Selection for abdominal tergite pigmentation and correlated responses in the trident: a case study in Drosophila melanogaster

In Drosophila melanogaster, abdominal tergite pigmentation and the appearance of a trident‐shaped thoracic pattern exhibit similar biogeographical variation and sensitivity to temperature. These pigmentation traits may be under common selection pressure in natural populations or may be genetically correlated. To investigate the nature of this interaction, replicated populations of D. melanogaster were selected for increased or decreased melanization of the abdominal tergites for 40 generations. Selection for abdominal tergite pigmentation leads to correlated changes in trident formation. Although selection was performed only on female flies, male pigmentation also responded to selection. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 287–294.     

UV-B dose/dose-rate responses of seasonally abundant copepods of Puget Sound

Summary Refinements in modeling stratospheric processes and recent observational data have generated estimates of moderate future reductions in total global ozone. Nevertheless, considerable uncertainty and concern remain about whether or not the resulting increases in incident solar UV-B could increase the risk of harmful biological effects. The UV-B dose/dose-rate thresholds for five species of copepods collected at the surface in Puget Sound were determined and compared to previously studied zooplankton groups. Generally, species appearing later in the spring and summer were less UV-B sensitive. The UV-B daily-dose and dose-rate thresholds for the five species of copepods, while apparently less than present median incident levels, range from above to below estimated present and future subsurface (1 m) UV-B levels. A separate experiment with a relatively large copepod, Calanus pacificus, in which above and below threshold UV-B dose-rates were administered with various levels of photoreactivating light(UV-A and visible light), indicated the presence of photorepair and its full activation at relatively low intensity. To improve estimates of the extent to which present and predicted UV-B levels affect local populations of copepods and zooplankton, it is essential to more fully understant the natural conditions or processes which influence the composition and intensity of the UV irradiation these animals receive.Contribution No. 1760 from the School of Oceanography, University of Washington, Seattle, WA 98195, USA     

Differing selection in alternative competitive environments: shade-avoidance responses and germination timing

Under competitive conditions, stem elongation in plants is thought to enhance fitness by increasing light interception. However, the onset of competition should vary with the species of competitor due to interspecific differences in timing of emergence and plant growth form. The fitness benefits of elongation may therefore depend on the timing of this plastic response. Phenotypic selection analyses and path analysis were used to evaluate selection acting on stem elongation at early and late life-history stages and the combination of germination timing and elongation in an annual plant. Velvetleaf (Abutilon theophrasti) were raised in one of three environments experienced by natural populations (cornfields; soybean fields; and disturbed, weedy sites). Due to the rapid growth rate and high density of plants in disturbed areas, selection to increase seedling-stage elongation was expected in weedy sites. Due to the wide spacing of crop plants, competition for light is initially low in cultivated fields, but intensifies as the season progresses. Selection for increased elongation at later nodes was expected in soybean fields because velvetleaf can often overtop soy and thereby increase leaf exposure. In contrast, selection against late elongation was expected in cornfields because velvetleaf are incapable of overtopping corn. Individuals that elongate would experience the carbon cost of allocating to structural tissue, but fail to experience a carbon return through increased light interception. The phenotypic selection analyses were consistent with these predictions and therefore support the role of stem elongation as an adaptation to interspecific competition. Selection also acted on the combination of germination timing and elongation. In the weedy environment, early emergence in conjunction with enhanced stem elongation conveyed the highest fitness. Reduced elongation was favored among individuals that emerged late, potentially because these individuals were unable to overtop neighbors. The results of this study demonstrate that the timing of stem elongation strongly affects competitive success. Environments that differ in the timing of competition for light select for elongation at different life-history stages, and this selection depends on the timing of emergence.     

