scholarly journals Selection for plasmid post–segregational killing depends on multiple infection: evidence for the selection of more virulent parasites through parasite–level competition

2005 ◽  
Vol 272 (1561) ◽  
pp. 403-410 ◽  
Author(s):  
T. F. Cooper ◽  
J. A. Heinemann
Keyword(s):  
Growth Rate ◽  
Growth Rates ◽  
Multiple Infection ◽  
Virulence Determinant ◽  
New Hosts ◽  
Parasite Reproduction ◽  
Selection For ◽  
The Cost ◽  
Selection Of

Is the virulence of parasites an outcome of optimized infection? Virulence has often been considered an inevitable consequence of parasite reproduction when the cost incurred by the parasite in reducing the fitness of its current host is offset by increased infection of new hosts. More recent models have focused on how competition occurring between parasites during co–infection might effect selection of virulence. For example, if co–infection was common, parasites with higher intrinsic growth rates might be selected, even at the expense of being optimally adapted to infect new hosts. If growth rate is positively correlated with virulence, then competition would select increased virulence. We tested these models using a plasmid–encoded virulence determinant. The virulence determinant did not contribute to the plasmid's reproduction within or between hosts. Despite this, virulent plasmids were more successful than avirulent derivatives during selection in an environment allowing within–host competition. To explain these findings we propose and test a model in which virulent parasites are selected by reducing the reproduction of competitors.

scholarly journals Growth Rate Variation and Larval Survival: Inferences from an Individual-Based Size-Dependent Predation Model

1993 ◽  
Vol 50 (1) ◽  
pp. 133-142 ◽  
Author(s):  
James A. Rice ◽  
Thomas J. Miller ◽  
Kenneth A. Rose ◽  
Larry B. Crowder ◽  
Elizabeth A. Marschall ◽  
...  
Keyword(s):  
Growth Rate ◽  
Growth Rates ◽  
Individual Variability ◽  
Individual Growth ◽  
Rate Variation ◽  
High Survival ◽  
Initial Growth ◽  
Size Dependent ◽  
The Mean ◽  
Selection For

We used an individual-based Monte Carlo simulation model to explore how changes in the mean and variance of growth rates of individuals in a larval fish cohort interact with size-dependent predation to affect the number and characteristics of individual survivors. Small changes in initial cohort mean growth rate can change survival over the first 60 d of life 10-to 30-fold. But when variance in growth rate among individuals is high, survival can be substantially higher than expected from the initial mean cohort growth rate. Selection for faster-growing individuals becomes stronger with increasing variance and increasing predation rate. In some cases, > 80% of the survivors may come from the upper 25% of the initial growth rate distribution, and the mean growth rate of the survivors may exceed twice the initial mean growth rate. When individual growth rates change from day to day rather than remaining constant, the contribution of atypical individuals is accentuated even further. Counterintuitively, most of the selection for faster-growing individuals happens only after the majority of mortality has already taken place. These results suggest that interactions between individual variability and selective mortality may have important cohort-level implications for survival in fishes.

scholarly journals Selection for antibiotic resistance is reduced when embedded in a natural microbial community

2019 ◽  
Author(s):  
Uli Klümper ◽  
Mario Recker ◽  
Lihong Zhang ◽  
Xiaole Yin ◽  
Tong Zhang ◽  
...  
Keyword(s):  
Antibiotic Resistance ◽  
Microbial Community ◽  
Single Species ◽  
Natural Environments ◽  
Order Of Magnitude ◽  
Natural Microbial Community ◽  
Cost Of Resistance ◽  
Selection For ◽  
The Cost ◽  
Selection Of

AbstractAntibiotic resistance has emerged as one of the most pressing, global threats to public health. In single-species experiments selection for antibiotic resistance occurs at very low antibiotic concentrations. However, it is unclear how far these findings can be extrapolated to natural environments, where species are embedded within complex communities. We competed isogenic strains of Escherichia coli, differing exclusively in a single chromosomal resistance determinant, in the presence and absence of a pig fecal microbial community across a gradient of antibiotic concentration for two relevant antibiotics: gentamicin and kanamycin. We show that the minimal selective concentration was increased by more than one order of magnitude for both antibiotics when embedded in the community. We identified two general mechanisms were responsible for the increase in minimal selective concentration: an increase in the cost of resistance and a protective effect of the community for the susceptible phenotype. These findings have implications for our understanding of the evolution and selection of antibiotic resistance, and can inform future risk assessment efforts on antibiotic concentrations.

