bluuebunny/crossref_metadata_2025_split huggingface dataset:
Myriapoda (Including Centipedes and Millipedes)
Authors: Wright Jonathan C 
Published: April 2013

AbstractThe Myriapoda comprises four classes of terrestrial arthropods: Chilopoda or centipedes, Diplopoda or millipedes, Symphyla and Pauropoda. Myriapods are generally found in soil and litter and have a worldwide distribution. Approximately 13 000 species are known. Myriapods share a five‐ or six‐segmented head, a single pair of antennae, uniramous (unbranched) limbs and an elongate trunk without obvious tagmatisation. The Chilopoda and Diplopoda are the largest classes, numbering respectively approximately 3000 and 10 000 described species. Centipedes are carnivorous and share poison claws derived from the first pair of trunk limbs, whereas the other classes are primarily detritivores and may be significant contributors to litter breakdown and nutrient turnover. Recent molecular phylogenetic studies indicate that the Myriapoda comprise a monophyletic group and a sister taxon to the Pancrustacea (Crustacea and Insecta). They were among the first animals to colonise land.Key Concepts:Myriapoda comprise four classes of terrestrial arthropods: Chilopoda (centipedes), Diplopoda (millipedes), Symphyla and Pauropoda.Centipedes are carnivorous, possessing unique poison claws on the first trunk (post head) segment.Millipedes are characterised by diplosegments – pairs of trunk segments sharing a single tergal plate.Millipedes, symphylans and pauropods are detritivores, occurring primarily in soils and leaf litter.Myriapods have separate sexes (gonochoristic), and sperm transfer generally involves the exchange of one or more spermatophores via specialised appendages.Molecular phylogenetic evidence supports monophyly of the Myriapoda, with the Myriapoda probably comprising a sister taxon to the Pancrustacea (Crustacea and Insecta).Both centipedes and millipedes have fossil records dating back to the mid‐upper Silurian (ca. 420 mya) and probably colonised land prior to insects.Myriapods and insects share several derived traits representing adaptations to land: tracheal systems, predominantly uniramous (unbranched) limbs and excretory Malpighian tubules opening into the hindgut.
Bryozoa (Ectoprocta: ‘Moss’ Animals)
Authors: Claus Nielsen 
Published: April 2013

AbstractThe Bryozoa are a phylum of small, colonial, filter‐feeding, almost exclusively sessile, aquatic organisms. Approximately 5600 living species have been described, and the fossil record comprises approximately 20 000 species. Bryozoans are found in all oceans and many freshwater areas. Most species encrust stones or algae, others form erect bushes and a few form free‐living colonies. The individuals in the colonies are almost always smaller than 1 mm, but colonies of freshwater species may grow to 0.5 m in diameter, and some of the marine species form tufts up to more than 25 cm in length. Each individual (zooid) in a colony consists of rather stiff, often calcified, main body wall (cystid) and a tentacle crown plus gut (polypide), which can be retracted into the cystid. Colonies are hermaphroditic, in some groups with hermaphroditic zooids, but a number of groups have separate male and female zooids. Development is indirect with triangular shelled cyphonautes larvae in a few groups, but brood protection and lecithotrophic larvae of many types are more widespread.Key Concepts:Bryozoans are colonial aquatic organisms most often growing on stones, shells or algae.Each individual (zooid) in a colony consists of a more or less stiff main body wall (cystid) and a retractable tentacle crown around the mouth and a gut (polypide), which can be retracted into the cystid.The almost cylindrical tentacles have bands of cilia which create a water current towards the mouth and between the tentacles. Food particles are strained from this water current.Colonies are hermaphroditic; many species show hermaphroditic zooids, but some show male and female zooids.Most species brood the embryos in more or less elaborate brooding structures, called ovicels in the cheilostomes; cyclostomes have large female zooids, which are brood chambers with a rudimentary polypide.The Bryozoa can be classified as follows: Bryozoa (Phylactolaemata+Gymnolaemata (Eurystomata (Cheilostomata+Ctenostomata)+Cyclostomata)).
Terrestrialisation (Precambrian–Devonian)
Authors: Selden Paul 
Published: April 2013

