bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of pre‐dispersal selection on offspring growth and survival in Erythronium grandiflorum
Authors: Cruzan M. B. , Thomson J. D. 
Published: December 2004

AbstractEffects of pre‐seed‐dispersal processes on offspring vigor were examined in Erythronium grandiflorum using manipulations of the number of pollen donors contributing to the pollen pool and comparisons of means and variances in offspring growth measurements. There were no effects of the number of donors on measures of pollen‐tube growth, ovule abortion, seed set, mean seed weight, or seedling germination. Seeds from pollinations with only one donor produced corms that averaged 5% lighter after one season of growth and had lower overall survival after three years compared to corms from pollinations with either three or ten donors. Patterns of within‐ and among‐family variance estimates for the different treatments were consistent with the hypothesis that less‐vigorous offspring were eliminated prior to seed dispersal in the multiple‐donor treatments. The difference in the growth of offspring from different treatments was apparently not due to pollen competition because pre‐zygotic attrition of pollen tubes led to incomplete fertilization of ovules. Results from this study suggest that post‐fertilization abortion of less‐vigorous progeny, perhaps as a consequence of early‐acting inbreeding depression, is responsible for the increase in the average vigor of offspring from multiply‐sired fruits.
Absence of direct sexual selection for parasitoid encapsulation in Drosophila melanogaster
Authors: Kraaijeveld A. R. , Emmett D. A. , Godfray H. C. J. 
Published: December 2004

AbstractResistance against parasites may play a role in female mate choice, especially if males that have actually survived parasitism can be discriminated from males that have not been parasitised. Larvae of several Drosophila species are subject to attack by hymenopteran parasitoids, but have the ability to kill the parasitoid egg through the process of encapsulation. Because an encapsulated egg remains visible in the abdomen of the adult fly throughout its life, its presence in a male signals to a female that the male has the genes to survive parasitism. The hypothesis that females preferentially mate with males bearing an encapsulated egg in their abdomen was tested using D. melanogaster. No indication was found for this female preference. The absence of preference for males with “good genes” could result from sensory constraints in the female or a negative correlation between encapsulation ability and some other fitness component. Alternatively, it is hypothesised that the black abdominal ends of the males of many species in the melanogaster‐group evolved to mimic encapsulated eggs, leading to the breakdown of capsule recognition by the female.
Selfing and outcrossing but no apomixis in two natural populations of diploid Potentilla argentea
Authors: Holm S. , Ghatnekar L. , Bengtsson B. O. 
Published: December 2004

AbstractIt has been suggested that diploid Potentilla argentea, hoary cinquefoil, is a facultative apomict. We have investigated the way such plants produce seeds under natural conditions in two populations from southern Sweden. About one hundred plants were studied cytometrically to ascertain their ploidy level. A standard population investigation based on two informative isozyme loci was then performed on the diploid plants. Finally, seeds were taken from heterozygous plants to determine the genetic constitution of their offspring. From the offspring analysis it followed that apomixis did not occur, at least not to any noticeable degree. From the population investigation it could be deduced that most seeds were produced by selfing.
Morphological variation in Plantago lanceolata L.: effects of light quality and growth regulators on sun and shade populations
Authors: Van Hinsberg A. 
Published: December 2004

AbstractThe effects of different ratios of red to far‐red light (R/FR‐ratio) and of exogenously applied growth regulators on the morphology of plants from sun and shade populations were studied. Large differences in growth form were found between populations adapted to either sun or shaded habitats. Low R/FR‐ratios, simulating vegetation shade, induced a growth form similar to that of plants from the shade population. High R/FR‐ratios, simulating sunlight, had the opposite effect. Most morphological differences between shade and sun populations and effects of low R/FR‐ratios on growth form could be mimicked by exogenously applied gibberellin (GA3). In contrast, application of a gibberellin inhibitor (CCC) induced a growth form similar to that of the sun population and of plants grown under a high R/FR‐ratio. Interactions between genetic background, the R/FR‐ratio, and hormone treatment, were small and the factors exerted their action independently. The results are discussed in relation to the influence of developmental constraints on the evolvability of optimal phenotypes and the plastic responses therein.
Optimum search speed and activity: a dynamic game in a three‐link trophic system
Authors: Leonardsson K. , Johansson F. 
Published: December 2004