The effect of correction factors on response to selection in beef cattle

1980 ◽  
Vol 30 (2) ◽  
pp. 211-216 ◽  
Author(s):  
L. P. Jones ◽  
I. R. Hopkins
Keyword(s):  
Growth Rate ◽  
Age Groups ◽  
Correction Factors ◽  
Response To Selection ◽  
Weaning Weight ◽  
Selection For ◽  
Rate Selection ◽  
Genetic Responses ◽  
Selection Differentials ◽  
Selection Of

ABSTRACTProgeny of younger dams grow more slowly than those of older dams. When the environmental effects of dam age are not allowed for in selection for growth rate, selection differentials and genetic responses to selection are reduced.In a model herd, with cows aged 2 to 8 years, it was found that neglecting the dam age effects reduced genetic gains by about 15% when selection is for weaning weight, and by 11 to 7 % when selection is at an age of 12 to 20 months. Much of the reduction occurs because of the selection of higher proportions from genetically inferior groups.If genetic differences among dam age groups are small the reduction is only 7% at weaning and less at older ages. The effect of ignoring calf age was also estimated. It was found that if calves born within a period of 33 days were compared and calf age was neglected, the response to selection for weaning weight would be reduced by about 6%.

Nutrient partitioning in Merino rams with different wool growth rates

1994 ◽  
Vol 59 (1) ◽  
pp. 55-60 ◽  
Author(s):  
P. B. Cronjé ◽  
M. Smuts
Keyword(s):  
Growth Rate ◽  
Production Potential ◽  
Physiological Basis ◽  
Wool Production ◽  
Available Nutrients ◽  
Wool Growth ◽  
Nutrient Partitioning ◽  
Ad Libitum ◽  
Selection For ◽  
The Cost

AbstractThe aim of this experiment was to determine whether there is any physiological basis for concerns that selection for fleece mass may decrease fitness by increasing the partitioning of nutrients to wool at the expense of other body functions.Forty-five Merino rams (24 months old) were given food at an ad libitum and a maintenance level of nutrition. Animals were grouped into high, average or low clean fleece growth-rate categories on the basis of measurements made during the ad libitum feeding period. During ad libitum feeding, high producers grew proportionately 0·42 more clean fleece, and deposited proportionately 0·36 more energy and 0·42 more nitrogen (N) as greasy fleece than average producers. This was achieved by partitioning a higher proportion of N consumed to wool (0·08 v. 0·06), and not by increased energy or N retention. High producers adapted to the maintenance diet by decreasing clean wool growth rate proportionately by 0·32. There were no differences between high and average wool producers in clean wool growth rate or the percentage of N or energy intake partitioned to wool at the maintenance level of feeding. Although there were no differences in initial live mass between groups, low producers gained proportionately 0·45 more live mass during the experiment than average producers.It was concluded that Merino rams of high clean-wool production potential are not more efficient, but partition more of the available nutrients to wool production at the cost of body tissue deposition.

scholarly journals Consequences of genetic change in farm animals on food intake and feeding behaviour

2001 ◽  
Vol 60 (1) ◽  
pp. 115-125 ◽  
Author(s):  
Gerry Emmans ◽  
Ilias Kyriazakis
Keyword(s):  
Growth Rate ◽  
Food Intake ◽  
Feeding Behaviour ◽  
Genetic Change ◽  
Farm Animals ◽  
The Past ◽  
Environmental Decisions ◽  
Selection For ◽  
The Cost ◽  
Over Time