Abstract

The emergence of plants and animals from the sea on to land – terrestrialisation – was one of the major advances in the history of life on Earth. Evidence for early colonisation is poor, but the fossil record reveals that by mid‐Palaeozoic times, complex terrestrial ecosystems had become established. The first phase of land colonisation by organisms may have started in the Precambrian, some 2.6 gigaannums (Ga) ago, in the form of microbially bound alluvial sands. The second phase began in earnest in Ordovician times, when early land plants, in the form of bryophyte‐like spores, first appear in the fossil record. By the Silurian, true vascular plants were present, and these green swards were inhabited by mainly detritivorous and predatory arthropods. By the late Devonian, true forests had developed, but it was not until the latest Palaeozoic that modern‐type terrestrial ecosystems, with abundant herbivores in the food chain.

Key Concepts:

Organisms need to be overcome many physiological barriers when colonising the land from the sea.

Conditions on the early Earth (∼4.6–1.0 Ga) were inhospitable to terrestrial life.

Microbial crusts were likely the earliest land life.

Higher plants appeared on land in the Ordovician period; vascular plants in the Silurian.

The first land animals (Silurian) were detritivorous and predatory arthropods.

Modern‐type ecosystems, with abundant herbivory and vertebrates, came in the latest Palaeozoic.
Extinction: End‐Triassic Mass Extinction
Authors: Hautmann Michael 
Published: April 2013

AbstractOne of the five greatest mass extinction events in Earth's history occurred at the end of the Triassic,c.200 million years ago. This event ultimately eliminated conodonts and nearly annihilated corals, sphinctozoan sponges and ammonoids. Other strongly affected marine taxa include brachiopods, bivalves, gastropods and foraminifers. On the land, there is evidence for a temporal disturbance of plant communities but only few plant taxa finally disappeared. Terrestrial vertebrates also suffered but timing and extent of this extinction remains equivocal. The cause of the end‐Triassic mass extinction was probably linked to the contemporary activity of the Central Atlantic Magmatic Province, which heralded the breakup of the supercontinent Pangaea. Possible kill mechanisms associated with magmatic activity include sea‐level changes, marina anoxia, climatic changes, release of toxic compounds and acidification of seawater. Remarkably, long‐term effects on marine biota were rather different between ecological groups: a nearly instantaneous recovery of level‐bottom communities is contrasted by the virtual absence of reef systems for nearly 10 million years after the extinction event.Key Concepts:Nearly half of all marine genera and a smaller but still significant proportion of terrestrial taxa went extinct at the end of the Triassic period,c.200 million years ago.The end‐Triassic mass extinction took place during a geologically short time interval, which coincided with the onset of massive magmatic extrusions along fracture zones of the disassembling supercontinent Pangaea.A cause‐and‐effect relationship between magmatic activity and mass extinction is indicated by the accordance of predicted extinction patterns and observed data from the fossil record.Ocean acidification as a kill mechanism in marine ecosystems is confirmed by preferential extinction of taxa with thick aragonitic skeletons.The end‐Triassic mass extinction event provides a test‐case for studying evolutionary responses to major environmental disturbances on the global scale and over geological time.Although there are differences in emission rates, the massive magmatic CO2release at the end of the Triassic is quantitatively similar to a potential release by complete combustion of the global fossil fuel reserves.A provisional prediction from the data of the fossil record is that in the marine realm level‐bottom communities are able to recover much more quickly from the effects of excess CO2than reef systems.
Geographical Variation
Authors: Olvido Alexander E , Mousseau Timothy A 
Published: April 2013

