bluuebunny/crossref_metadata_2025_split huggingface dataset:
Testing hypotheses on the dispersal and evolutionary history of freshwater mussels (Mollusca: Bivalvia: Unionidae)
Authors: Nagel  
Published: March 2003

Abstract
The relationship between dispersal and differentiation of the European freshwater mussel Unio pictorum (Linnaeus, 1758) was studied with molecular genetic methods. Forty-two populations from France, Italy and central Europe were analysed. Genetic relationships were assessed from the geographical distribution of allele frequencies at 17 enzyme loci. Neighbouring groups of populations show small to moderate mean genetic distances (0.020 &lt; Dmean &lt; 0.263). With a few exceptions the genetic affinities of the populations are the closest within the same drainage basin. In central Europe and Northern Italy genetic differences between drainage systems are relatively large. Populations from north-eastern Italy are genetically similar to Danubian populations. Mussels from the islands of Corsica and Sardinia are more closely related to populations from the Italian peninsula than to French populations from the Rhône drainage system. Genetic relationships within U. pictorum from central Europe reflect palaeogeographical relationships between river systems during the Pliocene and Pleistocene. Literature data on two North American unionid species and one European fish species show the same relationship between genetic diversity and the history of drainage systems, although the correlations are less strong. In France and Italy this correspondence is much less evident. Population dynamic processes and human activities leading to populational bottlenecks might have obscured it.
Estimating variance components and heritabilities in the wild: a case study using the ‘animal model’ approach
Authors: Milner  , Pemberton  , Brotherstone  , Albon  
Published: March 2003

Abstract
Using a genealogy containing over 1800 dams and nearly 400 sires (estimated by genetic paternity techniques), combined with maximum likelihood procedures and an ‘animal model’, we have estimated the heritabilities, genetic correlations and variance components of three morphometric traits in the Soay sheep (Ovis aries) on St Kilda, Scotland. This approach allows heritabilities to be estimated in natural populations that violate the assumptions of offspring–parent regression methods. Maternal (or paternal) effects can also be estimated under natural conditions. We demonstrate that all the traits, body weight, hind leg length and incisor arcade breadth, have low but significant heritabilities. Body weight, the trait that experiences the strongest selection, had the lowest heritability but the highest additive genetic coefficient of variation. An evolutionary response to selection is predicted. When maternal effects were not taken into consideration heritabilities were over-estimated, although this effect was only significant in female offspring.
Immunoglobulin plasma concentration in relation to egg laying and mate ornamentation of female barn swallows (Hirundo rustica)
Authors: Saino N. , Martinelli R. , Møller A. P. 
Published: March 2003

Abstract
In vertebrates, offspring have a relatively inefficient immune system soon after birth. Female birds transmit immunoglobulins to the egg, which can confer protection against parasites to their offspring after hatching, but allocation of immune factors can depend on the reproductive value of the offspring as affected, for example, by the quality of their father. We analyse the variation in immunoglobulin levels of female barn swallows (Hirundo rustica) during the breeding cycle in relation to the expression of a secondary sexual character of their mates. Circulating immunoglobulins peaked on approximately the day before that of laying of their first egg, but postlaying concentration was similar to the concentration well before laying. Immunoglobulin levels per unit volume of plasma were lower for females breeding late compared with those breeding early. Haematocrit of females reached an absolute minimum on the day of laying of the third egg. In males, concentration of immunoglobulins relative to other plasma proteins did not change in relation to the breeding stage. Smaller relative concentrations of immunoglobulins and haematocrit were observed in males breeding late in the season. Immunoglobulin concentration of females was positively correlated with the level of ornamentation of their mates. These results suggest that females alter their immune profile to transmit humoral factors providing immune defence against pathogens to their offspring after hatching. This enhancement of immune protection is larger when the offsprings are of relatively large reproductive value as when sired by high quality males. Alternatively, females with relatively large immunoglobulin concentration preferentially mate with the most ornamented males.
Resource allocation in the red ant Myrmica ruginodis– an interplay of genetics and ecology
Authors: Walin L. , Seppä P. 
Published: March 2003

