Home About us Contact
|
Home About us Contact | ||
|
|
||
Incompatibility
Kinds of Incompatibility Selected AbstractsYOU CAN'T KEEP A GOOD PARASITE DOWN: EVOLUTION OF A MALE-KILLER SUPPRESSOR UNCOVERS CYTOPLASMIC INCOMPATIBILITYEVOLUTION, Issue 5 2008Emily A. Hornett Maternally inherited parasites are known to impose a wide variety of reproductive manipulations upon their host. These often produce strong selection on the host to suppress the parasite, resulting in a reduction in the frequency of the parasite. However, in the butterfly Hypolimnas bolina, infected with a Wolbachia bacterium, field data demonstrate that suppression of the male-killing phenotype does not depress parasite frequency. Here we test and verify one hypothesis to explain this apparent paradox,Wolbachia induces a second phenotype, Cytoplasmic Incompatibility (CI), in populations where host suppression has evolved. We further demonstrate that the capacity to induce CI has not evolved de novo, but instead is instantaneously expressed upon the survival of infected males. The significance of these results is threefold: (1) multiple phenotypes can provide Wolbachia with the means to maintain itself in a host following suppression of a single manipulative phenotype; (2) the ability to induce CI can remain hidden in systems in which male-killing is observed, just as the ability to induce male-killing may be obscured in strains exhibiting CI; (3) the evolutionary maintenance of CI in a system in which it is not expressed suggests a functional link with male-killing or other traits under selection. [source] NATURAL VARIATION FOR A HYBRID INCOMPATIBILITY BETWEEN TWO SPECIES OF MIMULUSEVOLUTION, Issue 1 2007Andrea L. Sweigart Understanding the process by which hybrid incompatibility alleles become established in natural populations remains a major challenge to evolutionary biology. Previously, we discovered a two-locus Dobzhansky,Muller incompatibility that causes severe hybrid male sterility between two inbred lines of the incompletely isolated wildflower species, Mimulus guttatus and M. nasutus. An interspecific cross between these two inbred lines revealed that the M. guttatus (IM62) allele at hybrid male sterility 1 (hms1) acts dominantly in combination with recessive M. nasutus (SF5) alleles at hybrid male sterility 2 (hms2) to cause nearly complete hybrid male sterility. In this report, we extend these genetic analyses to investigate intraspecific variation for the hms1,hms2 incompatibility in natural populations of M. nasutus and M. guttatus, performing a series of interspecific crosses between individuals collected from a variety of geographic locales. Our results suggest that hms2 incompatibility alleles are common and geographically widespread within M. nasutus, but absent or rare in M. guttatus. In contrast, the hms1 locus is polymorphic within M. guttatus and the incompatibility allele appears to be extremely geographically restricted. We found evidence for the presence of the hms1 incompatibility allele in only two M. guttatus populations that exist within a few kilometers of each other. The restricted distribution of the hms1 incompatibility allele might currently limit the potential for the hms1,hms2 incompatibility to act as a species barrier between sympatric populations of M. guttatus and M. nasutus. Extensive sampling within a single M. guttatus population revealed that the hms1 locus is polymorphic and that the incompatibility allele appears to segregate at intermediate frequency, a pattern that is consistent with either genetic drift or natural selection. [source] EVOLUTION OF WOLBACHIA-INDUCED CYTOPLASMIC INCOMPATIBILITY IN DROSOPHILA SIMULANS AND D. SECHELLIAEVOLUTION, Issue 9 2002Sylvain Charlat Abstract., The intracellular bacterium Wolbachia invades arthropod host populations through various mechanisms, the most common of which being cytoplasmic incompatibility (CI). CI involves elevated embryo mortality when infected males mate with uninfected females or females infected with different, incompatible Wolbachia strains. The present study focuses on this phenomenon in two Drosophila species: D. simulans and D. sechellia. Drosophila simulans populations are infected by several Wolbachia strains, including w Ha and w No. Drosophila sechellia is infected by only two Wolbachia: w Sh and w Sn. In both Drosophila species, double infections with Wolbachia are found. As indicated by several molecular markers, w Ha is closely related to w Sh, and w No to w Sn. Furthermore, the double infections in the two host species are associated with closely related mitochondrial haplotypes, namely si I (associated with w Ha and w No in D. simulans) and se (associated with w Sh and w Sn in D. sechellia). To test the theoretical prediction that Wolbachia compatibility types can diverge rapidly, we injected w Sh and w Sn into D. simulans, to compare their CI properties to those of their sister strains w Ha and w No, respectively, in the same host genetic background. We found that within each pair of sister strains CI levels were similar and that sister strains were fully compatible. We conclude that the short period for which