bluuebunny/crossref_metadata_2025_split huggingface dataset:
Density-dependent natural selection in Drosophila: correlations between feeding rate, development time and viability
Authors: Borash  , Teotónio  , Rose  , Mueller  
Published: March 2003

Abstract
We have previously hypothesized that density-dependent natural selection is responsible for a genetic polymorphism in crowded cultures of Drosophila. This genetic polymorphism entails two alternative phenotypes for dealing with crowded Drosophila larval cultures. The first phenotype is associated with rapid development, fast larval feeding rates but reduced absolute viability, especially in the presence of nitrogenous wastes like ammonia. The second phenotype has associated with it the opposite set of traits, slow development, slow feeding rates and higher viability. We suggested that these traits are associated due to genetic correlations and that an important selective agent in crowded larval cultures was high levels of ammonia. To test this hypothesis we have examined viability and larval feeding rates in populations kept at low larval densities but selected directly for (i) rapid egg-to-adult development, (ii) tolerance of ammonia in the larval environment and (iii) tolerance of urea in the larval environment. Consistent with our hypothesis we found that (i) larvae selected for rapid development exhibited increased feeding rates, and decreased viability in food laced with ammonia or urea relative to controls, and (ii) larvae selected to tolerate either ammonia or urea in their larval environment show reduced feeding rates but elevated survival in toxin-laced food relative to controls. It would appear that development time and larval feeding rate are important characters for larvae adapting to crowded cultures. The correlated fitness effects of these characters provide important insights into the nature of density-dependent natural selection.
Temperature adaptation in a geographically widespread zooplankter, Daphnia magna
Authors: Mitchell  , Lampert  
Published: March 2003

Abstract
Evidence for temperature adaptation in Daphnia magna was inferred from variation in the shape of temperature reaction norms for somatic growth rate, a fitness-related trait. Ex-ephippial clones from eight populations across Europe were grown under standardized conditions after preacclimation at five temperatures (17–29 °C). Significant variation for grand mean growth rates occurred both within populations (among clones) and between populations. Genetic variation for reaction norm shape was found within populations, with temperature-dependent trade-offs in clone relative fitness. However, the population average responses to temperature were similar, following approximately parallel reaction norms. The among-population variation is not evidence for temperature adaptation. Lack of temperature adaptation at the population level may be a feature of intermittent populations where environmentally terminated diapause can entrain the planktonic stage of the life-history within a similar range of temperatures.
Courtship signals and mate choice of the flies of inbred Drosophila montana strains
Authors: Suvanto  , Liimatainen  , Tregenza  , Hoikkala  
Published: March 2003

Abstract
We studied genetic variation in fly mating signals and mate choice in crosses within and between inbred strains of Drosophila montana. Male songs and the cuticular hydrocarbons of both sexes as well as some of the flies’ behavioural traits differed significantly between strains. This did not, however, cause sexual isolation between strains. In fact, courtship was shorter if the female was courted by a male of a foreign strain than when courted by their own male. Heterosis was found for courtship duration and the carrier frequency of male song. Diallel analysis of male song revealed additive genetic variation in four out of the five traits studied. Two traits showed dominance variation and one of these, carrier frequency, expressed unidirectional dominance with alleles for higher carrier frequency being dominant. Direction of dominance in carrier frequency was the same as the direction of sexual selection exercised by D. montana females on this trait, which suggests that sexual selection could be a driving force in the evolution of song towards a higher carrier frequency.
Genetic conflict and changes in heterogametic mechanisms of sex determination
Authors: Caubet  , Hatcher  , Mocquard  , Rigaud  
Published: March 2003

