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At least 217 records · Page 12Linked to original sources
PubMed2003

Cooperative breeding in oscine passerines: does sociality inhibit speciation?

Cooperative breeding in birds is much more prevalent than has been previously realized, occurring in 18.5% of oscine passerines known to have biparental care, and is the predominant social system of some ancient oscine clades. Cooperation is distributed unevenly in clades that contain both cooperative and pair breeders, and is usually confined to a few related genera in which it can be ubiquitous. Cooperative clades are species poor compared with pair-breeding clades, because pair breeders evolve migratory habits, speciate on oceanic islands and are more likely to have distributions spread across more than one biogeographic region. These differences reflect the increased capacity for colonization by pair breeders because their young disperse. Thus cooperative breeding has macroevolutionary consequences by restricting rates of speciation and macroecological implications by influencing the assembly of island and migrant faunas.

Animal Migration↗
PubMed2004

Quaternary Ice-Age dynamics in the Colombian Andes: developing an understanding of our legacy.

Pollen records from lacustrine sediments of deep basins in the Colombian Andes provide records of vegetation history, the development of the floristic composition of biomes, and climate variation with increasing temporal resolution. Local differences in the altitudinal distribution of present-day vegetation belts in four Colombian Cordilleras are presented. Operating mechanisms during Quaternary Ice-Age cycles that stimulated speciation are discussed by considering endemism in the asteraceous genera Espeletia, Espeletiopsis and Coespeletia. The floristically diverse lower montane forest belt (1000-2300 m) was compressed by ca. 55% during the last glacial maximum (LGM) (20 ka), and occupied the slopes between 800 m and 1400 m during that period. Under low LGM atmospheric pCO2 values, C4-dominated vegetation, now occurring below 2200 m, expanded up to ca. 3500 m. Present-day C3-dominated paramo vegetation is therefore not an analogue for past C4-dominated vegetation (with abundant Sporobolus lasiophyllus). Quercus immigrated into Colombia 478 ka and formed an extensive zonal forest from 330 ka when former Podocarpus-dominated forest was replaced by zonal forest with Quercus and Weinmannia. During the last glacial cycle the ecological tolerance of Quercus may have increased. In the ecotone forests Quercus was rapidly and massively replaced by Polylepis between 45 and 30 ka illustrating complex forest dynamics in the tropical Andes.

Altitude↗
PubMed2006

Dynamics of host plant use and species diversity in Polygonia butterflies (Nymphalidae).

The ability of insects to utilize different host plants has been suggested to be a dynamic and transient phase. During or after this phase, species can shift to novel host plants or respecialize on ancestral ones. Expanding the range of host plants might also be a factor leading to higher levels of net speciation rates. In this paper, we have studied the possible importance of host plant range for diversification in the genus Polygonia (Nymphalidae, Nymphalini). We have compared species richness between sistergroups in order to find out if there are any differences in number of species between clades including species that utilize only the ancestral host plants ('urticalean rosids') and their sisterclades with a broader (or in some cases potentially broader) host plant repertoire. Four comparisons could be made, and although these are not all phylogenetically or statistically independent, all showed clades including butterfly species using other or additional host plants than the urticalean rosids to be more species-rich than their sisterclade restricted to the ancestral host plants. These results are consistent with the theory that expansions in host plant range are involved in the process of diversification in butterflies and other phytophagous insects, in line with the general theory that plasticity may drive speciation.

Animals↗
PubMed2004

Speciation in Hawaiian angiosperm lineages: cause, consequence, and mode.

The biota of Hawaiian Islands is derived entirely from long distance dispersal, often followed by in situ speciation. Species descended from each colonist constitute monophyletic lineages that have diverged to varying degrees under similar spatial and temporal constraints. We partitioned the Hawaiian angiosperm flora into lineages and assessed morphological, ecological, and biogeographic characteristics to examine their relationships to variation in species number (S). Lineages with external bird dispersal (through adhesion) were significantly more species-rich than those with abiotic dispersal, but only weakly more species-rich than lineages with internal bird dispersal (involving fleshy fruits). Pollination mode and growth form (woody vs. herbaceous) had no significant effect on S, in contrast to studies of angiosperm families. S relates positively to the geographic and ecological range size of whole lineages, but negatively to local abundance and mean range sizes of constituent species. Species-rich lineages represent a large proportion of major adaptive shifts, although this appears to be an artifact of having more species. Examination of 52 sister species pairs in numerous lineages provides evidence for allopatric (including peripheral isolates) and parapatric (ecological) modes, with 15 cases of each. Although postspeciational dispersal may obscure these modes in many of the remaining cases, instances of sympatric and hybrid speciation are also discussed. Because speciation is both a consequence and a cause of ecological and biogeographic traits, speciation mode may be integral to relationships between traits. We discuss the role of speciation in shaping the regional species pool.

