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 271 records · Page 15Linked to original sources
PubMed2000

The impact of Pu speciation on distribution coefficients in Mayak soil.

To assess the long-term consequences when radionuclides are released into the environment, information on the source term, transport and transformation processes, interaction with soils (KD) and biological uptake (CF) is needed. Among the artificial radionuclides released to the environment by nuclear activities, the transuranium elements are a major concern, due to very long half-lives and their accumulation in bone as well as high radiotoxicity. Plutonium has been produced in greater quantity than other transuranic elements, however, environmental assessments are complicated by the complex environmental behaviour. Physico-chemical forms of Pu will determine the interactions with soils and, thus, the degree to which soils can act as a sink or a potential diffuse source of contaminants. In the present work, dynamic tracer experiments have been performed where different Pu-species are added to a 'Mayak soil-rainwater system' to obtain information on KD values. After a defined contact time, the samples where then sequentially extracted and results are used in a dynamic box model to estimate interaction and fixation rates. The interaction of all Pu-species with soils seems to be rapid and follows a two-step reaction. Up to contact times of a few weeks, the KD for Pu(III,IV) (730 +/- 240 l/kg) is approximately one order of magnitude higher than for Pu(V,VI) (90 +/- 20 l/kg) and Pu(III,IV)-organic (40-60 l/kg). After 3 months contact time, the KD in only the two organic-bound Pu-species were significantly lower. This shows that the initial association with the soil is dependent on the Pu-species in the rainwater. After only 1 h of contact, between 33 and 40% of the plutonium was strongly bound to the soil components, i.e. only extractable with strong HNO3. The extraction of soil-bound Pu followed a similar pattern for all the original species, suggesting that the next step of Pu interaction mechanism with soil was rather independent of the original species. For both the Pu(V,VI) and Pu-organic species, the rainwater-desorption extract gave consistently higher KD values than that calculated from the rainwater-sorption data; whereas for Pu(III,IV), desorption KD values were more similar to sorption KD values. This supports the suggestion that the observed difference in Pu adsorption to soils reflects Pu-speciation in the water soluble phase, and that actual soil-Pu interactions are rather independent of the original speciation. Modelling of the extraction data show a different in association rate for the different Pu species, where the Pu(III,IV) has the fastest association rate as expected.

Absorption↗
PubMed2003

Sexual dimorphism and adaptive speciation: two sides of the same ecological coin.

Models of adaptive speciation are typically concerned with demonstrating that it is possible for ecologically driven disruptive selection to lead to the evolution of assortative mating and hence speciation. However, disruptive selection could also lead to other forms of evolutionary diversification, including ecological sexual dimorphisms. Using a model of frequency-dependent intraspecific competition, we show analytically that adaptive speciation and dimorphism require identical ecological conditions. Numerical simulations of individual-based models show that a single ecological model can produce either evolutionary outcome, depending on the genetic independence of male and female traits and the potential strength of assortative mating. Speciation is inhibited when the genetic basis of male and female ecological traits allows the sexes to diverge substantially. This is because sexual dimorphism, which can evolve quickly, can eliminate the frequency-dependent disruptive selection that would have provided the impetus for speciation. Conversely, populations with strong assortative mating based on ecological traits are less likely to evolve a sexual dimorphism because females cannot simultaneously prefer males more similar to themselves while still allowing the males to diverge. This conflict between speciation and dimorphism can be circumvented in two ways. First, we find a novel form of speciation via negative assortative mating, leading to two dimorphic daughter species. Second, if assortative mating is based on a neutral marker trait, trophic dimorphism and speciation by positive assortative mating can occur simultaneously. We conclude that while adaptive speciation and ecological sexual dimorphism may occur simultaneously, allowing for sexual dimorphism restricts the likelihood of adaptive speciation. Thus, it is important to recognize that disruptive selection due to frequency-dependent interactions can lead to more than one form of adaptive splitting.

Adaptation, Biological↗
PubMed2005

Out of Cuba: overwater dispersal and speciation among lizards in the Anolis carolinensis subgroup.

