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At least 19 recordsLinked to original sources
PubMed1992

Determination of trace element speciation and the role of speciation in aquatic toxicity.

Knowledge of trace element speciation in waters is essential to an understanding of aquatic toxicity and bioaccumulation, as well as to the partitioning of elements between water and colloidal and particulate phases. In natural waters, only very small percentages of the dissolved heavy metals, such as copper, lead cadmium or zinc, are present as free (aquo) metal ion; most of the metal is adsorbed to colloidal particles or combined in complexes. For aquatic toxicity studies, the aim of the speciation measurement is to determine the fraction of total dissolved metal (the 'toxic fraction') that will react with, and be transported across, a biological membrane such as a fish gill. In this review, a range of trace element speciation techniques is discussed and compared. A simple anodic stripping voltammetric method is recommended for the measurement of the fraction of electroactive metal in a sample, i.e. the fraction of total dissolved metal that can be deposited into a mercury electrode at the natural pH of the sample. The electroactive fraction is believed to approximate the toxic fraction. A rapid ion exchange method, suitable for field use, is proposed for the determination of the toxic fraction of copper in waters.

Adsorption↗
PubMedDate not supplied

[Populational speciation or chromosomal speciation? About the book of Jean de Grouchy "From the birth of species to the aberrations of life" (author's transl)].

According to Jean de Grouchy, the emergence of a new species is dependent on an "acceptable" chromosomic rearrangement, which passing from the heterozygous state (in the original bearer) to the homozygous state (in some of his enbred offspring) becomes definitively established and creates a population sexually isolated from its acestors. He is thus using the idea of karyotype to develop the typological theory put forward at the beginning of the century which postulates that a single mutant is at the origin of a new species. Although he gives an important place to chromosomic rearrangements in the sexual isolation of a new species, J. Ruffié demonstrates by arguments taken from population genetics and from the immunological polymorphism of wild populations that speciation is almost always the result of the evolution of an entire group, which, because of geographic isolation, drift, and differential selection, diverges from the ancestral branch and finally becomes totally incapable of breeding with it. He proposes a model of speciation which includes the two processes population and cytologic. At a first step, the group is isolated geographically and continues its independent evolution; the second step consists of chromosomic recombinations which render the sexual isolation complete. The modifications of the karyotype make the process of speciation irreversible.

Adaptation, Physiological↗
PubMed1977

Rapid speciation and chromosomal evolution in mammals.

To test the hypothesis that population subdivision into small demes promotes both rapid speciation and evolutionary changes in gene arrangement by inbreeding and drift, we estimated rates of speciation and rates of chromosomal evolution in 225 genera of vertebrates. Rates of speciation were estimated by considering the number of living species in each genus and the fossil record of each genus as well as information about extinction rates. Speciation rate was strongly correlated with rate of chromosomal evolution and average rates of speciation in lower vertebrate genera were one-fifth those in mammalian genera. Genera with high karyotypic diversity and rapid speciation rates may generally have small effective population size (Ne), whereas large Ne values may be associated with karyotypically uniform genera and slow rates of speciation. Speciation and chromosomal evolution seem fastest in those genera with species organized into clans or harems (e.g., some primates and horses) or with limited adult vagility and juvenile dispersal, patchy distribution, and strong individual territoriality (e.g., some rodents). This is consistent with the above hypothesis regarding the evolutionary importance of demes.

Animals↗
PubMed2024

Rapid vertebrate speciation via isolation, bottlenecks, and drift.

Speciation is often driven by selective processes like those associated with viability, mate choice, or local adaptation, and "speciation genes" have been identified in many eukaryotic lineages. In contrast, neutral processes are rarely considered as the primary drivers of speciation, especially over short evolutionary timeframes. Here, we describe a rapid vertebrate speciation event driven primarily by genetic drift. The White Sands pupfish (Cyprinodon tularosa) is endemic to New Mexico's Tularosa Basin where the species is currently managed as two Evolutionarily significant units (ESUs) and is of international conservation concern (Endangered). Whole-genome resequencing data from each ESU showed remarkably high and uniform levels of differentiation across the entire genome (global FST ≈ 0.40). Despite inhabiting ecologically dissimilar springs and streams, our whole-genome analysis revealed no discrete islands of divergence indicative of strong selection, even when we focused on an array of candidate genes. Demographic modeling of the joint allele frequency spectrum indicates the two ESUs split only ~4 to 5 kya and that both ESUs have undergone major bottlenecks within the last 2.5 millennia. Our results indicate the genome-wide disparities between the two ESUs are not driven by divergent selection but by neutral drift due to small population sizes, geographic isolation, and repeated bottlenecks. While rapid speciation is often driven by natural or sexual selection, here we show that isolation and drift have led to speciation within a few thousand generations. We discuss these evolutionary insights in light of the conservation management challenges they pose.

