Net Selection Research Articles

The effect of epistasis on sexually antagonistic genetic variation.

There is increasing evidence of segregating sexually antagonistic (SA) genetic variation for fitness in laboratory and wild populations, yet the conditions for the maintenance of such variation can be restrictive. Epistatic interactions between genes can contribute to the maintenance of genetic variance in fitness and we suggest that epistasis between SA genes should be pervasive. Here, we explore its effect on SA genetic variation in fitness using a two locus model with negative epistasis. Our results demonstrate that epistasis often increases the parameter space showing polymorphism for SA loci. This is because selection in one locus is affected by allele frequencies at the other, which can act to balance net selection in males and females. Increased linkage between SA loci had more marginal effects. We also show that under some conditions, large portions of the parameter space evolve to a state where male benefit alleles are fixed at one locus and female benefit alleles at the other. This novel effect of epistasis on SA loci, which we term the 'equity effect', may have important effects on population differentiation and may contribute to speciation. More generally, these results support the suggestion that epistasis contributes to population divergence.

Variable selection in international diffusion models

Prior research comes to different conclusions as to what country characteristics drive diffusion patterns. One prime difficulty that may partially explain this divergence between studies is the sparseness of the data, in terms of the periodicity as well as the number of products and countries, in combination with the large number of potentially influential country characteristics. In face of such sparse data, scholars have used nested models, bivariate models and factor models to explore the role of country covariates. This paper uses Bayesian Lasso and Bayesian Elastic Net variable selection procedures as powerful approaches to identify the most important drivers of differences in Bass diffusion parameters across countries. We find that socio-economic and demographic country covariates (most pronouncedly so, economic wealth and education) have the strongest effect on all diffusion metrics we study. Our findings are a call for marketing scientists to devote greater attention to country covariate selection in international diffusion models, as well as to variable selection in marketing models at large.

Evolution and maintenance of sexual size dimorphism: aligning phylogenetic and experimental evidence

Integrating the insights derived from both phylogenetic and experimental approaches offers a more complete understanding of evolutionary patterns and processes, yet it is rarely a feature of investigations of the evolutionary significance of trait variation. We combine these approaches to reinterpret the patterns and processes in the evolution of female biased sexual size dimorphism in Nephilidae, a spider lineage characterized by the most extreme sexual size dimorphism among terrestrial animals. We use a molecular phylogeny to reconstruct the size evolution for each sex and reveal a case of “sexually dimorphic gigantism”: both sexes steadily outgrow their ancestral sizes, but the female and male slopes differ, and hence sexual size dimorphism steadily increases. A review of the experimental evidence reveals a predominant net selection for large size in both sexes, consistent with the phylogenetic pattern for females but not for males. Thus, while sexual size dimorphism in spiders most likely originates and is maintained by fecundity selection on females, it is unclear what selection pressures prevent males from becoming as large as females. This integrated approach highlights the dangers of inferring evolutionary significance from experimental studies that isolate the effects of single selection pressures.

THERE IS MORE TO POLLINATOR-MEDIATED SELECTION THAN POLLEN LIMITATION

Spatial variation in pollinator-mediated selection (Δβpoll ) is a major driver of floral diversification, but we lack a quantitative understanding of its link to pollen limitation (PL) and net selection on floral traits. For 2-5 years, we quantified Δβpoll on floral traits in two populations each of two orchid species differing in PL. In both species, spatiotemporal variation in Δβpoll explained much of the variation in net selection. Selection was consistently stronger and the proportion that was pollinator-mediated was higher in the severely pollen-limited deceptive species than in the rewarding species. Within species, variation in PL could not explain variation in Δβpoll for any trait, indicating that factors influencing the functional relationship between trait variation and pollination success govern a major part of the observed variation in Δβpoll . Separating the effects of variation in mean interaction intensity and in the functional significance of traits will be necessary to understand spatiotemporal variation in selection exerted by the biotic environment.