AbstractWe analysed how a consumer should simultaneously trade‐off search speed and time active in a game with predators that optimise their search speed. Both the consumers and the predators are continuously reproducing and maximise fitness by maximising the per capita growth rate. The impact of the predator's presence on consumer behaviour, and the effects of type I and II functional responses on the behaviour of both species are considered. In the analyses, consumers were allowed to co‐ordinate activity or behave independently in relation to other consumers. The ESS‐analysis of the game ensures that no mutant can invade the system. The independent activity was found to be optimal in all analyses, while the co‐ordinated activity was only optimal at full activity where the two activity strategies coincided. The model showed that consumers should change activity to account for predation risk. Activity generally decreased with predation risk. Concerning the energetic aspects, both activity and search speed were important to account for the reproductive output. The functional responses influenced the optimum activity and search speed of consumers and predators. In general, the optimum behaviours showed complex non‐linear responses in relation to the resource and the consumer density. A predator type II functional response had profound impacts on the properties of the optima, the stability and presence of alternative strategies. As a result of the optimum behaviours, the realised functional responses of both species became sigmoidal.
Long‐term experimental evolution in Escherichia coli. V. Effects of recombination with immigrant genotypes on the rate of bacterial evolution
Authors: Souza V. , Turner P. E. , Lenski R. E. 
Published: December 2004

AbstractThis study builds upon an earlier experiment that examined the dynamics of mean fitness in evolving populations of Escherichia coli in which mutations were the sole source of genetic variation. During thousands of generations in a constant environment, the rate of improvement in mean fitness of these asexual populations slowed considerably from an initially rapid pace. In this study, we sought to determine whether sexual recombination with novel genotypes would reaccelerate the rate of adaption in these populations. To that end, treatment populations were propagated for an additional 1000 generations in the same environment as their ancestors, but they were periodically allowed to mate with an immigrant pool of genetically distinct Hfr (high frequency recombination) donors. These donors could transfer genes to the resident populations by conjugation, but the donors themselves could not grow in the experimental environment. Control populations were propagated under identical conditions, but in the absence of sexual recombination with the donors. All twelve control populations retained the ancestral alleles at every locus that was scored. In contrast, the sexual recombination treatment yielded dramatic increases in genetic variation. Thus, there was a profound effect of recombination on the rate of genetic change. However, the increased genetic variation in the treatment populations had no significant effect on the rate of adaptive evolution, as measured by changes in mean fitness relative to a common competitor. We then considered three hypotheses that might reconcile these two outcomes: recombination pressure, hitchhiking of recombinant genotypes in association with beneficial mutations, and complex selection dynamics whereby certain genotypes may have a selective advantage only within a particular milieu of competitors. The estimated recombination rate was too low to explain the observed rate of genetic change, either alone or in combination with hitchhiking effects. However, we documented comple x ecological interactions among some recombinant genotypes, suggesting that our method for estimating fitness relative to a common competitor might have underestimated the rate of adaptive evolution in the treatment populations.
Effects of temperature extremes on genetic variances for life history traits in Drosophila melanogaster as determined from parent‐offspring comparisons
Authors: Sgrò and C. M. , Hoffmann A. A. 
Published: December 2004