Overwater dispersal and subsequent allopatric speciation contribute importantly to the species diversity of West Indian Anolis lizards and many other island radiations. Here we use molecular phylogenetic analyses to assess the contribution of overwater dispersal to diversification of the Anolis carolinensis subgroup, a clade comprising nine canopy-dwelling species distributed across the northern Caribbean. Although this clade includes some of the most successful dispersers and colonists in the anole radiation, the taxonomic status and origin of many endemic populations have been ambiguous. New mitochondrial and nuclear DNA sequences from four species occurring on small islands or island banks (Anolis brunneus, Anolis longiceps, Anolis maynardi, Anolis smaragdinus) and one species from the continental United States (A. carolinensis) are presented and analysed with homologous sequences sampled from related species on Cuba (Anolis allisoni and Anolis porcatus). Our analyses confirm that all five non-Cuban species included in our study represent distinct, independently evolving lineages that warrant continued species recognition. Moreover, our results support Ernest Williams's hypothesis that all of these species originated by overseas colonization from Cuban source populations. However, contrary to Williams's hypothesis of Pleistocene dispersal, most colonization events leading to speciation apparently occurred earlier, in the late Miocene-Pliocene. These patterns suggest that overwater dispersal among geologically distinct islands and island banks is relatively infrequent in anoles and has contributed to allopatric speciation. Finally, our results suggest that large Greater Antillean islands serve as centres of origin for regional species diversity.

Animals↗
PubMed2000

The impact of plutonium speciation on the distribution coefficients in a sediment-sea water system, and radiological assessment of doses to humans.

When radionuclides are released from a source into the marine environment, the assessment of long term consequences to humans depends on information on the source term, transport in water, interactions with sediments (KD) and biological uptake (CF). Sensitivity analysis of assessment models demonstrates that KD is one of the most sensitive parameters contributing to large uncertainties in the assessment. Furthermore, the interaction of Pu-species with sediments is a time and temperature dependent process. The distribution coefficient, Bq kg(-1) sediment per Bq L(-1) sea water, increases with time until pseudo-equilibrium/equilibrium is reached (KD). Thus, the contact time between contaminated sea water and sediments should be taken into account in dispersion and dose assessment models. In the present work, dynamic tracer experiments have been performed where different Pu-species are added to a sediment-sea water system to obtain information on KD's. After a defined contact time, the samples have been sequentially extracted to determine mobile and bound fractions. The results indicate that the distribution coefficient, KD, for plutonium depends on Pu-species in question. Thus, sediments act as a sink for Pu(III, IV) (high KD), while Pu(III, IV)-organic and Pu(V, VI) should be considered more mobile (low KD). Furthermore, the interaction with inert fractions obtained from sequential extraction depends less on Pu-species but increase with time. For short time interactions, species-specific time functions rather than KD constants should be applied in assessment models. When the accepted KD (10(5) L kg(-1)) is implemented in the model, the estimated collective dose is about 8 x 10(-4) person-Sv, i.e., a factor of about 2 lower than for Pu(III, IV)-organic and Pu(V, VI). So changes in KD have an impact on the assessment of collective dose received from a potential release of plutonium from fallout, reactor accidents, etc., which underlines the need for more detailed studies on speciation, kinetics, and KD's in different sediment-sea water systems.

Acetates↗
PubMed2006

Optimal gene trees from sequences and species trees using a soft interpretation of parsimony.

Gene duplication and gene loss as well as other biological events can result in multiple copies of genes in a given species. Because of these gene duplication and loss dynamics, in addition to variation in sequence evolution and other sources of uncertainty, different gene trees ultimately present different evolutionary histories. All of this together results in gene trees that give different topologies from each other, making consensus species trees ambiguous in places. Other sources of data to generate species trees are also unable to provide completely resolved binary species trees. However, in addition to gene duplication events, speciation events have provided some underlying phylogenetic signal, enabling development of algorithms to characterize these processes. Therefore, a soft parsimony algorithm has been developed that enables the mapping of gene trees onto species trees and modification of uncertain or weakly supported branches based on minimizing the number of gene duplication and loss events implied by the tree. The algorithm also allows for rooting of unrooted trees and for removal of in-paralogues (lineage-specific duplicates and redundant sequences masquerading as such). The algorithm has also been made available for download as a software package, Softparsmap.

