Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “speciation dynamics”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4Linked to original sources
PubMed2006

Kinetic effects of temperature on rates of genetic divergence and speciation.

Latitudinal gradients of biodiversity and macroevolutionary dynamics are prominent yet poorly understood. We derive a model that quantifies the role of kinetic energy in generating biodiversity. The model predicts that rates of genetic divergence and speciation are both governed by metabolic rate and therefore show the same exponential temperature dependence (activation energy of approximately 0.65 eV; 1 eV = 1.602 x 10(-19) J). Predictions are supported by global datasets from planktonic foraminifera for rates of DNA evolution and speciation spanning 30 million years. As predicted by the model, rates of speciation increase toward the tropics even after controlling for the greater ocean coverage at tropical latitudes. Our model and results indicate that individual metabolic rate is a primary determinant of evolutionary rates: approximately 10(13) J of energy flux per gram of tissue generates one substitution per nucleotide in the nuclear genome, and approximately 10(23) J of energy flux per population generates a new species of foraminifera.

Animals↗
PubMed2002

Invasion of vacant niches and subsequent sympatric speciation.

An individual-based simulation study was conducted to examine the population dynamics of 'invasion of a vacant niche' and subsequent speciation (by reproductive isolation) when food resources are randomly distributed spatially within the habitat and the frequencies of different food types are bimodally distributed (i.e. smaller and larger sizes of food being most abundant). The initially vacant niche was that of unused larger sizes of food. When phenotypic variation for resource use (i.e. food sizes) was small in the initial population, and each female could choose a mate from anywhere in the habitat, the population could not invade the vacant niche. But when the dispersal distance of the offspring and the area within which a female could choose a mate were small (i.e. the genetic neighbourhood size was small), the population could, in most cases, evolve to use both smaller and larger food sizes and form sister species sympatrically, with each species utilizing one of the two niches (small and large sizes of food). When phenotypic variation in resource use in the initial population was large, the population could, in most cases, invade the vacant niche by evolving to use both smaller and larger sizes of food. The probability of speciation increased as the dispersal distance of offspring decreased. The results indicate that populations whose individuals have small Wright's genetic neighbourhoods may often exploit a vacant niche and diversify sympatrically in the process.

Animals↗
PubMed2005

Habitat avoidance: overlooking an important aspect of host-specific mating and sympatric speciation?

Understanding speciation requires discerning how reproductive barriers to gene flow evolve between previously interbreeding populations. Models of sympatric speciation for phytophagous insects posit that reproductive isolation can evolve in the absence of geographic isolation as a consequence of an insect shifting and ecologically adapting to a new host plant. One important adaptation contributing to sympatric differentiation is host-specific mating. When organisms mate in preferred habitats, a system of positive assortative mating is established that facilitates sympatric divergence. Models of host fidelity generally assume that host choice is determined by the aggregate effect of alleles imparting positive preferences for different plant species. But negative effect genes for avoiding nonnatal plants may also influence host use. Previous studies have shown that apple and hawthorn-infesting races of Rhagoletis pomonella flies use volatile compounds emitted from the surface of fruit as key chemosensory cues to recognize and distinguish between their host plants. Here, we report results from field trials indicating that in addition to preferring the odor of their natal fruit, apple and hawthorn flies, and their undescribed sister species infesting flowering dogwood (Cornus florida), also avoid the odors of nonnatal fruit. We discuss the implications of nonnatal fruit avoidance for the evolutionary dynamics and genetics of sympatric speciation. Our findings reveal an underappreciated role for habitat avoidance as a potential postmating, as well as prezygotic, barrier to gene flow.

Animals↗
PubMed1992

Applications of nuclear analytical techniques in environmental research. Plenary lecture.