Animals↗
PubMed1986

Multilocus model of sympatric speciation. III. Computer simulations.

In the previous papers some analytical results were obtained for the limit stages of sympatric speciation. The present paper aims at finding the scope of validity for these results. The Monte Carlo computer model of this process was created and studied. We deal with two aspects of the speciation process: the development of reproductive isolation between the forming species and the extinction of the intermediate individuals. It has been shown that the advantage of the allele of reproductive isolation increases with the growth of its frequency. The extinction of the intermediates goes differently with various numbers of loci involved in speciation. If reproductive isolation is due to differences in two or four loci, then the completion of extinction of the intermediates requires the strongest disruptive selection, so that the necessary conditions for speciation found previously are also proved to be sufficient. But with eight and probably with a larger number of loci, the selection required to promote speciation in a population that is far from it is considerably stronger than selection needed at the last stage of speciation. Consequently, under some intensities of disruptive selection the final state of a population depends initial state. The conditions under which the stationary state of a population is characterized by bimodal distribution of phenotypes are also found.

Alleles↗
PubMed1992

A two-locus model of speciation.

Speciation is considered as the evolution of partial or complete cross-incompatibility between the carriers of genes (at a locus called "object locus") that distinguish the prospective species populations. The mating relations at the object locus are modified by the alleles at a second mating modifier locus. Based on a widely applicable concept of fitness and mating preference, it is shown that heterozygote disadvantage in fitness at the object locus is necessary for speciation, which corroborates Wallace's hypothesis. It is pointed out that the difference between sympatric and parapatric speciation essentially lies in the mechanisms stabilizing the polymorphism required at the object locus as a prerequisite for speciation. In the presence of recombination between the object and mating modifier locus speciation may be prevented by forces maintaining gametic phase imbalance between these loci such as can result from unidirectional gene flow between parapatric populations.

Adaptation, Physiological↗
PubMed1992

Speciation of trace elements in biological materials: trends and problems.

In the determination of trace elements in biological materials, speciation is of particular importance as the essential effects or toxicity of an element and its metabolic behaviour depend to a large extent on the chemical forms in which it is present in the organism. Speciation is relatively easy if a property of a particular compound can be measured directly in the sample without interference from the other components of the material, e.g., the enzymic activities of the metallo-enzymes. Another possibility for speciation is immunoassay, which likewise allows direct determination of a particular trace element. At present, however, with most trace elements both fractionation methods and analytical procedures have to be combined and speciation has to be carried out by determining the elemental content in the separated fractions. The methods and apparatus used in taking, storing and preparing the samples can, therefore, not be selected solely according to the requirements of trace element determination, but it is also essential to ensure that the biological structures of the components to be separated remain intact. In this work the need for speciation in the investigation of the toxic and essential effects of trace elements is shown with the help of some examples, and the problems that can occur in the various steps of sampling, storage and sample preparation are discussed.

Animals↗
PubMed1975

Presumptive speciation of Streptococcus bovis and other group D streptococci from human sources by using arginine and pyruvate tests.

A simplified method for speciation of group D streptococci is described. A total of 4,156 streptococcal isolates from human clinical material was tested for ability to hydrolyze esculin in the presence of 40% bile, ferment pyruvate, hydrolyze arginine, and grow in media containing 40% bile or 6.5% NaCl. Streptococci which hydrolyzed esculin in 40% bile, but which did not hydrolyze arginine, were also tested for their ability to ferment raffinose or sorbose. Sixty percent (2,503) of the isolates hydrolyzed esculin in the presence of 40% bile and were thus presumptively identified as group D. By application of the other criteria, 84% of these were speciated as Streptococcus faecalis, 7% were speciated as S. faecium, 6% were speciated as S. bovis, 2% were speciated as S. avium, and 1% were not identified. This scheme was shown to be both reliable and practical for use in the diagnostic laboratory. S. avium and S. bovis isolates were characterized, and 18 S. bovis isolates from patients with bacterial endocarditis were compared physiologically with 151 isolates of this species from other sources.