Algorithms↗
PubMed2006

Characterization of H+ and Cd2+ binding properties of the bacterial exopolysaccharides.

The proton and Cd binding capacities of microbially produced exopolysaccharides, EPS, were quantified by the determination of stability constants and the concentration of complexing sites using H(+) or Cd(2+) selective electrodes in dynamic titrations. The influence of ionic strength, pH and the Cd to EPS ratio was evaluated over large concentration ranges. The applicability of the non-ideal competitive adsorption isotherm combined with a Donnan electrostatics approach was tested with respect to the EPS. Proton and cadmium binding data were compared with literature data examining other ubiquitous environmental ligands including humic substances, alginate, bacteria, etc. Subsequent modelling of Cd speciation in aquatic (fresh and marine waters) and soil systems suggested that the exopolysaccharides would play non-negligible role, under most conditions. The quantitative information provided in this paper thus represents an important advance in our understanding of Cd transport, bioavailability and impact in aquatic and terrestrial systems.

Cadmium↗
PubMed1993

Recent advances in epidemiological field techniques in filariasis.

There have been very few advances in epidemiological field techniques for filariasis in recent years. Advances in other areas of study of filariasis have been published and a summary of some of those which have some application to field technology will be given. Studies on vectors involving host influences on the development of filariae and the use of DNA probes for vector speciation were reported as well as the development of techniques that yielded species-specific identification of larvae in mosquito vectors. Experiments on animal transmission potentials also have been described. Mathematical models are becoming popular for various biological systems. It is postulated that models will enable workers to make predictions on prevalence of diseases and effect of control measures. A model has been proposed for bancroftian filariasis transmission dynamics and frequency distribution of microfilariae in blood samples. Other statistical methodologies have been published relating to age and sex distribution and frequency distribution and one suggested that females have increased resistance to filariasis, especially in the reproductive years. Advances in diagnostic technologies are highly relevant to the epidemiology of filariasis. The development of antibody and especially antigen detection systems using monoclonal antibodies, DNA probes, and polymerase chain reactions, etc, will make a significant impact on the identification of infected persons. Findings along other lines may also have application to field epidemiology. The quantitative blood count (QBC) acridine orange hematocrit tube has also been found to be of value in diagnosis. Elevated levels of ecdysteroids found in other filarial infections should be tested in cases of lymphatic filariasis.

Animals↗
PubMedDate not supplied

Tripropyltin(iv) complexes with some selected bioligands in 50% v/v dioxane/water mixture.

The interaction of the tri-n-propyltin(IV) (TPT) with some selected bioligands having a variety of model functional groups were investigated using potentiometric technique at 25 degrees C and 0.1 M ionic strength in 50% v/v dioxane/water mixture. TPT is hydrolyzed to give [(C3H7)3SnOH], [(C3H7)3Sn(OH)2]-, and [((C3H7)3Sn)2OH]+. Amino acids and DNA constituents form 1:1 and 1:2 complexes. Peptides form 1:1 complexes and the corresponding deprotonated amide species. The protonated complexes are formed with amino acids, peptides and some DNA constituents. The hydrolysis constants and the stepwise formation constants of the complexes formed in solution were calculated using the nonlinear least-square program MINIQUAD-75. The participation of different ligand functional groups in binding to organotin is discussed. The speciation diagrams of the various complex species were evaluated as a function of pH.

Amino Acids↗
PubMed2005

Evolution driven by differential dispersal within a wild bird population.