Analysis of Variance↗
PubMed2000

Simultaneous monitoring of atmospheric methane and speciated non-methane hydrocarbon concentrations using Peltier effect sub-ambient pre-concentration and gas chromatography.

Sub-ambient trapping, used to pre-concentrate atmospheric samples for non-methane hydrocarbon (NMHC) analysis by gas chromatography, can also be used to measure ambient methane concentrations. Above a sample volume of 40 ml, a dynamic equilibrium is established between ambient and trapped methane allowing for simultaneous quantitative determinations of methane and NMHC. The temperature stability of the trap is critical for quantitative methane analysis and this can be achieved by Peltier effect cooling. Simultaneous measurements of methane and NMHC reduce the equipment required for field trips and can ease the interpretation and modelling of atmospheric data. The feasibility for deployment of the system in remote locations was demonstrated by running the apparatus virtually unattended for a 5-day period. The correlations between the concentrations of methane, ethane and ethene measured during this period are discussed.

Air Pollutants↗
PubMed2004

Comparative primate genomics: the year of the chimpanzee.

This is the year of the chimpanzee genome. Chimpanzee chromosome 22 has been sequenced and soon will be followed by the whole genome, and thousands of chimpanzee cDNA sequences are available for comparative analysis. Not only does this genomic information allow us to identify human-specific changes in particular genes that are potentially under selection, but also to understand molecular evolutionary dynamics characterizing the two most closely related mammalian genomes sequenced so far. Studies comparing gene expression in chimpanzees and other closely related primates reveal significant species differences in brain, liver and fibroblasts. New empirical data, in combination with models of speciation, are giving insight into how humans and chimpanzees speciated.

Animals↗
PubMed2006

Defining parasite communities is a challenge for neutral theory.

The neutral theory of biodiversity and biogeography is a null model of community structure that suggests that it may be possible to explain the richness and relative abundance of species through neutral processes of immigration, extinction, and speciation, without resort to interactive processes such as competition. There have been no attempts to fit neutral models to parasite communities to date. The nature of parasite communities, however, challenges the basic assumptions of neutral theory. In particular, the spatially dynamic relationships between hosts as habitat patches result in immigration rates that are in a constant state of flux. In addition, the partial compositional overlap of many component communities means that they can affect each other's process rates, which violates the zero-sum assumptions of neutral theory. Despite these obstacles, many of the patterns that neutral theory seeks to explain are still present in parasite communities. Far from being an esoteric special case, parasite communities are ubiquitous in nature and, therefore, any attempts to produce unified theoretical frameworks should accommodate the characteristics of parasite communities, or risk obsolescence.

Animals↗
PubMed2005

Phosphorus speciation in manure and manure-amended soils using XANES spectroscopy.

Previous studies suggested an increase in the proportion of calcium phosphates (CaP) of the total phosphorus (P) pool in soils with a long-term poultry manure application history versus those with no or limited application histories. To understand and predict long-term P accumulation and release dynamics in these highly amended soils, it is important to understand what specific P species are being formed. We assessed forms of CaP formed in poultry manure and originally acidic soil in response to different lengths of mostly poultry manure applications using P K-edge X-ray absorption near-edge structure (XANES) spectroscopy. Phosphorus K-edge XANES spectra of poultry manure showed no evidences of crystalline P minerals but dominance of soluble CaP species and free and weakly bound phosphates (aqueous phosphate and phosphate adsorbed on soil minerals). Phosphate in an unamended neighboring forest soil (pH 4.3) was mainly associated with iron (Fe) compounds such as strengite and Fe-oxides. Soils with a short-term manure history contained both Fe-associated phosphates and soluble CaP species such as dibasic calcium phosphate (DCP) and amorphous calcium phosphate (ACP). Long-term manure application resulted in a dominance of CaP forms confirming our earlier results obtained with sequential extractions, and a transformation from soluble to more stable CaP species such as beta-tricalcium calcium phosphate (TCP). Even after long-term manure application (> 25 yr and total P in soil up to 13,307 mg kg(-1)), however, none of the manure-amended soils showed the presence of crystalline CaP. With a reduction or elimination of poultry manure application to naturally acidic soils, the pH of the soil is likely to decrease, thereby increasing the solubility of Ca-bonded inorganic P minerals. Maintaining a high pH is therefore an important strategy to minimize P leaching in these soils.

