Growth Rate Advantage Research Articles

Evolution of Recrystallization Texture in Non-Oriented Electrical Steel Containing Copper

The evolution of recrystallization texture in the non-orientation electrical steel containing copper during annealing at 950°C for 3～180s have been studied by EBSD (Electron Backscatter Diffraction) measurements. Goss grains({011}) are nucleated within shear bands in deformed {111} and{111} grains. {111} grains nucleate in deformed {111} grains and new{111} grains nucleate in deformed {111}grains. {111} grains have an evident advantage both in number and growth rate over α grains, thus the controlling of annealing time can contribute to the increase of {011} texture.

Growth and carcass characteristics of crossbred lambs in various production systems

Lamb growth, carcass and pelt measurements are reported from 5775 lambs born to Border Leicester × Merino (BLM) and Hyfer (Dorset × Merino composite) ewes joined to Dorset, Suffolk and Hyfer rams in three lamb-production systems at Cowra and Wagga Wagga over 5 years. The production systems involved lambings at different seasons of the year and increasing levels of intensification from autumn annual joining, spring joining with a backup mating for non-pregnant ewes, to an accelerated 8-monthly lambing system. Lambs from BLM ewes were 0.7 kg heavier at birth and grew 3% faster and reached slaughter, at 18 kg carcass weight, 1–2 weeks earlier than did lambs from Hyfer ewes (P < 0.01). The advantage in growth rate of lambs from BLM compared with Hyfer ewes was greater for lambs born in November. These lambs had poorer growing conditions over the summer months, with 22% lower growth rate and taking 5 weeks longer to reach slaughter than did lambs born in March or August. There was no difference between Dorset and Suffolk sire breeds for any lamb growth traits, with lambs from Hyfer sires growing 7% slower. Ram and cryptorchid lambs reached slaughter 1 week earlier than did wethers, with ewes a further 9 days later (P < 0.01). Sex differences were maximised when lamb growth was greatest. There were no differences in carcass fat measurements between ram and cryptorchid lambs, although both were considerably leaner than wethers (2.2–3.0 mm fat at the GR site), which were 1.3–2.1 mm leaner than ewes at 18-kg carcass weight. The range in average growth rate of progeny of the BLM ewes from the 12 different source flocks at Cowra and Wagga Wagga was 10–14% of the mean which was twice the difference in average growth rate of progeny from the BLM and Hyfer dams. There was also significant variation among the BLM source flocks for carcass fat measurements. Lamb progeny from the different sire- and dam-breed combinations had varying levels of heterozygosity. There appears to be little loss of heterosis or hybrid vigour for lamb growth, although the sire breed × dam breed interaction was significant (P < 0.01) for age at slaughter at Wagga Wagga, in which the ranking of the lamb types was consistent with the levels of heterozygosity. The estimates of between-lambing repeatability for the ewes were highest for birthweight (0.35 Cowra and 0.27 Wagga Wagga) and declined at later ages (0.26–0.17), with lower estimates for carcass traits.

