New Species

These new species may metabolise their substrates by new pathways whose nature is hidden in DNA sequences every bit genes coding for 'hypothetical' or 'conserved' proteins, or genes that have been annotated erroneously.

From: Advances in Microbial Physiology , 2016

Cladogenesis

Christopher J. Humphries , in Encyclopedia of Biodiversity (Second Edition), 2001

Anagenesis, Cladogenesis, and Stasis

New species can either become modified through gradual change in an entire lineage in response to a changing environment or can emerge through diversification into two or more than species through formation of internal and external isolating mechanisms. Anagenesis is gradual change in an entire lineage ( Figure 1). Division into ii or more species is termed cladogenesis (Figure ii). There are many modes of population differentiation and considerable debate as to their roles in speciation. Likewise the mechanisms for anagenesis and cladogenesis (speciation) are many and varied. Nevertheless, they all include some course of population differentiation, either by gradual change of genetic differences and natural selection (phyletic gradualism), or by abrupt punctuational changes, involving chromosome inversions or translocations and rapid isolation between populations, or past historical accidents, such as allopatric speciation by vicariance and isolation.

Figure 1. Anagenesis. The transformation of a species or taxon on an unbranched lineage of organisms. Departure has occurred to such an extent that information technology is justifiably chosen a new species or taxon.

Figure two. Cladogenesis. The transformation of a species or taxon into ii (or more) species (or taxa) by branching along a lineage.

There is considerable controversy among the theories of diversification and how evolution proceeds. The Darwinian hypothesis is phyletic gradualism, whereby the aforementioned microevolutionary processes that atomic number 82 to population differentiation cause ever-increasing divergence between populations (Figure three). Eventually, sufficient divergence has occurred for differentiation at species level to exist recognized. Differentiation continues at a steady charge per unit and new species originate by slow, gradual changes of bequeathed species. The neo-Darwinian perspective is that evolutionary transformation takes place within species, or lineages, and the branching procedure of cladogenesis accounts for diversification but relatively pocket-size amounts of evolutionary change.

Figure three. Phyletic gradualism. A fairly constant rate of change through fourth dimension.

An alternative theory of evolutionary rates and speciation, punctuated equilibrium, was proposed by Eldredge and Gould (1972; Effigy iv). Testify from paleontology on well-preserved fossils betoken long periods of stasis, where "species" remain relatively little inverse over long periods of fourth dimension. At other times there appears to accept been rapid evolution and great morphological differentiation. Eldredge and Gould (1972) thus concluded that rates of evolution were not constant over time. They hypothesized that little evolutionary modify occurs within species and that genetic changes within populations do not account for unlike species. Instead, the events of speciation account for evolutionary alter, and short periods of "punctuation" were interspersed with trivial of no evolutionary divergence.

Effigy 4. Punctuated equilibrium. Morphological stasis of fossil taxa over long periods plain punctuated with occasional instantaneous change.

Phyletic gradualism and punctuated equilibrium represent the opposite extremes of a continuum. Recent research, specially on rates of molecular alter, would advise that evolutionary rates are clocklike, or at least "clocky," caused by periods of dull rates of phylesis and rapid periods of cladogenesis. This is reflected in research of the 1980s and 1990s, which has full-bodied on uncovering the patterns of departure through systematic assay (particularly cladistics). Sustained application of cladistic methods has determined nature's hierarchy and techniques such every bit maximum likelihood have been used to assess rates of change amongst phylogenetic trees.

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Cladogenesis☆

C.J. Humphries , ... M. Escudero , in Reference Module in Life Sciences, 2017

The Evolutionary Dynamics of Anagenesis and Cladogenesis: Phyletic Gradualism and Punctuated Equilibrium

New species can either go modified through gradual, genetic and/or phenotypic, change in an entire lineage in response to a changing surroundings or tin can emerge through diversification into two or more than species through the evolution or reproductive isolation and/or genetic divergence. Anagenesis is gradual change in an entire lineage ( Fig. 1). Division into two or more independent lineages is termed cladogenesis (Fig. ii). At that place are many modes of population differentiation and considerable argue every bit to their roles in speciation. Also the mechanisms for anagenesis and cladogenesis (diversification) are many and varied. Nevertheless, they all include some form of population differentiation, either past (i) phyletic gradualism (Eldredge and Gould, 1972): gradual change of genetic differences (allele frequencies) and natural choice, or (2) punctuated equilibrium (Eldredge and Gould, 1972): long periods of stability interrupted past relatively rapid and abrupt changes, like those involving chromosome duplications (polyploidy) or rearrangements, hybridization or range shifts promoting population isolation, such as allopatric speciation past vicariance or dispersal (peripatric speciation).