Abstract
Worker-queen conflicts over reproductive allocation (colony maintenance vs. reproduction) and sex allocation (females vs. males) were examined in two populations of the facultatively polygynous ant Myrmica ruginodis. Plasticity of social organization in the form of two co-existing social types (microgyna and macrogyna) has a profound effect on reproductive allocation. Workers control sex allocation by biasing sex ratios towards their own interest, but local resource competition (LRC) because of restricted dispersal of microgyna females resulted in male bias in one study population. Colony sex ratios were split and followed the predictions of the split sex ratio theory: single queen colonies with higher relatedness asymmetry (RA) produced more females than multiple queen colonies with lower RA. Single and multiple queen colonies showed similar patterns in most aspects of their reproduction, and reproductive allocation could not be explained by the hypothesis tested. This suggests that reproductive allocation conflict is of minor importance in M. ruginodis.
The genic view of the process of speciation
Authors: Wu Chung-I 
Published: March 2003

Abstract
The unit of adaptation is usually thought to be a gene or set of interacting genes, rather than the whole genome, and this may be true of species differentiation. Defining species on the basis of reproductive isolation (RI), on the other hand, is a concept best applied to the entire genome. The biological species concept (BSC; Mayr, 1963) stresses the isolation aspect of speciation on the basis of two fundamental genetic assumptions – the number of loci underlying species differentiation is large and the whole genome behaves as a cohesive, or coadapted genetic unit. Under these tenets, the exchange of any part of the genomes between diverging groups is thought to destroy their integrity. Hence, the maintenance of each species’ genome cohesiveness by isolating mechanisms has become the central concept of species. In contrast, the Darwinian view of speciation is about differential adaptation to different natural or sexual environments. RI is viewed as an important by product of differential adaptation and complete RI across the whole genome need not be considered as the most central criterion of speciation. The emphasis on natural and sexual selection thus makes the Darwinian view compatible with the modern genic concept of evolution. Genetic and molecular analyses of speciation in the last decade have yielded surprisingly strong support for the neo-Darwinian view of extensive genetic differentiation and epistasis during speciation. However, the extent falls short of what BSC requires in order to achieve whole-genome ‘cohesiveness’. Empirical observations suggest that the gene is the unit of species differentiation. Significantly, the genetic architecture underlying RI, the patterns of species hybridization and the molecular signature of speciation genes all appear to support the view that RI is one of the manifestations of differential adaptation, as Darwin (1859, Chap. 8) suggested. The nature of this adaptation may be as much the result of sexual selection as natural selection. In the light of studies since its early days, BSC may now need a major revision by shifting the emphasis from isolation at the level of whole genome to differential adaptation at the genic level. With this revision, BSC would in fact be close to Darwin’s original concept of speciation.
Kin structure and queen execution in the Argentine ant Linepithema humile: M. REUTER ET AL.
Authors: Reuter M. , Balloux F. , Lehmann L. , Keller L. 
Published: March 2003

Abstract
Every spring, workers of the Argentine Ant Linepithema humile kill a large proportion of queens within their nests. Although this behaviour inflicts a high energetic cost on the colonies, its biological significance has remained elusive so far. An earlier study showed that the probability of a queen being executed is not related to her weight, fecundity, or age. Here we test the hypothesis that workers collectively eliminate queens to which they are less related, thereby increasing their inclusive fitness. We found no evidence for this hypothesis. Workers of a nest were on average not significantly less related to executed queens than to surviving ones. Moreover, a population genetic analysis revealed that workers were not genetically differentiated between nests. This means that workers of a given nest are equally related to any queen in the population and that there can be no increase in average worker–queen relatedness by selective elimination of queens. Finally, our genetic analyses also showed that, in contrast to workers, queens were significantly genetically differentiated between nests and that there was significant isolation by distance for queens.
Laboratory environments are not conducive for allopatric speciation
Authors: Florin A.-B. , Ödeen A. 
Published: March 2003

