Species and speciation.

2022 ◽  
pp. 7-8
Author(s):  
Richard A. I. Drew ◽  
Meredith C. Romig

Abstract This chapter discusses two species models, which are diametrically opposed. The first, often called the 'biological species concept', defines species in terms of 'reproductive isolation', convinced that species arise when subsets of a population are split off and remain geographically isolated over evolutionary time. If and when such new species are reunited with their founder population, interbreeding does not occur, or if it does, infertile progeny result. Hence, from the biological species concept, natural selection is a primary agent of change and directly selects for new species. In this sense, species are the direct products of natural selection and they are therefore 'adaptive devices'. When applying this species concept, it has been impossible to separate some sibling species of fruit flies in the genus Bactrocera where distinct morphological species can be similar in molecular analyses of certain DNA sequences, while similar species morphologically are distinct in the same molecular characters. A radically different model, the 'recognition concept of species', relies heavily on a knowledge of species ecology and behaviour, particularly in their natural habitat. The principal points in this concept are given. In contrast to the now-outdated biological species concept that leads one to depend on laboratory-based research to define species, the recognition concept requires workers to undertake extensive field research in the habitat of the taxon under investigation. In translating this approach to research in the insect family Tephritidae, particularly the Dacinae, some 35 years of field surveys have been undertaken throughout the Indian subcontinent, South-east Asia and the South Pacific region. These surveys included trapping using male lure traps and host fruit collections of commercial/edible fruits. The results of this work have included the provision of specimens of almost all known species for morphological descriptions (c.800 species), material for male pheromone chemistry, and data on host fruit relationships and biogeographical studies.

Author(s):  
Alessio Papini ◽  
Sara Falsini ◽  
Tiruha Habte Karssa

Cyanobacteria are prokaryotes whose taxonomy follows the same rules of a code (the International Botanical Nomenclature Code, IBNC) built for eukaryotic photosynthetic organisms. Hence, names of cyanobacteria follow the same rules and are assigned to biological entities (species) that should correspond to eukaryotic species. The main difficulty in the current situation is that the species concept in eukaryotes is based theoretically mainly on the biological species concept, that is centered on genetic exchange through sexual reproduction or lack of them. However, as shown, this difference is important from a theoretical point of view, but also in eukaryotes, the boundaries between different species are very rarely checked experimentally by direct observation of sexual barriers and hybridization events. The main concept for species delimitation is hence that related to morphology and, more recently and always in relation to morphology, DNA sequences. The introduction of distances obtained from matrixes of aligned sequences in the framework of a barcoding project provides a quantitative interpretation of species delimitation in relation to genetic distance that can be used both in eukaryotes and prokaryotes. However, the introduction of quantitative criteria needs the definition of distance thresholds to identify the boundaries between different species and, for doing that, it is necessary to test the distance thresholds in models of traditionally defined and recognized species. An alternative approach may be the comparison of the molecular distance (quantitative approach) to data about the capability of strains/species to exchange genetic information. Unfortunately data about this last question is still scarce. The adoption of molecular criteria to check species boundaries based on morphological characters has proved particularly challenging in cyanobacteria: a known example is provided. In conclusion, the only possible approach appears to be the association of molecular data to the increase of available data about the cell structure and the variation thereof in different physiological situations, particularly at the ultrastructural level. A further necessity is the check of the typus for a large number of cyanobacteria species, often based on old basionyms. In many of these cases the typus is often a drawing and more rarely a herbarium specimen or a microscope slide. In many cases an epitypification or a neotypification appears to be necessary.


Zootaxa ◽  
2004 ◽  
Vol 727 (1) ◽  
pp. 1 ◽  
Author(s):  
GERNOT VOGEL ◽  
PATRICK DAVID ◽  
OLIVIER S.G. PAUWELS