Evolutionary theory predicts that local population divergence will depend on the balance between the diversifying effect of selection and the homogenizing effect of gene flow. However, spatial variation in the expression of genetic variation will also generate differential evolutionary responses. Furthermore, if dispersal is non-random it may actually reinforce, rather than counteract, evolutionary differentiation. Here we document the evolution of differences in body mass within a population of great tits, Parus major, inhabiting a single continuous woodland, over a 36-year period. We show that genetic variance for nestling body mass is spatially variable, that this generates different potential responses to selection, and that this diversifying effect is reinforced by non-random dispersal. Matching the patterns of variation, selection and evolution with population ecological data, we argue that the small-scale differentiation is driven by density-related differences in habitat quality affecting settlement decisions. Our data show that when gene flow is not homogeneous, evolutionary differentiation can be rapid and can occur over surprisingly small spatial scales. Our findings have important implications for questions of the scale of adaptation and speciation, and challenge the usual treatment of dispersal as a force opposing evolutionary differentiation.

Aging↗
PubMed1985

Interaction of selection and biased gene conversion in a multigene family.

A model of the evolutionary dynamics of a multigene family in a finite population under the joint effects of selection and (possibly biased) gene conversion is analyzed. It is assumed that the loss or fixation of a polymorphism at any particular locus in the gene family occurs on a much faster time scale than the introduction of new alleles to a monomorphic locus by gene conversion. A general formula for the fixation of a new allele throughout a multigene family for a wide class of selection functions with biased gene conversion is given for this assumption. Analysis for the case of additive selection shows that (i) unless selection is extremely weak or bias is exceptionally strong, selection usually dominates the fixation dynamics, (ii) if selection is very weak, then even a slight conversion bias can greatly alter the fixation probabilities, and (iii) if both selection and conversion bias are sufficiently small, the substitution rate of new alleles throughout a multigene family is approximately the single locus mutation rate, the same result as for neutral alleles at a single-copy gene. Finally, I analyze a fairly general class of underdominant speciation models involving multigene families, concluding for these models under weak conversion that although the probability of fixation may be relatively high, the expected time to fixation is extremely long, so that speciation by "molecular drive" is unlikely. Furthermore, speciation occurs faster by fixing underdominant alleles of the same effect at single-copy genes than by fixing the same number of loci in a single multigene family under the joint effects of selection, conversion, and drift.

Alleles↗
PubMed2005

Patterns of cladogenesis in the venomous marine gastropod genus Conus from the Cape Verde islands.

Isolated oceanic archipelagos are excellent model systems to study speciation, biogeography, and evolutionary factors underlying the generation of biological diversity. Despite the wealth of studies documenting insular speciation, few of them focused on marine organisms. Here, we reconstruct phylogenetic relationships among species of the marine venomous gastropod genus Conus from the Cape Verde archipelago. This small island chain located in the Central Atlantic hosts 10% of the worldwide species diversity of Conus. Analyses were based on mtDNA sequences, and a novel nuclear marker, a megalin-like protein, member of the low-density lipoprotein receptor gene family. The inferred phylogeny recovered two well-defined clades within Conus. One includes Cape Verde endemic species with larger shells, known as the "venulatus" complex together with C. pulcher from the Canary Islands. The other is composed of Cape Verde endemic and West Africa and Canary Island "small" shelled species. In both clades, nonendemic Conus were resolved as sister groups of the Cape Verde endemics, respectively. Our results indicate that the ancestors of "small" and "large" shelled lineages independently colonized Cape Verde. The resulting biogeographical pattern shows the grouping of most Cape Verde endemics in monophyletic island assemblages. Statistical tests supported a recent radiation event within the "small shell" clade. Using a molecular clock, we estimated that the colonization of the islands by the "small" shelled species occurred relatively close to the origin of the islands whereas the arrival of "large" shelled Conus is more recent. Our results suggest that the main factor responsible for species diversity in the archipelago may be allopatric speciation promoted by the reduced dispersal capacity of nonplanktonic lecithotrophic larvae.

Africa, Western↗
PubMed2004

Influence of volcanic activity on the population genetic structure of Hawaiian Tetragnatha spiders: fragmentation, rapid population growth and the potential for accelerated evolution.

