overall brain size and size of its components, in reference to one general ecological and behavioral task: migration. We used data from three lineages of closely related species (14 Acrocephalines, 17 Sylvia and 49 parulid warblers). Within each group, species vary in their migratory tendencies. We found that species migrating long distances have lower skulls and smaller forebrains than resident species. We discuss four hypotheses that could explain smaller forebrain sizes, and suggest relevant taxa to use in comparative analyses to examine each of these hypotheses:

Changing perspectives on the origin of eukaryotes

From the initial application of molecular techniques to the study of microbial organisms, three domains of life emerged, with eukaryotes and archaea as sister taxa. However, recent analyses of an expanding molecular data set reveal that the eukaryotic genome is chimeric with respect to archaea and bacteria. Moreover, there is now evidence that the primitive eukaryotic group ‘Archezoa' once harbored mitochondia. These discoveries have challenged the traditional stepwise model of the evolution of eukaryotes, in which the nucleus and microtubules evolve before the acquisition of mitochondria, and consequently compel a revision of existing models of the origin of eukaryotic cells.     

Genetic,historical and linguistic perspectives on the origin of the Kelantanese Malays

The Kelantanese Malays who resided in the remote northeastern regions of the Malay Peninsula in the Kelantan state are believed to have a unique genetic signature. The objective of this review is to analyze the populational sub-structure of the Kelantanese Malays from historical, genetic and linguistic perspectives. Historical data suggest that the Semang were composed of the Jahai, Bateq and Kensiu sub-tribes, whereas the Senoi were composed of only the Temiar sub-tribe. The Mendriq sub-tribe is believed to be the first group of aborigines to land in Kelantan. Subsequently, genetic analysis showed that the Kelantanese Malays are an independent clade at the base of the phylogenetic tree and contain genetic material similar to that of the Semang, specifically the Jahai and the Kensiu sub-tribes. The genetic data are supported by the fact that the Aslian language, a branch of the Austroasiatic languages that is widely spoken by the Semang, was potentially transmitted through agricultural activities. However, the potential limitation of this mini-review is the lack of primary reliable sources covering the historical, linguistic and genetic features of the Kelantanese Malays.     

Novel opportunity for understanding origin and evolution of life: perspectives on the exploration of subglacial environment of Lake Vostok, Antarctica

The year 2012 began with reports on the completion of drilling over the largest subglacial lake of Antarctica, Lake Vostok. It has been sealed from free exchange with the atmosphere for ～420,000 years, making it a potentially rich and largely unexplored storehouse of genetic information for solving evolutionary queries. Indirect evidence suggests that many impediments exist in the subglacial environment, such as high oxygen tension, low inorganic and organic nutrient concentrations, etc., whereas analysis of glacial and accretion ice from Vostok also implies that the elemental requirements for microbial growth could be satisfied in the lake by many possible electron donors (like H₂, Fe²⁺ and NO ₂ ^? ). Recent reports on the recovery of the longest ever ice core of ～3,769 m open up a new window for answering many questions about microbiological life in extremes, evolution, and adaptations. This review attempts to present an updated understanding on the potential significance of subglacial environments in unraveling the mystery of evolution of life.     

A comparative analysis of the locomotory systems of medusoid Cnidaria

Summary 1. The locomotory systems of forty-two genera of hydro- and scyphomedusae, representing nine orders, were surveyed, to serve as a basis for generalizations about medusan locomotion. The more pertinent of these have been discussed. The comparisons are based on previous studies ofPolyorchis montereyensis andCyanea capillata (Gladfelter 1972a, b).2. The bell ranges from broad and flat to long, narrow and pointed; the mesoglea ranges from soft to rigid. Radial mesogleal fibers are distributed in the regions of the bell deformed during contraction, and are most densely arrayed along joint apices. A variety of joint systems is present, from none or temporary creases, to permanent exumbrellar creases, to elaborate systems in most Anthomedusae and Scyphomedusae: a classification of mesogleal skeletons was erected.3. The contractile elements of the swimming muscle vary from widely spaced cord-like elements in weak swimmers to tightly packed ribbon-like processes with aligned striations in small strong swimmers, to thick cord-like elements in closely spaced, highly convoluted array arranged on larger mesogleal folds. Radial swimming muscles are present in flat forms.4. The velum (Hydromedusae) or its analog, the velarium (Cubomedusae) is important in forms with strongly arched bells, where it functions as a nozzle during straight swimming and turning. It is less important in broader bells, which, however, can turn in a smaller radius than tall forms.

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Eine vergleichende Analyse der lokomotorischen Systeme von Cnidarier-Medusen

Kurzfassung Auf der Grundlage einer funktionell-morphologischen Analyse des lokomotorischen Systems bei Hydro- und Scyphomedusen wurde der Versuch unternommen, den Mechanismus ihrer Schwimmbewegungen allgemein zu charakterisieren. An Vertretern von insgesamt 42 Gattungen wurden der Bau und die funktionelle Variabilität des Schirmes, der Mesogloea, der Fibrillen der Mesogloea, der kontraktilen Elemente der Muskulatur und des Velums bzw. des Velariums untersucht und verglichen sowie eine Klassifizierung der Medusen nach der Struktur der Mesogloea und der Art der Fortbewegung vorgenommen.