bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fecundity, lifespan and egg mass in butterflies: effects of male‐derived nutrients and female size
Authors: OBERHAUSER K. S. 
Published: December 2004

1. Effects of larval reserves and nutrients received as adults on fecundity and lifespan in female Danaus plexippus (the Monarch Butterfly) were measured to determine the relative importance of different sources of nutrients for reproduction and somatic maintenance. 2. Egg‐laying lifespan was correlated with female size but not with the amount of male‐derived nutrients or adult food concentration. 3. Lifetime fecundity was higher when females received a large first spermatophore, but was not affected by female size when lifespan was controlled or by adult food concentration. 4. At the end of their lives, females contained unlaid eggs and retained, on average, 88% of their initial mass. This proportion was unchanged in two years, although mean egg‐laying lifespan varied from 22·5 to 28·7 days. 5. Egg mass decreased over the female lifespan, and was correlated with female size. 6. These results suggest that larval reserves are more important for somatic maintenance than adult income, but that the protein‐rich nutrients received from males contribute to egg production. This supports theoretical predictions and empirical studies of other Lepidoptera showing that larval reserves are less likely to affect fecundity when the adult income can contribute substantially to egg production.
Clonal variation in life‐history traits and feeding rates in the gastropod, Potamopyrgus antipodarum: performance across a salinity gradient
Authors: JACOBSEN R. , FORBES V. E. 
Published: December 2004

1. Parthenogenetic species are often geographically more widely distributed than their sexual relatives. This success in colonizing can be explained either by dispersal of one or a few clones of wide physiological tolerance or by the distribution of many locally adapted clones. 2. Here we compare the influence of salinity on reproductive output, feeding rate, growth rate and size at birth between two genotypes of Potamopyrgus antipodarum to address the questions (i) Do these traits vary in response to changing salinity? (ii) Does the response to a salinity gradient differ between genotypes? (iii) Can the patterns of variation, in relation to salinity, contribute to explaining the geographical distribution of P. antipodarum in Europe? 3. Our results demonstrate that genetic variation among populations of P. antipodarum is reflected in differences in life‐history traits and feeding rates in response to a salinity gradient. The phenotypic differences between the genotypes are consistent with the geographical distribution of P. antipodarum clones in Europe. 4. The overall response to salinity of both genotypes of P. antipodarum suggests an optimum at ≈ 5‰ S; however, both genotypes showed a broad salinity tolerance and were able to feed, grow and reproduce over the entire salinity range tested (0–15‰ S). The broad environmental tolerance of both genotypes together with their widespread geographical distribution across Europe provide evidence consistent with the general‐purpose genotype hypothesis.
The unrecognized posterior gastric artery: a potential cause of surgical complications in pancreas transplantation
Authors: Troppmann Christoph , Pirenne Jacques , Perez Richard V , Gruessner Rainer WG 
Published: December 2004

Abstract: Background: Our report describes, for the first time, a pre‐transplant vascular complication in a pancreas graft related to the posterior gastric artery – a major, but relatively unknown side branch of the splenic artery. The posterior gastric artery that was overlooked by a surgical procurement team during donor pancreatectomy led to distortion of the peripancreatic vascular anatomy and set the stage for a splenic artery injury.Methods: We identified the transected, partially resected graft splenic artery during backtable preparation of the pancreas, and repaired it using standard vascular surgical techniques.Results: The recipient's post‐operative course was uncomplicated. At 9‐yr post‐transplant, the recipient is alive with good pancreas graft function.Conclusions: The relevance of the posterior gastric artery with regard to general surgical procedures was only recently recognized. Our case demonstrates that the posterior gastric artery is also important in transplant surgery. Awareness of this anatomical structure during organ procurement would help minimize pre‐transplant vascular complications.
Pegylated interferon α‐2b plus ribavirin in the treatment of post‐liver transplant recurrent hepatitis C
Authors: Ross Andrew S , Bhan Atul K , Pascual Manuel , Thiim Michael , Benedict Cosimi A , Chung Raymond T 
Published: December 2004