Fig. 1. Anagenesis. The transformation of a species or taxon on an unbranched lineage of organisms. Eventually, divergence has occurred to such an extent that it is justifiably called a new species or taxon.

Fig. 2. Cladogenesis. The transformation of a species or taxon into 2 (or more) species (or taxa) past branching along a lineage.

There is considerable controversy among the theories of diversification and how evolution proceeds. Darwin's theory of evolution supports phyletic gradualism, whereby the differences inside and betwixt populations evolve incrementally, past small steps at a steady charge per unit (Fig. iii). Eventually, sufficient divergence has occurred to recognize one or more new species, unlike from the ancestral species. The neo-Darwinian perspective is that evolutionary transformation takes place within species, or lineages, and the branching process of cladogenesis accounts for diversification but relatively small amounts of evolutionary change.

Fig. 3. Phyletic gradualism. A fairly constant charge per unit of change through fourth dimension.

An alternative theory of evolutionary rates and speciation, punctuated equilibrium, was proposed by Eldredge and Gould (1972; Fig. 4). Evidence from paleontology on well-preserved fossils indicates long periods of stasis, where fossil "species" remain relatively phenotypically little changed over long periods of time. At other times there appears to accept been rapid evolution and great morphological differentiation. Eldredge and Gould (1972) thus concluded that rates of evolution were non abiding over fourth dimension. They hypothesized that little evolutionary alter occurs within species and that genetic changes within populations do non account for different species. Instead, the events of speciation account for evolutionary change, and short periods of "punctuation" were interspersed with picayune or no evolutionary divergence.

Fig. 4. Punctuated equilibrium. Morphological stasis of fossil taxa over long periods obviously punctuated with occasional, relatively fast change.

Phyletic gradualism and punctuated equilibrium represent the reverse extremes of a continuum. At that place are archetype examples inferred from the fossil record for both patterns (see MacFadden (1986) and Chaline and Laurin (1986) for phyletic gradualism; Williamson (1981) and Cheetham (1987) for punctuated equilibrium). However, the stardom between cladogenesis and anagenesis in the fossil record has been hindered by dubiety in deviation time estimation, gaps in fossil series, and difficulties in interpreting biological species from fossil morphospecies (Strotz and Allen, 2013). The hypothesis of punctuated equilibrium has been controversial considering graphic symbol evolution was linked to speciation (Eldredge and Gould, 1972). However, in that location is now ample evidence that evolutionary alter does not necessarily entail speciation (Futuyma, 2013). A combined model was proposed past Malmgrem et al. (1983), called "punctuated gradualism," in which both deadening, gradual and fast, abrupt changes may take place, simply speciation does non necessarily have to occur during periods of change.

Recently, a phylogenetic model that integrates variation in diversification rates associated to traits which evolve gradually or in punctuated bursts during speciation has been adult. This model (BiSSE-ness) estimates both the rate of alter occurring forth lineages and the probability of change occurring during speciation, as well equally independent diversification rates for each character state (Magnuson-Ford and Otto, 2012).