Small Firms, Their Growth and Product Differentiation

This paper investigates a model of endogenous product differentiation between large well established and small newly established firms. Small firms should have greater growth potential than large mature firms whose growth potential tapers off once they reach a certain size relative to the capacity of the market. The small firm with its newness has a product that is typically seen as being of a lower quality than the products of their larger counterparts. The model explores the interaction of product quality, firm size and the growth of small firms. This paper shows that firms choose size (large or small) and they will maintain their decision throughout any stage of the game. Large firms are more efficient at producing quality, therefore, despite a growth rate advantage, small firms remain small. Driving this result is the fact that the payoff from remaining small outweighs the payoff from its growth potential since becoming large is accompanied by heavy costs. This property ensures that the principle of maximal product differentiation is sustained. Models that investigate firm dynamics have predicted that small firms grow at a faster rate than large ones. Hall (1987) investigated the dynamics of firm growth in the US Manufacturing sector using econometric techniques. He suggested that possible reasons why small firms may grow faster than large ones are due to differences in the rate and direction of innovative activity, or simply because the economy is finite and it is expected that diminishing returns will eventually take effect. He observed large differences in the variance of growth rates across size classes of firms and that the smaller firms in the sample grow faster, but made no claim to be able to distinguish clearly the reasons for these differences. This paper investigates, firm size and their respective growth rates under variable marginal cost. Our analysis presents a two-stage non-cooperative game, in which the firm chooses its size in stage one and prices given its own type and that of the other firm in stage two. Shaked and Sutton (1983) showed that where two firms choose distinct qualities, they will both enjoy positive profit at equilibrium. The intuition behind their result is that where the product qualities converge, a price competition will result between both firms which will serve to erode their profits. This equilibrium runs counter to the wisdom of Hotelling's (1929) model of the linear city in which he concluded that the equilibrium outcome is characterized by minimal differentiation. In applying the wisdom of Shaked and Sutton we consider two firms of distinctive types; small and large. It is believed that small newly established firms should have greater growth potential than large mature firms whose growth potential tapers off once they reach a certain size relative to the capacity of the market. However, it has been argued that due to the product differentiation advantage that the large well established firm has and the demand disadvantage that may face the small firm it might be difficult for the small firm with the lower quality to settle in the market. Schmalensee (1982) reported that, once consumers are convinced that the first in any product class performs satisfactorily, that brand is seen as the standard against which subsequent entrants are judged. As a result, it presents a greater challenge for later entrants to attract consumers to invest in learning about their qualities than that faced by the first brand.The idea that there is product differentiation advantage for established sellers has been well supported by empirical investigations.

Competitive extinctions between asexual and sexual populations: simulations define criteria for sexual survival

ABSTRACT To investigate the reasons for the rarity of asexuality, despite the twofold advantage in growth rate of the latter, computer-simulated populations of asexual and sexual individuals of defined genetic composition were allowed to compete at a fixed carrying capacity. Variables included population size, mutation rate, selection coefficient, dominance coefficient, and percentages of mutations which were advantageous. Critical was to allow the two groups to evolve separately for a variable number of generations before being mixed in a single competing population, when one or other population would inevitably go extinct. Multiple reiterations under standard sets of conditions enabled accurate measures of extinction rates, loci carrying mutant alleles, fixed mutant alleles, and fitness values. For all of the above variables, values could readily be found which enabled the sexual population to survive in more than 50% of trials. The diploid state enables dominance to assist in the survival of sexuality. A general implication is that provided the two groups are not constrained geographically, or that niches are available which delay or avoid mixing, then the asexual competitors, under realistic values for mutation rate, population size and other parameters, will not drive the sexual population to extinction.

Optimal pattern of technology adoptions under embodiment: A multi‐stage optimal control approach

AbstractBy deriving the necessary conditions for a multi‐stage optimal control problem where the endogenous switching instants appear as an argument of the state equation, we analyze the optimal pattern of technology adoptions under embodiment with a finite planning horizon. We show that the optimal pattern of technology adoptions depends crucially on how the growth rate advantage compares to the adjustment and the obsolescence costs inherent to embodiment. We obtain non‐stationary lifetimes for the adopted technologies due to finite planning horizon. We analyze numerically the effects of planning horizon, speed of adjustment to the new technology, growth rate of technology and the impatience rate on the optimal pattern. Copyright © 2010 John Wiley & Sons, Ltd.

Quantifying the relative importance of niches and neutrality for coexistence in a model microbial system

Summary 1. Ecologists have identified two types of processes promoting species coexistence: stabilizing mechanisms (niche differentiation and related processes) that increase negative intraspecific interactions relative to negative interspecific interactions, and equalizing mechanisms (neutrality) that minimize the differences in species’ demographic parameters. It has been theoretically and empirically shown that the two types of mechanisms can operate simultaneously; however, their relative importance remains unstudied although this is a key question in the synthesis of niche and neutral theories. 2. We experimentally quantified the relative importance of niche and neutral mechanisms in promoting phenotypic diversity in a model microbial system involving different phenotypes of the bacterium Pseudomonas fluorescens. Initially isogenic populations of the bacterium can diversify into a series of major and minor classes of phenotypes that can be treated as analogues of species. We estimated the relative population growth rate when rare of 32 phenotypes from six replicate microcosms. Each phenotype was assessed in a re‐assembled microcosm in which the relative densities of all phenotypes remained the same except for the focal one which was reduced in frequency. A growth rate advantage when rare was considered evidence of non‐neutral processes. 3. Approximately one‐third of the phenotypes had a growth rate advantage when rare while the remaining two‐thirds showed neutral or near‐neutral dynamics. Furthermore, there was overall little evidence that productivity increased with phenotypic diversity. 4. Our results suggest that niche and neutral processes may simultaneously contribute to the maintenance of biodiversity, with the latter playing a more important role in our system, and that the operation of niche mechanisms does not necessarily lead to a positive biodiversity effect on ecosystem properties.