Abstract
The consequences of cytoplasmic sex-ratio distortion and host repression for the evolution of host sex-determining mechanisms are examined. Analytical models and simulations are developed to investigate whether the interplay between sex-ratio distorters and host masculinizers or resistance genes can cause heterogamety switching (changes between male and female heterogamety). Switches from female heterogamety to a system analogous to male heterogamety can occur when selection favours the spread of autosomal masculinizers. However, the evolutionary outcome depends on the type of repressor and costs associated with repression, and also on aspects of population structure. Under most conditions, systems evolved to a polymorphic sex-determining state although many systems were characterized by numerical dominance of male heterogamety.
Monogamous pair bonds and mate switching in the Western Australian seahorse Hippocampus subelongatus
Authors: Kvarnemo C. , Moore G. I. , Jones A. G. , Nelson W. S. , Avise J. C. 
Published: March 2003

Abstract
Apparently monogamous animals often prove, upon genetic inspection, to mate polygamously. Seahorse males provide care in a brood pouch. An earlier genetic study of the Western Australian seahorse demonstrated that males mate with only one female for each particular brood. Here we investigate whether males remain monogamous in sequential pregnancies during a breeding season. In a natural population we tagged males and sampled young from two successive broods of 14 males. Microsatellite analyses of parentage revealed that eight males re-mated with the same female, and six with a new female. Thus, in this first study to document long-term genetic monogamy in a seahorse, we show that switches of mates still occur. Polygynous males moved greater distances between broods, and tended to have longer interbrood intervals, than monogamous males, suggesting substantial costs associated with the breaking of pair bonds which may explain the high degree of social monogamy in this fish genus.
Facultative sex allocation in snow skink lizards (Niveoscincus microlepidotus)
Authors: Olsson M. , Shine R. 
Published: March 2003

Abstract
Mathematical models suggest that reproducing females may benefit by facultatively adjusting their relative investment into sons vs. daughters, in response to population-wide shifts in operational sex ratio (OSR). Our field studies on viviparous alpine skinks (Niveoscincus microlepidotus) document such a case, whereby among- and within-year shifts in OSR were followed by shifts in sex allocation. When adult males were relatively scarce, females produced male-biased litters and larger sons than daughters. The reverse was true when adult males were relatively more common. That is, females that were courted and mated by few males produced mainly sons (and these were larger than daughters), whereas females that were courted and mated by many males produced mainly daughters (and these were larger than sons). Maternal body size and condition also covaried with sex allocation, and the shifting pattern of sexual size dimorphism at birth may reflect these correlated effects rather than a discrete component of an evolved sex-allocation strategy.
Size-dependent sex allocation in a simultaneous hermaphrodite parasite
Authors: Schärer L. , Karlsson L. M. , Christen M. , Wedekind C. 
Published: March 2003

Abstract
Most models of sex allocation distinguish between sequential and simultaneous hermaphrodites, although an intermediate sexual pattern, size-dependent sex allocation, is widespread in plants. Here we investigated sex allocation in a simultaneous hermaphrodite animal, the tapeworm Schistocephalus solidus, in which adult size is highly variable. Sex allocation was determined using stereological techniques, which allow measuring somatic and reproductive tissues in a common currency, namely volume. We investigated the relationships between individual volume and allocation to different reproductive tissues using an allometric model. One measure of female allocation, yolk gland volume, increased more than proportionally with individual volume. This is in contrast to the measure of male allocation, testis volume, which showed a strong tendency to increase less than proportionally with individual volume. Together these patterns led to sex allocation being strongly related to individual volume, with large individuals being more biased towards female allocation. We discuss these findings in the light of current ideas about size-dependent sex allocation in, primarily, plants and try to extend them to simultaneous hermaphrodite animals.
Selection of evolutionary models for phylogenetic hypothesis testing using parametric methods
Authors: Emerson B. C. , Ibrahim K. M. , Hewitt G. M. 
Published: March 2003