Antagonistic multilevel selection on size and architecture in variable density settings

In some ecological settings, an individual's fitness depends on both its own phenotype (individual-level selection) as well as the phenotype of the individuals with which it interacts (group-level selection). Using contextual analysis to measure multilevel selection in experimental stands of Arabidopsis thaliana, we detected significant linear selection that reversed across individual versus group levels for two composite phenotypic traits, "size" and "elongation." In both cases, selection at the individual level acted to increase values of these traits, presumably due to their positive effect on resource acquisition. Group selection favored decreased values of the same traits. Nonlinear selection was weak but significant in several cases, including stabilizing selection on developmental rate; individuals with very rapid development likely had lower than average fitness due to their reduced resource level at reproduction, while very delayed reproduction may have resulted in lower fitness if prolonged competition for resources reduced overall environmental quality and fitness of all individuals in a group. Under this scenario, stabilizing selection on individual traits is evidence of selection at the group level. Significant density-dependent selection suggests that a threshold density must be reached before group selection acts. Below this threshold, selection at the individual level affects phenotypic evolution more strongly than group selection. A second experiment measured multilevel selection in progeny stands of the original experimental plants. Multilevel selection again acted antagonistically on a composite trait that included size and elongation as well as on an architectural trait, branch production. The magnitude of individual versus group selection was relatively similar in the progeny generation, and the observed balance of individual versus group selection across densities is generally consistent with the hypotheses that multilevel selection can contribute to phenotypic evolution and to important demographic phenomena, including soft selection and the "law of constant yield."     

Comparing model predictions and experimental data for the response of stomatal conductance and guard cell turgor to manipulations of cuticular conductance, leaf-to-air vapour pressure difference and temperature: feedback mechanisms are able to account for all observations

Stomata respond to increasing leaf-to-air vapour pressure difference (LAVPD) ( D ) by closing. The mechanism by which this occurs is debated. A role for feedback and peristomatal transpiration has been proposed. In this paper, we apply a recent mechanistic model of stomatal behaviour, and compare model and experimental data for the influence of increasing D on stomatal conductance.
We manipulated cuticular conductance ( g _c) by three independent methods. First, we increased g _c by using a solvent mixture applied to both leaf surfaces prior to determining stomatal responses to D ; second, we increased g _c by increasing leaf temperature at constant D ; and third, we coated a small area of leaf with a light oil to decrease g _c. In all three experiments, experimental data and model outputs showed very close agreement.
We conclude, from the close agreement between model and experimental data and the fact that manipulations of g _c, and hence cuticular transpiration, influenced g _s in ways consistent with a feedback mechanism, that feedback is central in determining stomatal responses to D .     

Correlated responses to selection for wing length in allozyme systems of Drosophila melanogaster

Summary Significant changes of genotypic structure in 20 lines selected for wing length are detected by analysis of the allelic frequencies of several enzyme loci (XDH, LAP-D, EST-6, 1-APH, ADH, -GPDH). These changes are not haphazard but a consequence of the effects of selection on the genetic structure of the population, since replicate lines always behave in a parallel way. The changes are larger in the lines selected for short wings, in which the genetic variability decreases considerably. This decrease is the result of selection for homozygosity, detected at the allozyme loci, but most probably reflects homozygosity of more or less extended chromosomal segments. Selection for wing length, especially for short wings, favoured recombinants of the initial founder chromosomes. Only in the 1-APH and the EST-6 loci, separated by 11.7 centimorgans on the genetic map, do the alleles linked in the founder lines change in parallel in the control and long wing lines. The correlated response in the allozyme allele frequencies cannot be accounted for by a direct influence of the allozymes on the variability in wing length. The changes in the EST-6, 1-APH and perhaps in the LAP-D, can be explained by a direct effect of natural selection on the allozyme loci, probably in interaction with the effect of selection for wing length on linked loci. This last effect seems to be the main factor contributing to the change detected in the XDH locus.     