The cost of gene expression underlies a fitness trade-off in yeast

Natural selection optimizes an organism's genotype within the context of its environment. Adaptations to one environment can decrease fitness in another, revealing evolutionary trade-offs. Here, we show that the cost of gene expression underlies a trade-off between growth rate and mating efficiency in the yeast Saccharomyces cerevisiae. During asexual growth, mutations that eliminate the ability to mate provide an approximately 2% per-generation growth-rate advantage. Some strains, including most laboratory strains, carry an allele of GPA1 (an upstream component of the mating pathway) that increases mating efficiency by approximately 30% per round of mating at the cost of an approximately 1% per-generation growth-rate disadvantage. In addition to demonstrating a trade-off between growth rate and mating efficiency, our results illustrate differences in the selective pressures defining fitness in the laboratory versus the natural environment and show that selection, acting on the cost of gene expression, can optimize expression levels and promote gene loss.

In this issue

In this issue

Quorum sensing and motility mediate interactions between Pseudomonas aeruginosa and Agrobacterium tumefaciens in biofilm cocultures

In the environment, multiple microbial taxa typically coexist as communities, competing for resources and, often, physically associated within biofilms. A dual-species cocultivation model has been developed by using two ubiquitous and well studied microbes Pseudomonas aeruginosa (P.a.) and Agrobacterium tumefaciens (A.t.) as a tractable system to identify molecular mechanisms that underlie multispecies microbial associations. Several factors were found to influence coculture interactions. P.a. had a distinct growth-rate advantage in cocultures, increasing its relative abundance during planktonic and biofilm growth. P.a. also demonstrated a slight quorum-sensing-dependent increase in growth yield in liquid cocultures. P.a. dominated coculture biofilms, "blanketing" or burying immature A.t. microcolonies. P.a. flagellar and type IV pili mutant strains exhibited deficient blanketing and impaired competition in coculture biofilms, whereas, in planktonic coculture, these mutations had no effect on competition. In contrast, A.t. used motility to emigrate from coculture biofilms. In both planktonic and biofilm cocultures, A.t. remained viable for extended periods of time, coexisting with its more numerous competitor. These findings reveal that quorum-sensing-regulated functions and surface motility are important microbial competition factors for P.a. and that the outcome of competition and the relative contribution of different factors to competition are strongly influenced by the environment in which they occur.

Early Starts, Reversals and Catchup in the Process of Economic Development

Early states like China, India, Italy and Greece have been experiencing more rapid economic growth in recent decades than have later-comers to agriculture and statehood like New Guinea, the Congo, and Uruguay. We show that more rapid growth by early starters has been the norm in economic history, and that the of fortune associated with the European overseas expansion that began around 1500 was both exceptional and temporary. We demonstrate not only that the post-1500 reversal was in the process of being reversed between 1960 and 1998, but also that the growth rate advantage conferred by early development in the latter period was several times greater than the growth rate disadvantage that it conferred during 1500-1960, implying a rapid undoing of the first reversal.