Among nuclear analytical techniques, neutron activation analysis (NAA) is particularly useful for environmental studies. It affords low detection limits for many elements, high specificity and few sources of systematic error, which means that high accuracy is attainable. Neutron activation analysis is particularly useful for trace and ultra-trace analysis of environmental samples (water, soils, rocks and biological material). In trace element work associated with pollution, instrumental NAA is a powerful technique for multi-element surveys, in particular when combined with other spectroscopic techniques. Nuclear techniques, as with most analytical techniques, cannot be used to distinguish between different physico-chemical forms of an element per se. When used in combination with appropriate separation techniques, however, nuclear techniques can provide valuable information about trace element speciation in environmental and biological systems. From dynamic tracer experiments, i.e., addition of chemically well defined labelled compounds to environmental systems, valuable information can be obtained on the distribution of species and on microchemical processes influencing the physico-chemical forms. In these laboratories, speciation studies on trace elements in natural waters have been carried out by using instrumental NAA in combination with physical separation techniques, such as dialysis and ultrafiltration, in situ and in the laboratory. Dynamic radiotracer experiments have provided important information about processes influencing the speciation of trace elements in aquatic systems. Sequential extraction techniques have proved to be useful in studies on sediments and soils when combined with NAA. Sequential extractions also provide significant information about the physico-chemical behaviour of radionuclides supplied to natural soils from the Chernobyl accident.

Environmental Pollution↗
PubMed2001

Thermally induced changes in metal solubility of contaminated soils is linked to mineral recrystallization and organic matter transformations.

Soils are biogeochemical systems under continual modification by biological and chemical processes. Trace element solid-solution partitioning is thus influenced by long-term changes to these solid phases. We study Pb, Cd, Zn, and Cu solution speciation and solid-phase dynamics in two soils of volcanic origin (Te Akatea and Egmont, high in noncrystalline aluminosilicates), an oxisol from Brazil (Oxisol, high in oxides of Al and Fe), and several sludge-treated soils (labeled NYS soils, high in organic materials). Total soluble (by ICP) and labile (by ASV) concentrations of Pb, Cd, Zn, and Cu were determined after incubation of the soils for about 1.5 yr at room (23 degrees C) and elevated (70 degrees C) temperatures. Changes occurring to the solid phases were monitored by FTIR and extraction with oxalate and pyrophosphate. It is shown that induced hydrolysis or decomposition of organic materials in soils results in increases in both labile and total soluble concentrations of Pb, Cd, Cu, and Zn in solution. Labile and total soluble concentrations of Cu and Zn increase concomitantly with dissolved organic carbon (DOC); the nonlabile soluble fraction also increases with increasing DOC. Similarly, the concentration of Cd and Pb in solution increases with increasing DOC; however, most soluble Cd and Pb is asv-labile. Only in the Egmont soil (mineralogy dominated by proto-imogolite allophane) was reduced Pb solubility observed after prolonged equilibration and heating. Lead solubility increased after partial crystallization of amorphous minerals in the Te Akatea and the Oxisol. Thus, for most of the metal-soil systems studied, prolonged thermal treatment at 70 degrees C increased total soluble and asv-labile metals, suggesting that aging effects on metals in contaminated soils could release metals to labile forms in some cases.

Metals, Heavy↗
PubMed2025

The effects of cryptic diversity on diversification dynamics analyses in Crocodylia.

Incomplete taxon sampling due to underestimation of present-day biodiversity biases diversification analysis by favouring slowdowns in speciation rates towards the recent time. For instance, in diversification dynamics studies in Crocodylia, long-term low net-diversification rates and slowdowns in speciation rates have been suggested to characterize crocodylian evolution. However, crocodylian cryptic diversity has never been considered. Here, we explore the effects of incorporating cryptic diversity into a diversification dynamics analysis of extant crocodylians. We inferred a time-calibrated cryptic-species-level phylogeny using cytochrome b sequences of 45 lineages compared with the formally recognized 26 crocodylian species. Diversification rate estimates using the cryptic-species-level phylogeny show increasing speciation and net-diversification rates towards the present time, which contrasts with previous findings. Cryptic diversity should be considered in future macroevolutionary analyses; however, the representation of cryptic extinct taxa represents a major challenge. Additionally, further investigation of crocodylian diversification dynamics under different underlying genomic data is encouraged upon advances in population genetics. Our case study adds to the diversification dynamics knowledge of extant taxa and demonstrates that cryptic species and robust taxonomic assessment are essential to study recent biodiversity dynamics with broad implications for evolutionary biology and ecology.