the Wolbachia sister strains have been evolving separated from each other was not sufficient for their CI properties to diverge significantly. [source] THE INCOMPATIBILITY OF VALUES AND THE IMPORTANCE OF CONSEQUENCES: MAX WEBER AND THE KANTIAN LEGACYPHILOSOPHICAL FORUM, Issue 1-2 2010HANS HENRIK BRUUN First page of article [source] Toward a New Sexual Selection Paradigm: Polyandry, Conflict and Incompatibility (Invited Article)ETHOLOGY, Issue 12 2003Jeanne A. Zeh Darwin's recognition that male,male competition and female choice could favor the evolution of exaggerated male traits detrimental to survival set the stage for more than a century of theoretical and empirical work on sexual selection. While this Darwinian paradigm represents one of the most profound insights in biology, its preoccupation with sexual selection as a directional evolutionary force acting on males has diverted attention away from the selective processes acting on females. Our understanding of female reproduction has been further confounded by discreet female mating tactics that have perpetuated the illusion of the monogamous female and masked the potential for conflict between the sexes. With advances in molecular techniques leading to the discovery that polyandry is a pervasive mating strategy, recognition of these shortcomings has brought the study of sexual selection to its current state of flux. In this paper, we suggest that progress in two key areas is critical to formulation of a more inclusive, sexual selection paradigm that adequately incorporates selection from the female perspective. First, we need to develop a better understanding of male × female and maternal × paternal genome interactions and the role that polyandry plays in providing females with non-additive genetic benefits such as incompatibility avoidance. Consideration of these interaction effects influencing natural selection on females is important because they can complicate and even undermine directional sexual selection on males. Secondly, because antagonistic coevolution maintains a balance between opposing sides that obscures the conflict itself, many more experimental evolution studies and interventionist investigations (e.g. gene knockouts) are needed to tease apart male manipulative adaptations and female counter-adaptations. It seems evident that the divisiveness and controversy that has plagued sexual selection theory since Darwin first proposed the idea has often stalled progress in this important field of evolutionary biology. What is now needed is a more pluralistic and integrative approach that considers natural as well as sexual selection acting on females, incorporates multiple sexual selection mechanisms, and exploits advances in physiology and molecular biology to understand the mechanisms through which males and females achieve reproductive success. [source] YOU CAN'T KEEP A GOOD PARASITE DOWN: EVOLUTION OF A MALE-KILLER SUPPRESSOR UNCOVERS CYTOPLASMIC INCOMPATIBILITYEVOLUTION, Issue 5 2008Emily A. Hornett Maternally inherited parasites are known to impose a wide variety of reproductive manipulations upon their host. These often produce strong selection on the host to suppress the parasite, resulting in a reduction in the frequency of the parasite. However, in the butterfly Hypolimnas bolina, infected with a Wolbachia bacterium, field data demonstrate that suppression of the male-killing phenotype does not depress parasite frequency. Here we test and verify one hypothesis to explain this apparent paradox,Wolbachia induces a second phenotype, Cytoplasmic Incompatibility (CI), in populations where host suppression has evolved. We further demonstrate that the capacity to induce CI has not evolved de novo, but instead is instantaneously expressed upon the survival of infected males. The significance of these results is threefold: (1) multiple phenotypes can provide Wolbachia with the means to maintain itself in a host following suppression of a single manipulative phenotype; (2) the ability to induce CI can remain hidden in systems in which male-killing is observed, just as the ability to induce male-killing may be obscured in strains exhibiting CI; (3) the evolutionary maintenance of CI in a system in which it is not expressed suggests a functional link with male-killing or other traits under selection. [source] Conjugal properties of the Sinorhizobium meliloti plasmid mobilomeFEMS MICROBIOLOGY ECOLOGY, Issue 3 2008Mariano Pistorio Abstract The biology and biochemistry of plasmid transfer in soil bacteria is currently under active investigation because of its central role in prokaryote adaptation and evolution. In this work, we examined the conjugal properties of the cryptic plasmids present in a collection of the N2 -fixing legume-symbiont Sinorhizobium meliloti. The study was performed on 65 S. meliloti isolates recovered from 25 humic soils of Argentina, which were grouped into 22 plasmid-profile types [i.e. plasmid operational taxonomic units (OTUs)]. The cumulative Shannon index calculated for the observed plasmid profiles showed a clear saturation plateau, thus indicating an adequate representation of the S. meliloti