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PubMed2001

Genetic evidence for adaptation-driven incipient speciation of Drosophila melanogaster along a microclimatic contrast in "Evolution Canyon," Israel.

Substantial genetic differentiation, as great as among species, exists between populations of Drosophila melanogaster inhabiting opposite slopes of a small canyon. Previous work has shown that prezygotic sexual isolation and numerous differences in stress-related phenotypes have evolved between D. melanogaster populations in "Evolution Canyon," Israel, in which slopes 100-400 m apart differ dramatically in aridity, solar radiation, and associated vegetation. Because the canyon's width is well within flies' dispersal capabilities, we examined genetic changes associated with local adaptation and incipient speciation in the absence of geographical isolation. Here we report remarkable genetic differentiation of microsatellites and divergence in the regulatory region of hsp70Ba which encodes the major inducible heat shock protein of Drosophila, in the two populations. Additionally, an analysis of microsatellites suggests a limited exchange of migrants and lack of recent population bottlenecks. We hypothesize that adaptation to the contrasting microclimates overwhelms gene flow and is responsible for the genetic and phenotypic divergence between the populations.

Adaptation, Physiological↗
PubMed1976

Species-distance relation for birds of the Solomon Archipelago, and the paradox of the great speciators.

For scattered remote islands and for likely forms of immigration and extinction curves, the equilibrium theory of island biogeography leads to the prediction [unk](2) log S/[unk]A[unk]D > 0, where S is the number of species on an island, A island area, and D island distance from the colonization source. This prediction is confirmed for birds of the Solomon Archipelago. Bird species can be classified into three types according to how distance affects their distributions: non-water-crossers, which are stopped completely (usually for psychological reasons) by water gaps of even 1 mile; short-distance colonists, successful at colonizing close but not remote islands; and long-distance colonists, successful at colonizing remote as well as close islands. Almost all of the "great speciators", the species for whose inter-island geographic variation the Solomons are famous, prove to be short-distance colonists. Lack's interpretation of the decrease in S with D is shown to rest on incorrect assumptions.

Journal Article↗
PubMed1979

Change in a secondary sexual character as evidence of incipient speciation in Drosophila silvestris.

Search for genetic changes that are pivotal in species formation has led to intraspecific studies of Drosophila silvestris, a giant species found only on the geologically new island of Hawaii. Males bear large, curved, modified bristles or cilia on the dorsal surface of the foreleg tibia and tarsus. In males from the south and west parts of the island there are two rows of cilia separated by a naked area, but in males from the north and east there is a mean of between 20 and 30 additional cilia between the two major rows on the tibia. These extra cilia are absent in closely related species of this subgroup, including the sympatric species D. heteroneura and three species from adjacent islands. Males use the foreleg tibiae in vibratory movements against the female's abdomen during courtship, so this character difference is likely to be important in the reproductive biology of the species. Inversion polymorphisms are similar in both northeast and southwest populations; they show large and strikingly parallel altitudinal shifts in frequency distributions involving the same inversions. Populations from various parts of the island cannot be distinguished by routine electrophoresis of soluble proteins encoded by 25 loci. Thus the "extra cilia" character is superimposed on a more ancient genetic background of similarity involving both chromosomal and electrophoretic polymorphisms. We interpret the extra cilia as a specific new embellishment of a secondary sexual character brought about by altered sexual selection occurring very recently in one part of the species range. This suggests incipient speciation.

Journal Article↗
PubMed1981

Models of speciation by sexual selection on polygenic traits.

The joint evolution of female mating preferences and secondary sexual characters of males is modeled for polygamous species in which males provide only genetic material to the next generation and females have many potential mates to choose among. Despite stabilizing natural selection on males, various types of mating preferences may create a runaway process in which the outcome of phenotypic evolution depends critically on the genetic variation parameters and initial conditions of a population. Even in the absence of genetic instability, rapid evolution can result from an interaction of natural and sexual selection with random genetic drift along lines of equilibria. The models elucidate genetic mechanisms that can initiate or contribute to rapid speciation by sexual isolation and divergence of secondary sexual characters.