Arginine↗
PubMed1990

Evolutionary innovation in behavior and speciation: opportunities for behavioral neuroethology.

Populations of animals differentiate by speciation. How speciation takes place, for long a puzzle for evolutionary biologists, should be regarded as a research opportunity for neuroethologists and comparative behaviorists. It is now clear that behavior may play an important part in the process of speciation. The existence of sexually dimorphic anatomy and behavior in many animals has provided a rich subject for investigation by comparative neurobiologists and behaviorists, who emphasize analysis of proximate mechanisms that generate dimorphism in phenotype. However, sexual dimorphisms also figure prominently in the theory of sexual selection. Sexual selection is viewed as a primary behavioral mechanism in the process of speciation. Some examples of 'explosive' speciation are presented, and the putative role that sexual selection plays in these cases is reviewed. A consideration of any evolutionary selective process must include genetics, and I will briefly summarize studies that indicate that even complex behavioral systems such as sexual selection, which sociobiologists refer to as a 'strategy', can have a relatively simple genetic basis.

Animals↗
PubMed2025

Are We Witnessing a Speciation Continuum? Evidence From Current and Past Gene Flow in the Genus Oritrophium s.s. (Asteraceae) From the Tropical High Andes.

Determining species boundaries is key for appropriately assessing biodiversity. However, the continuity of the speciation process makes delimiting species a difficult task, especially for recently diverged taxa. Furthermore, past introgression may leave traces that result in reticulate evolutionary patterns, challenging the estimation of species relationships. The fastest-evolving biodiversity hotspot on Earth is the Páramo. Its flora in the tropical high Andes is known for extraordinarily high species richness and endemism. However, the recent origin, fast diversification and complex taxonomy of many genera challenge species delimitation and phylogenetic reconstruction. In this study, we reconstructed phylogenetic relationships and addressed the role of introgression in the diversification of Oritrophium s.s. (Asteraceae) based on phylogenomic data. We combined genomic, phenotypic and ecological data to test species boundaries and compared trajectories across the speciation continuum within the taxonomically complex 'O. peruvianum group'. We found that historical introgression played an important role in the evolution of Oritrophium s.s., and many of the taxa within the 'O. peruvianum group' are at various stages of speciation. These results highlight the importance of testing for introgression to understand the diversification of recently evolved groups. Likewise, they suggest that heterogeneous speciation trajectories associated with geographic isolation and secondary contact, possibly during the Pleistocene, contributed to plant diversity in the tropical high Andes.

Genetic Speciation↗
PubMed1992

NSPEC: a chemical speciation program for personal computers.

The details of a computer program, NSPEC, which simulates chemical speciation in aqueous systems, are presented. NSPEC has been designed explicitly for the IBM PC family of computers and is a departure from normal speciation programs in that it is controlled through interaction with a series of menus. The program is more user-friendly than other comparable speciation programs, can write the results files in formats suitable for importing into other programs, and, in many instances gives results faster than speciation programs running on microcomputers.

Algorithms↗
PubMed1990

Biotoxicity of mercury as influenced by mercury(II) speciation.