Abstract
Recent molecular studies have incorporated the parametric bootstrap method to test a priori hypotheses when the results of molecular based phylogenies are in conflict with these hypotheses. The parametric bootstrap requires the specification of a particular substitutional model, the parameters of which will be used to generate simulated, replicate DNA sequence data sets. It has been both suggested that, (a) the method appears robust to changes in the model of evolution, and alternatively that, (b) as realistic model of DNA substitution as possible should be used to avoid false rejection of a null hypothesis. Here we empirically evaluate the effect of suboptimal substitution models when testing hypotheses of monophyly with the parametric bootstrap using data sets of mtDNA cytochrome oxidase I and II (COI and COII) sequences for Macaronesian Calathus beetles, and mitochondrial 16S rDNA and nuclear ITS2 sequences for European Timarcha beetles. Whether a particular hypothesis of monophyly is rejected or accepted appears to be highly dependent on whether the nucleotide substitution model being used is optimal. It appears that a parameter rich model is either equally or less likely to reject a hypothesis of monophyly where the optimal model is unknown. A comparison of the performance of the Kishino–Hasegawa (KH) test shows it is not as severely affected by the use of suboptimal models, and overall it appears to be a less conservative method with a higher rate of failure to reject null hypotheses.
Sexual cannibalism in Nephila plumipes as a consequence of female life history strategies
Authors: Schneider J. M. , Elgar M. A. 
Published: March 2003

Abstract
The evolution of sexual cannibalism has been modelled as both an adaptive and nonadaptive female strategy. Recent evidence from several species suggests a connection between female foraging and sexual cannibalism, but the precise benefits for females have remained obscure. Here, we investigate the difference between cannibalistic and noncannibalistic female Nephila plumipes by removing the potential nutritional benefit of cannibalism. Courting and mating males that were killed by a female were immediately removed so that the female could not consume them. Nevertheless, cannibalistic females gained more mass from maturation to oviposition and produced larger first clutches than noncannibalistic females, although cannibalistic females matured at a smaller size and mass than noncannibalistic females. In juvenile instars, mass gain was generally smaller in females that moulted in a good condition but intermoult intervals were shorter. However, the time from maturity to oviposition was not shorter in females that matured in a good condition. Male behaviour did not differ according to the risk of cannibalism. We suggest that sexual cannibalism in N. plumipes is a side-effect of an increased foraging vigour of females that matured at a smaller size and body mass. Selection pressure on males to avoid cannibalism may be weak because of limited mating opportunities.
Size-dependent resource allocation and sex allocation in herbaceous perennial plants
Authors: Zhang D.-Y. , Jiang X.-H. 
Published: March 2003

Abstract
Individuals within a population often differ considerably in size or resource status as a result of environmental variation. In these circumstances natural selection would favour organisms not with a single, genetically determined allocation, but with a genetically determined allocation rule specifying allocation in relation to size or environment. Based on a graphical analysis of a simple evolutionarily stable strategy (ESS) model for herbaceous perennial plants, we aim to determine how cosexual plants within a population should simultaneously adjust their reproductive allocation and sex allocation to their size. We find that if female fitness gain is a linear function of resource investment, then a fixed amount of resources should be allocated to male function, and to post-breeding survival as well, for individuals above a certain size threshold. The ESS resource allocation to male function, female function, and post-breeding survival positively correlate if both male and female fitness gains are a saturating function of resource investment. Plants smaller than the size threshold are expected to be either nonreproductive or functionally male only.
Sexual size dimorphism and timing of spring migration in birds
Authors: Kissner K. J. , Weatherhead P. J. , Francis C. M. 
Published: March 2003

Abstract
Sexually selected traits are limited by selection against those traits in other fitness components, such as survival. Thus, sexual selection favouring large size in males should be balanced by higher mortality of larger males. However, evidence from red-winged blackbirds (Agelaius phoeniceus) indicates that large males survive better than small males. A survival advantage to large size could result from males migrating north in early spring, when harsh weather favours large size for energetic reasons. From this hypothesis we predicted that, among species, sex differences in body size should be correlated with sex differences in timing of spring migration. The earlier males migrate relative to females, the larger they should be relative to females. We tested this prediction using a comparative analysis of data collected from 30 species of passerine birds captured on migration. After controlling for social mating system, we found that sexual size dimorphism and difference in arrival dates of males and females were significantly positively correlated. This result is consistent with the hypothesis that selection for survival ability promotes sexual size dimorphism (SSD), rather than opposes SSD as is the conventional view. If both natural selection and sexual selection favour large adult males, then limits to male size must be imposed before males become adults.
Spatial ecological and genetic structure of a mixed population of sexual diploid and apomictic triploid dandelions
Authors: Meirmans P. G. , VloT E. C. , Den Nijs J. C. M. , Menken S. B. J. 
Published: March 2003