AbstractParent‐offspring comparisons were used to investigate the effects of temperature extremes on genetic variances for two life history traits and one morphological trait in Drosophila melanogaster. We considered three temperatures (14 °C, 25 °C and 28 °C) for culturing and testing flies, and considered heritabilities, coefficients of additive variation (CVA) and evolvabilities (IA) for fecundity, development time and wing length. For fecundity, heritabilities and evolvabilities were higher when parents were exposed to 14 °C compared to 28 °C. Parent‐offspring comparisons suggested that genetic correlations among environments were close to 1, although lower correlations were obtained in comparisons of family means. Parent‐offspring correlations across environments seemed to depend on parental temperature. For development time, heritabilities and evolvabilities were low at 14 °C compared to 28 °C. However, parent‐offspring correlations were relatively high when the progeny of parents tested at 14 °C were raised at the opposite extreme, suggesting that genetic variation can be enhanced when parents and offspring experience different conditions. CVAs and IAs for development time were lower than for fecundity, even when heritability estimates were similar in magnitude. Genetic variation for wing length was generally not affected by the temperature extremes, and genetic correlations across the extremes estimated from the parent‐offspring comparison were close to 1. There was no evidence for tradeoffs between traits; rapid development time was associated with high fecundity at both the phenotypic and genetic levels. The findings highlight inherent difficulties of estimating genetic parameters from parent‐offspring comparisons when two generations experience different environmental extremes and also show how parent‐offspring comparisons can lead to unexpected findings about the expression of genetic variation.
Seasonality of births in Homo sapiens in pre‐industrial Finland: maximisation of offspring survivorship?
Authors: Lummaa V. , Lemmetyinen R. , Haukioja E. , Pikkola M. 
Published: December 2004

AbstractWe examined the seasonal variation in human birth and infant survival rates in pre‐modern Finland. If survival probabilities of children born during different seasons of the year differ and if timing of reproduction has been affected by natural selection, periodic variation in environment could have led to reproduction during the season of best infant survival expectations. Significant seasonal variation in both birth rate and survival probability was found, but the monthly birth and survival rates of newborn were uncorrelated. Hence, if there was any tendency to maximise the reproductive success, increase in some other component of fitness than the infant survival was probably targeted. The effect of major holidays on the birth rate was proved to be notable, suggesting that although the basis for seasonal variation in birth rate was biological, sociocultural factors had an impact on the timing of reproduction in humans. The overall mortality of infant boys exceeded that of infant girls in all seasons. This difference was smallest during the time of best food supplies, indicating that the development of males was less buffered against environmental disturbances than that of females.
Tracing the colonization of Madeira and the Canary Islands by Drosophila subobscura through the study of the rp49 gene region
Authors: Khadem M. , Rozas J. , Segarra C. , Brehm A. , Aguadé M. 
Published: December 2004

AbstractNucleotide variation at the nuclear ribosomal protein 49 (rp49) gene region has been analysed by fine restriction mapping in a sample of 47 lines from a population from Madeira. Five restriction‐site (out of 37 sites scored) and 3 length polymorphisms have been detected, resulting in 14 different haplotypes. This population shows less variation than both continental and Canary Island populations. The population from Madeira shows some differentiation from mainland populations, which does not favor the idea of extensive migration between the continent and Madeira. Chromosomal and restriction‐map variation of the rp49 region in D. subobscura populations, together with data on sequence comparison of this nuclear region in D. guanche and D. madeirensis clearly indicate that the Canary Islands underwent at least two colonization events from the nearby continent. Although the data for Madeira are compatible with a single colonization event by a continental sample polymorphic for gene arrangements O3 and O3 + 4, an alternative scenario with at least two colonization events seems more likely.
Geographic structure of lineage associations in a plant‐bacterial mutualism
Authors: Parker M. A. , Spoerke J. M. 
Published: December 2004