AbstractGeographical variation refers to differences among populations in genetically based traits across the natural geographic range of a species. Understanding the factors that give rise to and maintain geographical variation helps elucidate the causes and consequences of evolution. In the simplest case, we divide these factors into purely genetic versus environmental components to tease apart their relative contributions to observed phenotypic variation. Subsequent experiments allow us to partition further the genetic components of phenotypic variation towards a molecular understanding, hopefully to reveal the actualdeoxyribonucleic acid(DNA)‐scale changes giving rise to adaptations we see at the population level. Studies of a select number of organisms – all of which begin with geographic variation – demonstrate this highly productive strategy. Given its relevance to differentiation among populations, geographic variation also has direct bearing on the question of species origins.Key Concepts:Geographical variation refers to differences among populations of organisms in genetically based traits across the natural geographic range of that species.Understanding how initial population size, gene flow, mutation frequency, and environmental (abiotic) factors give rise to and maintain geographical variation can shed light on direction and rate of evolutionary change.Clinal variation – a form of geographic variation – suggests past or present action of natural selection.Reciprocal transplantation and ‘common garden’ experiments are two effective manipulations that can reveal genetically based phenotypic variation.A number of studies of geographic variation, including those about sickle‐cell anaemia, warfarin‐resistance, and lepidopteran colouration, have shifted to a more molecular focus.A number of other studies attempt to understand geographic variation in the broader context of community and ecosystem structure.Given the multi‐faceted approach to understanding it, geographic variation can help address the question of species’ origins.
Species and Speciation: Overview
Authors: Shaw Kerry L 
Published: April 2013

Abstract

The species is the fundamental or basic unit of organic or biological diversity, usually characterised as a group of individuals or populations of individuals with interbreeding or genealogical relationships. Understanding the nature of species can be challenging when considering sexual versus asexual organisms. Identifying species is also challenging, for example, when studying the fossil record, or when speciation is not yet complete. Speciation is the process leading to the formation or origin of species. As such, speciation is the process by which reproductive and/or genealogical boundaries form around groups of organisms. Commonly understood forces of evolution causing divergence in phenotypes contribute to the formation of species. Geographic, ecological, behavioural and genetic factors are also important to understanding how the process works.

Key Concepts:

Species are fundamental units of biodiversity but can be defined in different ways, from either a prospective (future) or retrospective (historical) perspective.

Speciation is the study of how new species form and may be brought about by a multitude of phenotypic changes.

The causes of speciation are complex and likely include a diversity of evolutionary forces such as natural selection, sexual selection and genetic drift that lead to divergence in phenotype.

Divergence in specific phenotypes is important to speciation if they directly or indirectly cause a reduction in gene flow between newly forming species.

The genetics of speciation is the study of the genetic basis of phenotypic evolution that leads to a reduction in gene flow between newly forming species.
Isolating Mechanisms
Authors: Butlin Roger K 
Published: April 2013

Abstract

Isolating mechanisms are intrinsic characteristics of species that reduce or prevent successful reproduction with members of other species. Viewed genetically, they are characters that act as barriers to the exchange of genes between populations. Most of these barriers are incidental consequences of divergence between populations but they can be elaborated by natural selection. They can take many forms, from mismatches between mating signals and preferences to genetic incompatibilities causing sterility of hybrids. A major outstanding challenge is to document the contributions of different forms of isolation to the overall barrier to gene exchange between species and to understand the order in which these barriers evolve.

Key Concepts:

Isolating mechanisms are intrinsic characteristics of species that reduce or prevent successful reproduction with members of other species.

Many, perhaps most, isolating mechanisms are incidental consequences of divergence between populations, not fashioned by selection for the purpose of preventing gene flow.

Individual barriers to gene exchange act sequentially, which means that early acting barriers tend to have the greatest effect even though they may not have been the first to evolve.

Ecological components of isolation evolve through adaptation to local conditions and may reduce the probability of mating or the fitness of hybrids.

Behavioural components of isolation prevent mating even when reproductively active individuals meet and may evolve due to sexual selection on mating signals and responses.

Barriers can occur after mating but before zygote formation. These barriers may be a side‐effect of evolutionary conflicts of interest between males and females.

Divergent populations accumulate genetic differences. Inevitably some of the new genes are incompatible resulting in isolation through reduced viability or fertility of hybrids, especially in the heterogametic sex.