Selection in commercial populations on aspects of output, such as for growth rate in poultry, against fatness and for growth rate in pigs, and for milk yield in cows, has had very large effects on such outputs over the past 50 years. Partly because of the cost of recording intake, there has been little or no selection for food intake or feeding behaviour. In order to predict the effects of such past, and future, selection on intake it is necessary to have some suitable theoretical framework. Intake needs to be predicted in order to make rational feeding and environmental decisions. The idea that an animal will eat ‘to meet its requirements’ has proved useful and continues to be fruitful. An important part of the idea is that the animal (genotype) can be described in a way that is sufficient for the accurate prediction of its outputs over time. Such descriptions can be combined with a set of nutritional constants to calculate requirements. There appears to have been no change in the nutritional constants under selection for output. Under such selection it is simplest to assume that changes in intake follow from the changes in output rates, so that intake changes become entirely predictable. It is suggested that other ways that have been proposed for predicting intake cannot be successful in predicting the effects of selection. Feeding behaviour is seen as being the means that the animal uses to attain its intake rather than being the means by which that intake can be predicted. Thus, the organisation of feeding behaviour can be used to predict neither intake nor the effects of selection on it.

Crossbred sheep production. III. Selection for growth rate and carcass attributes in the second-cross lamb

1964 ◽  
Vol 6 (2) ◽  
pp. 179-187 ◽  
Author(s):  
Maurice Bichard ◽  
B. C. Yalçin
Keyword(s):  
Growth Rate ◽  
Individual Performance ◽  
Small Scale ◽  
Progeny Testing ◽  
Genetic Merit ◽  
Ram Lambs ◽  
Selection For ◽  
Sheep Production ◽  
The Individual ◽  
Selection Of

Results have been presented from a small scale investigation into operational and theoretical aspects of progeny testing Down rams as sires of crossbred fat lambs. Twenty-six Suffolk rams were evaluated from the growth records of 922 lambs out of Border Leicester × Cheviot ewes. In addition measurements were recorded on 260 carcasses. Significant differences were found between corrected progeny means, which were equivalent t o heritabilities of between 0·03 and 0·13 for live-weights up to 15 weeks, and o t higher values for skeletal measurements.A scheme for the selection of Down rams was considered which involved measuring the individual performance of all ram lambs and then progeny testing the best of these by measuring a fixed total number of crossbred lambs. It was concluded that the proportion to be progeny tested could be varied within quite wide limits without seriously changing the genetic merit of the selected group.

scholarly journals PreDarwinian evolution, prebiotic change: a principle of least selection

2021 ◽  
Author(s):  
Michael Yarus
Keyword(s):  
Natural Selection ◽  
Standard Deviation ◽  
Molecular Complex ◽  
Minimal Change ◽  
Materials Chemistry ◽  
Evolutionary Path ◽  
Proportionality Constant ◽  
Selection For ◽  
The Cost ◽  
Selection Of

Evolution prior to its Darwinian era was an age of variation. Events allowed by starting materials, chemistry and physics were realized, directed by intrinsic probabilities. In this landscape, a principle of least selection defines the most probable evolutionary path. For selection from a population where x varies, the rate of x evolution dx/dt = αΔμ. μ is the population mean of the selected property x, [alpha] a proportionality constant. Explicit equations for selected change Δμ are presented. Simple results exist for frequent cases; for example, selection for x ≥ a threshold. Maximizing Δμ minimizes need for selection. Least selections for x demand maximal selection dependence on x, maximal x standard deviation σ, and maximal lower x threshold (consistent with the need for a survivor). Least selection is free of the cost of natural selection, thus can support rapid advance. Least selection also unites previous seemingly independent optima. As examples, evolution via ′starting bloc selection [prime] and ′chance utility′ (where selection spans a minimal change) and ′near-ideal reactions′ (where variable reactant supplies create easy reactions) occur via transitory paths of least selection. ′Bayesian convergence′ is guaranteed by least selection′s extremum (which sharply defines evolution′s path). [prime]Distribution fitness′ (where specific outcomes are selected among multiple concurrent variations) is least selection of rare functional minorities. Inheritance of encoded chemical capabilities first evolves because templating and catalysis are close, potentially joined in a single molecular complex. Least selection defines directions, biostructures define destinations in likely pathways of preDarwinian evolution.