plasmid-profile types in the isolates studied. The results show that isolates of nearly 14% of the plasmid OTUs hosted transmissible plasmids and that isolates of 29% of the plasmid OTUs were able to retransfer the previously characterized mobilizable-cryptic plasmid pSmeLPU88b to a third recipient strain. It is noteworthy that isolates belonging to 14% of the plasmid OTUs proved to be refractory to the entrance of the model plasmid pSmeLPU88b, suggesting either the presence of surface exclusion phenomena or the occurrence of restriction incompatibility with the incoming replicon. Incompatibility for replication between resident plasmids and plasmid pSmeLPU88b was observed in c. 20% of the OTUs. The results reported here reveal a widespread compatibility among the conjugal functions of the cryptic plasmids in S. meliloti, and this fact, together with the observed high proportion of existing donor genotypes, points to the extrachromosomal compartment of the species as being an extremely active plasmid mobilome. [source] REVIEW: Optimality models in the age of experimental evolution and genomicsJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 9 2010J. J. BULL Abstract Optimality models have been used to predict evolution of many properties of organisms. They typically neglect genetic details, whether by necessity or design. This omission is a common source of criticism, and although this limitation of optimality is widely acknowledged, it has mostly been defended rather than evaluated for its impact. Experimental adaptation of model organisms provides a new arena for testing optimality models and for simultaneously integrating genetics. First, an experimental context with a well-researched organism allows dissection of the evolutionary process to identify causes of model failure , whether the model is wrong about genetics or selection. Second, optimality models provide a meaningful context for the process and mechanics of evolution, and thus may be used to elicit realistic genetic bases of adaptation , an especially useful augmentation to well-researched genetic systems. A few studies of microbes have begun to pioneer this new direction. Incompatibility between the assumed and actual genetics has been demonstrated to be the cause of model failure in some cases. More interestingly, evolution at the phenotypic level has sometimes matched prediction even though the adaptive mutations defy mechanisms established by decades of classic genetic studies. Integration of experimental evolutionary tests with genetics heralds a new wave for optimality models and their extensions that does not merely emphasize the forces driving evolution. [source] Photoinduced Microphase Separation in Block Copolymers: Exploring Shape Incompatibility of Mesogenic Side GroupsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 11 2010Yi Zhao Abstract Photoinduced microphase separation in block copolymers (BCP) was achieved for the first time, using a rationally designed diblock copolymer composed of two side-chain liquid crystalline polymers (SCLCP). The miscibility of the two blocks was promoted by the miscibility between the two types of mesognic side groups, while upon UV exposure inducing the trans,cis isomerization of azobenzene mesogens on one SCLCP, the shape incompatibility of bent cis isomers with an ordered liquid crystalline phase drove the separation of the two blocks resulting in a microphase separated morphology. This result shows the perspective of using light to process and organize BCP morphology and related nanostructures in a lithography-free manner. [source] Hazard ratings for organic peroxidesPROCESS SAFETY PROGRESS, Issue 2 2008Yih-Shing Duh Abstract Nine of commercially available organic peroxides were assessed with differential scanning calorimeter (DSC) and adiabatic calorimeters. These organic peroxides are cumene hydroperoxide (CHP), di- tert -butyl peroxide (DTBP), methyl-ethyl-ketone peroxide (MEKPO), tert -butyl hydroperoxide (TBHP), benzoyl peroxide (BPO), hydrogen peroxide, lauroyl peroxide (LPO), tert -butyl peroxybenzoate (TBPBZ), and dicumyl peroxide (DCPO). Exothermic onset temperatures, self-heat temperature and pressure rates, and heats of decomposition were measured and assessed. Adiabatic runaway reaction characteristics were determined by using ARC (accelerating rate calorimeter) and VSP2 (vent sizing package). Incompatibility, tests with several potential contaminants, was made using DSC, VSP2, and microcalorimeter. An incompatibility rating was developed using onset temperature, lowering of the onset temperature, heat of decomposition, maximum self-heat rate, adiabatic temperature rise, maximum pressure of decomposition, and maximum pressure rising rate, etc. © 2008 American Institute of Chemical Engineers Process Saf Prog 2008 [source] Technological Incompatibility, Endogenous Switching Costs and Lock-inTHE JOURNAL OF INDUSTRIAL ECONOMICS, Issue 3 2001Begoña Garcia Mariñoso Systems are goods comprising of durables that are sequentially updated with complements. With sequential purchases, if suppliers produce incompatible brands, consumers who upgrade systems with complements