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Volume 1

Cletus P. Kurtzman , ... Teun Boekhout , in The Yeasts (Fifth Edition), 2011

two.1 Description of New Taxa

ii.1.one Species

Publication of new species must include a description of essential characters as well as a diagnosis that distinguishes the taxon from previously described species. Since January ane, 1935, the description and/or diagnosis must be given in Latin. Failure to comply with this requirement results in an invalidly described species termed a nomen invalidum (nom. inval.). A nomen invalidum also results if publication is not in a recognized scientific journal, e.yard., as in a patent or a trade magazine. If the new species is designated without a description or a diagnosis, it is invalid and termed a nomen nudum (nom. nud.). Names of taxa must exist given in Latin or modified in such a way that they follow the rules of Latin derivation including appropriate gender designations. If a proper noun has been incorrectly crafted, it may be treated every bit an "orthographic mistake" and corrected. An example is Pichia membranifaciens for which the 1888 spelling "membranaefaciens" has been corrected. The authorization name does not alter due to the spelling correction. Other requirements for valid publication include deposition of type fabric in a publicly accessible herbarium. This textile must be an original specimen of the organism, and it is to be dead and dried. The 1994 Code (Greuter et al. 1994) changed the requirements to allow lyophilized specimens to be valid type material (holotype) and that living cultures derived from the lyophilized material are considered ex typo, i.e., from the type. It seems that once the original material is wearied, in that location is no longer blazon material bachelor. A possible solution to this problem would be to lyophilize new material and designate it as a neotype, a convention permitted when the original type material is lost or destroyed and the species can be otherwise recognized. This word leads to the recognition that a bulk of presently accepted yeast species are technically invalid because legitimate blazon material has not been preserved. A portion of soon lyophilized stocks of the holotype that are maintained in culture collections should be withheld from distribution and designated every bit blazon. Consequently, the designation of "Blazon strain" given for each cultivatable species described in this volume can, at all-time, represent an ex-type. The 1994 Code recognized the need for living cultures in the practice of modern taxonomy and stated in Recommendation 8B.1:

"Whenever practicable a living culture should be prepared from the holotype material of the name of a newly described taxon of fungi or algae and deposited in at least ii institutional civilisation or genetic resource collections. (Such action does not obviate the requirement for a holotype specimen nether Art 8.ii)."

The 1994 Lawmaking further states in Recommendation 8B.ii:

"In cases where the nomenclatural type is a culture permanently preserved in a metabolically inactive state (see Art. 8 Ex. ane), any living isolates obtained from that should be referred to as 'ex-type' (ex typo), 'ex-holotype' (ex holotypo), 'ex-isotype' (ex isotypo), etc., in order to make it articulate they are derived from the blazon but are not themselves the nomenclatural blazon."

From these recommendations, information technology is clear that the Lawmaking strongly encourages scientific cooperation and communication through agile sharing of published taxonomic specimens. A listing of commonly used yeast civilisation collections is given in Chapter 7.

From gene sequence comparisons, strains that represent new species are ordinarily easily recognized (Chapter ten). Nonetheless, some would argue confronting description of a new species based on a unmarried strain. The argument is that a single strain does not reflect the genetic variation that might be establish in a species, and that little can exist learned of the ecology of a species when merely a single strain is bachelor. Nevertheless, nearly one-third of described yeast species are based on a unmarried strain. If these species had not been described, much less would be known virtually the phylogenetic diversity of the yeasts. From the perspective of understanding multifariousness among the yeasts, description of single-strain species is to be supported, although descriptions based on multiple strains are preferred. Further, information technology is recommended that the description should be based on multigene analysis to lessen the possibility that the strain represents a hybrid of known species.

2.1.2 Genera, Families, Orders

The rules for describing new genera, families and orders are similar to those for describing new species. The taxa must be based on a validly described species and provided with a Latin description and diagnosis. The rules of priority are briefly described below, merely one exception is that orders are exempt from priority usage.

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Biodiversity, Evolution and

Gregg Hartvigsen , in Encyclopedia of Biodiversity (Second Edition), 2013

The Big Question: How Will the Process of Evolution Influence Biodiversity Dynamics?

Development generates new species in the aftermath of mass extinction. This is well supported by the fossil record and appears, in geological time, to be rapid. The current extinction outcome taking place on Earth, however, appears to be more rapid than has occurred previously ( Smith et al., 1993). Speciation will undoubtedly lead to the rise of new taxa but over time scales that are likely to be too long to have a noticeable effect in our lifetime. In addition, and more than troubling, is the suggestion that relatively young taxa are likely to be more susceptible to extinction due to the smaller population sizes and the relatively limited geographic ranges (Boyanjian, 1991).