Agriculture↗
PubMed1987

The frequency of shifts between alternative equilibria.

We derive a formula giving the frequency with which random drift shifts a population between alternative equilibria. This formula is valid when such shifts are rare (Ns much greater than 1), and applies over a wide range of mutation rates. When the number of mutations entering the population is low (4 N mu much less than 1), the rate of stochastic shifts reduces to the product of the mutation rate and the probability of fixation of a single mutation. However, when many mutations enter the population in each generation (4 N mu much greater than 1), the rate is higher than would be expected if mutations were established independently, and converges to that given by a gaussian approximation. We apply recent results on bistable systems to extend this formula to the general multidimensional case. This gives an explicit expression for the frequency of stochastic shifts, which depends only on the equilibrium probability distribution near the saddle point separating the alternative stable states. The plausibility of theories of speciation through random drift are discussed in the light of these results.

Adaptation, Biological↗
PubMed2004

Kinetics of trace metal competition in the freshwater environment: some fundamental characteristics.

Freshwaters are recognized as dynamic systems that may be far-removed from equilibrium. A kinetic approach using the competing ligand exchange method with Chelex 100 as the competing ligand and inductively coupled plasmamass spectrometry to measure the dissociation kinetics was used to investigate the chemical speciation of Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Pb(II) in model solutions of a well-characterized fulvic acid (Laurentian fulvic acid) and a freshwater sample collected from the Grand River (Ontario, Canada). The kinetic distribution of the metal species were quantitatively characterized by their first-order dissociation rate constants. This kinetic speciation approach has the advantage of providing an objective method for estimating the dissociation rate constants without any a priori assumptions about the number of kinetically distinguishable components or the shape of the distribution. Three factors were found to influence the kinetics of trace metal competition in the freshwater environment: (i) metal-to-ligand ratio, (ii) ionic potential (z2/r), and (iii) ligand field stabilization energy. The results illustrate the importance of considering the valence-shell electron configuration in predicting the kinetics of trace metal competition in the freshwater environment. The markedly slow dissociation kinetics of Ni(II) and Cu(II) species suggest that the usual equilibrium assumption for freshwaters may not be valid. This study has demonstrated the ability of the kinetic model to correctly predict the relative rates of trace metal reactions, indicating that the kinetic model provides a chemically significant description of the kinetic processes in natural waters.

Kinetics↗
PubMedDate not supplied

Evolution: an axiomatic perspective.

In this paper we present an axiomatic theory of evolution which is inspired by the reading of a paper written by G.V. Schiaparelli in 1898. Schiaparelli was a famous astronomer, but he also studied the Darwinian ideas. We propose five axioms which can characterize the theory of evolution. We have also written these axioms using the language of the logic of predicates of first order with some constant monadic and dyadic predicates and appropriate functionals. But we can use other types of logic. So we can examine the concepts of species and of speciation. Then we introduce the interesting notion of generation distance. Moreover we give a theorem which establishes a geometrical model of our theory. If we analyze further the fourth axiom (which concerns the notion of generation distance) we can propose an elementary dynamical model by which we can represent possible evolutionary dynamics. These dynamics partially depend on random quantities.

Algorithms↗
PubMed2005

Tempo and mode of speciation in the Baja California disjunct fish species Anisotremus davidsonii.

The Baja California region provides a natural setting for studying the early mechanisms of allopatric speciation in marine systems. Disjunct fish populations from several species that occur in the northern Gulf of California and northern Pacific coast of Baja California, but are absent from its southern shores, were previously shown to be genetically isolated, making them excellent candidates for studying allopatry. In addition, one of these species, the sargo Anisotremus davidsonii, has two pairs of congeneric Panamic trans-isthmian geminate species that allow for internal molecular clock calibration. Phylogeographic and demographic approaches based on mitochondrial (cytochrome b) and nuclear (S7 ribosomal protein) sequences showed that A. davidsonii entered the gulf from the south, and later colonized the Pacific coast, approximately 0.6-0.16 million years ago. Pacific coast colonization may have used a route either around the southern cape of Baja California or across the peninsula through a natural seaway. However, while several seaways have been described from different geological times, none matches the dates of population disjunction, yet much geological work remains to be done in that area. At the present time, there is no evidence for dispersal around the southern tip of the Baja California Peninsula. Signatures of incipient allopatric speciation were observed, such as the reciprocal monophyly of disjunct populations for the mitochondrial marker. However, other characteristics were lacking, such as a strong difference in divergence and coalescence times. Taken together, these results suggest that disjunct populations of A. davidsonii may be consistent with the earliest stages of allopatric speciation.