Abstract:  Background:  Histological recurrence of the hepatitis C virus (HCV) occurs in the majority of persons transplanted for cirrhosis as a result of HCV. Herein we analyze our experience with the use of both conventional and pegylated (PEG) interferon (IFN) in combination with ribavirin (RBV) in liver transplant recipients with recurrent HCV.Methods:  Patients transplanted between 1992 and 2001 with post‐orthotopic liver transplantation (OLT) histological recurrence of HCV, and who were treated with at least 6 months of IFN or PEG‐IFN in combination with RBV were included in this analysis. A retrospective chart review was performed.Results:  A total of 31 patients were included. Fifteen were treated with IFN/RBV and 16 with PEG‐IFN/RBV. Of these 16, 11 had been begun on IFN/RBV and were changed to PEG‐IFN/RBV because of persistent viremia. Three patients (20%) in the IFN/RBV group and six patients (37.5%) in the PEG‐IFN/RBV group experienced a virologic response (VR) on therapy. Of the six patients experiencing VR in the PEG‐IFN/RBV group, three (50%) were IFN/RBV non‐responders. There were two sustained VRs (SVR). The 65.6% of all patients experienced a biochemical response (BR) on therapy. Seven deaths were observed. Dose modifications of IFN or PEG‐IFN (87.1%) and RBV (80.6%) and the requirement for hematopoietic growth factors were frequent.Conclusions:  Treatment of recurrent HCV infection with combination of IFN or PEG‐IFN and RBV produced an on‐therapy VR in 29% and BR in 65% of patients. Hematologic toxicity and dose modifications were frequent. Our experience with antiviral therapy for HCV post‐OLT remains disappointing but PEG‐IFN + RBV appears to produce VR in a sizable portion of IFN + RBV non‐responders.
The Tangled Bank: The maintenance of sexual reproduction through competitive interactions
Authors: Koella Jacob C. 
Published: December 2004

AbstractThe maintenance of sexual reproduction is discussed using a model based on the familiar Lotka‐Volterra competition equations. Both the equilibrium and the stability conditions that allow a sexual population to resist invasion by a single asexual clone are considered. The equilibrium conditions give results similar to previous models: When the cost of sex, within phenotype niche width, and environmental variance are low, the sexual population coexists with the asexual clone and remains at a high density. However, the asexual clone is never completely excluded. Analysis of the stability conditions shows a different picture: The introduction of an asexual clone considerably reduces the stability of the community. However, owing to its larger total niche width, the sexual population exists partly in a “competitor‐free space” where the asexual clone has almost no influence on the outcome of the interactions. Therefore the asexual clone is less stable than the sexual population and has a higher probability of extinction. In contrast, the sexual population does not become extinct, since the extreme phenotypes remain at a stable, though low, density, and the central phenotypes, where stability is low, are recreated every generation through recombination. I therefore conclude that the ecological conditions under which sexual reproduction is favored over asexual reproduction are fairly easily attained and are more general than previous analyses had suggested.
Variation in sex determination in natural populations of a shrimp
Authors: Naylor Caroline , Adams Jonathan , Greenwood Paul J. 
Published: December 2004

AbstractStrategies of sex determination were studied in Gammarus duebeni, a brackish water shrimp (Crustacea, Amphipoda). Animals from Budle Bay, northern England, have environmental sex determination (e. s. d.), in accord with a population studied in Germany. Males are produced in long day photoperiods and females in short days. By contrast, animals from southern England show no significant sex ratio variation with daylength. This is the first report of such variation in sex determination for an invertebrate. Detailed studies of Budle Bay animals show that sex is determined several weeks after young are released by the mother; that the critical daylength is longer at Budle Bay than in Germany; and that the critical response is cued at the onset of a photophase. The nature of sex determination in G. duebeni may be associated with population dynamics. Males gain greater relative fitness by large size than females. E. s. d. is then adaptive where the breeding season produces significant growth differences between early and late animals, but where generations do not overlap. Comparisons are drawn with the flexible sex determining system in Menidia menidia (Pisces).
Plasticity in age and size at maturity in male guppies (Poecilia reticulata): An experimental evaluation of alternative models of development
Authors: Reznick David N. 
Published: December 2004

AbstractI present two models for the genesis of phenotypic variation in age and size at maturity in male guppies. Both are qualitatively consistent with the observation that age at maturity increases and size at maturity decreases as food availability (and growth rate) decline. The first model (“fixed development”) has a constant size which signals the initiation of the process of maturation and a constant time interval between the initiation and completion of maturation. There is thus no response in the pattern of development to differences in growth rate. Variation in age at maturity results from the different amounts of time required to reach the size at initiation. Variation in size results from different amounts of growth between the initiation and completion of maturation. Phenotypic variation is therefore an epiphenomenon of expressing a fixed pattern of development in different environments. In the second model (“flexible development”), fast growers initiate maturation at a larger size than slow growers; this results in a later age and larger size at maturation than their fast growing counterparts in the fixed development model. Slow growers mature at an earlier age and smaller size than their counterparts in the fixed development model. In the second model, the pattern of development changes with the environment. Two experiments with guppies demonstrate that the second model accurately describes their pattern of development. I conclude that phenotypic plasticity is in part the product of plastic development and may represent an adaptation. Testing whether or not the response is adaptive will require further investigations. A general message of this investigation is that characterizing the reaction norm alone is not sufficient to evaluate the adaptive significance of plasticity; one must also consider the processes that generate this plasticity.
Rapid evolution of life history traits in populations of Poa annua L.
Authors: Till‐Bottraud Irène , Wu Lin , Harding James 
Published: December 2004