Genetic parameters and responses of performance and body composition traits in pigs selected for high and low growth rate on a fixed ration over a set time

Two lines of Large White pigs of common genetic origin were divergently selected over four years for high and low growth rate during a 6 week post-weaning test period in which all pigs were fed the same total amount of food (80% of estimated ad libitum intake). Genetic parameters and direct and correlated responses in performance and carcass traits were estimated on 2884 pigs with pedigrees comprising a total of 5324 animals, with restricted maximum likelihood and best linear unbiased prediction methods applied to a multi-trait animal model. Estimates of heritability (± SE) were 0.19 ± 0.04 for lifetime daily gain (LDG), 0.16 ± 0.03 for test daily gain (TDG), 0.25 ± 0.04 for ultrasound P2 backfat (UBF) and 0.16 ± 0.03 for food conversion ratio during test (TFC), and 0.15 ± 0.04 for daily carcass weight gain (CDG), 0.43 ± 0.06 for carcass backfat (CFT) and 0.40 ± 0.06 for carcass lean percentage (LEAN). Common litter effects for TDG, UBF and TFC were less than 5% and for LDG, 17% of total phenotypic variance. Genetic correlations between performance and carcass traits were moderately to highly favourable. After four years of divergent selection for growth rate, the selection responses in estimated breeding value (EBV) for TDG were 40.14 and -41.11 g (SED 2.95) for the high and low growth lines, respectively. The regressions of EBV on year of birth, indicate that the annual genetic trend for TDG, was 8.73 g/yr in the high and -8.48 g/yr in the low lines (P < 0.001). Correlated genetic responses in the high and low lines respectively were 5.28 g and -12.40 g (SED 2.09) in LDG, -0.35 mm and 0.56 mm (SED 0.009) in UBF, -0.145 units and 0.185 units (SED 0.012) in TFC, 3.17 g and -10.97 g (SED 1.53) in CDG, -1.13 mm and 1.01 mm (SED 0.155) in CFT and 1.24% and -1.27% (SED 0.150) in LEAN. It was concluded that selection for increased post-weaning daily gain on a ration of fixed amount reduces the age at slaughter and the level of backfat and increases the efficiency of food utilisation, weight and leanness of pig carcasses.     

Selection index for identifying high-yielding groundnut genotypes in irrigated and rainfed environments

Selection of high yielding genotypes to be carried over to subsequent selection cycles in a breeding programme can sometimes be accomplished using a suitable index of secondary traits that may be relatively less sensitive to genotype‐by‐environment interactions than yield. We used the concept of correlated response to selection to measure the relative efficiency of nine selection indices. The results showed that the selection index, based on median and semi inter‐quartile range, which was actually used in identifying high yielding genotypes, had an efficiency that is comparable to the best index, the latter being a modification of the Elston index.     

Fasciola hepatica: Comparative studies on fascioliasis in rats and mice

Chapman C. B. and Mitchell G. F. 1982. Fasciola hepatica: comparative studies on fascioliasis in rats and mice. International Journal for Parasitology12: 81–91. Certain characteristics of infection differ between rats and mice exposed to metacercariae of the trematode parasite, Fasciola hepatica. Rats develop a degree of age-related resistance (and infected older females contain fewer parasites than older males), resistance to reinfection in infected rats is demonstrated readily though is partial, and a comparable degree of resistance can be obtained in recipients of infected rat serum provided the serum is given at about the time of challenge. None of these features of F. hepatica infection is seen in mice. Rats also differ from mice in that they can be vaccinated against infection (although again, resistance is incomplete) using larval antigen mixtures in adjuvants. Mice do respond to infection by production of antilarval antibodies and a slight IgG₁ hypergammaglobulinaemia and larvae will sensitize mice for delayed hypersensitivity. The results of this study indicate that sera from infected rats versus infected mice will be useful in pinpointing antigens of F. hepatica larvae which are involved in expression of partial host protection.     

Long-term selection for 8-week body weight in chickens — direct and correlated responses

Summary A bidirectional selection experiment for 8-week body weight in chickens was conducted. In addition to 27 generations of selection, random samples were chosen from each selected line in generations 6, 13, 19 and 26 to initiate lines in which selection was relaxed. Genetic change was evident in the selected high-weight line through the first 75% of the study after which response in the direction opposing selection occurred. Selection for low body weight resulted in considerable reduction in body size, particularly in the last quarter of the study. Correlated responses evaluated were body weight at several ages, conformation, age at onset of lay, various reproductive and egg quality traits and ratio (female: male) of some traits. Data from lines where selection was relaxed indicated that natural selection opposed artificial selection with the effects greater in later generations.     