Variation in morphological characters were investigated among 136 specimens (128 specimens examined by us and eight specimens described in the literature) from 44 populations of the whole range of the pitviper currently known as Trimeresurus popeiorum Smith, 1937. Univariate and mul-tivariate analyses of these morphological characters allowed us to recognize six clusters of populations that are morphologically diagnosable, and that are here considered to represent independent lineages. Five of these clusters are considered to be distinct species following the Biological Species Concept and the Phylogenetic Species Concept. Two of them are described as new. Trimeresurus fucatus spec. nov. includes populations from southern Thailand and most of West Malaysia. Trimeresurus nebularis spec. nov. is described for populations from Cameron Highlands of West Malaysia. A population from Toba Massif, northern Sumatra, is referred to this complex, but cannot be assigned to a species at the present time. Trimeresurus popeiorum sabahi is raised to specific status, Trimeresurus sabahi new comb., to accommodate the populations from Borneo, whereas Trimeresurus barati new comb. includes the populations from western Sumatra and the Mentawai Archipelago. Separate keys to the two sexes of the recognised species of the T. popeiorum complex are provided.KEY WORDS: Thailand, West Malaysia, Sumatra, Borneo, Serpentes, Viperidae, Trimeresurus, Trimeresurus popeiorum, Trimeresurus fucatus spec. nov., Trimeresurus nebularis spec. nov., Trimeresurus sabahi, Trimeresurus baratiBefore the paper by Pope & Pope (1933), all green Trimeresurus species were gathered under the name Trimeresurus gramineus (Shaw, 1802). In a first step towards understanding the systematics of the genus, these authors split the nominal taxon gramineus into six species. The specific nomen gramineus was applied to a widespread species, ranging from northeastern India to western Indonesia. Indian populations were referred to a new species described as Trimeresurus occidentalis. Subsequently, Smith (1937) correctly showed that Pope & Pope (1933) misunderstood the type locality of gramineus, and showed that the type locality for T. gramineus was within the range of T. occidentalis. Therefore, Trimeresurus occidentalis Pope & Pope 1933 became a subjective junior synonym of T. gramineus (Shaw, 1802), leaving unnamed the distinct eastern taxon. Smith (1937) named it as Trimeresurus popeiorum. Unfortunately, he failed to designate a type specimen and a type locality for this new taxon. This interpretation was accepted by most subsequent authors except Hoge & Romano Hoge (1981) and Welch (1988). Another issue affecting the specific nomen is its spelling. Smith (1943) corrected the original spelling as popeorum on the basis that it was indeed a clerical error. This spelling was largely accepted, and was the subject of recent controversies. This problem will be addressed in another paper (David & Vogel, submitted). We consider that the correct spelling is indeed popeiorum. Eventually, Taylor & Elbel (1958), regarded as syntypes of Trimeresurus popeiorum Smith, 1937 all specimens referred by Pope & Pope (1933) to as T. gramineus, and designated the specimen BMNH 72.4.17.137 as the lectotype of the species. Consequently, the type locality was restricted to Khasi Hills, Assam , now in the State of Meghalaya, India.


2021 ◽  
Vol 102 (4) ◽  
Author(s):  
Yiyuan Li ◽  
Angela C. O’Donnell ◽  
Howard Ochman

Mosquito-borne arboviruses, including a diverse array of alphaviruses and flaviviruses, lead to hundreds of millions of human infections each year. Current methods for species-level classification of arboviruses adhere to guidelines prescribed by the International Committee on Taxonomy of Viruses (ICTV), and generally apply a polyphasic approach that might include information about viral vectors, hosts, geographical distribution, antigenicity, levels of DNA similarity, disease association and/or ecological characteristics. However, there is substantial variation in the criteria used to define viral species, which can lead to the establishment of artificial boundaries between species and inconsistencies when inferring their relatedness, variation and evolutionary history. In this study, we apply a single, uniform principle – that underlying the Biological Species Concept (BSC) – to define biological species of arboviruses based on recombination between genomes. Given that few recombination events have been documented in arboviruses, we investigate the incidence of recombination within and among major arboviral groups using an approach based on the ratio of homoplastic sites (recombinant alleles) to non-homoplastic sites (vertically transmitted alleles). This approach supports many ICTV-designations but also recognizes several cases in which a named species comprises multiple biological species. These findings demonstrate that this metric may be applied to all lifeforms, including viruses, and lead to more consistent and accurate delineation of viral species.


2006 ◽  
Vol 361 (1475) ◽  
pp. 2045-2053 ◽  
Author(s):  
Daniel Falush ◽  
Mia Torpdahl ◽  
Xavier Didelot ◽  
Donald F Conrad ◽  
Daniel J Wilson ◽  
...  

