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Hypothetical example showing the consequences of species turnover within isolated geographical regions. (a) Individuals from Africa colonize South America (t ¼ 0). (b) Speciation occurs in South America to fill available space (thick lines); speciation (thick lines) and extinction (dotted lines) occurs in Africa, i.e. species turnover (t ¼ 10). (c) After a sufficient period of time, turnover leads to reciprocal monophyly of species between the two regions. Note the divergence time between these two clades at the end depends on the time elapsed since the dispersal event plus the divergence at the time of the dispersal event between the colonizer of South America and the ancestors of those lineages surviving to the present in Africa (t ¼ 20). In this case, by chance the final date for the divergence time is more than twice the actual time since the dispersal event.
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Current approaches to studying the evolution of biodiversity differ in their treatment of species and higher level diversity patterns. Species are regarded as the fundamental evolutionarily significant units of biodiversity, both in theory and in practice, and extensive theory explains how they originate and evolve. However, most species are still...
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... some point, a member of the clade colonizes a new region, B. Assuming that sufficient resources are available, the clade diversifies to occupy available space in the new region. Initially, the clade in region B will be nested within the clade in region A ( figure 4b). However, after a sufficient period of time (determined by the rate of species turnover and the equilibrium number of species), assuming no subsequent dispersal, all of the species in region A will be descended by chance from a common ancestor more recent than their ances- tor with those from region B (figure 4c), and vice versa, in a manner equivalent to coalescence at the individual level between isolated populations. ...
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Despite persistent debate on the nature of species, the widespread adoption of Mayr's biological species concept has led to a heavy emphasis on the importance of reproductive isolation to the speciation process. Equating the origin of species with the evolution of reproductive isolation has become common practice in the study of speciation, coincid...
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... In the present paper, we want to know how well the data fit evolutionary theory (e.g. Pianka, 2000;Gould, 2002;Barraclough, 2010; and standard works such as that of Grant, 1985), in particular, how well traits of taxa support different orderings of ancestor and descendant species. Evolutionary theory is, of course, complex, but most simply, as here applied, ancestor-descendant order is expected to reflect reasonable interpretation of adaptations (Mayr, 1983) involving reduction and elaboration, given Darwinian gradualism (no or few major jumps in numbers of trait combinations, as in natura non facit saltus), reflective of Dollo parsimony (Gould, 1970). ...
... Evolutionary systematics holds, on the contrary, that the model must reflect ancestor-descendant relationships as determined by studies that reflect the established premises of evolutionary theory. Appropriate theory (Artzy-Randrup, Kondrashov, 2006;Barraclough, 2010;Lewontin, 1978;Mayr, 1983;Schneider, 2000) involves adaptation, chance of reversals, rarity and specialization of traits, non-saltational changes, and other elements used in generating optimal evolutionary trees. ...
Detailed evaluation is provided for the statistical methods intrinsic to interlocking Sequential Bayes analysis, which allows estimation of evidential support for stem-taxon dendrograms charting the macroevolution of taxa. It involves complexity functions, such as fractal evolution, to generate well-supported evolutionary trees. Required are data on trait changes from ancestral species to descendant species, which is facilitated by reduction of large genera to the smallest included mo-nophyletic groups (one inferred ancestral species each). The genus is here defined as the smallest monophyletic unit, which turns out to be monothetic at least for the direct descendant species. The key fact is that the most-recently acquired traits of the single ancestral species are apparently selectively inviolate and passed on without change to each immediate descendant species. The details of sequential Bayesian analysis were clarified by comparing support of the optimal model with summed support of the alternative models. Because analysis is confined to optimal arrangements of only immediate branches from ancestral species to descendant species, conjugate priors were found to operate such that all alternative models are simply one minus the probability of the optimal model. Such analysis demonstrated that the optimum arrangement of ancestor and descendant species leads to high support values for fitting evolutionary theory, comparable to statistical support levels reported for molecular evolutionary trees, and conjugate priors may be assumed for similar model-building. The method is simple, free of special computer analysis, and well-suited to standard taxonomic practice.