Integration of physicochemical procedures for studying mercury(II) speciation with microbiological procedures for studying the effects of mercury on bacterial growth allows evaluation of ionic factors (e.g., pH and ligand species and concentration) which affect biotoxicity. A Pseudomonas fluorescens strain capable of methylating inorganic Hg(II) was isolated from sediment samples collected at Buffalo Pound Lake in Saskatchewan, Canada. The effect of pH and ligand species on the toxic response (i.e., 50% inhibitory concentration [IC50]) of the P. fluorescens isolated to mercury were determined and related to the aqueous speciation of Hg(II). It was determined that the toxicities of different mercury salts were influenced by the nature of the co-ion. At a given pH level, mercuric acetate and mercuric nitrate yielded essentially the same IC50s; mercuric chloride, on the other hand, always produced lower IC50s. For each Hg salt, toxicity was greatest at pH 6.0 and decreased significantly (P = 0.05) at pH 7.0. Increasing the pH to 8.0 had no effect on the toxicity of mercuric acetate or mercuric nitrate but significantly (P = 0.05) reduced the toxicity of mercuric chloride. The aqueous speciation of Hg(II) in the synthetic growth medium M-IIY (a minimal salts medium amended to contain 0.1% yeast extract and 0.1% glycerol) was calculated by using the computer program GEOCHEM-PC with a modified data base. Results of the speciation calculations indicated that complexes of Hg(II) with histidine [Hg(H-HIS)HIS+ and Hg(H-HIS)2(2+)], chloride (HgCl+, HgCl2(0), HgClOH0, and HgCl3-), phosphate (HgHPO4(0), ammonia (HgNH3(2+), glycine [Hg(GLY)+], alanine [Hg(ALA)+], and hydroxyl ion (HgOH+) were the Hg species primarily responsible for toxicity in the M-IIY medium. The toxicity of mercuric nitrate at pH 8.0 was unaffected by the addition of citrate, enhanced by the addition of chloride, and reduced by the addition of cysteine. In the chloride-amended system, HgCl+, HgCl2(0), and HgClOH0 were the species primarily responsible for observed increases in toxicity. In the cysteine-amended system, formation of Hg(CYS)2(2-) was responsible for detoxification effects that were observed. The formation of Hg-citrate complexes was insignificant and had no effect on Hg toxicity.

Biological Assay↗
PubMed2025

Host-Associated Genetic Differentiation in the Face of Ongoing Gene Flow: Ecological Speciation in a Pathogenic Parasite of Freshwater Fish.

Adaptive evolution in response to varying environments, leading to population divergence, is among the most intriguing processes of speciation. However, the extent to which these adaptive processes effectively drive population divergence amidst ongoing gene flow remains controversial. Our study addresses this by analyzing population genetic structure, gene flow, and genomic divergence between lineages of a tapeworm parasite (Ligula intestinalis) isolated from sympatric fish hosts. This parasite, which must overcome host immunological defenses for successful infection, significantly impacts host health. Utilizing genome-wide Single Nucleotide Polymorphisms (SNPs) and transcriptome data, we investigated whether host species impose distinct selection pressures on parasite populations. Genetic clustering analyses revealed clear divergence, with parasites from bream (Abramis brama) forming a distinct genetic cluster separate from those infecting roach (Rutilus rutilus), rudd (Scardinius erythrophthalmus), and bleak (Alburnus alburnus). Demographic modeling indicated isolation with continuous gene flow as the most plausible scenario for this divergence. Selection analyses identified 896 SNPs under selection, displaying low to moderate nucleotide diversity and genetic divergence compared with neutral loci. Transcriptome profiling supported these findings, revealing distinct gene expression profiles between parasite populations. Examination of selected SNPs and differentially expressed genes identified candidate genes linked to immune evasion mechanisms, potentially driving ecological speciation. This research highlights the interplay of host specificity, population demography, and disruptive selection in ecological speciation. By dissecting genomic factors, our study improves the understanding of mechanisms facilitating population divergence despite ongoing gene flow.

Animals↗
PubMed2025

Rapid Divergence of Visual Systems and Signaling Traits to Contrasting Light Regimes During Early Speciation of African Crater Lake Cichlid Fish.

Sensory adaptation is widely hypothesized to drive ecological speciation, yet empirical evidence from natural populations undergoing early stage divergence remains limited. In Lake Masoko, a young crater lake in East Africa, the haplochromine cichlid Astatotilapia calliptera is undergoing early stage sympatric speciation into shallow-water littoral and deep-water benthic ecotypes that experience contrasting light environments. Here, we integrate retinal transcriptomics, phenotypic analyses, and visual modeling to uncover rapid sensory divergence associated with this ecological transition. We find striking shifts in cone opsin expression, with the benthic ecotype exhibiting a switch from short-wavelength sensitive SWS2B to SWS2A and an overall narrowing of cone sensitivity toward the center of the light spectrum, consistent with changes in deep-water light environment. In contrast, coding sequence variation in opsin genes was limited and no significant differences in allele frequencies were detected across nine polymorphic sites, pointing to expression regulation as the primary axis of early divergence in visual systems. In parallel, we observed divergence in male signaling traits, with benthic males displaying deeper red egg-spots, aligning with predictions from visual modeling of signal efficiency in different light environments. These results demonstrate rapid transcriptomic and phenotypic divergence in associated signaling traits-within ∼1,000 years-supporting a potential role for regulatory evolution in sensory adaptation during early ecological speciation.