Journal Article↗
PubMed1987

Extensive genetic divergence associated with speciation in filamentous fungi.

Little is known about genetic differentiation during speciation in fungi. The Collybia dryophila complex (Basidiomycetes: Tricholomataceae) contains several closely related groups of fungi at various levels of evolutionary divergence. Mating compatibility studies show there are several intersterile groups within the complex, three of which are distributed over two or more continents. Genetic relationships among five intersterility groups were compared by the method of DNA.DNA hybridization. Clustering techniques were used to reconstruct phylogenetic relationships of these fungi. Genic identity based on DNA.DNA hybridization corresponds well with mating compatibility. Reduced genic identity was observed between geographically isolated populations of a single mating group. This evidence suggests an allopatric mode of evolution for the C. dryophila group. These results indicate extensive genic divergence is associated with the appearance of intersterility barriers in basidiomycetous fungi. The levels of divergence observed in these and in other fungi are significantly higher than that observed in many other eukaryotes, and this suggests that the rate of molecular or morphological evolution in fungi may differ from that found in other organisms.

Journal Article↗
PubMed1989

The homeotic gene spalt (sal) evolved during Drosophila speciation.

The region-specific homeotic gene spalt (sal) acts in two separate domains in the head and tail region of the Drosophila melanogaster embryo. Based on comparative morphology, sal is likely to be involved in the establishment of the head during the evolution of invertebrates and thus, it should be conserved. We have analyzed the conservation of the segmentation genes Krüppel (Kr) and even-skipped (eve) in parallel with sal coding sequences in several Drosophila species that are evolutionarily separated by up to 60 million years. To our surprise, sal sequences appear to be conserved in the Sophophora subgenus of the Drosophila genus but not in the Drosophila subgenus. On the other hand, the segmentation and other homeotic genes are conserved in the Drosophila subgroup as well. Our data suggest that sal encodes an accessory function that evolved relatively late during Drosophila speciation rather than playing a fundamental evolutionary role similar to that of other homeotic genes.

Amino Acid Sequence↗
PubMed1993

RNS2: a senescence-associated RNase of Arabidopsis that diverged from the S-RNases before speciation.

Several self-compatible species of higher plants, such as Arabidopsis thaliana, have recently been found to contain S-like RNases. These S-like RNases are homologous to the S-RNases that have been hypothesized to control self-incompatibility in Solanaceous species. However, the relationship of the S-like RNases to the S-RNases is unknown, and their roles in self-compatible plants are not understood. To address these questions, we have investigated the RNS2 gene, which encodes an S-like RNase (RNS2) of Arabidopsis. Amino acid sequence comparisons indicate that RNS2 and other S-like RNases make up a subclass within an RNase superfamily, which is distinct from the subclass formed by the S-RNases. RNS2 is most similar to RNase LE [Jost, W., Bak, H., Glund, K., Terpstra, P., Beintema, J. J. (1991) Eur. J. Biochem. 198, 1-6.], an S-like RNase from Lycopersicon esculentum, a Solanaceous species. The fact that RNase LE is more similar to RNS2 than to the S-RNases from other Solanaceous plants indicates that the S-like RNases diverged from the S-RNases prior to speciation. Like the S-RNase genes, RNS2 is most highly expressed in flowers, but unlike the S-RNase genes, RNS2 is also expressed in roots, stems, and leaves of Arabidopsis. Moreover, the expression of RNS2 is increased in both leaves and petals of Arabidopsis during senescence. Phosphate starvation can also induce the expression of RNS2. On the basis of these observations, we suggest that one role of RNS2 in Arabidopsis may be to remobilize phosphate, particularly when cells senesce or when phosphate becomes limiting.

Amino Acid Sequence↗
PubMed1995

Founder-effect speciation theory: failure of experimental corroboration.

