scholarly journals Female resource limitation does not make the opportunity for selection more female biased

2019 ◽  
Author(s):  
Ivain Martinossi-Allibert ◽  
Johanna Liljestrand Rönn ◽  
Elina Immonen
Keyword(s):  
Resource Limitation ◽  
Reproductive Age ◽  
Relative Fitness ◽  
Sex Bias ◽  
Common Environment ◽  
Physiological Conditions ◽  
Mean Fitness ◽  
Female Specific ◽  
Opportunity For Selection ◽  
Oviposition Sites

AbstractEnvironmental and physiological conditions affect how individual variation is expressed and translated into variance in fitness, the opportunity for natural selection. Competition for limiting resources can magnify variance in fitness and therefore selection, while abundance of resources should reduce it. But even in a common environment the strength of selection can be expected to differ across the sexes, as their fitness is often limited by different resources. Indeed most taxa show a greater opportunity for selection in males than in females, a bias often ascribed to intense competition among males for access to mating partners. This sex-bias could reverberate on many aspects of evolution, from speed of adaptation to genome evolution. It is unclear however, whether the sex-bias in opportunity for selection is robust to variations in environment or physiological condition that limit sex-specific resources. Here we test this in the model species C. maculatus by comparing female and male variance in relative fitness (opportunity for selection) under mate competition (i) with and without limitation of quality oviposition sites, and (ii) under delayed age at oviposition. Decreasing the abundance of the resource key to females or increasing their reproductive age was indeed challenging as shown by a reduction in mean fitness, however variance in fitness remained male-biased across the three treatments, with even an increased male-bias when females were limited by oviposition sites. This suggests that males remain the more variable sex independent of context, and that the opportunity for selection through males is indirectly affected by female-specific resource limitation.

scholarly journals Female‐specific resource limitation does not make the opportunity for selection more female biased

Evolution ◽  
2020 ◽  
Vol 74 (12) ◽  
pp. 2714-2724
Author(s):  
Ivain Martinossi‐Allibert ◽  
Johanna Liljestrand Rönn ◽  
Elina Immonen
Keyword(s):  
Resource Limitation ◽  
Female Specific ◽  
Opportunity For Selection

scholarly journals An estimator of the Opportunity for Selection that is independent of mean fitness

2020 ◽  
Author(s):  
Robin S. Waples
Keyword(s):  
Null Model ◽  
Relative Fitness ◽  
Offspring Number ◽  
Evolutionary Response ◽  
Fisher Model ◽  
Wide Range ◽  
Mean Fitness ◽  
Selection For ◽  
Opportunity For Selection ◽  
Straightforward Interpretation

AbstractVariation among individuals in number of offspring (fitness, k) sets an upper limit to the evolutionary response to selection. This constraint is quantified by Crow’s Opportunity for Selection (I), which is the variance in relative fitness . Crow’s I has been widely used but remains controversial because it depends on mean offspring number in a sample . Here I used a generalized Wright-Fisher model that allows for unequal probabilities of producing offspring to evaluate behavior of Crow’s I and related indices under a wide range of sampling scenarios. Analytical and numerical results are congruent and show that rescaling the sample variance to its expected value at a fixed removes dependence of I on mean offspring number, but the result still depends on choice of . A new index is introduced, , which makes Î independent of sample without the need for variance rescaling. ΔI has a straightforward interpretation as the component of variance in relative fitness that exceeds that expected under a null model of random reproductive success. ΔI can be used to directly compare estimates of the Opportunity for Selection for samples from different studies, different sexes, and different life stages.

scholarly journals Sex Differences in Constitutive Autophagy

2014 ◽  
Vol 2014 ◽  
pp. 1-5 ◽  
Author(s):  
Sara Oliván ◽  
Ana Cristina Calvo ◽  
Raquel Manzano ◽  
Pilar Zaragoza ◽  
Rosario Osta
Keyword(s):  
Skeletal Muscle ◽  
Spinal Cord ◽  
Sex Differences ◽  
Sexual Dimorphism ◽  
Animal Models ◽  
Sex Bias ◽  
Wild Type ◽  
Male And Female ◽  
Physiological Conditions ◽  
Sequestosome 1

Sex bias has been described nowadays in biomedical research on animal models, although sexual dimorphism has been confirmed widely under pathological and physiological conditions. The main objective of our work was to study the sex differences in constitutive autophagy in spinal cord and skeletal muscle tissue from wild type mice. To examine the influence of sex on autophagy, mRNA and proteins were extracted from male and female mice tissues. The expressions of microtubule-associated protein 1 light chain 3 (LC3) and sequestosome 1 (p62), markers to monitor autophagy, were analyzed at 40, 60, 90, and 120 days of age. We found significant sex differences in the expression of LC3 and p62 in both tissues at these ages. The results indicated that sex and tissue specific differences exist in constitutive autophagy. These data underlined the need to include both sexes in the experimental groups to minimize any sex bias.