Animals↗
PubMed2006

Bioavailability of trace metals to aquatic microorganisms: importance of chemical, biological and physical processes on biouptake.

An important challenge in environmental biogeochemistry is the determination of the bioavailability of toxic and essential trace compounds in natural media. For trace metals, it is now clear that chemical speciation must be taken into account when predicting bioavailability. Over the past 20 years, equilibrium models (free ion activity model (FIAM), biotic ligand model (BLM)) have been increasingly developed to describe metal bioavailability in environmental systems, despite the fact that environmental systems are always dynamic and rarely at equilibrium. In these simple (relatively successful) models, any reduction in the available, reactive species of the metal due to competition, complexation or other reactions will reduce metal bioaccumulation and thus biological effects. Recently, it has become clear that biological, physical and chemical reactions occurring in the immediate proximity of the biological surface also play an important role in controlling trace metal bioavailability through shifts in the limiting biouptake fluxes. Indeed, for microorganisms, examples of biological (transport across membrane), chemical (dissociation kinetics of metal complexes) and physical (diffusion) limitation can be demonstrated. Furthermore, the organism can employ a number of biological internalization strategies to get around limitations that are imposed on it by the physicochemistry of the medium. The use of a single transport site by several metals or the use of several transport sites by a single metal further complicates the prediction of uptake or effects using the simple chemical models. Finally, once inside the microorganism the cell is able to employ a large number of strategies including complexation, compartmentalization, efflux or the production of extracellular ligands to minimize or optimize the reactivity of the metal. The prediction of trace metal bioavailability will thus require multidisciplinary advances in our understanding of the reactions occurring at and near the biological interface. By taking into account medium constraints and biological adaptability, future bioavailability modeling will certainly become more robust.

Bacteria↗
PubMed2002

Correlational selection and the evolution of genomic architecture.

We review and discuss the importance of correlational selection (selection for optimal character combinations) in natural populations. If two or more traits subject to multivariate selection are heritable, correlational selection builds favourable genetic correlations through the formation of linkage disequilibrium at underlying loci governing the traits. However, linkage disequilibria built up by correlational selection are expected to decay rapidly (ie, within a few generations), unless correlational selection is strong and chronic. We argue that frequency-dependent biotic interactions that have 'Red Queen dynamics' (eg, host-parasite interactions, predator-prey relationships or intraspecific arms races) often fuel chronic correlational selection, which is strong enough to maintain adaptive genetic correlations of the kind we describe. We illustrate these processes and phenomena using empirical examples from various plant and animal systems, including our own recent work on the evolutionary dynamics of a heritable throat colour polymorphism in the side-blotched lizard Uta stansburiana. In particular, male and female colour morphs of side-blotched lizards cycle on five- and two-generation (year) timescales under the force of strong frequency-dependent selection. Each morph refines the other morph in a Red Queen dynamic. Strong correlational selection gradients among life history, immunological and morphological traits shape the genetic correlations of the side-blotched lizard polymorphism. We discuss the broader evolutionary consequences of the buildup of co-adapted trait complexes within species, such as the implications for speciation processes.

Animals↗
PubMed2004

Genomic evidence for divergence with gene flow in host races of the larch budmoth.

Ecological divergence in the face of gene flow has recently become implicated as a potentially important cause of speciation and adaptive radiation. Here, we develop a genomic approach to test for divergent selection in sympatric host races of the larch budmoth Zeiraphera diniana (Lepidoptera: Tortricidae). We analysed hundreds of amplified fragment length polymorphism markers in 92 individuals in sympatric and allopatric populations, and in two backcross broods used to map the markers to individual chromosomes. The results directly confirm the existence of natural hybridization and demonstrate strong heterogeneity between chromosomes in terms of molecular divergence between host races (the average level of divergence was FST = 0.216). However, genomic heterogeneity was not found when we analysed divergence between geographically separated populations of the same host race. We conclude that the variance of the level of sympatric divergence among chromosomes is the footprint of divergent selection acting on a few linkage groups, combined with appreciable gene flow that homogenizes between-race variation at the remaining linkage groups. These results, coupled with other recent multilocus analyses of sister species pairs, demonstrate that selection-driven sympatric phase of genetic divergence in the presence of gene flow is a likely feature of speciation.