Volcanic activity on the island of Hawaii results in a cyclical pattern of habitat destruction and fragmentation by lava, followed by habitat regeneration on newly formed substrates. While this pattern has been hypothesized to promote the diversification of Hawaiian lineages, there have been few attempts to link geological processes to measurable changes in population structure. We investigated the genetic structure of three species of Hawaiian spiders in forests fragmented by a 150-year-old lava flow on Mauna Loa Volcano, island of Hawaii: Tetragnatha quasimodo (forest and lava flow generalist), T. anuenue and T. brevignatha (forest specialists). To estimate fragmentation effects on population subdivision in each species, we examined variation in mitochondrial and nuclear genomes (DNA sequences and allozymes, respectively). Population subdivision was higher for forest specialists than for the generalist in fragments separated by lava. Patterns of mtDNA sequence evolution also revealed that forest specialists have undergone rapid expansion, while the generalist has experienced more gradual population growth. Results confirm that patterns of neutral genetic variation reflect patterns of volcanic activity in some Tetragnatha species. Our study further suggests that population subdivision and expansion can occur across small spatial and temporal scales, which may facilitate the rapid spread of new character states, leading to speciation as hypothesized by H. L. Carson 30 years ago.

Animals↗
PubMed1992

Dynamics of coagulase-negative staphylococcal colonization in patients and employees in a surgical intensive care unit.

Because there is little information about the frequency of carriage of various species of coagulase-negative staphylococci (CNS) in hospital staff, we prospectively investigated nasal CNS in patients and personnel in a Surgical Intensive Care Unit (SICU). The majority of CNS from personnel were Staphylococcus epidermiditis. The CNS species from patients on admission were more diverse and included multiply antibiotic-resistant S. haemolyticus. Patients' CNS became more like CNS colonizing personnel after admission with respect to both antimicrobial susceptibility and speciation. Plasmid and antibiotic sensitivity profiles of S. epidermidis resistant to multiple antibiotics from five patients were identified as those from one employee, but there was no evidence that this was of clinical significance. A variety of factors influence nasal colonization by CNS in SICUs. The nasal CNS of patients change after admission and may become more resistant and less diverse. The factors influencing changes in the antibiotic susceptibility and the aetiology of CNS infection require further study.

Anti-Bacterial Agents↗
PubMed2001

The systematic study of aluminium speciation in medium concentrated aqueous solutions.

Industrial applications and environmental problems involving the aqueous chemistry of aluminium require an understanding of the speciation of this metal ion at a wide range of concentrations. The formation of polynuclear species is of special interest due to the complexity of the hydrolysis mechanisms and the diversity of the hydrolysis products. Kinetic aspects of speciation are also important considering the different stability ranges of polycationic species formed during the hydrolysis process. In the present paper we report results of systematic studies on the formation of aluminium polycations at room temperature. Automated potentiometric titrations have been used to study the hydrolysis of aluminium-ions in solutions (0.01-0.2 M) on a short time scale (2 min between titrant additions). (27)Al NMR spectroscopy and dynamic light scattering have been used for investigations on a longer time scale (24 h). The effects of alkali strength (KOH, NH(4)OH and KHCO(3)) and concentration (0.45-2.0 M), counterion identity (Cl(-), NO(3)(-), SO(4)(2-)) and ionic strength have been investigated. Optimum conditions for the generation of Al(13)-mer are proposed on short and long time scales. On a short time scale, aluminium chloride and nitrate should be used as starting materials, KOH and KHCO(3) should be used for hydrolysis and experiments conducted at low ionic strength. For solutions that have been left to age, there is a considerable hydrolysis window that can be used to generate significant quantities of the Al(13)-mer that vary little with the alkali used. Al(13)-mer species are not generated from alum as the precursor. The presence of sulphate ions alters the pathway of aluminium polymerisation to form polymeric and solid materials. On the basis of the potentiometric titration data, dynamic light scattering and (27)Al NMR measurements evidence is provided for the detrimental role of sulphate-ions in the formation of Al(13)-mer and an alternative mechanism of aluminium ion polycondensation is proposed, based on the increased stability of monomeric and oligomeric species (dimer and trimer) in the presence of sulphate-ions.

Alkalies↗
PubMed2004

Community assembly through adaptive radiation in Hawaiian spiders.