Mean fitness and the equilibria in multilocus polymorphisms

1967 ◽  
Vol 169 (1014) ◽  
pp. 31-58 ◽  
Keyword(s):  
Population Density ◽  
Gene Frequency ◽  
Random Mating ◽  
Relative Fitness ◽  
Gene Frequencies ◽  
Theory Of Evolution ◽  
Density Control ◽  
Mean Fitness ◽  
Fundamental Law ◽  
Matter Energy

A precise theorem is given for the increase in fitness due to natural selection on diploids subject to random mating, non-overlapping generations and not more than two loci; the method of extension to more loci is given by Kojima & Kelleher, and a precise theorem is given here for any number of loci when there is no recombination. The increase is equal to the haploid (or genic) variance in fitness, multiplied by a factor which is equal to two in the absence of dominance, but which otherwise is a function of gene frequency and dominance. The theorem is compared with that of Kimura, which is more general but harder to apply, and to those of Kojima & Kelleher and Fisher, which are respectively restricted to slow selection and absence of epistasis. The new theorem is used to predict the equilibria in populations polymorphic for two loci, and to deal especially with the quasi-stable equilibrium, for which the critical value of recombination is formulated, and the through point, at which a stable and unstable equilibrium meet and annihilate each other. The effect of this in space is to produce a stepped cline, in which gene frequencies and gametic excess change suddenly over a short distance; in time, the through point brings a new slant to Wright’s multiple peak theory of evolution, as populations can move precipitately from peak to peak without the help of random processes. Mean fitness is related only indirectly to population density. By distinguishing carefully between mean absolute fitness (which is the rate of population growth) and mean relative fitness (which is more useful than the absolute parameter for predicting genetical equilibria) we can show the effects of various types of density control on the genetical composition of the population; density dependent selection may appear to be gene-frequency dependent. The fundamental law of evolution is probably a thermodynamic law of increasing matter energy, which is related only tenuously to the law of increasing genetical fitness.

scholarly journals A Comparison of Methods to Measure Fitness in Escherichia coli

2015 ◽  
Author(s):  
Michael J Wiser ◽  
Richard E Lenski
Keyword(s):  
Escherichia Coli ◽  
Traditional Method ◽  
Experimental Studies ◽  
Alternative Methods ◽  
Relative Fitness ◽  
Initial Population ◽  
Common Reference ◽  
Evolution Experiment ◽  
Mean Fitness ◽  
Changes Over Time

In order to characterize the dynamics of adaptation, it is important to be able to quantify how a population's mean fitness changes over time. Such measurements are especially important in experimental studies of evolution using microbes. The Long-Term Evolution Experiment (LTEE) with Escherichia coli provides one such system in which mean fitness has been measured by competing derived and ancestral populations. The traditional method used to measure fitness in the LTEE and many similar experiments, though, is subject to a potential limitation. As the relative fitness of the two competitors diverges, the measurement error increases because the less-fit population becomes increasingly small and cannot be enumerated as precisely. Here, we present and employ two alternatives to the traditional method. One is based on reducing the fitness differential between the competitors by using a common reference competitor from an intermediate generation that has intermediate fitness; the other alternative increases the initial population size of the less-fit, ancestral competitor. We performed a total of 480 competitions to compare the statistical properties of estimates obtained using these alternative methods with those obtained using the traditional method for samples taken over 50,000 generations from one of the LTEE populations. On balance, neither alternative method yielded measurements that were more precise than the traditional method.

scholarly journals Mapping the Peaks: Fitness Landscapes of the Fittest and the Flattest

2018 ◽  
Author(s):  
Joshua Franklin ◽  
Thomas LaBar ◽  
Christoph Adami
Keyword(s):  
Fitness Landscapes ◽  
Complete Analysis ◽  
Evolution System ◽  
Digital Evolution ◽  
Mutational Robustness ◽  
Mean Fitness ◽  
Selection For ◽  
Negative Epistasis ◽  
Opportunity For Selection ◽  
Type Sequence