Abstract
Ecological differentiation is widely seen as an important factor enabling the stable coexistence of closely related plants of different ploidy levels. We studied ecological and genetic differentiation between co-occurring sexual diploid and apomictic triploid Taraxacum section Ruderalia by analysing spatial patterns both in the distribution of cytotypes and in the distribution of genetic variation within and between the cytotypes. A significant relationship between ploidy level and elevation was found. This mode of ecological differentiation however, was not sufficient to explain the significant spatial structure in the distribution of diploids and triploids within the population. Strong congruence was found between the spatial genetic patterns within the diploids and within the triploids. We argue that this congruence is an indication of gene flow between neighbouring plants of different ploidy levels.
Human T‐cell leukaemia/lymphoma virus risk may be enhanced in some selected donor populations
Authors: Price J. , Cant B. A. , Barbara J. A. J. , Tedder R. S. 
Published: March 2003

Background and ObjectivesCertain patient ethnic groups may require blood components from donors under‐represented in the UK donor population. Selective recruitment of Afro‐Caribbean donors is therefore necessary but was considered to pose an increased risk of human T‐cell leukaemia/lymphoma virus (HTLV) infection. To assess this a seroprevalence study of HTLV was undertaken in Afro‐Caribbean and Caucasian donors.Materials and MethodsSera from 1100 Afro‐Caribbean and 1100 Caucasian donors were tested for antibody to HTLV. Reactive samples were confirmed for specificity using an algorithm comprising two additional assays and polymerase chain reaction (PCR) where possible.ResultsSix Afro‐Caribbean donors (0·55%) were considered to be infected with HTLV I.ConclusionDonor selection in this case caused a significantly elevated prevalence of HTLV infection and serves as a warning of the need for care in the design of policies for selective donor recruitment.
Including polymerase chain reaction in screening for hepatitis C virus RNA in blood donations is not cost‐effective
Authors: Loubière S. , Rotily M. , Durand‐Zaleski I. , Costagliola D. 
Published: March 2003

Background and ObjectivesTo assess the cost and effectiveness of adding a system of polymerase chain reaction (PCR) testing to the current enzyme‐linked immunosorbent assay (ELISA) screening for hepatitis C virus (HCV) in blood donations.Materials and MethodsWe performed a cost‐effectiveness analysis comparing three HCV screening strategies in French blood donors: detection of antibodies against HCV by an ELISA on blood donations (the current policy) vs. ELISA and PCR either on each blood donation or on blood pools. We combined national surveillance data on HCV antibody‐positive blood donors with a literature review in a Markov model for natural history of HCV disease and its treatment.ResultsPCR testing performed in parallel with ELISA will potentially add less than 1 year of life for all French recipients compared to ELISA screening alone. The incremental costs per life year saved were, respectively, ∈84·6 million with ELISA and PCR testing of blood pools, and ∈891·1 million with testing of individual blood donations.ConclusionPCR testing performed in parallel with antibody screening, either on pools or on single donations is not currently a cost‐effective option for the detection of HCV RNA virus in blood donors.
Early detection of hepatitis B surface antigen and detection of HBsAg mutants: a comparison of five assays
Authors: Zaaijer H. L. , Vrielink H. , Koot M. 
Published: March 2003