Intraspecific responses to climate in Pinus sylvestris

Abstract Five population-specific response functions were developed from quadratic models for 110 populations of Pinus sylvestris growing at 47 planting sites in Eurasia and North America. The functions predict 13 year height from climate: degree-days > 5 °C; mean annual temperature; degree-days < 0 °C; summer-winter temperature differential; and a moisture index, the ratio of degree-days > 5 °C to mean annual precipitation. Validation of the response functions with two sets of independent data produced for all functions statistically significant simple correlations with coefficients as high as 0.81 between actual and predicted heights. The response functions described the widely different growth potentials typical of natural populations and demonstrated that these growth potentials have different climatic optima. Populations nonetheless tend to inhabit climates colder than their optima, with the disparity between the optimal and inhabited climates becoming greater as the climate becomes more severe. When driven by a global warming scenario of the Hadley Center, the functions described short-term physiologic and long-term evolutionary effects that were geographically complex. The short-term effects should be negative in the warmest climates but strongly positive in the coldest. Long-term effects eventually should ameliorate the negative short-term impacts, enhance the positive, and in time, substantially increase productivity throughout most of the contemporary pine forests of Eurasia. Realizing the long-term gains will require redistribution of genotypes across the landscape, a process that should take up to 13 generations and therefore many years.     

The evolution of threshold traits: effects of selection on fecundity and correlated response in wing dimorphism in the sand cricket

The quantitative genetic basis of traits can be determined using a pedigree analysis or a selection experiment. Each approach is valuable and the combined data can contribute more than either method alone. Analysis using both sib analysis and selection is particularly essential when there are likely to be nonlinearities in the functional relationships among traits. A class of traits for which this occurs is that of threshold traits, which are characterized by a dichotomous phenotype that is determined by a threshold of sensitivity and a continuously distributed underlying trait called the liability. In this case, traits that are correlated with the liability may show a nonlinear relationship due to the dichotomy of expression at the phenotypic level. For example, in wing dimorphic insects fecundity of the macropterous (long-winged) females appears in part to be determined by the allocation of resources to the flight muscles, which are almost invariably small or absent in the micropterous (short-winged, flightless) females. Pedigree analysis of the cricket Gryllus firmus has shown that wing morph, fecundity and the trade-off between the two have additive genetic (co)variance. It has also been shown that selection on proportion macroptery produced an asymmetric correlated response of fecundity. The present paper details the results of direct selection on fecundity and the correlated response in proportion macroptery. Selection for increased fecundity resulted in increased fecundity within both wing morphs and a correlated decrease in proportion macroptery. Similarly, selection for decreased fecundity resulted in a decrease within morphs and a correlated increase in the proportion of macropterous females. This provides additional evidence that the trade-off between fecundity and wing morphology has a genetic basis and will thus modulate the evolution of the two traits.     

Age-dependent female responses to a male ejaculate signal alter demographic opportunities for selection

A central tenet of evolutionary explanations for ageing is that the strength of selection wanes with age. However, data on age-specific expression and benefits of sexually selected traits are lacking—particularly for traits subject to sexual conflict. We addressed this by using as a model the responses of Drosophila melanogaster females of different ages to receipt of sex peptide (SP), a seminal fluid protein transferred with sperm during mating. SP can mediate sexual conflict, benefitting males while causing fitness costs in females. Virgin and mated females of all ages showed significantly reduced receptivity in response to SP. However, only young virgin females also showed increased egg laying; hence, there was a narrow demographic window of maximal responses to SP. Males gained significant ‘per mating’ fitness benefits only when mating with young females. The pattern completely reversed in matings with older females, where SP transfer was costly. The overall benefits of SP transfer (hence opportunity for selection) therefore reversed with female age. The data reveal a new example of demographic variation in the strength of selection, with convergence and conflicts of interest between males and ageing females occurring over different facets of responses to a sexually antagonistic trait.     

Direct and indirect responses to selection on pollen size in Brassica rapa L.