AbstractBackgroundPopulations exposed to a high mutation rate harbor abundant deleterious genetic variation, leading to depressed mean fitness. This reduction in mean fitness presents an opportunity for selection to restore adaptation through the evolution of mutational robustness. In extreme cases, selection for mutational robustness can lead to “flat” genotypes (with low fitness but high robustness) out-competing “fit” genotypes with high fitness but low robustness—a phenomenon known as “survival of the flattest”. While this effect was previously explored using the digital evolution system Avida, a complete analysis of the local fitness landscapes of “fit” and “flat” genotypes has been lacking, leading to uncertainty about the genetic basis of the survival of the flattest effect.ResultsHere, we repeated the survival of the flattest study and analyzed the mutational neighborhoods of fit and flat genotypes. We found that flat genotypes, compared to the fit genotypes, had a reduced likelihood of deleterious mutations as well as an increased likelihood of neutral and, surprisingly, of lethal mutations. This trend holds for mutants one to four substitutions away from the wild-type sequence. We also found that flat genotypes have, on average, no epistasis between mutations, while fit genotypes have, on average, positive epistasis.ConclusionsOur results demonstrate that the genetic causes of mutational robustness on complex fitness landscapes are multifaceted. While the traditional idea of the survival of the flattest effect emphasized the evolution of increased neutrality, others have argued for increased mutational sensitivity in response to strong mutational loads. Our results show that both increased neutrality and increased lethality can lead to the evolution of mutational robustness. Furthermore, strong negative epistasis is not required for mutational sensitivity to lead to mutational robustness. Overall, these results suggest that mutational robustness is achieved by minimizing heritable deleterious variation.

scholarly journals Mapping the Peaks: Fitness Landscapes of the Fittest and the Flattest

2019 ◽  
Vol 25 (3) ◽  
pp. 250-262 ◽  
Author(s):  
Joshua Franklin ◽  
Thomas LaBar ◽  
Christoph Adami
Keyword(s):  
Fitness Landscapes ◽  
Complete Analysis ◽  
Evolution System ◽  
Digital Evolution ◽  
Mutational Robustness ◽  
Mean Fitness ◽  
Selection For ◽  
Negative Epistasis ◽  
Opportunity For Selection ◽  
Type Sequence

Populations exposed to a high mutation rate harbor abundant deleterious genetic variation, leading to depressed mean fitness. This reduction in mean fitness presents an opportunity for selection to restore fitness through the evolution of mutational robustness. In extreme cases, selection for mutational robustness can lead to flat genotypes (with low fitness but high robustness) outcompeting fit genotypes (with high fitness but low robustness)—a phenomenon known as survival of the flattest. While this effect was previously explored using the digital evolution system Avida, a complete analysis of the local fitness landscapes of fit and flat genotypes has been lacking, leading to uncertainty about the genetic basis of the survival-of-the-flattest effect. Here, we repeated the survival-of-the-flattest study and analyzed the mutational neighborhoods of fit and flat genotypes. We found that the flat genotypes, compared to the fit genotypes, had a reduced likelihood of deleterious mutations as well as an increased likelihood of neutral and, surprisingly, of lethal mutations. This trend holds for mutants one to four substitutions away from the wild-type sequence. We also found that flat genotypes have, on average, no epistasis between mutations, while fit genotypes have, on average, positive epistasis. Our results demonstrate that the genetic causes of mutational robustness on complex fitness landscapes are multifaceted. While the traditional idea of the survival of the flattest emphasized the evolution of increased neutrality, others have argued for increased mutational sensitivity in response to strong mutational loads. Our results show that both increased neutrality and increased lethality can lead to the evolution of mutational robustness. Furthermore, strong negative epistasis is not required for mutational sensitivity to lead to mutational robustness. Overall, these results suggest that mutational robustness is achieved by minimizing heritable deleterious variation.

A method of age determination in Lucilia cuprina (Wied.) (Diptera, Calliphoridae) using cyclic changes in the female reproductive system

1974 ◽  
Vol 64 (3) ◽  
pp. 365-370 ◽  
Author(s):  
W. G. Vogt ◽  
T. L. Woodburn ◽  
Marina Tyndale-Biscoe
Keyword(s):  
Age Determination ◽  
Ovarian Cycle ◽  
Reproductive Age ◽  
Lucilia Cuprina ◽  
Egg Formation ◽  
Temperature Regimes ◽  
Minimum Age ◽  
Time Required ◽  
Cyclic Changes ◽  
Oviposition Sites

AbstractThe stage of egg formation and density of follicular relics enable Lucilia cuprina (Wied.) females to be sorted into 16 ovarian stages, covering the period from emergence to the beginning of the fourth ovarian cycle. The correspondence between the actual age of a fly and its stage of ovarian development was determined at constant temperatures. Where developmental delays were absent, “reproductive age” gave reliable estimates of actual age under both constant and fluctuating temperature regimes. In the field protein shortages and lack of oviposition sites may prolong the time required to complete each ovarian cycle, and flies will be older than their ovaries would indicate. In practice the ovarian stages described provide estimates of minimum age for L. cuprina females.

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