We still need to know more about the range of barriers operating in individual species pairs, the reasons for their evolution and the order in which they evolved.
Ring Species and Speciation
Authors: Blackmon Heath , Demuth Jeffery P 
Published: April 2013

AbstractA ring species is a monophyletic group whose range has extended around a geographic barrier to produce a ring‐shaped distribution. The populations that make up the ring should be contiguous and without barriers to gene flow anywhere in the ring except where the terminal populations are sympatric but reproductively isolated from one another. Few, if any of the species that have been described as ring species, actually meet all of these requirements. The best documented example of a species that exhibits all of these traits is the greenish warbler complex (Phylloscopus trochiloides). However, even species like the herring gull complex orEnsatinasalamanders that fail to exhibit some of the characteristics of a true ring species offer opportunities to study important evolutionary processes. These species are particularly helpful in understanding how microevolutionary changes can create two unique species, how speciation can occur in spite of gene flow, and how geographic speciation with or without adaptive divergence can occur.Key Concepts:Few organisms exhibit all of the requirements to be considered a true ring species.Ring species are helpful tools that can be used to help elucidate evolutionary processes.The preponderance of avian and mammal ring species may be an ascertainment bias.
Hybrid Zones
Authors: Kawakami Takeshi , Butlin Roger K 
Published: April 2013

AbstractA hybrid zone occurs where two distinct genetic forms meet, mate and produce offspring with mixed genomes. Such zones may vary in width, length and patchiness, and are found between species, subspecies, races or forms. Stable hybrid zones may be maintained by selection against hybrids, environmental selection, or a combination of the two. A hybrid zone can arise either by direct environmental selection in contiguous populations or by renewed contact between previously isolated populations. Hybrid zones act as semi‐permeable barriers, which allow gene exchange for neutral or adaptive characters, whereas restricting introgression of alleles that contribute to local adaptation or reduced hybrid fitness. The study of genomic regions that experience barriers to gene flow can provide an important window for identifying specific genes and mutations that underlie reproductive isolation and local adaptation. With the help of recent technological advances in development of thousands of molecular markers, distributed genome‐wide, identification of such genomic regions is becoming possible in natural hybrid zones.Key Concepts:A hybrid zone is a narrow geographic region where two genetically distinct populations or species are found in close proximity and hybridise to produce offspring of mixed ancestry.Hybrid zones are widespread, both geographically and across animal and plant taxa.A hybrid zone is maintained by a balance between selection and dispersal.Selective forces can be intrinsic (e.g. selection against less‐fit hybrids) or extrinsic (e.g. environment‐dependent selection).Spatial analysis of allele‐frequency clines across a hybrid zone provides estimates of important population genetic parameters (e.g. selection, dispersal and linkage disequilibrium).Surveys of differential gene flow across a hybrid zone have the potential to localise genomic regions that habour genes responsible for barriers to gene exchange.
Hybrid Speciation
Authors: Abbott Richard J , Rieseberg Loren H 
Published: April 2013