Abstract
We review published records of laboratory experiments on peripatric and vicariance allopatric speciation to address the following three questions: (1) What was the true effect size of reproductive isolation? (2) Was the reproductive isolation persistent? (3) What influenced the development of isolation? Contrary to popular belief, laboratory evidence for allopatric speciation is quite weak. Assortative mating was only found among derived populations in vicariance experiments. Reproductive isolation against control populations was only intermittent, so there is reason to doubt if some cases showing significant reproductive isolation really should be attributed to speciation. The method of testing was at least as important as the speciation model. Experimental populations tested against each other were the most likely to demonstrate reproductive isolation. This study suggests that allopatric speciation experiments are more likely to yield conclusive results under divergent selection than under drift, and points to the benefits of large populations and many generations.
Evolutionary dynamics of a selfishly spreading gene that stimulates sexual reproduction in a partially sexual population
Authors: Johnson L. J. , Brookfield J. F. Y. 
Published: March 2003

Abstract
The ability of selfishly spreading DNA sequences to invade host populations is intimately bound up with sex. In the absence of sexual reproduction, an element that lowers the fitness of its host and which is initially found in only some of the population will inevitably be lost by natural selection. This will occur even if the element can spread selfishly in the genomes of those individuals which initially possessed it. Here, we create a model in which such a gene is introduced into a population in which individuals sometimes reproduce sexually and sometimes asexually. The element can raise the level of sexuality in its bearers. There is selection against those individuals with the gene (i.e. it is selfish), and a further selective cost to sexual reproduction. The dynamics of the model that arises from these simple assumptions are remarkably complex, with fixation or loss of the selfish gene, unstable and stable equilibria, and effective neutrality all being possible dependent on the parameter values. A selfish gene that increases the level of sexuality of its bearers will tend to have a higher likelihood of invading a host population, and faster spread, but a lower likelihood of spreading to fixation, than an equivalent gene with no effect on sex.
Control of male production in the swarm-founding wasp, Polybioides tabidus
Authors: Henshaw M. T. , Queller D. C. , Strassmann J. E. 
Published: March 2003

Abstract
In social insect colonies, male production may involve conflicts over the sex ratio, worker vs. queen reproduction, and each queen's contribution to the males when there are multiple queens. We examined male production in the swarm-founding, multiple-queened wasp, Polybioides tabidus, for which previous work suggested worker control of the sex ratios. We found that queens produced the males in accord with the collective worker preference. We also found that diploid males were produced, but only in association with haploid males. Simulations show they should have been produced in other colonies as well and their absence indicates that they were killed in some of these other colonies. The pattern of their removal indicates that P. tabidus cannot distinguish diploid from haploid males, and that haploid males would have been removed from these colonies too. This provides evidence that the workers are able to manipulate male production when collective preferences dictate.
A gene's eye view of epistasis, selection and speciation
Authors: Wade M. J. 
Published: March 2003

Abstract
In this mini-review, I discuss the effects of gene interaction or epistasis from a `gene's eye view.' By a `gene's eye view' of epistasis, I mean that I will consider a single, bi-allelic locus, A, whose effects on fitness result only from its interactions with alleles of another, unknown locus, X. I will show how changes in the frequencies of alleles at the background locus affect the relationship of alleles at the A-locus to fitness. Changing the genetic background changes the fundamental characteristics of the A-locus, such as the magnitude and sign of allelic effects on fitness, and, consequently, it changes the strength and pattern of selection. I consider each of the four kinds of pair–wise interactions between two loci and show that some kinds of epistasis are more sensitive than others to population genetic subdivision. Lastly, I show that some kinds of epistasis are more likely than others to affect the process of speciation and contribute to or be responsible for general genetic features of interspecific hybrids, such as Haldane's rule.
No evidence for parallel sympatric speciation in cichlid species of the genus Pseudotropheus from north-western Lake Malawi
Authors: Rico C. , Bouteillon P. , Van Oppen M. J. H. , Knight M. E. , Hewitt G. M. , Turner G. F. 
Published: March 2003