Composite Portfolio Performance: An Investigation into Indian Mutual Funds

Earlier in the 1960s, though they were aware of the concept of risk, the portfolio managers did not know as to how to measure and hence their performance was measured only in terms of rate of return. Though quite a few measures were developed in 1960s, it was Friend, Blume and Crockett who developed a mechanism to group portfolios into similar risk class. This in fact helped the portfolio managers to compare the performance of various funds more meaningfully in terms of risk-return relationship. Keeping the importance of two sides of investment coin: the Risk and the Return, we, in this paper attempted to analyze the performance of equity linked and diversified funds. We also tested if the portfolio managers' stock selection ability enhanced the performance. We have used measures like Treynor's, Sharpe's, Jensen's Alpha, the Information Ratio and Net Selectivity. Using these measures, we attempted to find out if the portfolio managers could generate above-average rate of return for a given risk class. The sample comprised equity linked savings and diversified funds in Indian context. The analysis was done on quarterly, half yearly, yearly and five yearly basis for each fund. This facilitated us to identify if the time factor played a role in the performance of a given fund. The results revealed that the performance of the fund managers primarily depended on the type of measure. While the fund(s) performed better according to a given method, than that of others in a given risk class, it was vice versa according to other measures. This reveals that the selection of performance measure matters a lot while assessing the performance of a fund. Analysis of Variance (ANOVA) revealed that the performance of a fund depended on time factor also. The results of our study carry very significant implications with respect to portfolio performance analysis.

Composite Portfolio Performance: An Investigation into Indian Mutual Funds

Earlier in the 1960s, though they were aware of the concept of risk, the portfolio managers did not know as to how to measure and hence their performance was measured only in terms of rate of return. Though quite a few measures were developed in 1960s, it was Friend, Blume and Crockett who developed a mechanism to group portfolios into similar risk class. This in fact helped the portfolio managers to compare the performance of various funds more meaningfully in terms of risk-return relationship. Keeping the importance of two sides of investment coin: the Risk and the Return, we, in this paper attempted to analyze the performance of equity linked and diversified funds. We also tested if the portfolio managers' stock selection ability enhanced the performance. We have used measures like Treynor's, Sharpe's, Jensen's Alpha, the Information Ratio and Net Selectivity. Using these measures, we attempted to find out if the portfolio managers could generate above-average rate of return for a given risk class. The sample comprised equity linked savings and diversified funds in Indian context. The analysis was done on quarterly, half yearly, yearly and five yearly basis for each fund. This facilitated us to identify if the time factor played a role in the performance of a given fund. The results revealed that the performance of the fund managers primarily depended on the type of measure. While the fund(s) performed better according to a given method, than that of others in a given risk class, it was vice versa according to other measures. This reveals that the selection of performance measure matters a lot while assessing the performance of a fund. Analysis of Variance (ANOVA) revealed that the performance of a fund depended on time factor also. The results of our study carry very significant implications with respect to portfolio performance analysis.

THE COSTS AND BENEFITS OF TOLERANCE TO COMPETITION INIPOMOEA PURPUREA, THE COMMON MORNING GLORY

Tolerance to competition has been hypothesized to reduce the negative impact of plant-plant competition on fitness. Although competitive interactions are a strong selective force, an analysis of net selection on tolerance to competition is absent in the literature. Using 55 full/half-sibling families from 18 maternal lines in the crop weed Ipomoea purpurea, we measured fitness and putative tolerance traits when grown with and without competition in an agricultural field. We tested for the presence of genetic variation for tolerance to competition and determined if there were costs and benefits of this trait. We also assessed correlations between tolerance and potential tolerance traits. We uncovered a fitness benefit of tolerance in the presence of competition and a cost in its absence. We failed to detect evidence of additive genetic variation underlying tolerance, but did uncover the presence of a significant maternal-line effect for tolerance, which suggests its evolutionary trajectory is not easily predicted. The cost of tolerance is likely due to later initiation of flowering of tolerant individuals in the absence of competition, whereas relative growth rate was found to positively covary with tolerance in the presence of competition, and can thus be considered a tolerance trait.