AbstractHybridisation between genetically divergent populations may lead to the formation of new evolutionary lineages. This may occur via the duplication of a hybrid's chromosome complement (allopolyploid speciation) or by the stabilisation of a fertile hybrid segregant (homoploid hybrid speciation). Although more common in plants, both modes of hybrid speciation also occur in animals, including fish, amphibians and insects. The successful origin and establishment of hybrid species is highly dependant on an ability to occupy novel and/or spatially isolated habitats, in order to escape the effects of competition and gene flow from parental species. This ability is favoured by the generation of genetic novelty resulting from the dramatic effects that hybridisation (and genome duplication in allopolyploids) have on modifying genome structure and gene expression. Examples of new allopolyploid and homoploid hybrid species originating within the last 200–300 years are important models for investigating processes involved in hybrid speciation and establishment.Key Concepts:Hybridisation between genetically divergent populations is promoted by habitat disturbance and may lead to the formation of new evolutionary lineages.Hybrid speciation may occur via the duplication of a hybrid's chromosome complement (allopolyploid speciation) or by the stabilisation of a fertile hybrid segregant (homoploid hybrid speciation).Allopolyploidy leads to instantaneous reproductive isolation between the allopolyploid neospecies and its parents, and is therefore an example of very rapid speciation.Allopolyploidy is very common in higher plants, but less common in animals, although examples are known in insects, crustaceans, molluscs, fish, amphibians, reptiles and mammals.Homoploid hybrid speciation is thought to be relatively rare, although an increasing number of homoploid hybrid species of animals, plants and fungi are being recognised using molecular markers.Homoploid hybrid speciation can be completed within a few generations, although several hundred generations may be required before the genome of the hybrid neospecies is fully stabilised.Considerable genetic novelty is generated in the early stages of allopolyploidy and homoploid hybrid speciation due to the marked effects that hybridisation (and genome duplication in the case of allopolyploidy) have on modifying genome structure and gene expression.Such genetic novelty aids the establishment of hybrid neospecies in ecologically divergent habitats, thus reducing the likelihood of competition and crossing with parents.Several examples are known of new allopolyploid and homoploid hybrid species originating within the last 200–300 years and these have become important models for investigating processes involved in hybrid speciation and establishment.
Coevolution: Plant–Insect
Authors: Whitney Heather M , Glover Beverley J 
Published: April 2013

Abstract

Coevolution between plants and insects is a relatively frequent phenomenon, in part because of the enormous species diversity of both groups. It is often diffuse, resulting in variability and radiation, and is presumed to result in unstable relationships. Coevolutionary relationships mainly occur between plants and herbivorous insects and between plants and pollinating insects. The mechanisms by which plants and insects interact and perceive each are very diverse, but can be broadly split into two categories: chemical and physical. Insects use a combination of chemical and physical cues to detect and discriminate plants, whereas plants manipulate both of these to either deter or attract insect visitors. These cues can be used either honestly (as warning of potential defences or to advertise offered rewards) or deceptively.

Key Concepts:

Plants and insects have coexisted and interacted for more than 350 million years.

There is a huge diversity of plant–insect interactions; the equally vast diversity of plant and animal species is thought to be due in part to the selective pressures arising from these interactions.

Mechanisms by which plant–insect interactions occur include both physical and chemical.

Multiple physical and chemical mechanisms may be involved in an individual interaction.

Selection has therefore occurred on multiple aspects of both plants and insects, including their morphology, biochemistry, development, sensory systems and life cycles.

Plant–insect relationships are not stable; mutualisms can shift to the detriment of either of the partners.
Functional Constraint and Molecular Evolution
Authors: Forsdyke Donald R 
Published: April 2013

AbstractWhile having one or more specific functions, macromolecules have collective functions (e.g. Donnan equilibrium and aggregation pressure), and general functions (e.g. contribution to organism weight). Successful molecular evolution requires an appropriate balance between the constraints on these functions, which arise from selective pressures acting at the levels of conventional phenotypes (natural selection) and genome phenotypes (reprotypic selection). Genome‐wide constraints include fold pressure (nucleic acid stem‐loop extrusion pressure) and GC‐pressure (the pressure for a certain base composition). When these bring about within‐genome reprotypic selection (hybrid sterility), there is the potential for new species to emerge (speciation). Local constraints include protein pressure (the pressure to encode a protein) and purine‐loading pressure (purine‐richmessenger ribonucleic acid(mRNA) synonymous strands). As more pressures are identified, arguments for neutral evolution weaken.Key Concepts:Molecules have specific, collective and general functions.Most macromolecules function by virtue of their higher ordered structure.Nucleic acids have both structural and templating functions.Each species achieves its own balance between the competing demands (constraints) of external and internal environments.The organismal phenotype comprises the classical phenotype and the genome phenotype.Natural selection operates on the classical phenotype.Reprotypic selection operates on the genome phenotype.By balancing natural and reprotypic selection mechanisms, the ‘hand of nature’ resolves conflicts between functions.