scholarly journals Using knockout mutants to reveal the growth costs of defensive traits

2011 ◽  
Vol 278 (1718) ◽  
pp. 2598-2603 ◽  
Author(s):  
Tobias Züst ◽  
Bindu Joseph ◽  
Kentaro K. Shimizu ◽  
Daniel J. Kliebenstein ◽  
Lindsay A. Turnbull
Keyword(s):  
Growth Rate ◽  
Flowering Time ◽  
Growth Rates ◽  
Strongly Correlated ◽  
Wild Type ◽  
Cascading Effects ◽  
Knockout Mutants ◽  
Defence Genes ◽  
Predictor Of Success ◽  
Selection Of

We used a selection of Arabidopsis thaliana mutants with knockouts in defence genes to demonstrate growth costs of trichome development and glucosinolate production. Four of the seven defence mutants had significantly higher size-standardized growth rates (SGRs) than the wild-type in early life, although this benefit declined as plants grew larger. SGR is known to be a good predictor of success under high-density conditions, and we confirmed that mutants with higher growth rates had a large advantage when grown in competition. Despite the lack of differences in flowering-time genes, the mutants differed in flowering time, a trait that strongly correlated with early growth rate. Aphid herbivory decreased plant growth rate and increased flowering time, and aphid population growth rate was closely coupled to the growth rate of the host plant. Small differences in early SGR thus had cascading effects on both flowering time and herbivore populations.

The effect of stocking rate and deferred Autumn grazing of pasture on liveweight and wool production of Merino wethers in a Mediterranean-type climate

1976 ◽  
Vol 16 (79) ◽  
pp. 189 ◽  
Author(s):  
TH Brown
Keyword(s):  
Growth Rate ◽  
Growth Rates ◽  
South Australia ◽  
Management Systems ◽  
Research Centre ◽  
Stocking Rate ◽  
Wool Production ◽  
Wool Growth ◽  
The Cost ◽  
Stocking Rates

Liveweight, seasonal wool growth rates, annual wool production, wool quality and hand feeding requirements were recorded for Merino wethers when autumn deferred or continuously grazed. The two management systems were compared at a series of eight stocking rates from 12.4 to 29.7 sheep per hectare for five years from 1967 to 1971 at the Kybybolite Research Centre, South Australia. Autumn deferment resulted in increased liveweight and wool growth rate during the months of June to September. However, liveweights and wool production under either management were similar for the remainder of the year. Because deferred grazing did not increase liveweights during the critical autumn period, and since hand feeding requirements were similar under either management system at the higher stocking rates, it is suggested that yearly stocking rates can not be increased by autumn deferment. Apart from the drought year of 1967, the continuously grazed sheep required little or no hand feeding up to 22.2 wethers per hectare. It is unlikely that the cost of hand feeding deferred sheep up to this stocking rate would be covered by the small increase in wool production. However, this would depend on the cost of conserved fodder and price received for the wool.

Identifying Measurement Invariant Item Sets in Cross-Cultural Settings Using an Automated Item Selection Procedure

Methodology ◽  
2018 ◽  
Vol 14 (4) ◽  
pp. 177-188 ◽  
Author(s):  
Martin Schultze ◽  
Michael Eid
Keyword(s):  
Measurement Invariance ◽  
Optimal Solution ◽  
Selection Procedure ◽  
Cross Cultural ◽  
Item Selection ◽  
Ant System ◽  
Item Quality ◽  
Ant System Algorithm ◽  
Selection For ◽  
Selection Of

Abstract. In the construction of scales intended for the use in cross-cultural studies, the selection of items needs to be guided not only by traditional criteria of item quality, but has to take information about the measurement invariance of the scale into account. We present an approach to automated item selection which depicts the process as a combinatorial optimization problem and aims at finding a scale which fulfils predefined target criteria – such as measurement invariance across cultures. The search for an optimal solution is performed using an adaptation of the [Formula: see text] Ant System algorithm. The approach is illustrated using an application to item selection for a personality scale assuming measurement invariance across multiple countries.

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