Stuck in the middle with you: close concordance between geographical clines in a cricket hybrid zone

Students of speciation have long recognized that hybridization between populations does not affect all parts of the genome in the same way (Key 1968, Bazykin 1969, Wu 2001, Nosil et al. 2009). For example, divergence is expected to be high at loci involved in Dobzhansky-Muller incompatibilities or at loci under divergent natural selection, while those that are effectively neutral should show only weak divergence. Studies that examine geographical clines at divergent loci in a hybrid zone can be particularly powerful, as here one can estimate how net selection is affecting each locus (Payseur 2010). An excellent example of this approach appears in this issue (Larson et al. 2014) for a hybrid zone between the crickets Gryllus firmus and Gryllus pennsylvanicus in the eastern United States.

Gill net selectivity of yellow perch

Yellow perch Perca flavescens (Mitchill) are typically collected using multi-mesh gill nets; however, gear selectivity information for this species is sparse. Selectivity using experimental gill nets was determined for yellow perch using data collected from southern Lake Michigan from 2007 to 2012 using stretch mesh sizes of 12.5, 16, 20, 25, 32, 38, 46, 51, 64, and 76 mm. Female selectivity was best described by a model with a skewed (log-normal) distribution while males were best described by a normal distribution. When sex data were combined, the skewed (log-normal) distribution provided the best model. Differences in selectivity between sexes were minimal, but likely due to the variant size structure of the local population sampled, with females the larger sex. These findings suggest that bias in individual gill net selectivity can be used to target specific yellow perch size groups or to replace other gear types with unknown selectivity.

Short communication: Genetic evaluation of stillbirth in US Brown Swiss and Jersey cattle

Stillbirth (SB) often results in reduced milk yield, compromised reproductive performance, and decreased dam longevity. Corrective mating can be used as a short-term solution to the problem, but long-term improvement of the population requires the routine calculation of genetic evaluations. Breeding values for SB have been available for Holstein (HO) bulls since 2006, but not for Brown Swiss (BS) or Jersey (JE) bulls. In this study, a multi-breed sire-maternal grandsire threshold model was used to perform genetic evaluations for SB of BS, JE, and HO bulls using more than 14 million purebred and crossbred calving records. Phenotypically, the percentage of SB (%SB) across all lactations were 3.7% in JE, 5.1% in BS, and 6.3% in HO. Direct heritabilities for BS, JE, and HO were 0.008, 0.007, and 0.008, and maternal heritabilities were 0.002, 0.016, and 0.021, respectively. Compared with HO, crossbred calvings from BS and JE bulls bred to HO cows lowered %SB by 1.5 and 1.2%, respectively. In general, %SB increased considerably as calving difficulty increased in all 3 breeds; however, in JE, %SB was constant for dystocia scores of 3 (needed assistance), 4 (considerable force), and 5 (extreme difficulty). Compared with purebred HO calvings, purebred BS and JE calvings had lower phenotypic %SB by up to 5.5 and 7.8%, respectively, and BS × HO and JE × HO crossbred calvings decreased %SB by up to 3.8 and 4.1%, respectively. As expected, SB rates in primiparous cows were higher than those in multiparous cows. Female calves had greater %SB than male calves in all parities for JE and in second-and-later parities for BS. Favorable (decreasing) phenotypic and genetic trends from 1999 to 2009 were observed in all 3 breeds. Heterosis of SB for BS and JE was −0.026 and −0.149, respectively, on the underlying scale, which corresponds to effects on service-sire SB (SSB) and daughter SB (DSB) predicted transmitting ability (PTA) of −0.3 and −0.5% in BS, and −1.5 and −2.7% in JE. Overall, in the current population, BS bulls had the most desirable average SSB PTA of 4.8%, compared with 5.6% for JE and 5.5% for HO. Brown Swiss and JE bulls both had average DSB PTA of 6.5%, lower than that of 7.7% in HO. Average reliabilities of SSB and DSB in 3 breeds ranged from 45 to 50%. The use of a BS-JE-HO multibreed genetic evaluation for SB in the United States is feasible, and the addition of SSB and DSB to the lifetime net merit selection index will help improve the profitability of BS and JE cattle in the United States.