Abstract
To test the hypothesis of parallel speciation by sexual selection, we examined length variation at six microsatellite loci of samples from four sites of four to six putative species belonging to two subgenera of rocky shore mbuna cichlids from Lake Malawi. Almost all fixation indices were significantly different from zero, suggesting that there is presently little or no gene flow among allopatric populations or sympatric species. Analysis of variance indicated that genetic distances among allopatric populations of putative conspecifics were significantly lower than among sympatric populations of heterospecifics. The topology of trees based on distance matrices was also largely consistent with the hypothesis that the putative species are monophyletic and have thus not evolved in parallel in their present locations. If parallel speciation does occur in Malawi cichlids, it may be on a larger spatial scale than investigated in our study.
Frequency dependence in matings with water-borne sperm
Authors: Pemberton A. J. , Noble L. R. , Bishop J. D. D. 
Published: March 2003

Abstract
Negative frequency-dependent mating success – the rare male effect – is a potentially powerful evolutionary force, but disagreement exists as to whether previous work, focusing on copulating species, has robustly demonstrated this phenomenon. Noncopulating sessile organisms that release male gametes into the environment but retain their eggs for fertilization may routinely receive unequal mixtures of sperm. Although promiscuity seems unavoidable it does not follow that the resulting paternity obeys ‘fair raffle’ expectations. This study investigates frequency dependence in the mating of one such species, the colonial ascidian Diplosoma listerianum. In competition with an alternative sperm source males fathered more progeny if previously mated to a particular female than if no mating history existed. This suggests positive frequency-dependent selection, but may simply result from a mate order effect involving sperm storage. With fewer acclimation matings, separated by longer intervals, this pattern was not found. When, in a different experimental design, virgin females were given simultaneous mixtures of gametes at widely divergent concentrations, sperm at the lower frequency consistently achieved a greater than expected share of paternity – a rare male effect. A convincing argument as to why D. listerianum should favour rare sperm has not been identified, as sperm rarity is expected to correlate very poorly with ecological or genetic male characteristics in this pattern of mating. The existence of nongenetic female preferences at the level of colony modules, analogous in effect to fixed female preferences, is proposed. If visible to selection, indirect benefits from increasing the genetic diversity of a sibship appear the only likely explanation of the rare male effect in this system as the life history presents virtually no costs to multiple mating, and a near absence of direct (resource) benefits, whereas less controversial hypotheses of female promiscuity (e.g. trade up, genetic incompatibility) do not seem appropriate.
Differential strength of sex-biased hybrid inferiority in impeding gene flow may be a cause of Haldane's rule
Authors: Wang Ren-Xue 
Published: March 2003

Abstract
In animals, if one sex of the F1 hybrid between two species is sterile or inviable, it is usually the heterogametic (XY or WZ) sex. This phenomenon, known as Haldane's rule, is currently thought to be coincidentally caused by different mechanisms in separate entities. The following questions have never been asked: Are heterogametic and homogametic inferiority (sterility or inviability) equivalent as isolating mechanisms? Could discrepancies between them, if existing, produce Haldane's rule? Here I consider sex-biased hybrid inferiority strictly as an isolating mechanism, and quantitatively evaluate its strength in impeding gene flow. The comparison reveals that the ability of sex-biased inferiority to impede gene flow varies according to the sex and chromosome involved. Heterogametic inferiority is a weaker barrier when unidirectional and a much stronger one when in compound reciprocal directions, compared with homogametic inferiority. Such differential strength may affect divergence in speciation and produce Haldane's rule.
Blood donors infected with the hepatitis B virus but persistently lacking antibodies to the hepatitis B core antigen
Authors: Laperche S. , Guitton C. , Smilovici W. , Courouce A. M. 
Published: March 2003