of a different brand must replace the durables they own. Thus, the price of these durables is an endogenous switching cost. The paper deals with the concern that firms may use incompatibility to create consumer's switching costs to reduce competition in aftermarkets. However, it shows that, with homogenous durables, and small costs of reaching compatibility, endogenous switching costs increase intertemporal price competition to the extent that producers prefer to have compatible technologies. [source] Incompatibility of prochlorperizine and ketoprofenANAESTHESIA, Issue 9 2001S. Kannan First page of article [source] Elementary Process Theory: a formal axiomatic system with a potential application as a foundational framework for physics supporting gravitational repulsion of matter and antimatterANNALEN DER PHYSIK, Issue 10 2010M.J.T.F. Cabbolet Abstract Theories of modern physics predict that antimatter having rest mass will be attracted by the earth's gravitational field, but the actual coupling of antimatter with gravitation has not been established experimentally. The purpose of the present research was to identify laws of physics that would govern the universe if antimatter having rest mass would be repúlsed by the earth's gravitational field. As a result, a formalized axiomatic system was developed together with interpretation rules for the terms of the language: the intention is that every theorem of the system yields a true statement about physical reality. Seven non-logical axioms of this axiomatic system form the Elementary Process Theory (EPT): this is then a scheme of elementary principles describing the dynamics of individual processes taking place at supersmall scale. It is demonstrated how gravitational repulsion functions in the universe of the EPT, and some observed particles and processes have been formalized in the framework of the EPT. Incompatibility of Quantum Mechanics (QM) and General Relativity (GR) with the EPT is proven mathematically; to demonstrate applicability to real world problems to which neither QM nor GR applies, the EPT has been applied to a theory of the Planck era of the universe. The main conclusions are that a completely formalized framework for physics has been developed supporting the existence of gravitational repulsion and that the present results give rise to a potentially progressive research program. [source] Oviposition preference and larval performance within a diverging lineage of lycaenid butterfliesECOLOGICAL ENTOMOLOGY, Issue 3 2004Matthew L. Forister Abstract. 1. The butterfly genus Mitoura in Northern California includes three nominal species associated with four host plants having parapatric or interdigitated ranges. Genetic analyses have shown the taxa to be very closely related, and adults from all host backgrounds will mate and produce viable offspring in the laboratory. Oviposition preference and larval performance were investigated with the aim of testing the hypothesis that variation in these traits can exist in a system in which non-ecological barriers to gene flow (i.e. geographic barriers and genetic incompatibilities) appear to be minimal. 2. Females were sampled from 12 locations throughout Northern California, including sympatric and parapatric populations associated with the four different host-plant species. Oviposition preference was assayed by confining wild-caught females with branches of all four host species and counting the number of eggs laid on each. Offspring were reared on the same host species and two measures of larval success were taken: per cent survival and pupal weight. 3. For populations associated with one of the hosts, incense cedar, the preference,performance relationship is simple: the host that females chose is the plant which results in the highest pupal weights for offspring. The preference,performance relationship for populations associated with the other hosts is more complex and may reflect different levels of local adaptation. The variation in preference and performance reported here suggests that these traits can evolve when non-ecological barriers to gene flow are low, and that differences in these traits may be important for the evolution of reproductive isolation within Mitoura. [source] Ecological selection maintains cytonuclear incompatibilities in hybridizing sunflowersECOLOGY LETTERS, Issue 10 2008Julianno B. M. Sambatti Abstract Despite the recent renaissance in studies of ecological speciation, the connection between ecological selection and the evolution of reproductive isolation remains tenuous. We tested whether habitat adaptation of cytoplasmic genomes contributes to the maintenance of reproductive barriers in hybridizing sunflower species, Helianthus annuus and Helianthus petiolaris. We transplanted genotypes of the parental species, reciprocal F1 hybrids and all eight possible backcross combinations of nuclear and cytoplasmic genomes into the contrasting xeric and mesic habitats of the parental species. Analysis of survivorship across two growing seasons revealed that the parental species' cytoplasms were strongly locally adapted and that cytonuclear interactions (CNIs) significantly affected the fitness and architecture of hybrid plants. A significant fraction of the CNIs have transgenerational effects, perhaps due to divergence in imprinting patterns. Our results suggest a common means by which ecological selection may contribute to speciation and have significant implications for the persistence of hybridizing species. [source] A reversibly immortalized human hepatocyte cell line as a source of hepatocyte-based biological supportADDICTION BIOLOGY, Issue 4 2001Naoya Kobayashi The application of hepatocyte transplantation (HTX) is increasingly envisioned for temporary metabolic support during acute liver failure and provision of specific liver functions in inherited liver-based metabolic diseases. Compared with whole liver transplantation, HTX is a technically simple procedure and hepatocytes can be cryopreserved for future use. A major limitation of this form of therapy in humans is the worldwide shortage of human livers for isolating an adequate number of transplantable human hepatocyes when needed. Furthermore, the numbers of donor livers available for hepatocyte isolation is limited by competition for their use in whole organ transplantation. Considering the cost of hepatocyte isolation and the need for immediate preparation of consistent and functional cells, it is unlikely that human hepatocytes can be obtained on such a scale to treat a large number of patients with falling liver functions. The utilization of xenogenic hepatocytes will result in additional concerns regarding transmission of infectious pathogens and immunological and physiological incompatibilities between animals and humans. An attractive alternative to primary human hepatocytes is the use of tightly regulated human hepatocyte cell lines. Such cell lines can provide the advantages of unlimited availability, sterility and uniformity. We describe here methods for creating transplantable human hepatocyte cell lines using currently available cell cultures and gene transfer technology. [source] The anatomy of autonomy: Reassessing the autonomy of the European CommissionEUROPEAN JOURNAL OF POLITICAL RESEARCH, Issue 4 2008JARLE TRONDAL Yet, the factual autonomy of the Commission remains largely unexplored, contributing to contradictory assessments of it. This study reassesses the behavioural autonomy of the Commission, as well as organisational conditions thereof. The article utilises one under-researched laboratory of the Commission: temporary officials (SNEs). SNEs may serve as a crucial test-bed of Commission autonomy due to their ambiguous affiliation towards the Commission. Whereas past studies claim that SNEs have a predominantly intergovernmental behavioural pattern, this study demonstrates that the SNEs blend departmental, epistemic and supranational behavioural dynamics, thereby safeguarding their behavioural autonomy. Understanding Commission autonomy requires that the organisational anatomy of the Commission organisation be carefully considered. The organisational anatomy is measured by considering four independent variables: the organisational composition of the Commission services; organisational incompatibilities across levels of governance; recruitment procedures of Commission officials through a so-called ,submarine' approach; and socialisation dynamics inside the Commission. The autonomy of the Commission is organisationally contingent and not only subject to what has been called ,actors' conspicuous desire for autonomy'. [source] DO WOLBACHIA- ASSOCIATED INCOMPATIBILITIES PROMOTE POLYANDRY?EVOLUTION, Issue 1 2008Fleur E. Champion de Crespigny The genetic incompatibility avoidance hypothesis as an explanation for the polyandrous mating strategies (mating with more than one male) of females of many species has received significant attention in recent years. It has received support from both empirical studies and a meta-analysis, which concludes that polyandrous females enjoy increased reproductive success through improved offspring viability relative to monandrous females. In this study we investigate whether polyandrous female Drosophila simulans improve their fitness relative to monandrous females in the face of severe Wolbachia- associated reproductive incompatibilities. We use the results of this study to develop models that test the predictions that Wolbachia should promote polyandry, and that polyandry itself may constrain the spread of Wolbachia. Uniquely, our models allow biologically relevant rates of incompatibility to coevolve with a polyandry modifier allele, which allows us to evaluate the fate of the modifier and that of Wolbachia. Our empirical results reveal that polyandrous females significantly reduce the reproductive costs of Wolbachia, owing to infected males being poor sperm competitors. The models show that this disadvantage in sperm competition can inhibit or prevent the invasion of Wolbachia. However, despite the increased reproductive success obtained by polyandrous females, the spread of a polyandry modifier allele is constrained by any costs that might be associated with polyandry and the low frequency of incompatible matings when Wolbachia has