Differentiation of cancer cells in two-dimensional and three-dimensional breast cancer models by Raman spectroscopy.

We demonstrate the first application of Raman spectroscopy in diagnosing nonmalignant, premalignant, malignant, and metastatic stages of breast cancer in a three-dimensional (3-D) cell culture model that closely mimics an in vivo environment. Comprehensive study comparing classification in two-dimensional (2-D) and 3-D cell models was performed using statistical methods composed of principal component analysis for exploratory analysis and outlier removal, partial least squares discriminant analysis, and elastic net regularized regression for classification. Our results show that Raman spectroscopy with an appropriate classification tool has excellent resolution to discriminate the four stages of breast cancer progression, with a near 100% accuracy for both 2-D and 3-D cell models. The diversity in chemical groups related to nucleic acids, proteins, and lipids, among other chemicals, were identified by appropriate peaks in the Raman spectra that correspond to the correct classification of the different stages of tumorigenesis model comprising of MCF10A, MCF10AneoT, MCF10CA1h, and MCF10CA1a cell lines. An explicit relationship between wavenumber and the stages of cancer progression was identified by the elastic net variable selection.

Study of Badminton Net Shot Technology Based on Dynamics

In the sport of badminton, net shot is one of the extremely important technologies. With the continuous development and innovation of badminton sport, net technology has been paid more and more attention to. In addition, in many badminton games, it has become an important technical means to change active to passive by taking effective use of net shot changes. Firstly, this paper elaborates the division of badminton net technology area and technology selection. And then, based on this, combined with the principle of aerodynamics, this paper makes an analysis on the dynamics of badminton net techniques. At the same time, this paper also makes an analysis on the dynamics of net ball chop technique. Thus, to some extent, it provides theoretical basis and technical guidance for the teaching and practice of badminton net shot.

Pulp feeders alter plant interactions with subsequent animal associates

Summary Community context can alter the likelihood of interactions among community members and thus exert critical ecological effects with potential evolutionary implications. For instance, plant–animal mutualisms can be exploited by third species that usurp the resources and/or service that the mutualists offer, while delivering limited or no benefits in return. We experimentally revealed for the first time how exploiters of plant–disperser mutualisms (i.e. pulp feeders) alter the frequency of plant interactions with subsequent mutualistic (seed dispersers) and antagonistic (seed predators) animal associates. In doing so, we chose to study the endozoochore Pyrus bourgaeana, which interacts with a diverse assemblage of frugivores including exploiters (pulp‐feeding rabbits), legitimate seed dispersers (mammalian carnivores) and seed and fruit predators (rodents and deer, respectively). We hypothesized that pulp feeders would render fruit barely rewarding, affecting subsequent tree–animal interactions. As predicted, pulp removal lessened tree dispersal success (i.e. lowered interaction frequency with seed dispersers) causing an indirect negative effect on its fitness. Furthermore, pulp feeders facilitated foraging by seed‐eating rodents, leading to a negative indirect effect on seed survival. Nonetheless, these negative effects of pulp removal on tree fitness were partly counterbalanced by a noticeable decrease in fruit predation by deer. Because both seed dispersers and seed predators preferred large fruits, they exerted selection pressures on fruit size in opposite directions; thus, the net selection regime on fruit size experienced by the tree appeared largely contingent on community composition. Synthesis. Our results illustrate how interactions among functionally distinct frugivores can act synergistically or antagonistically and thus alter their ecological outcomes in ways that differ from those predicted by pairwise interactions. Further research on the relationships between fruiting plants and their consumers will certainly further our understanding of how community context can modify ecological and evolutionary outcomes of complex multispecies interactions.