Animals↗
PubMed2026

Phylogenomic evidence provides insights into the phylogeny and speciation patterns in the subgenus Caloscordum (Allium, Amaryllidaceae).

Phylogenomics with abundant informative sites offers a powerful means for elucidating complex diversification history. Here, we collected 22 samples from 18 populations representing all species of subgenus Caloscordum (Allium). Using transcriptome and whole-genome resequencing data, we generated 1755 low-copy nuclear genes and 81 plastid genes. By integrating morphological and phylogenomic evidence, we clarified the subgenus's complex evolutionary histories and speciation patterns. A total of 18 morphological characteristics were analysed, with a taxonomic framework established. Our analyses resolved robust species relationships despite detecting extensive phylogenetic discordances, which were attributed to incomplete lineage sorting (ILS) and hybridization. Specifically, our results suggest that A. inutile originated via rapid budding speciation from the widespread A. tubiflorum. This process likely coincided with mid-Pleistocene glacial-interglacial cycles and may have been reinforced by geographic isolation and ecological adaptation. In contrast, the sole tetraploid species, A. peikingense, was confirmed to be of hybrid origin, derived from A. neriniflorum and A. tubiflorum. This allopolyploidization event appears to have been facilitated by secondary contact between the parent species, which was likely associated with climatic oscillations within the 35° N-45° N arid belt. Overall, our findings elucidate the intricate speciation patterns within Caloscordum and highlight how the interplay of polyploidization, ecological isolation, and tectonic uplift-driven aridification has shaped plant diversity in East Asia.

Phylogeny↗
PubMed2025

Aplf/Dna2 variants drive chromosomal fission and accelerate speciation in zokors.

Chromosomal fissions and fusions are common, yet the molecular mechanisms and implications in speciation remain poorly understood. Here, we confirm a fission event in one zokor species through multiple-omics and functional analyses. We traced this event to a mutation in a splicing enhancer of the DNA repair gene Aplf in the fission-bearing species, which caused exon skipping and produced a truncated protein that disrupted DNA repair. An intronic deletion in Dna2, known to facilitate neo-telomere formation when knocked out, reduced gene activity. These variants collectively drove chromosomal fission in this zokor species. The newly formed chromosome became fixed due to carrying essential genes and strong selective pressure. While geographic isolation likely initiated the divergence of this species and the sister one, the fission event and associated decline at the chromosome level in gene flow probably exacerbated the speciation process. Our work elucidates the genetic basis of chromosomal fission and underscores its role in speciation dynamics.

Multiomics↗
PubMed1992

Change of speciation of Cu(II) in growth medium due to uptake of ammonia by Pseudomonas testosteroni during growth.

Growth of Pseudomonas testosteroni in a medium containing 1 mM Cu(II) causes a color change from blue to green. The spectrum of the supernatant solution from the blue culture shows an absorption at 660 nm, identical to that of 1 mM [Cu(II)] in the medium. The green supernatant solution shows a UV absorption, which tails into the visible and so is responsible for the green color, and a d-d absorption at 720 nm. The absorption at 660 nm for the blue supernatant solution is probably due to [Cu(NH3)3(H2O)3]2+. Growth of the organism causes loss of ammonia and a speciation change to [CU(NH3)2(H2O)4]2+, with a shift in absorption maximum from 660 to 720 nm. These conclusions are based upon the spectra of known aquaammine complexes of Cu(II) and calculations of the speciation of Cu(II) before and after growth. Change in metal speciation owing to nutrient uptake by an organism does not appear to have been recognized previously.

Ammonia↗
PubMedDate not supplied

Speciation of chromium in plasma and liver tissue of endstage renal failure patients on continuous ambulatory peritoneal dialysis.

This work is a first attempt to determine the speciation of Cr in human plasma. With the aid of in vitro and in vivo 51Cr-labeled experiments, it was possible to develop the necessary biochemical techniques for the separation of the plasma proteins. Further work will use real samples, taking care to avoid contamination of the various fractions and to preserve the original binding of the Cr to the specific plasma compounds. In a first attempt on the distribution of Cr over the different organelles of liver tissue, work will be restricted to in vivo labeled experiments with rats. The procedure to do the speciation work seems so elaborate that it may be impossible ever to achieve the contemplated speciation of Cr in human liver tissue by subcellular fractionation.

Adult↗