reached a stable equilibrium. Therefore, although incompatibility avoidance may be a benefit of polyandry, our findings do not support the hypothesis that genetic incompatibilities caused by Wolbachia promote the evolution of polyandry. [source] POPULATION DIFFERENTIATION IN THE BEETLE TRIBOLIUM CASTANEUM.EVOLUTION, Issue 3 2007We used joint-scaling analyses in conjunction with rearing temperature variation to investigate the contributions of additive, non-additive, and environmental effects to genetic divergence and incipient speciation among 12 populations of the red flour beetle, Tribolium castaneum, with small levels of pairwise nuclear genetic divergence (0.033 < Nei's D < 0.125). For 15 population pairs we created a full spectrum of line crosses (two parental, two reciprocal F1's, four F2's, and eight backcrosses), reared them at multiple temperatures, and analyzed the numbers and developmental defects of offspring. We assayed a total of 219,388 offspring from 5147 families. Failed crosses occurred predominately in F2's, giving evidence of F2 breakdown within this species. In all cases where a significant model could be fit to the data on offspring number, we observed at least one type of digenic epistasis. We also found maternal and cytoplasmic effects to be common components of divergence among T. castaneum populations. In some cases, the most complex model tested (additive, dominance, epistatic, maternal, and cytoplasmic effects) did not provide a significant fit to the data, suggesting that linkage or higher order epistasis is involved in differentiation between some populations. For the limb deformity data, we observed significant genotype-by-environment interaction in most crosses and pure parent crosses tended to have fewer deformities than hybrid crosses. Complexity of genetic architecture was not correlated with either geographic distance or genetic distance. Our results support the view that genetic incompatibilities responsible for postzygotic isolation, an important component of speciation, may be a natural but serendipitous consequence of nonadditive genetic effects and structured populations. [source] ACCUMULATING DOBZHANSKY-MULLER INCOMPATIBILITIES: RECONCILING THEORY AND DATAEVOLUTION, Issue 6 2004John J. Welch Abstract Theoretical models of the accumulation of Dobzhansky-Muller incompatibilities (DMIs) are studied, and in particular, the framework introduced by Orr (1995) and a verbal model introduced by Kondrashov et al. (2002). These models embody very different assumptions about the relationship between the substitution process underlying evolutionary divergence and the formation of incompatibilities. These differences have implications for our ability to make inferences about the divergence from patterns in the relevant data. With this in mind, the models are investigated for their ability to account for three patterns evident in this data: (1) the asymmetrical nature of incompatibilities under reciprocal introgression; (2) the finding that multiple concurrent introgressions may be necessary for an incompatibility to form; and (3) the finding that the probability of obtaining an incompatibility by introgressing a single amino acid remains roughly constant over a wide range of genetic distances. None of the models available in the literature can account for all of the empirical patterns. However, modified versions of the models can do so. Ways of discriminating between the different models are then discussed. [source] THE EVOLUTION OF PREMATING ISOLATION: LOCAL ADAPTATION AND NATURAL AND SEXUAL SELECTION AGAINST HYBRIDSEVOLUTION, Issue 5 2004Maria R. Servedio Abstract Although reinforcement is ostensibly driven by selection against hybrids, there are often other components in empirical cases and theoretical models of reinforcement that may contribute to premating isolation. One of these components is local adaptation of a trait used in mate choice. I use several different comparisons to assess the roles that local adaptation and selection against hybrids may play in reinforcement models. Both numerical simulations of exact recursion equations and analytical weak selection approximations are employed. I find that selection against hybrids may play a small role in driving preference evolution in a reinforcement model where the mating cue is separate from loci causing hybrid incompatibilities. When females have preferences directly for purebreds of their own population, however, selection against hybrids can play a large role in premating isolation evolution. I present some situations in which this type of selection is likely to exist. This work also illustrates shortfalls of using a weak selection approach to address questions about reinforcement. [source] INITIAL STAGES OF REPRODUCTIVE ISOLATION IN TWO SPECIES OF THE ENDANGERED SONORAN TOPMINNOWEVOLUTION, Issue 12 2003Carla R. Hurt Abstract Long-term geographic isolation can result in reproductive incompatibilities due to forces such as mutation, genetic drift, and differential selection. In the Sonoran topminnow, molecular genetic studies of mtDNA, microsatellites, and MHC genes have shown that the endangered