Pollen size varies little within angiosperm species, but differs extensively between species, suggesting the action of strong selection. Nevertheless, the potential for genetic responses of pollen size to selection, as determined by additive genetic variance and genetic correlations with other floral traits, has received little attention. To assess this potential, we subjected Brassica rapa to artificial selection for large and small pollen during three generations. This selection caused significant divergence in pollen diameter, with additive genetic effects accounting for over 30% of the observed phenotypic variation in pollen size. Such heritable genetic variation suggests that natural selection could effect evolutionary change in this trait. Selection on pollen size also elicited correlated responses in pollen number (–), flower size (+), style length (+), and ovule number (+), suggesting that pollen size cannot evolve independently. The correlated responses of pollen number, flower size and ovule number probably reflect the genetically determined and physically constrained pattern of resource allocation in B. rapa. In contrast, the positive correlation between pollen size and style length may represent a widespread gametic‐phase disequilibrium in angiosperms that arises from nonrandom fertilization success of large pollen in pistils with long styles.     

Is the cardiac monitoring function related to the self in both the default network and right anterior insula?

The self has been proposed to be rooted in the neural monitoring of internal bodily signals and might thus involve interoceptive areas, notably the right anterior insula (rAI). However, studies on the self consistently showed the involvement of midline default network (DN) nodes, without referring to visceral monitoring. Here, we investigate this apparent discrepancy. We previously showed that neural responses to heartbeats in the DN encode two different self-dimensions, the agentive ‘I’ and the introspective ‘Me’, in a whole-brain analysis of magnetoencephalography (MEG) data. Here, we confirm and anatomically refine this result with intracranial recordings (intracranial electroencephalography, iEEG). In two patients, we show a parametric modulation of neural responses to heartbeats by the self-relatedness of thoughts, at the single trial level. A region-of-interest analysis of the insula reveals that MEG responses to heartbeats in the rAI encode the ‘I’ self-dimension. The effect in rAI was weaker than in the DN and was replicated in iEEG data in one patient out of two. We propose that a common mechanism, the neural monitoring of cardiac signals, underlies the self in both the DN and rAI. This might reconcile studies on the self highlighting the DN, with studies on interoception focusing on the insula.This article is part of the themed issue ‘Interoception beyond homeostasis: affect, cognition and mental health’.     

Selection on skewed characters and the paradox of stasis

Observed phenotypic responses to selection in the wild often differ from predictions based on measurements of selection and genetic variance. An overlooked hypothesis to explain this paradox of stasis is that a skewed phenotypic distribution affects natural selection and evolution. We show through mathematical modeling that, when a trait selected for an optimum phenotype has a skewed distribution, directional selection is detected even at evolutionary equilibrium, where it causes no change in the mean phenotype. When environmental effects are skewed, Lande and Arnold's (1983) directional gradient is in the direction opposite to the skew. In contrast, skewed breeding values can displace the mean phenotype from the optimum, causing directional selection in the direction of the skew. These effects can be partitioned out using alternative selection estimates based on average derivatives of individual relative fitness, or additive genetic covariances between relative fitness and trait (Robertson–Price identity). We assess the validity of these predictions using simulations of selection estimation under moderate sample sizes. Ecologically relevant traits may commonly have skewed distributions, as we here exemplify with avian laying date — repeatedly described as more evolutionarily stable than expected — so this skewness should be accounted for when investigating evolutionary dynamics in the wild.     

The danger of applying the breeder's equation in observational studies of natural populations

The breeder's equation, which predicts evolutionary change when a phenotypic covariance exists between a heritable trait and fitness, has provided a key conceptual framework for studies of adaptive microevolution in nature. However, its application requires strong assumptions to be made about the causation of fitness variation. In its univariate form, the breeder's equation assumes that the trait of interest is not correlated with other traits having causal effects on fitness. In its multivariate form, the validity of predicted change rests on the assumption that all such correlated traits have been measured and incorporated into the analysis. Here, we (i) highlight why these assumptions are likely to be seriously violated in studies of natural, rather than artificial, selection and (ii) advocate wider use of the Robertson–Price identity as a more robust, and less assumption‐laden, alternative to the breeder's equation for applications in evolutionary ecology.     