Bi-directional sex change: testing the growth-rate advantage model

Bi-directional sex change in coral-dwelling fishes (genera Gobiodon and Paragobiodon) has been attributed to a growth-rate advantage for females during the non-breeding season. This model predicts that the smallest individual in a newly formed pair should always be female. To determine if a growth-rate advantage exists for female Gobiodon histrio, I monitored the growth of males and females in natural pairs during the breeding and non-breeding season. I then used a manipulative field experiment to test four predictions of the growth-rate advantage model: (1) the larger individual should change sex to male in new pairs containing two females; (2) the smaller individual should change sex to female in new pairs containing two males; (3) neither individual should change sex in heterosexual pairs where the male is larger than the female; and (4) both individuals should change sex in heterosexual pairs where the female is larger than the male. A growth-rate advantage was detected for female G. histrio during the non-breeding season; however, only the first three of the predicted outcomes were observed in the manipulative experiment. Sex change did not occur in heterosexual pairs where the female was larger than the male. Furthermore, growth did not differ between sex-changed and non-sex-changed fish; therefore, the absence of sex change in these pairs is not due to a growth cost to sex change. I propose that the risk of moving among spatially isolated habitat patches and the low probability of finding a mate have been more important than sex-specific differences in growth rates to the evolution of bi-directional sex change in coral-dwelling gobies.

Stability studies of recombinant Saccharomyces cerevisiae in the presence of varying selection pressure

A recombinant yeast plasmid carrying the Ieu2 gene for auxotrophic complementation and a reporter gene for β-galactosidase under the control of Gal10 promoter was studied in Saccharomyces cerevisiae. Growth, product formation, and plasmid stability were studied in defined, semi-defined, and complex media. The biomass concentration and specific activity were higher in complex medium than in defined medium, which was selective for the growth of plasmid-containing cells, leading to a 10-fold increase in volumetric activity. However, plasmid instability was very high in complex media with 50% plasmid-free cells emerging in the culture within 75 h of cultivation. In order to control instability, the growth rates of the plasmid-containing and plasmid-free cells were determined in semi-defined media, which consisted of defined medium supplemented with different concentrations of yeast extract. Below a critical concentration of yeast extract (0.05 g/L), the plasmid-containing cells had a growth rate advantage over the plasmid-free cells. This was possibly because, at this concentration of yeast extract, the availability of leucine became the rate-determining factor in the specific growth rate of plasmid-free cells. A feeding strategy was designed which maintained a low concentration of the residual yeast extract in the medium and thus continuously provided the plasmid-containing cells with a competitive advantage over the plasmid-free cells. This resulted in high stability as well as high cell density under non-selective conditions, which led to a 10-fold increase in the volumetric activity compared to that achieved in defined selective media. A simple mathematical model was formulated to verify the experimental data. The important state variables and process parameters, i.e., biomass concentration, β-galactosidase expression, sucrose consumption, yeast extract consumption, and specific growth rates of the two cell populations, were evaluated. These variables and parameters along with the differential equations based on material balances as well as the experimental results obtained were used in a mathematical model for the fed-batch cultivation. These correctly verified the experimental data and clearly illustrated the concept behind the success of the fed-batch strategy under yeast extract starvation. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 78: 475–488, 2002.

Two-stage cultivation of recombinant Saccharomyces cerevisiae to enhance plasmid stability under non-selective conditions: experimental study and modeling.

A leucine auxotroph strain of Saccharomyces cerevisiae was used to study plasmid stability and expression using a recombinant plasmid, which contained a foreign gene for firefly luciferase (luc). This recombinant yeast was tested in a series of continuous cultures in semi-defined media with varying concentrations of yeast extract in order to study its effect on stability. While the biomass concentration and luciferase activity increased with increasing concentrations of yeast extract, the plasmid stability declined. An analysis of the growth rates showed that the recombinants enjoyed a growth rate advantage over the plasmid-free cells at critically low yeast extract concentrations, possibly due to leucine starvation in the media. A two-stage cultivation strategy was designed in order to create a yeast extract limited environment so that plasmid-free cells could not grow and overtake the recombinant cells. The cells were cultivated in selective media in the first stage, and then transferred continuously to the second stage where the media was enriched by feeding yeast extract. The feed rate was kept low in order to ensure yeast extract and hence leucine starvation, thereby selecting against the plasmid-free cells. This strategy resulted in a stable existence of recombinant cells, which stabilized around 60% at steady state during the tested period of cultivation. The complex nitrogen feed helped in increasing the cell density and volumetric activity by approximately 9 and 18-fold respectively with respect to that achieved in minimal medium. The experimental data was used to formulate a mathematical model to predict cell growth and plasmid stability in two-stage cultivation, which correctly explained the experimental data.