... ,b, 2023. In the present paper, we want to know how well the data fit evolutionary theory (e.g., Barraclough, 2010;Gould, 2002;Pianka, 2000; and standard works such as that of Grant, 1985), in particular, how well traits of taxa support different orderings of ancestor and descendant species. Evolutionary theory is, of course, complex, but most simply, as here applied, ancestor-descendant order is expected to reflect reasonable interpretation of adaptations (Mayr, 1983) involving reduction and elaboration, given Darwinian gradualism (no or few major jumps in numbers of trait combinations, as in natura non facit saltus). ...
... Ancestral species are mostly ignored in modern taxonomic work because: (1) classical taxonomy commonly assigns species to polythetic genera and relegates trait changes to the intellectual domain of evolutionists, (2) systematics in the cladistic context focuses on clustering taxa by relative degree of shared ancestry, without identifying particular species as ancestors, i.e., all species are terminal on a cladogram, and (3) molecular systematics depends on relative degree of shared apparently non-expressed and randomly fixed molecular sequences, and simply maps expressed traits to the molecular cladogram assumed to track expressed-trait evolution. 3 The monothetic group is most easily dealt with if named as a separate genus, but for convenience a subgenus or section may be used. The work of Zander (2023) summarizes several papers dealing with monothetic genera and trait changes between ancestral species and descendants, and also between ancestral monothetic genera and descendant monothetic genera. ...
... Evolutionary systematics holds, on the contrary, that the model must reflect ancestor-descendant relationships as determined by studies that establish the premises of evolutionary theory. Appropriate theory (Artzy-Randrup & Kondrashov, 2006; Barraclough, 2010;Lewontin, 1978;Mayr, 1983;Schneider, 2000) involves adaptation, chance of reversals, rarity and specialization of traits, saltational changes, and other elements used in generating optimal evolutionary trees. ...
Detailed evaluation is provided for the likelihood statistics intrinsic to interlocking Sequential Bayes analysis, which allows estimation of evidential support for dendrograms charting the macroevolution of taxa. It involves complexity functions, such as fractal evolution, to generate well-supported evolutionary trees. Required are data on trait changes from ancestral species to descendant species, which is facilitated by reduction of large genera to monothetic groups (one ancestral species each), most conveniently named as separate genera. Assigning each species one Shannon informational bit per new trait, then adding the traits as sequential Bayesian analysis (each posterior probability used as the prior for the next iteration of Bayes Formula), then interpretation with an odds chart, provides a posterior probability that the ancestor-descendant order is correct, that is, entirely follows evolutionary theory involving adaptation and rarity of total trait reversals. The key fact is that the most recently acquired traits of the ancestral species are selectively inviolate and passed on without change to each descendant species. The details of sequential Bayesian analysis were clarified by calculation of likelihood ratios and Bayes factors that compare optimal models with the next most likely model. Such analysis demonstrated that the optimum arrangement of ancestor and descendant species leads to high support values for fitting evolutionary theory, comparable to statistical support levels reported for molecular evolutionary trees. The fact that phylogenetic analysis does not offer an ancestor-descendant model in is found to be conducive of precision at the expense of accuracy, and leads to wrong ancestor-free models with likelihoods explaining data at high credible levels. The number of advanced traits in the outgroup as a Bayesian prior greatly enhances posterior probability. The method is simple, free of special computer analysis, and well-suited to standard taxonomic practice.
... "Morphology" is a catch-all term for any expressed trait potentially important in natural selection. Adaptation is considered here a real process in nature (Kauffman, 2000: 182) as opposed to, say, the nihilism of the neutral theory of morphological speciation, in which fixation of traits is mostly stochastic (e.g., Bell, 2001;Bennett, 2010;Crutchfield, 2003: 126;Hubble, 2001, and contrary arguments of Barraclough, 2010), or that of rankless taxonomy, in which species names are replaced by informal phylogenetic clade names (e.g., Mishler, 2021;Wall, 2005). ...
... The possibility of there being clusters of diversity discernable at hierarchical levels of taxa at different scales has been discussed by Barraclough (2010), and for microbiome ecology by Agler et al. (2016). Scales may be crossed by evolutionary and ecological processes that may involve fractal patterns (Binning, 1989) or chaos and non-linearity (Doebeli & Ispolitov, 2014;Ferriere & Fox, 1995;Rogers et al., 2022). ...