The other role that evolution plays in biodiversity is its power to influence the stability of communities. Little is known most this function of evolution. Empirical data for plant communities suggest that stability is correlated with biodiversity, such that more than diverse communities are more than resilient to disturbance. Natural communities are often composed of genetically variable individuals, which provide the foundation that enables species to evolve in response to biotic and abiotic factors over time. Besides, communities with more than species are in general more diverse genetically. If the time frame of environmental change can be matched by choice operating on genetic diversity, communities may resist disturbances past adjusting to changes over fourth dimension. The illustration of species wandering over an "adaptive mural" (sensu Sewall Wright) produces an epitome of communities operation as complex adaptive systems. Ecosystems that function equally complex adaptive systems may resist environmental fluctuations. If, yet, environmental disturbances are abrupt, communities may either not be able to react quickly plenty or endure overloads that essentially shake species out of the customs. There is show that communities harbor redundancy at the species level, but we take not withal determined patterns that place which species are necessarily of import or unimportant for community role. Therefore, the loss of species from communities is likely to subtract, if but slowly, the stability of communities.

Theoretical piece of work suggests that the process of evolution may increment the resilience of communities to disturbance. This expanse of enquiry is in its infancy and will likely go an of import and quickly developed discipline in the following decades.

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Other Coryneform Leaner and Rhodococci

Rose Kim , Annette C. Reboli , in Mandell, Douglas, and Bennett's Principles and Do of Infectious Diseases (8th Edition), 2015

Corynebacterium amycolatum

Divers as a new species in 1988 by Collins, C. amycolatum was first isolated from the skin of good for you humans. 66 Noted for its lack of mycolic acids, the species corresponds to the CDC coryneform groups F-2 and I-2. Information technology is the nonlipophilic coryneform bacteria about frequently isolated from clinical specimens. vii,8 C. amycolatum forms small dry nonhemolytic colonies of 1- to 2.0-mm in diameter when cultured at 37° C. 3 The organisms are pleomorphic and vary from single organisms to an array of Chinese letters. Because of variability in biochemical reactions, C. amycolatum had been misidentified previously as C. minutissimum, C. xerosis, and C. striatum. Currently, the API Coryne system can correctly identify C. amycolatum, but confirmatory tests should be performed. 3

Although case reports of infections attributed to C. amycolatum are rare, many previously reported infections by other members of the nonlipophilic fermentative group were well-nigh likely caused by C. amycolatum. Reports with reliable information on organism identification include nosocomial endocarditis after intravenous catheter–related infection, septic arthritis, a case of native valve endocarditis with aorta-to–left atrial fistula, and sepsis in pediatric oncology patients. 67-lxx Susceptibility testing has shown resistance to penicillins, cephalosporins, macrolides, fluoroquinolones, and rifampin and susceptibility to vancomycin, daptomycin, linezolid, and teicoplanin. 71 There is variable resistance to aminoglycosides and tetracyclines. 23,26 Reports of successful treatment of endovascular infection include the utilise of vancomycin and daptomycin in combination with rifampin. 58,72

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Evolution of Epigenetic Mechanisms in Animals and Their Part in Speciation

Günter Vogt , in Handbook of Epigenetics (Second Edition), 2017

Polyploid Speciation and Reproductive Isolation

The origin of new species and higher taxa by polyploidy, particularly allopolyploidy, is mutual in plants simply was for long considered insignificant in animals [lxx]. Meanwhile, there is increasing evidence that chromosomal speciation has as well played a considerable function in creature development [71,72]. A well established case of ancient polyploidy is the vertebrates, which are thought to take experienced 2 rounds of polyploidy in their stalk line (Fig. 27.two) and a further round in the stem line of the teleost fishes [72]. These events were presumably responsible for the expansion of the Deoxyribonucleic acid methylation toolkit described previously [13]. Recent polyploids are relatively frequent in water fleas, insects, fish and amphibians. For case, in the teleost family unit Cyprinidae more than than 50 species from several subfamilies are polyploids, suggesting multiple hybridization events [71].

