Effects Of Directional Selection Research Articles

Phylogenetic processes in dog domestication and breeding

Aim. The significance of the problem of origin and selection of animals for practice is that by studying the main stages of formation of modern domestic animals in the past, scientists and breeders develop even more effective methods of improving existing breeds by targeted changes in their hereditary properties in purebred breeding, using hybridization and modern biotechnological technologies. Methods. Using archaeological, morphological, biochemical and genetic research methods, scientists managed to establish the karyotype and genome of the wild European wolf and domestic dog. Results. Domestication is the process of turning wild animals into domesticated ones. Over many generations, people have gradually accumulated experience in keeping animals, learned the laws of animal heredity, which helped to accelerate the domestication process and the formation of the original breed populations. The dog is the first domesticated animal, and the history of its domestication dates back to the Mesolithic period (12-15 thousand years BC). The wild European wolf is considered to be the wild ancestor of the dog, since wolves and dogs have 78 chromosomes in their karyotype, and when they mate, they produce fertile offspring. In the process of dog domestication, both morphological and physiological changes occurred compared to the wild European wolf. Since the domestication of dogs involved adaptation to new conditions in captivity, important genetic mechanisms such as mutations, recombination, a hidden reserve of heredity, and the direct effect of selection and selection were important. Conclusions. The representatives of two families of carnivores were domesticated – Canidae and Felidae. Dogs, as already mentioned, were the first domesticated animals tamed and domesticated by humans. The taming and domestication of the wild ancestor of dogs, the wolf, took place in the Mesolithic period, as is known from bone remains discovered by scientists. In different centres of domestication, different forms of wolves have been found that could be domesticated and gave rise to many varieties of dogs since ancient times. Further selection by humans has led to an even greater diversity of domestic dog breeds that serve a variety of purposes (guarding, hunting, sledding, service, and decorative breeds).

Ancistroceruswasps (Hymenoptera, Vespidae) from the Centre of Europe: Phylogeny, cryptic species, neutral and non‐neutral markers

AbstractThe aim of the study was to clarify the phylogenetic relationships among Northern EuropeanAncistrocerusand comparison of the applicability of evolutionarily neutral and non‐neutral markers for reconstruction of phylogeny. We used a 19,400 bp long dataset that included parts of mitochondrial DNA, nuclear rDNA operon, and 10 nuclear protein‐coding genes. Application of molecular barcoding and species delimitation algorithms unveiled a presence of cryptic species,A. balticussp. n., in the trap‐nesting wasp communities of the centre of Europe. We assessed the morphological, biological, and ecological differences of it from the siblingA. trifasciatusand updated the regional identification key. Phylogeny reconstruction using the neutral and the presumably non‐neutral markers resulted in different tree topologies. Evolutionary congruence of the rDNA operon with the other markers was relatively low. Evolutionary rate of the mitochondrial genes was 7–8 times as high as that of the exons of the nuclear genes, therefore, the mitochondrial markers overshadowed the nuclear ones in the phylogeny reconstructions. We assumed that at the speciation level, we might consider two different patterns of phylogeny: one based on evolutionary time and neutral changes, and the other based on adaptive evolutionary pathways under directional selection pressures. We assessed the effect of directional selection on the nuclear protein‐coding genes, applying the Spearman's rank correlation between pairwise phylogenetic distances among species, estimated using exons, and these distances, estimated using introns. One of these markers demonstrated a lack of positive correlation, implying a variable directional selection pressure on the coded protein. The publication has been registered on ZooBank: urn:lsid:zoobank.org:pub:13BD28D0‐736D‐4B2A‐B5CF‐4824BD4CDCFB.

Exploration of Genetic Variability and Trait Association in High Protein Landraces of Rice (Oryza sativa L.)

The present investigation was carried out at the Indian Institute of Rice Research farm, ICRISAT, Hyderabad with 31 genotypes of rice in a randomized block design with three replications, and observations were recorded on grain yield, yield components and quality characters. Analysis of variance revealed significant differences among the genotypes for all characters studied. The studies on variability, heritability and genetic advance as per cent mean thus revealed high GCV and PCV for grains panicle-1 and iron content. High heritability coupled with high genetic advance as per cent mean was recorded for plant height, ear bearing tillers plant-1, grains panicle-1, grain yield plant-1 and iron content indicating, the effectiveness of simple selection for improvement of these traits. The results on character associations and path analysis revealed positive and significant association coupled with high positive direct effect for ear bearing tillers plant-1, panicle length, grains panicle-1, and amylose content indicating the effectiveness of direct selection for these traits in the improvement of grain yield plant-1. However, for test weight, days to 50 percent flowering, plant height, head rice recovery (%), and zinc content, indirect effects seemed to be the cause of correlation, while for days to maturity, protein and iron content, the use of restricted simultaneous selection model is suggested with restrictions imposed for nullifying the undesirable indirect effects in order to make use of the high positive direct effect observed for these traits on grain yield plant-1.