... Does this scale further? The above data supports Barraclough's (2010) contention that higher taxa are not arbitrary units of diversity. And, for what it is worth, Mandelbrot (1983: 85) estimated that galaxies are generated at the superstructure level with a fractal dimension of 1.23. ...
An evolutionary lineage may be analyzed as a complex adaptive system. It cycles through time from monothetic genus to monothetic realized niche, and forward again genus to niche. A genus is a set consisting of an ancestor species and its descendants each with the same ancestron traits. A niche is a physically coherent nexus of convergent species sharing the same novon of a virtual ancestor species (stochastic plus natural selection). Like speciation, nicheation is a complex, fractal process governed by non-linear processes. Superimposition of Turing patterns of separately evolved species may be a process that minimizes negetropic open space. The genus is here taken as the fundamental unit of evolution, tested and modified through interaction with environments oscillating across geological time. Four major modeling methods are used: radiate monothetic genera, NK-parallels of random Boolean networks, oscillations of the logistic map, and fractal dimensions. It is then possible to provide precise measures of resilience in species, genera and higher taxa, including survival-associated traits, changes in traits between and through periodic extinction events, and potential continuation of lineage and ecosystem niche complexity in the future. Systematics, evolution, and niche theory are linked by the same analytic modeling reflecting similar complex processes in speciation and “nicheation.” The model organism is the bryophyte, particularly the moss family Pottiaceae.
... Although there are taxonomic proposals for defining supraspecific categories (Avise & Johns, 1999;Dubois, 1988aDubois, , 1988bSchaefer, 1976), genera generally represent a consensual classification among taxonomists, as the use of these categories is relevant not only because it reflects phylogenetic relationships (de Queiroz, 1988;Dubois, 1988aDubois, , 1988b, but are also relevant in communicating, estimating, evaluating, investigating patterns and processes, and retrieving information on biodiversity (Barraclough, 2010;Clayton, 1972;Dubois, 1988b;Nee et al., 1994;Simpson, 1961). Within a zoological concept, a genus would be a well-defined and well-supported monophyletic group of closely related species that share several characters, with morphological, behavioural, and ecological diagnoses (Dubois, 1988a(Dubois, , 1988bDubois & Raffaëlli, 2009). ...
The genus Saguinus comprises three principal clades that diverged in the Middle to Late Miocene. Their taxa are ecologically differentiated and allopatrically distributed. These clades were recently recognized as different genera, Saguinus, Tamarinus and Oedipomidas. In Tamarinus, the phylogenetic relationships among species/subspecies are poorly understood. Thus, in this study we present a comprehensive dated genomic phylogeny based on double digest restriction associated DNA for all known species and subspecies of Tamarinus. We also tested whether that Tamarinus imperator and Tamarinus subgrisescens are different species, as morphology-based taxonomy, phenotypical divergences and mitochondrial genes recognized them as two different species. Additionally, we reconstructed time-calibrated phylogenetics tree hypotheses of all extant species and subspecies of the genera Saguinus, Tamarinus and Oedipomidas. Our analysis robustly supported the phylogenetic hypothesis of all species/subspecies of the genus Tamarinus; strongly supported a divergence between the three clades, Saguinus, Oedipomidas and Tamarinus; and provided support for T. imperator and T. subgrisescens as distinct species. Therefore, we reiterate and ratify the division of Saguinus into three genera, supporting the taxonomic proposal for these genera.
... Whilst nowadays the evolutionary thinking is an absolutely unavoidable base for any scientific and biological study, the main taxonomic framework, e.g. the hierarchical system of taxa and the binomial pairing of genus species has been formed yet in pre-evolutionary times (e.g., Linnaeus, 1758). This is indeed in an immediate contradiction with scientific evolutionary approach which implies a permanent process of modifications at organism level and higher (e.g., Barraclough, 2010;Zachos, 2018). Therefore, we cannot exclude from consideration that we actually still use basically antievolutionary taxonomy, despite all achievements of the molecular phylogenetics. ...