The theory of founder-effect speciation proposes that colonization by very few individuals of an empty habitat favors rapid genetic changes and the evolution of a new species. We report here the results obtained in a 10-year-long and large-scale experiment with Drosophila pseudoobscura designed to test the theory. In our experimental protocol, populations are established with variable numbers of very few individuals and allowed to expand greatly for several generations until conditions of severe competition for resources are reached and the population crashes. A few random survivors are then taken to start a new population expansion and thus initiate a new cycle of founding events, population flushes, and crashes. Our results provide no support for the theories proposing that new species are very likely to appear as by-products of founder events.

Animals↗
PubMed1997

Molecular keys to speciation: DNA polymorphism and the control of genetic exchange in enterobacteria.

Speciation involves the establishment of genetic barriers between closely related organisms. The extent of genetic recombination is a key determinant and a measure of genetic isolation. The results reported here reveal that genetic barriers can be established, eliminated, or modified by manipulating two systems which control genetic recombination, SOS and mismatch repair. The extent of genetic isolation between enterobacteria is a simple mathematical function of DNA sequence divergence. The function does not depend on hybrid DNA stability, but rather on the number of blocks of sequences identical in the two mating partners and sufficiently large to allow the initiation of recombination. Further, there is no obvious discontinuity in the function that could be used to define a level of divergence for distinguishing species.

Biological Evolution↗
PubMed1999

Molecular evidence of cryptic speciation in planktonic foraminifers and their relation to oceanic provinces.

The fossil record of planktonic foraminifers is a key source of data on the biodiversity and evolution of marine plankton. One of the most distinctive foraminiferal taxa, Orbulina universa, widely used as a stratigraphic and paleoclimatic index, has always been regarded as a single species. Here we present a phylogenetic analysis of Orbulina small subunit rDNA sequences from 25 pelagic stations covering 100 degrees latitude in the Atlantic Ocean. The genetic data reveal the presence of three cryptic species, whose distribution is clearly correlated to hydrographic provinces, and particularly to sea-surface total chlorophyll a concentration. Our results, together with previous studies, suggest that a considerable part of the diversity among planktonic foraminifers has been overlooked in morphological taxonomies. Our data also support the idea that planktonic foraminifers, even if adapted to particular hydrographic conditions, are high-dispersal organisms whose speciation may be similar to that of other high-dispersal taxa in which reproductive mechanisms and behavior, rather than just geographic barriers to dispersal, play key roles in species formation and maintenance.

Animals↗
PubMed2003

Conserved Ser residues, the shutter region, and speciation in serpin evolution.

The suicide inhibitory mechanism of serine protease inhibitors of the serpin superfamily depends heavily on their structural flexibility, which is controlled in large part by the breach and shutter regions of the central Abeta-sheet. We examined codon usage by the highly conserved residues, Ser-53 and Ser-56, of the shutter region and found a TCN-AGY usage dichotomy for Ser-56 that remarkably is linked to the protostome-deuterostome split. Our results suggest that serpin evolution was driven by phylogenetic speciation and not pressure to fulfill new physiologic functions mitigating against coevolution with the family of serine proteases they inhibit.

Codon↗
PubMed2003

Early hominin speciation at the Plio/Pleistocene transition.