In bacteria, DNA sequence mismatches act as a barrier to recombination between distantly related organisms and can potentially promote the cohesion of species. We have performed computer simulations which show that the homology dependence of recombination can cause de novo speciation in a neutrally evolving population once a critical population size has been exceeded. Our model can explain the patterns of divergence and genetic exchange observed in the genus Salmonella , without invoking either natural selection or geographical population subdivision. If this model was validated, based on extensive sequence data, it would imply that the named subspecies of Salmonella enterica correspond to good biological species, making species boundaries objective. However, multilocus sequence typing data, analysed using several conventional tools, provide a misleading impression of relationships within S. enterica subspecies enterica and do not provide the resolution to establish whether new species are presently being formed.


2018 ◽  
Vol 93 (2) ◽  
pp. 226-241 ◽  
Author(s):  
S.P. Stock ◽  
R. Campos-Herrera ◽  
F.E. El-Borai ◽  
L.W. Duncan

AbstractIn this study, molecular (ribosomal sequence data), morphological and cross-hybridization properties were used to identify a newSteinernemasp. from Florida, USA. Molecular and morphological data provided evidence for placing the novel species into Clade V, or the ‘glaseri-group’ ofSteinernemaspp. Within this clade, analysis of sequence data of the rDNA genes, 28S and internal transcribed spacer (ITS), depicted the novel species as a distinctive entity and closely related toS. glaseriandS. cubanum.Additionally, cross-hybridization assays showed that the new species is unable to interbreed with either of the latter two species, reinforcing its uniqueness from a biological species concept standpoint. Key morphological diagnostic characters forS. khuongin. sp. include the mean morphometric features of the third-stage infective juveniles: total body length (average: 1066 μm), tail length (average: 65 μm), location of the excretory pore (average: 80.5 μm) and the values ofc(average: 16.4),D% (average: 60.5),E% (average: 126) andH% (average: 46.6). Additionally, males can be differentiated fromS. glaseriandS. cubanumby the values of several ratios:D% (average: 68),E% (average: 323) and SW% (average: 120). The natural distribution of this species in Florida encompasses both natural areas and citrus groves, primarily in shallow groundwater ecoregions designated as ‘flatwoods’. The morphological, molecular, phylogenetic and ecological data associated with this nematode support its identity as a new species in theS. glaseri-group.


PLoS ONE ◽  
2013 ◽  
Vol 8 (6) ◽  
pp. e68267 ◽  
Author(s):  
Lélia Lagache ◽  
Jean-Benoist Leger ◽  
Jean-Jacques Daudin ◽  
Rémy J. Petit ◽  
Corinne Vacher

Phytotaxa ◽  
2020 ◽  
Vol 455 (4) ◽  
pp. 262-266
Author(s):  
LIANG ZHANG ◽  
LI-BING ZHANG

The biological species concept is not exclusively applicable in many groups of organisms including ferns. Interspecific fern hybrids are not rare: there are 16 intergeneric hybrid genera in ferns confirmed with molecular data. Here we add one more hybrid genus in the tribe Lepisoreae of Polypodiaceae, ×Lepinema, formed via hybridization between parents in two genera: Ellipinema and Lepisorus.


2005 ◽  
Vol 176 (2) ◽  
pp. 221-225
Author(s):  
Jean Génermont

Abstract In 1980, Henri Tintant advocated the usefulness of the biological species concept in paleontology. At this time, this concept was still accepted by many neontologists, but it was already rather severely criticized by some others. In fact, a lot of new concepts appeared in the course of the following two decades. While a few ones are mere adjustments of the biological concept, for instance taking in account ecological criteria, in such a way that it could be applied to clonal organisms, some others, which were developed in connexion with the cladistic theory of taxonomy, are truly new from a conceptual point of view. The diagnosable version of the phylogenetic species concept is somewhat reminiscent of Simpson’s evolutionary species concept, since it accepts phyletic speciation as well as survival of the stem species after a cladogenetic event. One of its more criticizable features, from a cladistic point of view, is that the species are not necessarilly monophyletic. On another hand, according to the monophyly version of the phylogenetic species concept, species are recognized rather subjectively as monophyletic taxa revealed by some previous cladistic analysis dealing with operational taxonomic units. A consensus on the definition of species cannot be expected, since all concepts related to the biological one are founded on population grouping on the basis of potentially identical evolutionary fates, while those which are related to cladistic taxonomy are exclusively concerned with historical features.


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