AbstractTwo species linked by a mutualistic relationship may evolve correlated population differentiation if there is long‐term continuity of interactions between specific partners. This phenomenon was analyzed by multilocus enzyme electrophoresis on the annual legume Amphicarpaea bracteata and its nitrogen‐fixing bacterial symbionts (Bradyrhizobium sp.) sampled from >20 sites over a 1000 km area. Three analyses indicated that genetic differentiation was correlated in the two organisms. First, the genetic distance between bacterial populations at each pair of sites was significantly positively related to the genetic distance between their host plant populations, as evaluated by the Mantel test. Second, a cluster analysis revealed that several divergent lineages were present both among plants and among bacteria. Bacterial lineages showed a highly nonrandom distribution across plant lineages that was consistent in each of two regions sampled. Finally, there were numerous cases where populations of the same plant lineage 1000 km apart harbored bacterial isolates with an identical multilocus genotype. Thus, despite recurrent opportunities for partner switching, particular genotypes of these two organisms associate consistently across multiple habitats throughout their geographic range.
The evolution of diet breadth: Monophagy and polyphagy in swallowtail butterflies
Authors: Thompson J. N. 
Published: December 2004

AbstractMuch of the world's biodiversity has resulted from specialization of insect populations onto different plant species, partially through evolution of preference in ovipositing females. Here I report an experimental analysis of how an oviposition preference hierarchy has evolved during the evolutionary diversification of an insect group to produce taxa ranging from monophagous to polyphagous. Tests on the Papilio machaon group of swallowtail butterflies show that the preference hierarchy for plant species is evolutionarily dynamic within this species complex, yet constrained among most populations within species, creating a geographic mosaic of populations differing to various degrees in patterns of host preference. The results indicate that different diet breadths can evolve within a group of closely‐related species through a combination of conservatism in preference hierarchy among some populations, occasional but rare rearrangements in preference among others, correlations in preference for some plant species, and availability of similarly ranked hosts.
Phenotypic selection in a natural population of Impatiens pallida Nutt. (Balsaminaceae)
Authors: Gross J. , Husband B. C. , Stewart S. C. 
Published: December 2004

AbstractIn the annual plant Impatiens pallida, individuals exhibit a floral heteromorphism consisting of autogamously selfing, cleistogamous (CL) flowers and partially outcrossing, chasmogamous (CH) flowers. As part of an investigation into natural selection and mating system evolution in I. pallida, we measured the magnitude and direction of phenotypic selection on nine life history characters (two traits measured on three dates, one measured on two dates and one measured once). Three of these characters were positively correlated with the ratio of CH/CL flowers produced per plant, which is an important determinant of the mating system. Values for the nine characters and three different measures of fitness (viability, fecundity, lifetime) were estimated for 500 plants in five locations over a single growing season. Based on lifetime fitness, linear selection differentials were significant for all nine characters, indicating a selective advantage to tall, leafy, highly branched plants that flowered early. However, only two of these characters had a direct effect on fitness. Selection was significant on all nine characters when based on fecundity as well as lifetime fitness; however, only three of five characters examined had significant selection based on viability fitness. For all fitness components, the frequency of significant linear and nonlinear selection coefficients was comparable (23% vs 17% of all cases, respectively), but nonlinear coefficients were generally larger. Finally, the magnitude and direction of direct linear selection was heterogeneous among locations, for all characters and all fitness components. Collectively these results suggest that selection is strong, favouring large size, high allocation to reproduction and high CH/CL flower ratios. However, any directional evolutionary changes in vegetative or reproductive characters may be constrained by strong non‐linear and correlational selection.
Evolutionary genetics and ecology of sperm‐dependent parthenogenesis
Authors: Beukeboom L. W. , Vrijenhoek R. C. 
Published: December 2004