Animals↗
PubMed2006

Mechanisms of speciation and faunal enrichment in Atlantic parrotfishes.

Relationships based on mtDNA and nDNA sequences were used to assess effects of two major geographic barriers (the >30 myo Atlantic ocean and the approximately 11 myo Amazon-Orinoco outflow) on speciation among Atlantic parrotfishes (Sparisoma and Nicholsina). Allopatric distributions of sister taxa implicate isolating actions of both barriers in all recent speciation in these fishes, with no clear indications that any speciation resulted from other mechanisms. Molecular clock estimates of the timing of lineage splits indicate that both barriers acted by limiting dispersal well after they formed, although the Amazon barrier also may have been a vicariance agent. Fluctuations in sealevel, climate, and ocean-current dynamics over the past approximately 10 my likely produced marked variation in the effectiveness of both barriers, but particularly the Amazon barrier, allowing intermittent dispersal leading to establishment and allopatric speciation. A dynamic Amazon barrier represents a major engine of West Atlantic faunal enrichment that has repeatedly facilitated bidirectional dispersal, allopatric speciation, and remixing of the Caribbean and Brazilian faunas.

Animals↗
PubMed2004

Molecular evidence links cryptic diversification in polar planktonic protists to Quaternary climate dynamics.

It is unknown how pelagic marine protists undergo diversification and speciation. Superficially, the open ocean appears homogeneous, with few clear barriers to gene flow, allowing extensive, even global, dispersal. Yet, despite the apparent lack of opportunity for genetic isolation, diversity is prevalent within marine taxa. A lack of candidate isolating mechanisms would seem to favor sympatric over allopatric speciation models to explain the diversity and biogeographic patterns observed in the oceans today. However, the ocean is a dynamic system, and both current and past circulation patterns must be considered in concert to gain a true perspective of gene flow through time. We have derived a comprehensive picture of the mechanisms potentially at play in the high latitudes by combining molecular, biogeographic, fossil, and paleoceanographic data to reconstruct the evolutionary history of the polar planktonic foraminifer Neogloboquadrina pachyderma sinistral. We have discovered extensive genetic diversity within this morphospecies and that its current "extreme" polar affinity did not appear until late in its evolutionary history. The molecular data demonstrate a stepwise progression of diversification starting with the allopatric isolation of Atlantic Arctic and Antarctic populations after the onset of the Northern Hemisphere glaciation. Further diversification occurred only in the Southern Hemisphere and seems to have been linked to glacial-interglacial climate dynamics. Our findings demonstrate the role of Quaternary climate instability in shaping the modern high-latitude plankton. The divergent evolutionary history of N. pachyderma sinistral genotypes implies that paleoceanographic proxies based on this taxon should be calibrated independently.

Animals↗
PubMed2003

A dynamic numerical model to characterize labile metal complexes collected with diffusion gradient in thin films devices.