Background and objectivesAntibodies to the core of hepatitis B virus (anti‐HBc) are considered to be the best serologically reliable markers of hepatitis B virus (HBV) infection. Through a national epidemiological survey, two young and first‐time blood donors, originating from HBV‐endemic areas, were identified as HBV carriers with an absence of anti‐HBc reactivity.Materials and MethodsWe followed up these two subjects in order to investigate the evolution of their HBV serological profiles. Nucleotide sequencing was performed of the entire pre‐C/C region of the strains infecting these donors.ResultsThe same serological profile of active viral replication with an apparent persistent lack of anti‐HBc and normal alanine aminotransferase (ALT) levels was found for both subjects throughout a follow‐up of 19 months and 4 months, respectively. Neither donor was immunocompromised. Nucleotide sequence analysis of the pre‐C/C region did not show mutations or deletions in encoded proteins.ConclusionThe hypothesis of an in utero HBV infection responsible for an immune tolerance to HBV seems to be the most probable explanation for this particular immunological situation. Such occurrences in the blood donor population are probably rare as less than 0·1% of hepatitis B surface antigen (HBsAg)‐positive donors exhibit such a profile, in our experience. Moreover, this phenomenon does not impose a risk of HBV transmission by blood donation, as the exclusion of HBV‐infected blood donation is based on HBsAg detection. However, such a risk might be encountered with the hepatitis C virus (HCV) for which at present only antibodies to HCV are screened.
Collaborative study to calibrate hepatitis C virus genotypes 2–6 against the HCV International Standard, 96/790 (genotype 1)
Authors: Saldanha J. , Heath A. ,   Collaborative Study Group
Published: March 2003

Background and ObjectivesA major requirement of a hepatitis C virus (HCV) RNA nucleic acid amplification technology (NAT) assay validation is the ability of the assay to detect the six major genotypes of HCV with equivalent sensitivities. The aim of this study was to characterize and calibrate an HCV genotype panel for use in such studies.Materials and MethodsPanels consisting of the first International Standard (IS) for HCV RNA NAT assays (96/790; HCV genotype 1a) and isolates of genotypes 2–6 were sent to 17 laboratories worldwide which use a variety of NAT tests, both qualitative and quantitative. The HCV RNA content of each panel member was determined and the mean titre calculated in International Units/ml (IU/ml).ResultsThe calculated mean titres (calibrated against the HCV International Standard), in log10IU/ml, of the genotype 2–6 samples were 3·99, 3·81, 4·14, 4·18 and 4·61, respectively.ConclusionsAn HCV genotype panel, calibrated in IU/ml, has been established and should be valuable for assay validation. All the genotypes were detected by all the assays used, but it was not possible to demonstrate that the genotypes were detected with equal efficiencies.
Stage Sensitivity of Mungbean (Vigna radiata L. Wilczek) to an Elevated Level of Carbon Dioxide
Authors: Das M. , Zaidi P. H. , Pal M. , Sengupta U. K. 
Published: March 2003

AbstractAn experiment was undertaken using open‐top chambers to study the effect of CO2 enrichment on crop growth and to assess the variation related to the time of CO2 exposure. In general, enriched CO2 conditions (600 ± 50 p.p.m.) in the chamber positively affected the growth and development of mungbean (Vigna radiata), a short‐duration (60–65 days) summer pulse crop. However, there was significant variability in the effect of the crop stage/time of CO2 exposure. It was observed that high CO2 exposure at an early growth stage [0–20 days after germination (DAG)] had a larger effect than that at a later growth stage (21–40 DAG). The experiment also provided a means of assessing the short‐ and long‐term effects of elevated CO2 on the carbon exchange rate at both stages of exposure. The study revealed that the sensitivity of plants to high CO2 was more pronounced with respect to net photosynthetic rate. The overall photosynthetic activity gave greater growth and development of plants under high CO2.