Speciation by polyploidy is normally accompanied past reproductive isolation and alterations of the DNA content, Dna methylation level, and life history traits. An case is given in Fig. 27.5 for the marbled crayfish Procambarus virginalis, which originated from slough crayfish Procambarus fallax past autotriploidy in evolutionarily recent times [22,73]. Concomitantly, the sexual system has shifted from gonochorism to parthenogenesis. Marbled crayfish has a one.iv-fold increased Dna content when compared to its parent species, suggesting loss of DNA after polyploidization. Body size and fecundity are significantly enhanced, indicating superior fettle. In contrast, global Dna methylation is about 20% lower in marbled crayfish, arguing for a considerable rearrangement of the DNA methylation pattern during speciation. In 2013, we take started a whole-genome and whole-methylome sequencing project for both crayfish to estimate the genetic and epigenetic contributions to speciation in detail and to place the genetic and epigenetic causes for the transition from gonochorism to parthenogenesis [22,74–76].

Figure 27.5. Alteration of genome size, global Dna methylation, and fitness traits during chromosomal speciation.

Marbled crayfish Procambarus virginalis (Pv) has originated from slough crayfish Procambarus fallax (Pf) past autotriploidization and concomitant change of the sexual system from gonochorism to parthenogenesis. It has a larger genome size, grows bigger and is much more fecund than its parent species, just has significantly lower levels of Dna methylation. Horizontal confined signal means and ranges. Vertical bars are standard deviations of three samples.

 Figures in brackets give number of specimens. Based on Ref. [22] Vogt G, Falckenhayn C, Schrimpf A, Schmid K, Hanna K, Panteleit J, et al. The marbled crayfish as a prototype for saltational speciation by autopolyploidy and parthenogenesis in animals. Biol Open 2015;4(11):1583–94; photos past Chris Lukhaup.

Comparison of both species at the whole genome level identified hundreds of Mb of genomic information specific to P. fallax [74]. Information technology also revealed numerous differentially expressed and differentially methylated genes [74,75], suggesting the involvement of Dna methylation in alteration of gene expression during speciation. Preliminary genome note of poly peptide coding transcripts suggests alterations in meiosis related genes every bit potential causes of parthenogenesis [76].

Reproductive isolation is an of import requirement for speciation. It is defined as the absenteeism of gene flow betwixt parent species and neospecies, assuasive conservation of genetic and phenotypic distinctiveness and split future development. In plants, there are multiple evidences on the contribution of DNA methylation to hybrid incompatibility [77]. An animal example is the deer mouse species complex (Peromyscus maniculatus), in which imprinting of genes involved in placentation has led to reproductive isolation [78]. These examples show that epigenetic mechanisms tin principally contribute to the establishment of reproductive barriers.

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Species Concepts and Speciation

D. Ortiz-Barrientos , in Encyclopedia of Evolutionary Biology, 2016

The Nature of Species

The origin of new species can be understood in two major ways. On ane manus, speciation is the fix of processes that create morphological and genotypic discontinuity in populations. Darwin was the starting time to provide a meaningful caption for this procedure past suggesting that natural option is responsible for the phenotypic gaps seen in nature ( Darwin, 1859). These gaps ascend from the elimination of unfit individuals with intermediate phenotypes, which leads to the origin of forms often distinguished by multiple traits and past their disability to occupy each other's niche. More recently, these ideas accept been extended to include the formation of genotypic gaps betwixt populations, or the germination of genotypic clusters in sympatry (Mallet, 1995). Although these 'Darwinian species' are probably common, many could be curt-lived given that environmental conditions can be unstable over long periods of time, and the homogenizing effects of gene flow tin ofttimes overpower the differentiating effects of natural selection.

On the other hand, species originate when interbreeding groups of individuals can no longer reproduce with other such groups (Dobzhansky, 1937, 1940; Mayr, 1942a, 1963). In this view, reproductive gaps, and not necessarily morphological ones (e.g., sibling species are nearly identical), define biological species, and neither environmental fluctuations nor hybridization can eliminate the genetic differences that accept accumulated between them. (Coyne and Orr, 2004; Rieseberg et al., 2006). These two major solutions to the species problem, Darwinian and biological species, accept helped us understand how natural option and other evolutionary forces play a role in the origin of biodiversity. However, the ii solutions assign a different emphasis to the office of evolutionary forces: while Darwinian species arise by divergent natural or sexual choice during primary contact, many different evolutionary forces acting in a variety of geographic settings (including secondary contact) can fuel the origin of biological species (Box 1; Figure two).