Pollinators and seed predators generate conflicting selection onDalechampiablossoms

Plant–pollinator relationships are often mediated by floral traits that advertise the presence or amount of rewards. However, herbivores may also use these traits to find their hosts. InDalechampia scandens, we tested whether floral advertisements that attract pollinators were also used by seed predators, and whether this generated conflicting selection pressures. We studied the influence of natural variation in the size of showy bracts, amount of reward, and two shape traits on pollinator visitation, pollen arrival on stigmas, seed production and seed predation. We then built a multivariate fitness function for these traits to estimate selection generated by pollinators and seed predators. Blossoms with larger bracts were visited by bees more frequently and received more pollen on their stigmas. Seed predators laid more eggs on blossoms with larger bracts and also on blossoms later producing more seeds. Consequently, selection for larger bract size exerted by pollinators was counteracted by the selection exerted by seed predators. As a result, net selection on bract size tended to be stabilizing. Additionally, we found selection on traits that increased the rate of self‐pollination (assuming uniform seed quality). These results illustrate the importance of both mutualists and antagonists in floral evolution, as well as the value of taking an integrative approach to assessing selection on floral traits.

HOMAGE TO BATEMAN: SEX ROLES PREDICT SEX DIFFERENCES IN SEXUAL SELECTION

Classic sex role theory predicts that sexual selection should be stronger in males in taxa showing conventional sex roles and stronger in females in role reversed mating systems. To test this very central prediction and to assess the utility of different measures of sexual selection, we estimated sexual selection in both sexes in four seed beetle species with divergent sex roles using a novel experimental design. We found that sexual selection was sizeable in females and the strength of sexual selection was similar in females and males in role-reversed species. Sexual selection was overall significantly stronger in males than in females and residual selection formed a substantial component of net selection in both sexes. Furthermore, sexual selection in females was stronger in role-reversed species compared to species with conventional sex roles. Variance-based measures of sexual selection (the Bateman gradient and selection opportunities) were better predictors of sexual dimorphism in reproductive behavior and morphology across species compared to trait-based measures (selection differentials). Our results highlight the importance of using assays that incorporate components of fitness manifested after mating. We suggest that the Bateman gradient is generally the most informative measure of the strength of sexual selection in comparisons across sexes and/or species.

Fluctuating viability selection on morphology of cliff swallows is driven by climate

The extent to which fluctuating selection can maintain evolutionary stasis in most populations remains an unresolved question in evolutionary biology. Climate has been hypothesized to drive reversals in the direction of selection among different time periods and may also be responsible for intense episodic selection caused by rare weather events. We measured viability selection associated with morphological traits in cliff swallows (Petrochelidon pyrrhonota) in western Nebraska, USA, over a 14-year period following a rare climatic event. We used mark-recapture to estimate the annual apparent survival of over 26000 individuals whose wing, tail, tarsus and bill had been measured. The fitness functions associated with tarsus length and bill dimensions fluctuated depending on annual climate conditions on the birds' breeding grounds. The oscillating yearly patterns may have slowed and occasionally reversed directional change in trait trajectories, although there was a trend over time for all traits except tarsus to increase in size. The net positive directional selection on some traits, despite periodic climate-associated fluctuations, suggests that cliff swallow morphology in the population is likely to keep changing and supports recent work contending that selection in general does not fluctuate enough to be an effective driver of stasis.

A Novel Heuristic Method for Application-Dependent Testing of a SRAM-Based FPGA Interconnect

This paper presents a new method for generating configurations for application-dependent testing of a SRAM-based FPGA interconnect. This method connects an activating input to multiple nets, thus generating activating test vectors for detecting stuck-at, open, and bridging faults. This arrangement permits a reduction in the number of redundant configurations, thus also achieving a reduction in test time for application-dependent testing at full fault coverage. As the underlying solution requires an exponential complexity, a heuristic algorithm that is polynomial and greedy in nature (based on sorting) is used for net selection in the configuration generation process. It is proved that this algorithm has an execution complexity of O(L <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) (where L is the number of LUTs in the design). The proposed method requires at most log <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (M + 2) configurations (where M denotes the number of activating inputs) as Walsh coding is employed. Moreover, it is scalable with respect to LUT inputs. Extensive logic-based simulation results are provided for ISCAS89 sequential benchmark designs implemented on Xilinx Virtex4 FPGAs; these results shows that the proposed method achieves a considerable reduction in the number of test configurations compared with methods found in the technical literature (on average, a reduction of 49.5 percent).