Background and ObjectivesAssays for the detection of hepatitis B surface antigen (HBsAg) face two challenges: the emergence of sensitive techniques for detection of hepatitis B virus DNA and the existence of HBsAg mutant hepatitis B viruses. We studied the sensitivity of five modern assays for detection of HBsAg.Materials and MethodsThe sensitivity of two mini robot‐based assays – IMx HBsAg V2 and Vidas HBsAg – and three enzyme‐linked immunosorbent assays (ELISAs) with microtitre plate format – Hepanostika Uni‐Form II v1.2, Monolisa Ag HBs Plus and HBsAg Test System 3 – was compared testing 11 HBsAg seroconversion series, serial dilutions prepared from three HBsAg standards and nine HBsAg mutant samples.Results and ConclusionOverall, the IMx HBsAg V2 assay showed the highest sensitivity. It outperformed the Vidas HBsAg in analytical sensitivity and in detection of HBsAg mutants. Among the microtitre plate ELISAs, the Monolisa Ag HBs Plus outperformed the HBsAg Test System 3 in detection of HBsAg mutants and it surpassed the Hepanostika Uni‐Form II v1.2 in analytical sensitivity.
Apoptosis in leucodepleted packed red blood cells
Authors: Bontadini A. , Tazzari P. L. , Manfroi S. , Tassi C. , Conte R. 
Published: March 2003

Background and Objectives Packed red blood cells (pRBCs) contain apoptotic white cells. We studied apoptotic cells in pRBCs after filtration and at various time‐points during storage.Materials and Methods To maintain the same subset of cells, seven pRBC units were pooled in a single bag and divided equally into seven aliquots. Two series of five experiments were performed: in the first we utilized the Biofil R01 Max filter, and in the second the Pall BPF4 filter was used. One aliquot was immediately leucodepleted while the others were stored at 4 °C and filtered on days 3, 7, 10, 14, 21 and 42 of storage. The postfiltration leucocyte counts and apoptotic evaluations were performed by using the Nageotte chamber and flow cytometry.Results The absolute number of residual leucocytes was always less than 0·5 × 106 in each experiment. Nageotte chamber counts showed a greater number of white blood cells than flow cytometry during the 42 days of storage. On day 0, the percentage of apoptotic cells in non‐leucodepleted pRBCs was 1·1 ± 0·4 and 1·2 ± 0·4, while in filtered pRBCs it was high from day 0, at 53·5 ± 16·3 and 52 ± 18·5, respectively, with Biofil and Pall filters. On day 10 of storage, apoptotic cells reached a percentage of 42·5 ± 15·8 and 41·6 ± 18·6 in non‐leucodepleted pRBCs, while in filtered units an average value of ≈ 90% was found with both filters.Conclusions The percentage of apoptotic cells was higher in leucodepleted than in non‐leucodepleted pRBCs. After filtration, the degree of apoptosis was already high on day 0, and reached a mean of ≈ 90% by day 10. The difference in residual WBC counts between the Nageotte chamber and flow cytometry could be related to the presence of a high percentage of apoptotic cells in filtered blood components, and to the method used to distinguish viable from apoptotic cells.
Non‐steroidal anti‐inflammatory analgesics: a review of current practice
Authors: Mathews Karol A. 
Published: March 2003

AbstractObjective:This review is intended to update the reader on the clinical aspects of the non‐steroidal anti‐inflammatory analgesics (NSAIAs) currently used in veterinary practice. Most NSAIAs act by selectively, or preferentially, inhibiting the synthesis of cyclooxygenase (COX)‐1 or COX‐2, or both COX‐1 and COX‐2 enzymes which oxidize arachadonic acid to a series of prostenoids. The prostenoids are precursors of various prostaglandins required for many homeostatic functions throughout the body. The COX‐1 and COX‐2 enzymes are constitutive, however the COX‐2 enzyme is also induced following injury or inflammation facilitating the transmission of pain. As the newer NSAIAs focus on the inhibition of COX‐2, this review offers a more detailed discussion of this enzyme.Data synthesis:This data was obtained from recent review articles and original published reports in both the veterinary and human literature. A CAB and Medline search was also used.Conclusions:The NSAIAs are effective analgesics for managing moderate to severe pain in many species of animals; however, potential adverse effects may occur if used inappropriately. Guidelines, including indications, contraindications and dosing regimens for the commonly available NSAIAs are included.