Box 1

Speciation and gene flow

Sympatric and parapatric speciation, every bit well equally reinforcement of reproductive isolation, are difficult because gene flow antagonizes the forces that create divergence (such as drift and natural pick). Cistron flow tin be present since the get-go of sympatric and parapatric speciation (master contact), or during the completion of allopatric speciation (when populations come into secondary contact). Although main contact may never pb to divergence of populations, and secondary contact can fuse them, theoretical models suggest that strong divergent pick, concrete linkage between genes responsible for adaptation, and stable genetic associations between prezygotic and postzygotic reproductive isolation can facilitate speciation with gene flow in both cases. Sympatric and parapatric speciation are likely to always atomic number 82 to the origin of Darwinian species, simply maybe less likely to the origin of biological species.

Effigy Box 1. Speciation with gene period during primary and secondary contact. (a) Populations showing stiff associations between phenotype and habitat ofttimes form conspicuously divers clusters in multivariate trait space (clusters 1 and 2), and are likely to be reproductively isolated. (b) However, some populations may partially overlap in morphology, either considering they are in the early on stages of speciation, or because they accept come back into contact after a previous period of allopatric divergence (clusters four–six). Natural pick can resolve these stages and pb to the formation of populations clearly separated by consummate extrinsic or intrinsic reproductive isolation. (c) Test of variability in multiple genetic markers is expected to reveal the history of their divergence, although patterns of factor flow can distort relationships amongst populations. g represents migration rate betwixt populations, and its strength is denoted past the thickness of the inverted arrows connecting a population pair.

Effigy ii. Primary and secondary contact speciation, and the distribution of speciation events. The left console shows primary contact speciation, where divergent natural option, mainly leads to the cosmos of Darwinian species, and less often to the germination of biological species. The transition from Darwinian to biological species might occur merely if there is either the right genetic architecture for linking extrinsic and intrinsic reproductive isolation or cistron flow fully ceased betwixt Darwinian species so intrinsic isolation can evolve unimpeded by homogenizing gene period. Fusion and lack of difference are likewise possible outcomes. The correct panel shows secondary contact speciation, where previously allopatric populations come into contact and either fuse, remain separated past a hybrid zone, or consummate the speciation process via reinforcement of reproductive isolation. Allopatric populations might have differentiated via natural pick (either divergent or compatible) or drift, and the outcomes of speciation do not necessarily lead to morphologically singled-out species (i.east., sibling and cryptic species). Dotted vertical line represents the moment at which speciation becomes irreversible.

Dissimilar from its sexual counterparts, asexual organisms are difficult to sort into these views (Holman, 1987; Cohan, 2002, 2006; Barraclough et al., 2003; Cohan and Koeppel, 2008; Tang et al., 2014). However, given that natural selection oft favors single asexual genotypes that replace the entire population in a given habitat, asexual species can be ameliorate understood in terms of their adaptations, and perhaps as genotypic clusters suited to particular environments. This is because complete replacement of genetic variability leads to a correlation between genotype and phenotype, and thus to organic aperture. In groups of organisms where both sexual and asexual reproductions is rampant (agamic complexes; e.g., Krak et al., 2013), organic aperture does non ascend, suggesting that the origin of species is intimately related to the way and prevalence of sexual reproduction in whatsoever given system.

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River Ecosystems

K.E. Limburg , ... D.Fifty. Strayer , in Encyclopedia of Biodiversity, 2001

VI.F. Introduced Species

Humans are also introducing new species into ecosystems at an unprecedented charge per unit. Some of these introductions are intentional: for example, salmon, trout, and bass are stocked into rivers and lakes all around the world for sport fishing, and grass carp are introduced to control aquatic weeds. Many introductions are unintentional, arising from the pumping out of ballast h2o in big tankers, overland transfer of boats with attached organisms from i drainage to some other, or accidental spills. Although virtually organisms that are introduced into a novel environment perish, the increase in commercial gunkhole traffic particularly increases the likelihood of a successful introduction.