Over the last half-decade or so, there has been an explosion in the recognition of hominin genera and species. We now have the late Miocene genera Orrorin and Sahelanthropus, the mid Pliocene genus Kenyanthropus, three new Pliocene species of Australopithecus (A. anamensis, A. garhi and A. bahrelghazali) and a sub species of Ardipithecus (Ar. r. kadabba) to contend with. Excepting also the more traditional species allocated to Paranthropus, Australopithecus and early Homo we are approaching around 15 species over 5 million years (excluding hominin evolution over the last one million years). Can such a large number of hominin species be justified? An examination of extant hominid (Gorilla gorilla, Pan troglodytes, and Pan paniscus) anatomical variability indicates that the range of fossil hominin variability supports the recognition of this large number of fossil species. It is also shown that not all hominins are directly related to the emergence of early Homo and as such have become extinct. Indeed the traditional australopithecine species 'A'. anamensis, 'A'. afarensis and 'A'. garhi are considered here to belong to a distinct genus Praeanthropus. They are also argued not be hominins, but rather an as yet undefined hominid group from which the more derived hominins evolved. The first hominin is represented by A. africanus or a hominin very much like it. The Paranthropus clade is defined by a derived heterochronic condition of peramorphosis, associated with sequential progenesis (contraction of successive growth stages) in brain and dental development, but a mixture of peramorphic and paedomorphic features in its craniofacial anatomy. Conversely, Kenyanthropus and Homo both share a pattern of peramorphosis, associated with sequential hypermorphosis (prolongation of successive growth stages) in brain development, and paedomorphosis processes in cranial, facial and dental development. This suggests, that these two clades share an important synapomorphy not recognised in the parsimony analyses, suggesting that they may form a sister group relationship to the exclusion of Paranthropus. This highlights the need to re-interpret phylogenetic results in terms of function and development. The rapid speciation and extinction as argued here is in keeping with other fossil groups in Africa at the Plio/Pleistocene transition. This emphasises that we must approach the pre-australopithecines and hominins as part of the endemic African fauna, and not in isolation to the evolutionary and climatic processes that were operating all around them.

Africa↗
PubMedDate not supplied

Speciation of mercury excreted in feces from individuals with amalgam fillings.

Investigators established methods for the analysis of total mercury (Hg-total), oxidized mercury and mercury bound to sulfhydryl groups (Hg-S), mercury vapor (Hg0), and mercury from amalgam particles (APs) in fecal samples. Two individuals consumed mercury as a mercury-cysteine complex mercury vapor, and mercury from amalgam particles, and the cumulative excretion of mercury in feces was followed. Investigators found that 80% of the mercury from amalgam particles and mercury bound to sulfhydryl groups was excreted, but only 40% of the mercury vapor was excreted. Speciation of mercury excreted in feces from 6 individuals with a moderate loading of amalgam fillings showed that most of the mercury originating from the fillings consisted of oxidized mercury, which was probably bound to sulfhydryl-containing compounds. The proportion of amalgam particles in fecal samples from these individuals was low, and it did not exceed 26% of the total amount of mercury excreted.

Adult↗
PubMed2001

Cadmium in caribou (Rangifer tarandus) kidneys: speciation, effects of preparation and toxicokinetics.

Caribou kidney is a major source of cadmium (Cd) in the traditional diets of many aboriginal communities in the Arctic. In order to characterize the risk of Cd exposure, we studied the speciation of Cd in caribou kidneys and how, it can be affected by food preparation. Cd in caribou kidneys was bound to metallothionein (MT) (40%) high molecular weight proteins (50-500 kDa) (30%) and existed as free ions (10%). There was no change in Cd concentrations after the samples were baked at 350 degrees C for 30 min but the MT level was significantly decreased. Food preparation also denatured the high molecular weight proteins, resulting in a significant increase of free Cd. The toxicokinetics of Cd in caribou kidney was studied using a rodent model. Four groups (n = 6) of adult Sprague-Dawley rats were fed with rat chow with the addition of one of the following: 10% veal kidney with 0 microg/g Cd, 10% veal kidney spiked with CdCl2 to make up to 66 microg Cd; 10% caribou kidney containing 20 microg/g Cd and 10% caribou kidney containing 66 microg/g Cd. After 14 days, Cd accumulation increased with dose but less than 1% of the dosed Cd accumulated in the liver and kidney of rats. The percentage of Cd accumulated in the liver was higher in the group fed with caribou kidney than that dosed with spiked veal kidney. Our results suggest that caribou kidney is a major source of Cd exposure among the Arctic populations but moderate consumption may be considered unavoidable.

Absorption↗
PubMed2002

Metabolic pathway for selenium in the body: speciation by HPLC-ICP MS with enriched Se.