Gila and Yaqui topminnows are substantially different, suggesting that divergence took place approximately two million years ago. Here we examined hybrid crosses and backcrosses between these two allopatric taxa to evaluate the accumulation of postmating barriers to reproduction. These results are then compared with results from a previous study where male topminnows were shown to mate assortatively with conspecific females. Despite their preference for conspecific mates, both types of interspecific crosses successfully produced offspring. There was evidence of reduced hybrid fitness, including smaller mean brood size and male-biased sex ratio, for some classes of backcrosses. Brood sizes and interbrood intervals varied significantly when hybrids were subdivided into different cross categories. Our results illustrate the importance of distinctly defining hybrid classes in studies of reproductive isolation. To our knowledge, this is the first such detailed evolutionary analysis in endangered fish taxa. [source] GENETIC DISSECTION OF HYBRID INCOMPATIBILITIES BETWEEN DROSOPHILA SIMULANS AND D. MAURITIANA.: III.EVOLUTION, Issue 11 2003AND IMPLICATIONS FOR HALDANE, DEGREE OF DOMINANCE, HETEROGENEOUS ACCUMULATION OF HYBRID INCOMPATIBILITIES Abstract The genetic basis of Haldane,rule was investigated through estimating the accumulation of hybrid incompatibilities between Drosophila simulans and D. mauritiana by means of introgression. The accumulation of hybrid male sterility (HMS) is at least 10 times greater than that of hybrid female sterility (HFS) or hybrid lethality (HL). The degree of dominance for HMS and HL in a pure D. simulans background is estimated as 0.23,0.29 and 0.33,0.39, respectively; that for HL in an F1 background is unlikely to be very small. Evidence obtained here was used to test the Turelli-Orr model of Haldane's rule. Composite causes, especially, faster-male evolution and recessive hybrid incompatibilities, underlie Haldane's rule in heterogametic male taxa such as Drosophila (XY male and XX female). However, if faster-male evolution is driven by sexual selection, it contradicts Haldane's rule for sterility in hetero-gametic-female taxa such as Lepidoptera (ZW female and ZZ male). The hypothesis of a faster-heterogametic-sex evolution seems to fit the current data best. This hypothesis states that gametogenesis in the heterogametic sex, instead of in males per se, evolves much faster than in the homogametic sex, in part because of sex-ratio selection. This hypothesis not only explains Haldane's rule in a simple way, but also suggests that genomic conflicts play a major role in evolution and speciation. [source] ACCUMULATING POSTZYGOTIC ISOLATION GENES IN PARAPATRY: A NEW TWIST ON CHROMOSOMAL SPECIATIONEVOLUTION, Issue 3 2003Arcadi Navarro Abstract Chromosomal rearrangements can promote reproductive isolation by reducing recombination along a large section of the genome. We model the effects of the genetic barrier to gene flow caused by a chromosomal rearrangement on the rate of accumulation of postzygotic isolation genes in parapatry. We find that, if reproductive isolation is produced by the accumulation in parapatry of sets of alleles compatible within but incompatible across species, chromosomal rearrangements are far more likely to favor it than classical genetic barriers without chromosomal changes. New evidence of the role of chromosomal rearrangements in parapatric speciation suggests that postzygotic isolation is often due to the accumulation of such incompatibilities. The model makes testable qualitative predictions about the genetic signature of speciation. [source] ACCUMULATION OF DOBZHANSKY-MULLER INCOMPATIBILITIES WITHIN A SPATIALLY STRUCTURED POPULATIONEVOLUTION, Issue 1 2003ALEXEY S. KONDRASHOV Abstract., A simple, deterministic analysis predicts that accumulation of Dobzhansky-Muller incompatibilities by a spatially structured population strongly depends on the number of negative interactions of an allele. If an allele can be incompatible with alleles at only one locus, incompatibilities accumulate linearly with time. In contrast, if an allele can participate in multiple pairwise incompatibilities with alleles at different loci, the expected number of incompatibilities eventually increases quadratically. [source] Two Job Cyclic Scheduling With Incompatibility ConstraintsINTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 2 2001Piero Persi The present paper deals with the problem of scheduling several repeated occurrences of two jobs over a finite or infinite time horizon in order to maximize the yielded profit. The constraints of the problem are the incompatibilities between some pairs of tasks which require a same resource. [source] Economic and Legal Issues in Reducing the Eurosystem's Excess of International ReservesJCMS: JOURNAL OF COMMON MARKET STUDIES, Issue 3 2004Harald Badinger Economic studies suggest that the Eurosystem's international reserves ($370 billion) could be reduced by up to half of its existing level. The article discusses the likely size and distribution of excess reserves and proposals for their uses. Small economic gains