Emergence of a Subpopulation in a Computational Model of Tumor Growth

Malignant brain tumors consist of a number of distinct subclonal populations. Each of these subpopulations may be characterized by its own behaviors and properties. These subpopulations arise from the constant genetic and epigenetic alteration of existing cells in the rapidly growing tumor. However, since each single-cell mutation only leads to a small number of offspring initially, very few newly arisen subpopulations survive more than a short time. The present work quantifies “emergence”, i.e. the likelihood of an isolated subpopulation surviving for an extended period of time. Only competition between clones is considered; there are no cooperative effects included. The probability that a subpopulation emerges under these conditions is found to be a sigmoidal function of the degree of change in cell division rates. This function has a non-zero value for mutations which confer no advantage in growth rate, which represents the emergence of a distinct subpopulation with an advantage that has yet to be selected for, such as hypoxia tolerance or treatment resistance. A logarithmic dependence on the size of the mutated population is also observed. A significant probability of emergence is observed for subpopulations with any growth advantage that comprise even 0.1% of the proliferative cells in a tumor. The impact of even two clonal populations within a tumor is shown to be sufficient such that a prognosis based on the assumption of a monoclonal tumor can be markedly inaccurate.

Effect of ewe milk production on profitability of dryland lamb production systems

A farmlet study was carried out over 2 years to examine the role of milk production in dryland lamb production systems. Poll Dorset ewes (high milk producers) were mated with Romney rams and Romney ewes (average milk producers) were mated with Poll Dorset rams to produce lambs of a similar genotype. As well as two levels of milk production, two fecundity treatments were used and farmlets were replicated. Farmlets were 2.9 ha and stocked at a rate of 15 ewes/ha. Farmlets were managed to ensure similar pasture covers at the start of winter and at lambing. Poll Dorset ewes produced more milk and in both years their twin lambs had a small but significant advantage in lamb growth rate. This resulted in earlier drafting of lambs and the ability to obtain early season premiums. In the low fecundity farmlets, net financial returns for Romney and Poll Dorset ewes were $605/ha and $676/ha (+ 12%) in Year 1 and $709/ ha and $762/ha (+ 7%) in Year 2. For the high fecundity farmlets, financial returns for Romney and Poll Dorset ewes were $637/ha and $818/ha (+ 28%) in Year 1 and $866/ha and $921/ha (+ 6%) in Year 2. The greatest financial benefits to increased milk production were achieved in high fecundity ewes in Year 1 when feeding during lactation was less than optimal and this resulted in a significant effect on the rate at which twin lambs were drafted to achieve early season premiums. Lambs failing to reach minimum drafting weights were also penalised because of the prevailing drought conditions and low market prices for lighter lambs. Keywords: breed, dryland, ewes, farming systems, fecundity, milk production, pre-weaning growth, profitability, sheep

The Migration of High Angle Grain Boundaries during Recrystallization

When plastically deformed metallic materials are annealed, new strain free grains emerge from the microstructure and grow by means of grain boundary migration until the deformation microstructure is eliminated. This process is called recrystallization. In this paper the various methods by which grain boundary migration rates are measured stereologically in order to characterize the growth process are described and compared using illustrations from recrystallization experiments on commercial AA1050 aluminum. It seems abundantly clear that during recrystallization of cold-deformed materials, isothermal grain boundary migration rates decrease with time and reasons for such a decrease are discussed. A new methodology whereby migration rates of the individual recrystallization texture components may be quantified by combining stereology and orientation imaging by the electron back scattered pattern analysis is outlined. By illustration, recent experiments on aluminum and copper are summarized documenting the slight growth rate advantage the cube texture component (001)[100] possesses during recrystallization of cold rolled material. The role of orientation pinning effects on grain boundary migration is described briefly. It appears that such pinning effects allow recrystallized grains emerging from the weaker deformation texture components to enjoy an average growth rate advantage over those emerging from the stronger deformation texture components.

Both-ways sex change in monogamous coral gobies, Gobiodon spp.