AbstractSperm‐dependent (or pseudogamous) forms of parthenogenetic reproduction occur in a wide variety of animals. Inheritance is typically clonal and matroclinous (of female descent), but sperm are needed to initiate normal development. As opposed to true parthenogenesis (i.e., sperm‐independent reproduction), pseudogamous parthenogenetic lineages must coexist with a ‘sperm donor’— e.g., males from a conspecific sexual lineage, conspecific hermaphrodites, or males from a closely related sexual species. Such sperm donors do not contribute genetically to the next generation. The parasitic nature of sperm‐dependent parthenogenesis raises numerous ecological and evolutionary questions. How do they arise? What factors help stabilize coexistence between the pseudogamous parthenogens and their sperm donors (i.e., ‘sexual hosts’)? Why do males waste sperm on the asexual females? Why does true parthenogenesis not evolve in pseudogamous lineages and free them from their dependency on sperm donors? Does pseudogamous parthenogenesis provide compensatory benefits that outweigh the constraints of sperm‐dependence? Herein, we consider some genetic, ecological, and geographical consequences of sperm‐dependent parthenogenesis in animals.
Phenol hydroxylase from Acinetobacter radioresistens S13
Authors: Griva Ersilia , Pessione Enrica , Divari Sara , Valetti Francesca , Cavaletto Maria , Rossi Gian Luigi , Giunta Carlo 
Published: December 2004

This paper reports the isolation and characterization of the regulatory moiety of the multicomponent enzyme phenol hydroxylase from Acinetobacter radioresistens S13 grown on phenol as the only carbon and energy source. The whole enzyme comprises an oxygenase moiety (PHO), a reductase moiety (PHR) and a regulatory moiety (PHI). PHR contains one FAD and one iron‐sulfur cluster, whose function is electron transfer from NADH to the dinuclear iron centre of the oxygenase. PHI is required for catalysis of the conversion of phenol to catechol in vitro, but is not required for PHR activity towards alternative electron acceptors such as cytochrome c and Nitro Blue Tetrazolium. The molecular mass of PHI was determined to be 10 kDa by SDS/PAGE, 8.8 kDa by MALDI‐TOF spectrometry and 18 kDa by gel‐permeation. This finding suggests that the protein in its native state is a homodimer. The isoelectric point is 4.1. PHI does not contain any redox cofactor and does not bind ANS, a fluorescent probe for hydrophobic sites. The N‐terminal sequence is similar to those of the regulatory proteins of phenol hydroxylase from A. calcoaceticus and Pseudomonas CF 600.In the reconstituted system, optimal reaction rate was achieved when the stoichiometry of the components was 2 PHR monomers: 1 PHI dimer: 1 PHO (αβγ) dimer. PHI interacts specifically with PHR, promoting the enhancement of FAD fluorescence emission. This signal is diagnostic of a conformational change of PHR that might result in a better alignment with respect to PHO.
Mapacalcine specifically blocks hypoxia‐induced calcium influx in rat hepatocytes
Authors: Crenesse Dominique , Neuilly Ghislaine , Gugenheim Jean , Ferre Catherine , Hugues Michel 
Published: December 2004

Post ischaemic cell calcium invasion has been described as one of the main causes of graft failure. Protective effects of calcium antagonists have been investigated but are not convincing and their mechanisms of action remain unclear. In this work we tested the protective effect of a new calcium inhibitor described to block a calcium current insensitive to all known calcium blockers. Specific mapacalcine receptors were first characterized on rat hepatocytes membranes using the 125I‐labeled mapacalcine. 45Ca fluxes were then measured on cultured hepatocytes submitted (or not) to an hypoxic period. The action of mapacalcine was investigated on the ischaemia‐induced calcium influx. We demonstrate here that: (a) there are specific receptors for mapacalcine in rat hepatocytes; (b) Mapacalcine is able to specifically block ischaemia–induced calcium influx with an IC50 of 0.3 µm and does not significantly interact with the basal calcium flux.Our work demonstrates that the mapacalcine receptor is a cellular structure directly involved in the phenomenon of postischaemic cell invasion by calcium. Specific block of ischaemia‐induced Ca2+ influx by mapacalcine suggests that the development of a panel of pharmacological drugs acting on this receptor could lead to the discovery of therapeutic agents able to protect cells against one of the events responsible for organ failure after transplantation or simply after an ischaemic period. Moreover, identification of the cellular protein which binds mapacalcine may become an important step in the research of mechanisms involved in postischaemic cell invasion by calcium.