By applying morphological and molecular data on two genera of the nudibranch molluscs it is shown that the tension between taxonomic practice and evolutionary processes persists. A review of the related genera Catriona and Tenellia is used to demonstrate that the fine‐scale taxonomic differentiation is an important tool in the integration of morphological and molecular data. This is highlighted by the hidden species problem and provides strong argument that the genus must be kept as a maximally narrowly‐defined entity. Otherwise, we are forced to compare a highly disparate species under the putatively lumped name “Tenellia”. We demonstrate this in the present study by applying a suite of delimitation methods and describing a new species of Tenellia from the Baltic Sea. The new species possesses fine‐scale morphological distinguishing features, which were not investigated before. The true, narrowly defined genus Tenellia represents a peculiar taxon with a clearly expressed paedomorphic characters and predominantly brackish‐water habitats. The phylogenetically related genus Catriona, of which three new species are described here, clearly demonstrates different features. A lumping decision to call many morphologically and evolutionary different taxa as “Tenellia” will downgrade the taxonomic and phylogenetic resolution of the entire family Trinchesiidae to just a single genus. The dissolution of the dilemma of “lumpers & splitters”, which still significantly affects taxonomy, will further help to make systematics a true evolutionary discipline.
... However, an alternative consequence of interspecific hybridization is the origin of asexual forms (Schultz 1973;Vrijenhoek 1989). These forms are able to escape the constraints of sex and, if parthenogenetic reproduction is successful, develop into new asexual "species" (sensu Barraclough 2010). In vertebrates, interspecific hybridization is the process responsible for the origin of all known parthenogenetic species (e.g., Murphy et al. 2000;Alves et al. 2001;Fujita and Moritz 2009;Freitas et al. 2016a;Brunes et al. 2019;Fujita et al. 2020). ...
Hybridisation is a common evolutionary process with multiple possible outcomes. In vertebrates, interspecific hybridisation has repeatedly generated parthenogenetic hybrid species. However, it is unknown whether the generation of parthenogenetic hybrids is a rare outcome of frequent hybridisation between sexual species within a genus or the typical outcome of rare hybridisation events. Darevskia is a genus of rock lizards with both hybrid parthenogenetic and sexual species. Using capture sequencing, we estimate phylogenetic relationships and gene flow among the sexual species, to determine how introgressive hybridisation relates to the origins of parthenogenetic hybrids. We find evidence for widespread hybridisation with gene flow, both between recently diverged species and deep branches. Surprisingly, we find no signal of gene flow between parental species of the parthenogenetic hybrids, suggesting that the parental pairs were either reproductively or geographically isolated early in their divergence. The generation of parthenogenetic hybrids in Darevskia is, then, a rare outcome of the total occurrence of hybridisation within the genus, but the typical outcome when specific species pairs hybridise. Our results question the conventional view that parthenogenetic lineages are generated by hybridisation in a window of divergence. Instead, they suggest that some lineages possess specific properties that underpin successful parthenogenetic reproduction. This article is protected by copyright. All rights reserved
... Asexual organisms such as bacteria also engage in a struggle for survival and reproduction, and they too adapt to their environment through natural selection. Despite that, there is not an endless diversity of form or genetic variety among bacteria and other asexual organisms; they too cluster into distinct groups based on shared inherited characteristics that, importantly, evolve through time [84]. This has led to the concept of the 'ecotype' in asexual evolution, in which the 'force of cohesion' is not the reproductive connectivity of a species but a shared ecological strategy that places its members in competition with each other for resources within a set environmental carrying capacity. ...
Planktonic foraminifera are heterotrophic sexually reproducing marine protists with an exceptionally complete fossil record that provides unique insights into long-term patterns and processes of evolution. Populations often exhibit strong biases towards either right (dextral) or left (sinistral) shells. Deep-sea sediment cores spanning millions of years reveal that some species show large and often rapid fluctuations in their dominant coiling direction through time. This is useful for biostratigraphic correlation but further work is required to understand the population dynamical processes that drive these fluctuations. Here we address the case of coiling fluctuations in the planktonic foraminifer genus Pulleniatina based on new high-resolution counts from two recently recovered sediment cores from either side of the Indonesian through-flow in the tropical west Pacific and Indian Oceans (International Ocean Discovery Program Sites U1486 and U1483). We use single-specimen stable isotope analyses to show that dextral and sinistral shells from the same sediment samples can show significant differences in both carbon and oxygen isotopes, implying a degree of ecological separation between populations. In one case we detect a significant difference in size between dextral and sinistral specimens. We suggest that major fluctuations in coiling ratio are caused by cryptic populations replacing one another in competitive sweeps, a mode of evolution that is more often associated with asexual organisms than with the classical ‘biological species concept’.