The speciation of metal species extracted by diffusion gradient in thin films (DGT) devices during experimental deployments in simple metal-ligand synthetic solutions was numerically modeled, analyzed at steady state, and simulated in the dynamic regime. The modeled speciation of two well-known complexes (Cu-citrate and Cu-EDTA) are in good agreement with experimental data obtained in NaNO3 solutions. For any metal complex, the rate at which the metal accumulates on the chelating resin is proportional to the concentration of free metal in solution plus a fraction of the metal complex concentration in solution equivalent to xiD(ML)/D(M). D(M) and D(ML) are the diffusion coefficients of the free and metal complex, respectively, and xi characterizes the complex lability: it is defined as the fraction of metal complex lost when diffusing from the bulk solution to the chelating resin. Numerical simulations were used to explore the variations of xi as a function of several operational and chemical parameters. Lability increases when the dissociation rate constant or the residence time of the metal complex within the hydrogel increase (i.e., by either increasing the thickness of the hydrogel or decreasing D(ML)). Overall, the fraction of metal complex extracted by the DGT decreases when D(ML) decreases, which confirms the ability of diffusion-restrictive hydrogels to separate the free metal fraction from complex solutions. Although the DGT model does not exactly comply with the voltammetric formalism, the lability criteria deltatau(1/2) used with voltammetric macroelectrodes is similar to the lability criteria xi, except that it is valid for high metal-ligand ratio. To determine free metal concentrations in aquatic systems using DGT, it is necessary to account for the presence of numerous ligands with different complexing properties. Soon, the numerical model will be improved to include additional ligands competing for the metal, and new experiments will be designed to discriminate between different labile complexes. Experimental results obtained with different DGT devices (of different hydrogel thicknesses, for example) could be interpreted in terms of conditional kinetic characteristics of the dominant metal-ligand complex in solution.

Chelating Agents↗
PubMed2005

Environmental microbes can speciate and cycle arsenic.

Naturally occurring arsenic is found predominantly as arsenate [As(V)] or arsenite [As(III)], and can be readily oxidized or reduced by microorganisms. Given the health risks associated with arsenic in groundwater and the interest in arsenic-active microorganisms, we hypothesized that environmental microorganisms could mediate a redox cycling of arsenic that is linked to their metabolism. This hypothesis was tested using an As(V) respiring reducer (strain Y5) and an aerobic chemoautotrophic As(II) oxidizer (strain OL1 ) both isolated from a Superfund site, Onondaga Lake, in Syracuse, NY. Strains were grown separately and together in sealed serum bottles, and the oxic/anoxic condition was the only parameter changed. Initially, under anoxic conditions when both isolates were grown together, 2 mM As(V) was stoichiometrically reduced to As(III) within 14 days. Following complete reduction, sterile ambient air was added and within 24 h As(III) was completely oxidized to As(V). The anoxic-oxic cycle was repeated, and sterile controls showed no abiotic transformation within the 28-day incubation period. These results demonstrate that microorganisms can cycle arsenic in response to dynamic environmental conditions, thereby affecting the speciation, and hence mobility and toxicity of arsenic in the environment.

Anaerobiosis↗
PubMed2002

Telomere dynamics, aneuploidy, stem cells, and cancer (review).

The real cause of genetic instability, which is the hall-mark of most cancers, is poorly understood. Specific gene mutations and acquired aneuploidy have been implicated as the root causes of genetic instability. Here we propose and cite evidence for the hypothesis that genetic instability of cancer cells is caused by telomere dynamics, erosion and/or amplification of the TTAGGG repeat sequences present at chromosomal termini. Since telomeres determine the domain of individual chromosomes within a nucleus and protect them from internal and external challenges, their erosion will destabilize the cell karyotype. Our hypothesis predicts that telomere dynamics provides the single unifying mechanism playing a major role in speciation, aging and cancer development. It was found that metastatic cancers of different histologic phenotypes, as well as mammalian taxa with active speciation and larger numbers of species exhibit amplification of their telomeric DNA as compared to non-metastatic counterpart cancers and taxa with only a limited number of species. The dynamic nature of this DNA can be found not only in the cancer cells but also in the peripheral lymphocytes of cancer patients. Human syndromes such as Down, Turner, Bloom, Werner, Fanconi, ataxia and many others, show aneuploidy and also are prone to develop various malignancies and premature aging. We have found that of all these syndromes have a reduced amount of telomeric DNA associated with specific mitotic catastrophes as compared to cells of age- and sex-matched normal individuals. From these and additional data generated by our group concerning speciation, aging and cancer karyotypes, we conclude that aneuploidy, which is responsible for birth defects, cancer initiation and is a major player in natural speciation, is a consequence of telomere dynamics. Because telomere reduction is linked to the aging process, which is a risk factor for cancer development in the human population, our hypothesis offers a unifying mechanism for the initiation of both hematologic and solid cancers, as well as for the origin of new species.