can be expected from a reserve reduction, as well as an elimination of incompatibilities and conflicts of interest between the conduct of monetary and investment policy. A careful and co-ordinated reserve reduction would pose no threat to financial stability, making it also admissible from a legal perspective against the background of Art. 31 of the ESCB (European System of Central Banks) Statute. Finally, transferring reserves as an extraordinary gain to the government does not constitute monetary financing as prohibited by Art. 101 EC Treaty. [source] Differential performance of reciprocal hybrids in multiple environmentsJOURNAL OF ECOLOGY, Issue 6 2008Sarah Kimball Summary 1Closely related taxa may be maintained as distinct species by a variety of reproductive isolating mechanisms. These include: inability to produce hybrid offspring, endogenous selection against hybrids in the form of genomic incompatibilities, and exogenous selection observable in genotype-by-environment interactions. To understand the relative importance of these three isolating mechanisms, we performed hand-pollination and reciprocal transplant experiments in a natural plant hybrid zone. 2We measured reproductive isolation by making crosses between two parent species of Penstemon and naturally occurring hybrids. Inclusion of reciprocal hybrid crosses allowed us to determine whether fitness components differed depending on the identity of the mother. 3Hybrid performance was evaluated in the greenhouse and in a reciprocal transplant experiment in the field. We measured fruit set, seed set, seed weight, time required for fruits to mature and seedling growth for potted plants. To test for exogenous isolation, we planted pure parents, reciprocal F1 hybrids and later generation hybrids in a reciprocal transplant experiment, and measured survival. 4On average, interspecific crosses produced as many seeds as conspecific crosses. Hybrid performance was also equal to or greater than parents in all environments, including the greenhouse and all field gardens, indicating a lack of endogenous isolation. Parent species and reciprocal F1 hybrids differed in many traits measured. In each field garden, the hybrid with the native cytoplasm had a higher survival rate, suggesting local adaptation to different elevations. 5Synthesis. Exogenous factors that differ along elevational gradients can be more important than intrinsic genetic incompatibilities in determining the fitness of plant hybrids. Our results illustrate the importance of studying hybrid performance in multiple environments and in generating reciprocal hybrids to test for isolating mechanisms in natural hybrid zones. [source] Postzygotic incompatibilities between the pupfishes, Cyprinodon elegans and Cyprinodon variegatus: hybrid male sterility and sex ratio biasJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 6 2006C. TECH Abstract I examined the intrinsic postzygotic incompatibilities between two pupfishes, Cyprinodon elegans and Cyprinodon variegatus. Laboratory hybridization experiments revealed evidence of strong postzygotic isolation. Male hybrids have very low fertility, and the survival of backcrosses into C. elegans was substantially reduced. In addition, several crosses produced female-biased sex ratios. Crosses involving C. elegans females and C. variegatus males produced only females, and in backcrosses involving hybrid females and C. elegans males, males made up approximately 25% of the offspring. All other crosses produced approximately 50% males. These sex ratios could be explained by genetic incompatibilities that occur, at least in part, on sex chromosomes. Thus, these results provide strong albeit indirect evidence that pupfish have XY chromosomal sex determination. The results of this study provide insight on the evolution of reproductive isolating mechanisms, particularly the role of Haldane's rule and the ,faster-male' theory in taxa lacking well-differentiated sex chromosomes. [source] Synthesis and self-assembly of fluorinated block copolymersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2002Marc A. Hillmyer Abstract Fluorinated block copolymers combine the unique properties of fluoropolymers and the intriguing self-assembly of hybrid macromolecules. The preparation of the title molecules by selective fluorination procedures and the effect of fluorine incorporation on the material thermodynamics are presented. We highlight two fluorination schemes developed in our laboratory, difluorocarbene and perfluoroalkyliodide additions to polydienes, that allow for the selective and tunable incorporation of different fluorinated groups into model block copolymers. The fluorination changes the physical properties of the parent materials and leads to interesting changes in the component incompatibilities. The role of fluorination in determining block copolymer thermodynamics in both the solid state and in solution and in ultimately exploiting fluorination to produce novel, higher order structures is central to our research efforts. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 1,8, 2002 [source] | |||||||||||||||||||||||||||||||||||||||||||