Communities arising through adaptive radiation are generally regarded as unique, with speciation and adaptation being quite different from immigration and ecological assortment. Here, I use the chronological arrangement of the Hawaiian Islands to visualize snapshots of evolutionary history and stages of community assembly. Analysis of an adaptive radiation of habitat-associated, polychromatic spiders shows that (i) species assembly is not random; (ii) within any community, similar sets of ecomorphs arise through both dispersal and evolution; and (iii) species assembly is dynamic with maximum species numbers in communities of intermediate age. The similar patterns of species accumulation through evolutionary and ecological processes suggest universal principles underlie community assembly.

Adaptation, Physiological↗
PubMed2006

The coexistence of hybrid and parental Daphnia: the role of parasites.

Parasite driven time-lagged negative frequency-dependent selection of hosts has been studied in natural populations by following changes in host genotype frequencies over time. However, such dynamics have not been considered at higher taxonomic levels, for example, between parental species and their hybrids. In a field study on a Daphnia hybrid system, we observed that one Daphnia taxon first was relatively under-infected, but became over-infected after a strong increase in frequency. This finding is consistent with the idea of parasite evolution towards the most frequent host taxon. In two experiments, we investigated whether the assumptions made by a model of negative frequency-dependent selection apply to our host taxa system. First, we showed that the parasite can change the outcome of taxa competition and secondly, we confirmed that the over-infection of one host taxon observed in the field has a genetic basis. Our results indicate that the incorporation of host-parasite interactions at the species level may allow us to gain a more complete picture of forces driving dynamic taxa coexistence in Daphnia hybrid systems. More generally, we suggest that if hybrids coexist in sympatry with parental taxa, the infection patterns as observed under natural conditions may be rather temporal and unstable.

Animals↗
PubMed1998

Sexual conflict and speciation.

We review the significance of two forms of sexual conflict (different evolutionary interests of the two sexes) for genetic differentiation of populations and the evolution of reproductive isolation. Conflicting selection on the alleles at a single locus can occur in males and females if the sexes have different optima for a trait, and there are pleiotropic genetic correlations between the sexes for it. There will then be selection for sex limitation and hence sexual dimorphism. This sex limitation could break down in hybrids and reduce their fitness. Pleiotropic genetic correlations between the sexes could also affect the likelihood of mating in interpopulation encounters. Conflict can also occur between (sex-limited) loci that determine behaviour in males and those that determine behaviour in females. Reproductive isolation may occur by rapid coevolution of male trait and female mating preference. This would tend to generate assortative mating on secondary contact, hence promoting speciation. Sexual conflict resulting from sensory exploitation, polyspermy and the cost of mating could result in high levels of interpopulation mating. If females evolve resistance to make pre- and postmating manipulation, males from one population could be more successful with females from the other, because females would have evolved resistance to their own (but not to the allopatric) males. Between-locus sexual conflict could also occur as a result of conflict between males and females of different populations over the production of unfit hybrids. We develop models which show that females are in general selected to resist such matings and males to persist, and this could have a bearing on both the initial level of interpopulation matings and the likelihood that reinforcement will occur. In effect, selection on males usually acts to promote gene flow and to restrict premating isolation, whereas selection on females usually acts in the reverse direction. We review theoretical models relevant to resolution of this conflict. The winning role depends on a balance between the 'value of winning' and 'power' (relating to contest or armament costs): the winning role is likely to correlate with high value of winning and low costs. Sperm-ovum (or sperm-female tract) conflicts (and their plant parallels) are likely to obey the same principles. Males may typically have higher values of winning, but it is difficult to quantify 'power', and females may often be able to resist mating more cheaply than males can force it. We tentatively predict that sexual conflict will typically result in a higher rate of speciation in 'female-win' clades, that females will be responsible for premating isolation through reinforcement, and that 'female-win' populations will be less genetically diverse.

Alleles↗
PubMed2001

Shape of ecological networks.

We study the statistics of ecosystems with a variable number of coevolving species. The species interact in two ways: by prey-predator relationships and by direct competition with similar kinds. The interaction coefficients change slowly through successful adaptations and speciations. They are treated as quenched random variables. These interactions determine long-term topological features of the species network, which are found to agree with those of biological systems.

Animals↗