Aging↗
PubMed2006

What is a gene? From molecules to metaphysics.

Mendelian genes have become molecular genes, with increasing puzzlement about locating them, due to increasing complexity in genomic webworks. Genome science finds modular and conserved units of inheritance, identified as homologous genes. Such genes are cybernetic, transmitting information over generations; this too requires multi-leveled analysis, from DNA transcription to development and reproduction of the whole organism. Genes are conserved; genes are also dynamic and creative in evolutionary speciation-most remarkably producing humans capable of wondering about what genes are.

Adaptation, Biological↗
PubMed2006

Dispersal and vicariance: the complex evolutionary history of boid snakes.

Since the early 1970s, boine snakes (Boidae: Boinae) have served as a prime example of a group whose current distribution was shaped by vicariant events associated with the fragmentation of the supercontinent Gondwana. Early phylogenetic treatments of this group, and what were thought to be closely related groups (Erycinae and Pythoninae) based on morphological features, produced a relatively stable view of relationships that has strongly influenced subsequent molecular-based work. We examined 4307 base pairs (bp) of nucleotide sequence data obtained from five nuclear loci (c-mos, NT3, BDNF, RAG1, and ODC) and one mitochondrial locus (cyt b) for all genera of erycines and boines, plus representatives of other groups, including those previously thought to be closely allied with boines (Ungaliophiidae, Loxocemidae, Xenopeltidae, and Pythoninae). Our results suggest that the Boidae is not monophyletic, and its current division into three subfamilies (Erycinae, Boinae, and Pythoninae) does not accurately reflect evolutionary history. We find that the evolutionary relationships are better reflected by current geographic distributions and tectonic history than by the morphological characters that have long served as the foundation of boid phylogeny. Divergence time estimates suggest that this strong congruence between geography and phylogeny is the result of several vicariant and dispersal events in the Late Cretaceous and Paleocene associated with the fragmentation of the Gondwanan supercontinent. Our results demonstrate the importance of both vicariance and dispersal in shaping the global distributions of terrestrial organisms.

Animals↗
PubMed2006

Disassociation between weak sexual isolation and genetic divergence in a hermaphroditic land snail and implications about chirality.

Examination of the association between reproductive isolation and genetic divergence in a variety of organisms is essential for elucidating the mechanisms causing speciation. However, such studies are lacking for hermaphrodites. We measured premating (sexual) isolation in species pairs of the hermaphroditic land snail Albinaria and we compared it with their genetic divergence. We did not find substantial sexual isolation barriers between the species studied. The absence of strong sexual isolation between species implies its minor effect in the evolution of this genus, because distributional, population and life-history characteristics of Albinaria make mate-choice possibly redundant. Furthermore, we found disassociation between genetic divergence and sexual isolation, suggesting that they do not form necessarily a cause-effect duet. However, Albinaria voithii, the only dextral Albinaria species, shows strong sexual isolation against the other sinistral species. We discuss whether change in coiling either has triggered instantaneous speciation, or is an example of character displacement.

Animals↗
PubMed1998

Modelling Coevolution in Multispecies Communities.

We introduce the Webworld model, which links together the ecological modelling of food web structure with the evolutionary modelling of speciation and extinction events. The model describes dynamics of ecological communities on an evolutionary time-scale. Species are defined as sets of characteristic features, and these features are used to determine interaction scores between species. A simple rule is used to transfer resources from the external environment through the food web to each of the species, and to determine mean population sizes. A time step in the model represents a speciation event. A new species is added with features similar to those of one of the existing species and a new food web structure is than calculated. The new species may (i) add stably to the web, (ii) become extinct immediately because it is poorly adapted, or (iii) cause one or more other species to become extinct due to competition for resources. We measure various properties of the model webs and compare these with data on real food webs. These properties include the proportions of basal, intermediate and top species, the number of links per species and the number of trophic levels. We also study the evolutionary dynamics of the model ecosystem by following the fluctuations in the total number of species in the web. Extinction avalanches occur when novel organisms arise which are significantly better adapted than existing ones. We discuss these results in relation to the observed extinction events in the fossil record, and to the theory of self-organized criticality.Copyright 1998 Academic Press

Journal Article↗
PubMed2001

The influence of predator--prey population dynamics on the long-term evolution of food web structure.