Allometry of secondary, primary, and nonsexual traits in the beautiful demoiselle (Calopteryx virgo meridionalis)

The static allometry between the size of a trait and the body size results from the net selection forces acting on the evolution of both the trait and the body size. An increased knowledge of the functional significance of traits is necessary to understand observed allometric patterns. We studied several traits of males of the beautiful demoiselle ( Calopteryx virgo meridionalis Sélys, 1873), for which there is a good functional knowledge of the genitalic traits and ornaments. We found positive allometry for the wing spot size (considered a secondary sexual trait) and for the distal width (but not length) of the anal appendages, which are used for grasping the female prior to copulation. Regarding the male secondary genitalia, the length but not the width of the big horns of the aedeagus showed an isometric pattern. The aedeagus shaft length showed a negative allometric pattern, while its distal width did not show a significant regression. The slopes of the regressions were higher when using wing length than when using body length as estimators of body size, with the exception of wing spot length. Results are discussed based on the functional significance of the study traits, as well as the pre- and post-copulatory selective pressures acting on them.

Consistency and variation in phenotypic selection exerted by a community of seed predators.

Phenotypic selection that is sustained over time underlies both anagenesis and cladogenesis, but the conditions that lead to such selection and what causes variation in selection are not well known. We measured the selection exerted by three species of predispersal seed predators of lodgepole pine (Pinus contorta latifolia) in the South Hills, Idaho, and found that net selection on different cone and seed traits exerted by red crossbills (Loxia curvirostra) and cone borer moths (Eucosma recissoriana) over 10 years of seed crops was similar to that measured in another mountain range. We also found that the strength of selection increased as seed predation increased, which provides a mechanism for the correlation between the escalation of seed defenses and the density of seed predators. Red crossbills consume the most seeds and selection they exert accounts for much of the selection experienced by lodgepole pine, providing additional support for a coevolutionary arms race between crossbills and lodgepole pine in the South Hills. The third seed predator, hairy woodpeckers (Picoides villosus), consumed less than one-sixth as many seeds as crossbills. Across the northern Rocky Mountains, woodpecker abundance and therefore selective impact appears limited by the elevated seed defenses of lodgepole pine.

Lactation persistency as a component trait of the selection index and increase in reliability by using single nucleotide polymorphism in net merit defined as the first five lactation milk yields and herd life.

We first sought to clarify the effects of discounted rate, survival rate, and lactation persistency as a component trait of the selection index on net merit, defined as the first five lactation milks and herd life (HL) weighted by 1 and 0.389 (currently used in Japan), respectively, in units of genetic standard deviation. Survival rate increased the relative economic importance of later lactation traits and the first five lactation milk yields during the first 120 months from the start of the breeding scheme. In contrast, reliabilities of the estimated breeding value (EBV) in later lactation traits are lower than those of earlier lactation traits. We then sought to clarify the effects of applying single nucleotide polymorphism (SNP) on net merit to improve the reliability of EBV of later lactation traits to maximize their increased economic importance due to increase in survival rate. Net merit, selection accuracy, and HL increased by adding lactation persistency to the selection index whose component traits were only milk yields. Lactation persistency of the second and (especially) third parities contributed to increasing HL while maintaining the first five lactation milk yields compared with the selection index whose only component traits were milk yields. A selection index comprising the first three lactation milk yields and persistency accounted for 99.4% of net merit derived from a selection index whose components were identical to those for net merit. We consider that the selection index comprising the first three lactation milk yields and persistency is a practical method for increasing lifetime milk yield in the absence of data regarding HL. Applying SNP to the second- and third-lactation traits and HL increased net merit and HL by maximizing the increased economic importance of later lactation traits, reducing the effect of first-lactation milk yield on HL (genetic correlation (rG) = −0.006), and by augmenting the effects of the second- and third-lactation milk yields on HL (rG = 0.118 and 0.257, respectively).