... Application of molecular methods in combination with traditional morphological techniques or alone have expanded in the last two decades with regard to species delimitation in annelids in general, and in Sabellida, in particular. These methods are sustained by the definition of species as independently evolving entities (metapopulations), that are genetically (and often phenotypically) distinct [246,247]. Thus, species are expected to be reciprocally monophyletic clusters, morphologically distinct and/or genetically divergent, as a result of evolutionary forces applied to closely related lineages. Molecular-based approaches have not only improved species delimitation by providing additional evidence to morphological taxonomy, but also helped to reveal cryptic (only genetically distinct) species [248]. ...
Sabellida Levinsen, 1883 is a large morphologically uniform group of sedentary annelids commonly known as fanworms. These annelids live in tubes made either of calcareous carbonate or mucus with agglutinated sediment. They share the presence of an anterior crown consisting of radioles and the division of the body into thorax and abdomen marked by a chaetal and fecal groove inversion. This study synthesises the current state of knowledge about the diversity of fanworms in the broad sense (morphological, ecological, species richness), the species occurrences in the different biogeographic regions, highlights latest surveys, provides guidelines for identification of members of each group, and describe novel methodologies for species delimitation. As some members of this group are well-known introduced pests, we address information about these species and their current invasive status. In addition, an overview of the current evolutionary hypothesis and history of the classification of members of Sabellida is presented. The main aim of this review is to highlight the knowledge gaps to stimulate research in those directions.
... The organization of biodiversity in discrete entities as species, in opposition to a vision with which diversity represents a continuum, is a matter of debate in prokaryotes [17,[50][51][52]. The extreme position of researchers who retain the continuum as the best way to describe diversity in bacteria suggests we should simply use the strain as the basic unit [53,54] and, maybe, its phylogenetic position. ...
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.
... Nevertheless, molecular taxonomy approaches performed recently in a comprehensive sample of NEA Terebellides have substantially changed the understanding of the species diversity hidden within members of this genus in European waters. Studies by Nygren et al. (2018) and Lavesque et al. (2019) showed a number of genetic lineages, compatible with the species concept -independently evolving entities that are genetically (and phenotypically) distinct (Barraclough 2010). As a result, the total number of species in the NEA has increased dramatically from seven to 32 (Nygren et al. 2018;Lavesque et al. 2019), but some of these still remain unnamed or not formally described. ...
The number of described species of the genus Terebellides Sars, 1835 (Annelida, Trichobranchidae) has greatly increased in the last years, particularly in the North East Atlantic. In this context, this paper deals with several putative species recently delineated by molecular means within a well delimited clade of Terebellides. Species are characterised here by a combination of morphological characters, and a complementary nucleotide diagnostic approach. Three species were identified as the nominal species T. stroemii Sars, 1835, T. bigeniculatus Parapar, Moreira & Helgason, 2011 and T. europaea Lavesque et al., 2019. Five species are described as new: T. bakkeni sp. nov., T. kongsrudi sp. nov., T. norvegica sp. nov., T. ronningae sp. nov. and T. scotica sp. nov. The distinctive morphological characters refer to the branchial shape, absence or presence of papillae on lamellae of anterior margin of branchial dorsal lobes, absence or presence of ciliated papillae dorsal to thoracic notopodia, geniculate chaetae in one or two chaetigers, and the morphology of thoracic and abdominal uncini teeth. Furthermore, the description of T. bigeniculatus is revised and complemented after examination of type specimens. An updated identification key to all species of the genus in NE Atlantic and a proposal of a classification of different types of abdominal uncini to be used in taxonomy are also included.