Rates of exotic species introductions are difficult to quantify, in role considering many of the species are also pocket-sized to notice. However, Mills et al. (1996) documented the charge per unit of species introductions into the Hudson River, in New York State; since 1840, the rate has been virtually one successful introduction per year—much higher than natural rates of species flow.

Direct perturbations of the mix of species, either by introduction of new species or past removal of extant species by overharvesting, may crusade dramatic changes in relations of the food web, thereby also affecting predators and prey. Some species additions affect their physical and chemical environment as well: in Due north America, zebra mussels, which were introduced into the Bang-up Lakes in 1988 and which spread speedily through the Mississippi and eastern drainages, have been documented to increase the clarity of the water column by virtue of their filter feeding and too carpet big areas of the benthos, where they take successfully colonized.

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River Ecosystems

K.E. Limburg , ... D.L. Strayer , in Encyclopedia of Biodiversity (2d Edition), 2013

Introduced Species

Humans are besides introducing new species into ecosystems at an unprecedented rate. Some of these introductions are intentional: for case, salmon, trout, and bass are stocked into rivers and lakes all around the world for sport fishing, and grass carp are introduced to control aquatic weeds. Many introductions are unintentional, arising from the pumping out of ballast water in large tankers, overland transfer of boats with fastened organisms from one drainage to another, or accidental spills. Although almost organisms that are introduced into a novel environment perish, the increase in commercial boat traffic specially increases the likelihood of a successful introduction.

The rates of exotic species introductions are difficult to quantify, in role considering many of the species are too small-scale to notice. Still, Mills et al. (1996) documented the rate of species introductions into the Hudson River, in New York Land; since 1840, the rate has been almost one successful introduction per yr – much college than natural rates of species flow.

Direct perturbations of the mix of species, either by introduction of new species, or removal of extant species past overharvesting, may cause drastic changes in the relations of the food web, thereby also affecting predators and casualty. Some species additions touch their physical and chemic surroundings as well: in North America, zebra mussels, which were introduced into the Corking Lakes in 1988 and spread rapidly through the Mississippi and eastern drainages, accept been documented to increase the clarity of the water column past virtue of their filter feeding, and also carpeting large areas of the benthos, where they take successfully colonized.

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Volume one

Chester R. CooperJr., in The Yeasts (5th Edition), 2011

2.ane.2 Candida Dubliniensis

In 1995, a new species of Candida was isolated from the oral cavity of HIV-infected patients. This new species was designated as C. dubliniensis. Subsequently, like C. albicans, C. dubliniensis proved to be readily recovered from HIV-positive patients across the world. This yeast has also been isolated from os marrow transplant patients and those persons on broad-spectrum antibiotics. A recent review highlights the condition of this pathogen since its discovery (Sullivan et al. 2005).

Candida dubliniensis is morphologically similar to C. albicans in that information technology forms germ tubes and chlamydospores. These two backdrop are only exhibited by these two species amidst all members of the genus Candida. However, a published report suggests that Staib agar supports chlamydospore formation only by C. dubliniensis, thereby providing a possible diagnostic tool for differentiating these species (Staib and Morschhauser 1999). A more contempo study suggests that the regulatory signals that control chlamydospore formation differ between C. dubliniensis and C. albicans (Staib and Morschhauser 2007). Such data may aid decipher the biological function of this curious structure. In add-on to the morphological and developmental resemblance of C. dubliniensis and C. albicans, both of these species are physiologically similar bearing only subtle differences. However, the two species can be distinguished from ane another by incubating strains at 45°C. At this temperature, C. dubliniensis will not grow, whereas C. albicans readily forms colonies under the aforementioned weather condition. On CHROMagar Candida, C. dubliniensis also forms dark-green colonies like C. albicans, though on newer formulations of the medium the colonies are darker. There are differences in karyotypes and rDNA sequences, merely the applications that would be employed to assess these characteristics are usually beyond the purview of a typical clinical laboratory.

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