AbstractTwo populations of Poa annua L., one from an irrigated area and one from a dry area, were studied to test the following hypothesis: different life cycles should be selected in habitats of contrasting mortality regime. Plants from the irrigated area exhibited a typical perennial habit (indeterminate growth and low reproductive effort) while those from the dry area showed traits characteristic of annuals (determinate growth, high reproductive effort and flowering synchrony) although total annuality was not achieved. The antagonism between growth and reproduction was expressed at the individual tiller level and was reflected in the life history traits of the populations. The characters studied exhibited a high broad sense heritability which is required for a rapid evolution of life cycles when selection pressures are strong. Different levels of constraints (ecological, evolutionary, physiological and developmental) have to be taken into account in order to understand this evolution.
Temperature‐related divergence in experimental populations of Drosophila melanogaster. III. Fourier and centroid analysis of wing shape and relationship between shape variation and fitness.
Authors: Cavicchi Sandro , Giorgi Gianfranco , Natali Vanna , Guerra Daniela 
Published: December 2004

AbstractFrom a laboratory stock of Drosophila melanogaster (Oregon), reared for more than 20 years at 18°C, two new populations were derived and maintained at 25° and 28°C for 8 years. The chromosomal and cytoplasmic contribution to genetic divergence between the two more extreme populations was estimated at 18°C and 28°C. Wing shape and two fitness components (fecundity and fertility) were taken into account. Fourier descriptors and the position of the centroid were taken as indicators either of wing shape variation, determined by a different response of the two wing compartments to temperature selection, or of wing shape variation determined by both compartments. The descriptors appear to be good characters: they show a variability which is genetically controlled and ascribable to genes located on specific chromosomes. The third chromosome is responsible for the adaptive difference to temperature. The genes which control wing shape are located on the second and third chromosome, although the contribution of each chromosome depends on the environment in which the flies develop. Cytoplasmic genes display an effect as large as that of chromosomes, and nucleus × cytoplasm interaction is present. The correlation between the genetic contributions to compartment‐dependent wing shape variation and the contributions to fitness is highly significant, especially at 28°C. Wing shape has, therefore, an adaptive significance in relation to temperature, which is particularly expressed in the environment where selection occurred.
Non‐equilibrium gene frequency divergence: persistent founder effects in natural populations
Authors: Boileau Marc G. , Hebert Paul D. N. , Schwartz Steven S. 
Published: December 2004

AbstractThe estimation of gene flow using gene frequency divergence information has become increasingly popular because of the difficulty involved in the direct determination of gene flow among populations. The present study examined allozyme gene frequencies in populations of eighteen aquatic invertebrate taxa at two sites in northern Canada. Gene frequencies at polymorpic loci were significantly different among 8–31 localized populations of all species at Igloolik and among 10–36 populations at Churchill confirming the generality of gene pool fragmentation in pond‐dwelling organisms. Measures of gene flow estimated from gene frequency divergence, which assume that gene frequency distributions are at equilibrium, were inconsistent with the probable dispersal capacities of taxa. This provoked an examination of historical events as alternative explanations. Both theory and computer simulations demonstrated that when populations grow rapidly in size after founding from few individuals, the gene frequency divergence established during colonization is resistant to decay by gene exchange. Our work suggests that gene frequency distributions are often not in equilibrium and that caution should be employed in attempts to infer gene flow from them in natural populations.
Parasitism as a constraint on the rate of life‐history evolution
Authors: Hochberg M. E. , Michalakis Y. , De Meeus T. 
Published: December 2004

AbstractThere are a number of ways in which a host can respond in evolutionary time to reductions in survival and reproduction due to a virulent parasite. These include evolving physiological morphological, or behavioural mechanisms of resistance to infection (or to proliferation, once infection has occurred). But a more unexpected tactic is also possible. This is for hosts to reproduce (slightly) sooner when in the presence of a virulent parasite as compared to when the parasite is less virulent or absent. As such, hosts which reproduce younger may be at a selective advantage, since they can both evade parasitism in time and, even when parasitised, can reduce the likely impact of the parasite on survival and reproductive success. We employ a simple mathematical model to propose that parasites and pathogens can act as important agents in the evolution of the timing of reproduction and associated life‐history characters (e.g. body size). Once established in a semelparous host population, evolutionary increases in parasite virulence should result in the evolution of shorter lived hosts; whereas the evolution of less virulent forms of the parasite should be accompanied by the evolution of longer lived hosts. We argue that in the presence of a sufficiently virulent parasite the evolution of longer pre‐reproductive life‐spans should require the previous or concomitant evolution of morphological, behavioural or physiological resistance to parasitic infection and proliferation.
The inversion polymorphism of D. subobscura revisited: Synthetic maps of gene arrangement frequencies and their interpretation*
Authors: Menozzi P. , Krimbas C. B. 
Published: December 2004