Selenium (Se) is an ultramicro essential nutrient and both inorganic (selenite and selenate) and organic (selenocysteine and selenomethionine) forms of Se can be used as nutritional sources. Metabolic pathways for Se in the body were studied for selenite and selenate, with the use of enriched 82Se, by speciation with separation by gel filtration HPLC and detection by element-specific mass spectrometry with ionization with inductively coupled argon plasma (HPLC-ICP MS). The concentrations of 82Se in organs and body fluids and the distributions of their constituents depending on the dose and time after the intravenous administration of 82Se-selenite and -selenate to rats were determined. Selenite was taken up by red blood cells within several minutes, reduced to selenide by glutathione, and then transported to the plasma, bound selectively to albumin and transferred to the liver. Contrary to selenite, intact selenate was either taken up directly by the liver or excreted into the urine. The 82Se of selenite origin and that of selenate origin were detected in the forms of the two Se peak materials in the liver, A and B. The former one was methylated to the latter in vivo and in vitro. The latter one was identical with the major urinary metabolite and it was identified as Se-methyl-N-acetyl-selenohexosamine (selenosugar). The chemical species-specific metabolic pathway for Se was explained by the metabolic regulation through selenide as the assumed common intermediate for the inorganic and organic Se sources and as the checkpoint metabolite between utilization for the selenoprotein synthesis and methylation for the excretion of Se.

Animals↗
PubMed1986

Determination and speciation of mercury in a dental work-place by cold vapour atomic absorption spectrometry and gas-liquid chromatography.

Cold Vapour Atomic Absorption Spectrometry (CVAAS) and Gas-Liquid Chromatography (GLC) have been used for determination and speciation of mercury. Total mercury, methylmercury, ethylmercury and phenylmercury concentrations in urine samples taken from students and staff of a dental work-place were investigated. Air samples were also analyzed. Detection limits, as three times the standard deviation, and in units of ng analyte per ml urine were found to be 1.7, 12, 2.4 and 21 for total mercury, methylmercury chloride, ethylmercury chloride and phenylmercury chloride, respectively.

Air Pollutants, Occupational↗
PubMed1986

Determination of the speciation of chromium from a bicycle factory discharge.

The discharge from a bicycle factory in Dar-es-Salaam was analysed for dissolved trace metals so as to monitor what was being introduced onto the environment. An X-ray Fluorescence Spectrophotometer with a Si (Li) detector connected to a multichannel analyser Canberra 40 series was used for the analysis. Computation of the peaks and results was done by a Professional Deck 350 computer. The elements contained in the discharge were Ca (596 ppm), Ti (369 ppm), Cr (11 ppm), Zn (0.98%) and Sr (73.5 ppm). Further analysis of the speciation of chromium revealed that there was Cr(III) (9 ppm) and Cr(VI) 2 ppm. The level of Cr(VI) was considered too high considering its toxicity.

Chromium↗
PubMed2002

[Study of the effect of earthworm Lumbricus terrestris on the speciation of heavy metals in soils].

Evaluation of the effect of earthworm Lumbricus terrestris on the speciation of copper and cadmium was carried out on two types of soils with a high metallic contamination due to municipal wastes spreading. The concentrations of total dissolved metals were higher in the soil containing earthworms. This increase was larger for the soil submitted to disturbance by earthworms for a long time (3 months). The main chemical species in the lixiviates of all type of soils including controls, were labile forms of cadmium with 52 to 87% and stable forms of copper which represents 67 to 95% of total concentration of dissolved metal. In the solid phase, there was a slight transfer of cadmium and copper from the oxidizable fraction into the exchangeable and acid soluble fractions. This suggests that soil disturbance by earthworms increases the mobility of these metals particularly cadmium. On the contrary copper appears in lixiviates as non labile organic complexes. Analysis of the whole results showed differences between soils as regards the mobility of the metals studied, which reflected the role of the mains physico-chemical characteristics (pH, C.E.C. and total calcareous content).

Animals↗