We develop a set of equations to describe the population dynamics of many interacting species in food webs. Predator-prey interactions are nonlinear, and are based on ratio-dependent functional responses. The equations account for competition for resources between members of the same species, and between members of different species. Predators divide their total hunting/foraging effort between the available prey species according to an evolutionarily stable strategy (ESS). The ESS foraging behaviour does not correspond to the predictions of optimal foraging theory. We use the population dynamics equations in simulations of the Webworld model of evolving ecosystems. New species are added to an existing food web due to speciation events, whilst species become extinct due to coevolution and competition. We study the dynamics of species-diversity in Webworld on a macro-evolutionary time-scale. Coevolutionary interactions are strong enough to cause continuous overturn of species, in contrast to our previous Webworld simulations with simpler population dynamics. Although there are significant fluctuations in species diversity because of speciation and extinction, very large-scale extinction avalanches appear to be absent from the dynamics, and we find no evidence for self-organized criticality.

Animals↗
PubMed2005

The genetic basis for fruit odor discrimination in Rhagoletis flies and its significance for sympatric host shifts.

Rhagoletis pomonella (Diptera: Tephritidae) use volatile compounds emitted from the surface of ripening fruit as important chemosensory cues for recognizing and distinguishing among alternative host plants. Host choice is of evolutionary significance in Rhagoletis because these flies mate on or near the fruit of their respective host plants. Differences in host choice based on fruit odor discrimination therefore result in differential mate choice and prezygotic reproductive isolation, facilitating sympatric speciation in the absence of geographic isolation. We test for a genetic basis for host fruit odor discrimination through an analysis of F2 and backcross hybrids constructed between apple-, hawthorn-, and flowering dogwood-infesting Rhagoletis flies. We recovered a significant proportion (30-65%) of parental apple, hawthorn, and dogwood fly response phenotypes in F2 hybrids, despite the general failure of F1 hybrids to reach odor source spheres. Segregation patterns in F2 and backcross hybrids suggest that only a modest number of allelic differences at a few loci may underlie host fruit odor discrimination. In addition, a strong bias was observed for F2 and backcross flies to orient to the natal fruit blend of their maternal grandmother, implying the existence of cytonuclear gene interactions. We explore the implications of our findings for the evolutionary dynamics of sympatric host race formation and speciation.

Animals↗
PubMed2006

Speciation of the curium(III) ion in aqueous solution: a combined study by quantum chemistry and molecular dynamics simulation.

The structures of aquo complexes of the curium(III) ion have been systematically studied using quantum chemical and molecular dynamics (MD) methods. The first hydration shell of the Cm3+ ion has been calculated using density functional theory (DFT), with and without inclusion of the conductor-like polarizable continuum medium (CPCM) model of solvation. The calculated results indicate that the primary hydration number of Cm3+ is nine, with a Cm-O bond distance of 2.47-2.48 A. The calculated bond distances and the hydration number are in excellent agreement with available experimental data. The inclusion of a complete second hydration shell of Cm3+ has been investigated using both DFT and MD methods. The presence of the second hydration shell has significant effects on the primary coordination sphere, suggesting that the explicit inclusion of second-shell effects is important for understanding the nature of the first shell. The calculated results indicate that 21 water molecules can be coordinated in the second hydration shell of the Cm3+ ion. MD simulations within the hydrated-ion model suggest that the second-shell water molecules exchange with the bulk solvent with a lifetime of 161 ps.

Journal Article↗