AbstractPrincipal component maps of the gene arrangement frequencies of 108 natural populations in Europe, North Africa and the Middle East were prepared to investigate the evolutionary forces shaping the geographic variation of inversion frequencies. Principal component maps were also prepared from ten climate variables at 347 localities of the same region. The first inversion principal component (18% of total variation) showed a N‐S cline strikingly similar to the pattern exhibited by the first principal component of climatic variables. This resemblance is interpreted as showing the outcome of a selective process, which favors the increase in frequency of the Standard gene arrangements when moving to the north. This interpretation is corroborated by the fact that such clines were formed in South and North America, following recent colonization by this species. Patterns shown by the second (12% of total variance) and third (8% of total variance) principal components are interpreted as related to historical events, the migrational advance to the north after the end of the last glaciation and the locations of the species refugia at that time.
Allelic ratios and sterility in the agamic complex of the Maximae (Panicoideae): evolutionary role of the residual sexuality
Authors: Noirot M. 
Published: December 2004

AbstractThe agamic complex of the tribe Maximae is constituted by two pools characterized by their own breeding system (sexuality on the one hand, facultative apomixis on the other hand). Facultative apomicts shows two types of embryo‐sacs (aposporic or meiotic). Presence of aposporic embryo‐sacs is genetically controlled by the dominant allele A (all apomictic plants are Aaaa). Meiotic embryo‐sacs, constituting residual sexuality, can allow crosses between apomicts and theoretically the generation of other genotypes than Aaaa. Additionally, some cases of sterile apomicts appears in a breeding system known to bypass it.This led us to study these two paradoxes. In fact, the sterility would exist when the ratio A/a is greater than 0.25. This would prevent the total overrunning of an apomictic population by AAAA genotypes. The role of residual sexuality is then to allow generation of true sexuals (aaaa) from apomicts (Aaaa).
The evolution of unusual chromosomal systems in sciarid flies: intragenomic conflict and the sex ratio
Authors: Haig David 
Published: December 2004

AbstractA model is presented for the evolution of the sciarid chromosomal system. In this model, a driving X chromosome caused female‐biased sex ratios. The drive was exploited by maternal autosomes that segregated with the X at spermatogenesis. Genes in mothers converted some of their XX daughters into sons by eliminating a paternal X from the embryonic soma. L chromosomes were derived from X chromosomes and favored male‐biased sex ratios. An X' chromosome arose that suppressed the effects of L chromosomes. The 1:1 sex ratio is a stalemate between the X' and X'X mothers causing all‐female broods and the L chromosomes in XX mothers causing all‐male broods. Any element (such as an L chromosome) that is preferentially transmitted through one sex will be selected to bias the sex ratio towards this sex.
On the origin of the cyanogenic polymorphism in Trifolium repens L.
Authors: Kakes P. , Hakvoort H. W. J. 
Published: December 2004

Abstract Trifolium repens
L. and
Trifolium nigrescens
Viv. are two of the approximately six cyanogenic species known in the genus Trifolium. The two species are closely related:
T. nigrescens
is considered to be one of the diploid ancestors of the amphidiploid
T. repens
. We studied morphology, meiosis and the cyanogenic system in
T. repens
(amphidiploid),
T. nigrescens
(diploid) and their reciprocal hybrids. A comparison of the enzyme linamarase in the species and hybrids shows that there is a general resemblance between their linamarases. Immunological studies indicate that the linamarases must have a somewhat different three‐dimensional structure. These facts are consistent with the view that
T. nigrescens
(or an ancestral form of this species) has donated the
Li
gene of
T. repens
. The other putative parent,
T. occidentale
has probably not donated an active
Li
gene. The hypothesis of the origin of the
Li
gene does not explain its polymorphism in European populations of
T. repens
, as
T. nigrescens
is monomorphic for cyanogenesis and amphidiploids do not segregate for genes which are homozygous dominant in one of the parents. Segregation for
Li
could be caused by a gene mutation or a small exchange between homeologous chromosomes. The latter event is more probable. A nigrescens‐repens exchange would give rise to a chromosomal region with reduced homology to both parental chromosomes. The genes in the region of exchange will be tightly linked due to diminished cross‐over frequency. It has been known for years that
Li
has effects on the vegetative and reproductive characters in
T. repens
and we have recently shown that these effects must be the result of genes linked to
Li
. As the associated characters influence the fitness of the cyanotypes, not only the origin but also the maintenance of the cyanogenic polymorphism is closely related to the evolutionary history of
T. repens .