Selection response and efficiency of doubled-haploid recurrent selection in a cross-fertilized species

Summary Computer simulation was used to compare the simulated response to doubled-haploid (DH) mass selection with the response predicted by mathematical formulae. The efficiency of DH versus diploid mass selection in a cross-fertilized species was also studied by means of theoretical consideration and computer simulation. Simulated gain was in agreement with the predicted gain in the DH population under both additive and complete dominance models. The simulated variance of response to DH mass selection was close to the predicted variance at both the 5% and 25% selection regimes under additive and complete dominance models. The efficiency of DH over diploid mass selection was shown to be dependent upon the allelic frequency, the degree of dominance, and the amount of environmental variance. In theory the efficiency can range from zero to infinity, but in reality it should be greater than one. The efficiency ranges from 2 to 2 in the absence of dominance; it can be greater than two only in the presence of dominance and a small environmental variance. The variance of response to DH mass selection can be smaller than or up to twice as large as the variance of response to diploid mass selection. Computer simulation results agreed with the predicted efficiency of DH mass selection and with the predicted variance-of-response ratio of DH mass selection to diploid mass selection.Joint Contribution from the Charlottetown Research Station, contribution no. 604 and Department of Crop Science, University of Guelph     

Tameness correlates with domestication related traits in a Red Junglefowl intercross

Early animal domestication may have been driven by selection on tameness. Selection on only tameness can bring about correlated selection responses in other traits, not intentionally selected upon, which may be one cause of the domesticated phenotype. We predicted that genetically reduced fear towards humans in Red Junglefowl, ancestors of domesticated chickens, would be correlated to other traits included in the domesticated phenotype. Fear level was determined by a standardised behaviour test, where the reaction towards an approaching human was recorded. We first selected birds for eight generations for either high or low fear levels in this test, to create two divergent selection lines. An F3 intercross, with birds from the eighth generation as parentals, was generated to study correlations between fear-of-human scores and other unselected phenotypes, possibly caused by pleiotropy or linkage. Low fear-of-human scores were associated with higher body weight and growth rates, and with increased activity in an open field test, indicating less general fearfulness. In females, low fear-of-human scores were also associated with more efficient fear habituation and in males with an increased tendency to emit food calls in a mirror test, indicating increased social dominance. Low fear-of-human scores were also associated with smaller brain relative to body weight, and with larger cerebrum relative to total brain weight in females. All these effects are in line with the changes observed in domesticated chickens compared to their ancestors, and we conclude that tameness may have been a driving factor underlying some aspects of the domesticated phenotype.     

粗山羊草CCT家族基因序列分析及激素响应

开花是植物生长发育的重要过程。CCT家族基因在植物中广泛存在, 参与植物花期的调控过程。该文从粗山羊草(Aegilops tauschii)全基因组中分离出26个CCT基因, 它们分布于7对染色体上, 按照排列顺序将其命名为AetCCT1-26。AetCCT蛋白分子量介于14.9 kDa (AetCCT3)-83.2 kDa (AetCCT12)之间, 其中有25个蛋白包含完整的CCT保守结构域。系统发育分析显示, 12对粗山羊草/乌拉尔图小麦(Triticum urartu) CCT蛋白和9对粗山羊草/水稻(Oryza sativa) CCT蛋白为直系同源蛋白。通过公共数据的数字表达分析表明, AetCCT具有组织特异性和组成型2种表达形式, 其中AetCCT3、AetCCT4、AetCCT7及AetCCT9等9个基因在大部分组织中都有表达, 而AetCCT15、AetCCT21和AetCCT25等基因分别在种子、叶和根等少数组织中特异表达。AetCCT家族可以响应不同外源激素, 施用激素24小时和72小时后各成员对激素响应整体表现一致, 但不同成员对于不同激素的响应存在差异, 表明该家族成员在功能和行使方式等方面具有一定的多样性, 可能参与不同生长发育过程。光照条件影响AetCCT的表达, 说明光照和春化作用是影响与调控该家族基因表达的重要因素。研究结果有助于探索小麦(T. aestivum)进化、驯化和演变的规律, 以及认识重要农艺性状的形成与互作网络。