Analysis of Variance↗
PubMed2002

Speciation and the establishment of zonation in an intertidal barnacle: specific settlement vs. selection.

The tropical barnacle Tetraclita forms a belt on hard substrates in the intertidal zone of the Red Sea. Based on morphological data, three distinct species were suggested to exist, occupying different vertical levels - T. barnesorum, T. rufotincta and T. achituvi. In this study we used molecular (12S mitochondrial ribosomal DNA) and ecological data to examine whether this morphological variability reflects genetic differences, or is a result of environmental factors. Adults and spats, collected from settlement plates, were censused and screened genotypically using single strand conformation polymorphism (SSCP) analysis, and settlement dynamics was recorded. We provide evidence for the existence of only two distinct species, and point out both phenotypic plasticity and convergence within and between the proposed species. Cyprids of T. achituvi settle specifically at the lower part of the Tetraclita belt, and feature one phenotype. In contrast, T. rufotincta, occupying the upper and middle portions of the Tetraclita belt, settles throughout the range, shows phenotypic plasticity (three variants), and presumably undergoes selection at the lower part. Thus, the vertical zonation of Tetraclita is produced by the combination of pre-settlement and post-settlement factors, in T. achituvi and T. rufotincta, respectively. The examined system may offer a model in which to study the mechanisms underlying sympatric speciation.

Animals↗
PubMed2004

Quantum speciation in Aegilops: molecular cytogenetic evidence from rDNA cluster variability in natural populations.

Data are presented on quantum speciation in the Sitopsis section of the genus Aegilops (Poaceae, Monocotyledones). Two small, peripheral, isolated, wild populations of annual cross-pollinated Ae. speltoides and annual self-pollinated Ae. sharonensis are located 30 m apart on different soil types. Despite the close proximity of the two species and their close relatedness, no mixed groups are known. Comparative molecular cytogenetic analysis based on the intrapopulation variability of rRNA-encoding DNA (rDNA) chromosomal patterns of individual Ae. speltoides geno-types revealed an ongoing dynamic process of permanent chromosomal rearrangements. Chromosomal mutations can arise de novo and can be eliminated. Analysis of the progeny of the investigated genotypes testifies that inheritance of de novo rDNA sites happens frequently. Heterologous recombination and/or transposable elements-mediated rDNA transfer seem to be the mechanisms for observed chromosomal repatterning. Consequently, several modified genomic forms, intermediate between Ae. speltoides and Ae. sharonensis, permanently arise in the studied wild population of Ae. speltoides, which make it possible to recognize Ae. sharonensis as a derivative species of Ae. speltoides, as well as to propose rapidness and canalization of quantum speciation in Sitopsis species.

Chromosomes, Plant↗
PubMed1998

Evolution of satellite DNAs from the genus Palorus--experimental evidence for the "library" hypothesis.

Satellite DNA profiles have been characterized in the congeneric species Palorus ratzeburgii, Palorus subdepressus, Palorus genalis, and Palorus ficicola (Coleoptera, Insecta), each of which contains a single, A + T-rich satellite DNA comprising a considerable portion of the genome (20%-40%). These satellites exhibit insignificant mutual sequence similarity. Using PCR assay, it has been shown that all four sequences are present in each of the tested Palorus species: one of them is amplified into a high copy number or a major satellite, while the three others are in the form of low-copy-number repeats estimated to make up approximately 0.05% of the genome. Each of the four satellites is interspecifically high conserved concerning the sequence, monomer length, and tandem repeat organization. Major, as well as low-copy-number, satellites are colocalized in the regions of pericentromeric heterochromatin on all chromosomes of the complement. The low-copy-number satellites are dispersed between the large arrays of the major satellite over the whole heterochromatic block. Our results explain satellite DNA evolution, confirming the hypothesis that related species share a "library" of conserved satellite sequences, some of which could be amplified into a major satellite. Due to the evolutionary dynamics of satellite DNAs, the content of the "library" is variable; the elimination of some sequences parallels the creation of the new ones. Quantitative changes in satellite DNAs, induced by occasional amplification of satellite repeat from the "library", could possibly occur in the course of the speciation process, thus forming a species-specific profile of satellite DNAs.

Animals↗