We confirmed both-ways sex change in the coral-dwelling gobies Gobiodon micropus, G. oculolineatus, G. quinquestrigatus and G. rivulatus rivulatus by mate-removal experiment in the field and by the aquarium experiment of keeping two consexual fish in a coral. Eight species of Gobiodon were found in Acropora corals on the reef flat of Sesoko Island, Okinawa, southern Japan. The 4 species mentioned above bred in monogamous pairs composed of a male and a female matched by size, and the male took care of eggs deposited on the coral branch. In G. quinquestrigatus and G. rivulatus rivulatus males were larger than females in newly formed pairs, and females grew faster than their mates until breeding. The growth-rate advantage in females seems to be the major factor in the evolution of female to male sex change. The gobies strongly depended on host corals, but they moved between the corals after mate loss or coral death to form new pairs. This provides opportunities for the evolution of male to female sex change; the ability to change sex in both directions reduces the frequency of risky movement between host corals to form new pairs. These conditions are very similar to those reported in the both-ways sex change of another coral-dwelling goby Paragobiodon echinocephalus.

Studies on maintenance of vector pBK2 in Corynebacterium acetoacidophilum by co-culture experiments in a continuous bioreactor

A plasmid vector pBK2 was tested for maintenance in Corynebacterium acetoacidophilum and found to be 100% stable for 90 generations. In co-culture experiments in absence of any selection pressure it was able to cause washout of plasmid free cells. Deletion mutagenesis of the plasmid was done to identify the regions of DNA responsible for its stable maintenance. This led to the identification of a region of DNA in pBB1, an endogenous plasmid used in the construction of pBK2, which is responsible for providing a growth rate advantage to the plasmid containing cell in co-culture with plasmid-free cells. To explain this observed stability we postulate the production of a “growth-inhibiting factor” by the plasmid-containing cells. Inclusion of a death rate term for the plasmid free cells in the computer simulation of the growth kinetics in a chemostat successfully predicts, depending upon the magnitude of the kinetic parameters, a stable coexistence of the two or washout of the plasmid-free cells, an observation that matches the experimental data. Because of its stable maintenance and its ability to select against plasmid-free cells this host-vector system is a natural candidate for cloning and use in large-scale fermentations.

Barley grass seed and shearing effects on summer lamb growth and pelt quality

The effects of mature barley grass (Hordeum spp.) pasture on lamb growth rates, carcass180 crossbred lambs finished on summer pastures. The effect of shearing at weaning, using 2 types of combs (traditional or cover) was compared with a 'no shearing' treatment.Exposure to barley grass pasture over November and December produced growth rates of 82 � 5 g/day for lambs slaughtered in January compared with growth rates of 141 � 5 g/day on lucerne pasture over the same period. On the barley grass pasture, shearing gave an immediate and sustained advantage (P<0.05) in growth rate but no difference between cover or traditional comb. Carcass weights were 21.4 � 0.3 and 19.0 � 0.4 kg for lambs grazing lucerne pasture and barley grass pasture, respectively. Shearing reduced pelt damage from barley grass seed to the extent that 85% of unshorn pelts had >5 scars per pelt compared with 13% in pelts from shorn lambs. Type of shearing comb did not influence the result. The results suggest that maturing barley grass pastures must be avoided if adequate growth rates are to be achieved in weaner lambs.

Effect of selection for wool growth on seasonal patterns of yield, fibre diameter, and colour in Romney lines

Seasonal wool growth and associated wool characteristics were measured in a Romney line selected for high fleece weight and an unselected control line in 1990 and 1991. Both had a significant (P<0.01) decline in wool growth rate in winter compared with summer. The wool growth rate advantage (P<0.001) of the selected line over the control averaged 19 and 33% for ewes, and 24 and 36% for hoggets, in summer and winter, respectively. Staple strength, yield, and fibre diameter differences were closely associated with wool growth. Colour analysis showed no difference between lines in either brightness (Y) or yellowness (Y - Z). However, both the Y and Z values were lower in spring and summer, while Y - Z was highest in summer. The results suggest that selection for high fleece weight also improves major wool characteristics and reduces the relative winter wool growth decline in Romneys.