An analysis of direct and indirect effects in Drosophila melanogaster undergoing a few cycles of experimental evolution for stress-related traits.

The physiological mechanisms underpinning adaptations to starvation and cold stresses have been extensively studied in Drosophila, yet the understanding of correlated changes in stress-related and life-history traits, as well as the energetics of stress tolerance, still remains elusive. To answer the questions empirically in this context, we allowed D. melanogaster to evolve for either increased starvation or cold tolerance (24-generations / regime) in an experimental evolution system, and examined whether selection of either trait affects un-selected stress trait, as well as the impacts potential changes in life-history and mating success-related traits. Our results revealed remarkable changes in starvation/cold tolerance (up to 1.5-fold) as a direct effect of selection, while cold tolerance had been dramatically reduced (1.26-fold) in the starvation tolerant (ST) lines compared to control counterparts, although no such changes were evident in cold-tolerant (CT) lines. ST lines exhibited a higher level of body lipids and a reduced level of trehalose content, while CT lines accumulated a greater levels of body lipid and trehalose contents. Noticeably, we found that selection for starvation or cold tolerance positively correlates with larval development time, longevity, and copulation duration, indicating that these traits are among the most common targets of selection trajectories shaping stress tolerance. Altogether, this study highlights the complexity of mechanisms evolved in ST lines that contribute to enhanced starvation tolerance, but also negatively impact cold tolerance. Nevertheless, mechanisms foraging enhanced cold tolerance in CT lines appear not to target starvation tolerance. Moreover, the parallel changes in life history/mating success traits across stress regimes could indicate some generic pathways evolved in stressful environments, targeting life-history and mating success characteristics to optimize fitness.

Genetic Variability, Correlation and Path Coefficient Analysis in Hybrid Maize (Zea mays L.)

The goal of the current investigation was to determine correlation coefficient, path analysis and genetic variability among twenty four maize hybrids for ten characters in a Randomized Block Design (RBD) with three replications at the research field of Plant Breeding Division, Regional Agricultural Research Station, Barisal, Bangladesh Agricultural Research Institute (BARI), Bangladesh during rabi season of 2014-15.
 The measured traits were Days to 50% tasseling (DT), days to 50% silking (DS), anthesis silking interval (ASI), plant height (PH), ear height (EH), days to maturity (DM), cob length (CL), cob diameter (CD), thousand seed weight (TSW) and yield(yield t/ha). Here yield was considered as dependent variable and the rest of the parameters were independent variable. The data were submitted to analysis of variance and mean values were compared by DMRT test at both 5% and 1% of probability. Positive and significant genotypic, phenotypic correlation coefficient were recorded for yield with cob diameter (rg=0.75**, rp=0.61**), cob length (rg=0.66**and rp=0.42**), plant height (rg=0.62**and rp=0.55**), ear height (rg=0.66**and rp=0.55**) and thousand seed weight (rg=0.36**and rp=0.44**). High genotypic coefficient of variation (GCV) was obtained from anthesis silking interval (17.26), yield (15.17), ear height (13.80) and thousand seed weight (9.43). The highest phenotypic coefficient of variation (PCV) were observed in anthesis silking interval (26.49) followed by yield (20.51), ear height (16.19) and the lowest in days to maturity (0.70). The difference between GCV and PCV of yield indicated that the characters had some environmental influence. The highest heritability was observed for plant height (73.78) followed by ear height (72.67), thousand seed weight (59.52) and days to maturity (55.97) but the lowest heritability identified for days to silking (18.98). The characters with higher values of GCV and heritability of the aforementioned traits were indicative for selection. The plant height had the highest positive direct effect (1.34) on yield followed by days to silking (0.75), cob diameter CD (0.46) and thousand seed weight (0.41), days to maturity (0.21) and cob length (0.20) indicating the effectiveness of direct selection. Direct negative effect on yield was shown by ear height (-1.03), days to tasseling (-0.52) and anthesis silking interval (-0.50) was indicating the effectiveness of indirect selection.

Common microgeographical selection patterns revealed in four European conifers.

Microgeographical adaptation occurs when the effects of directional selection persist despite gene flow. Traits and genetic loci under selection can then show adaptive divergence, against the backdrop of little differentiation at other traits or loci. How common such events are and how strong the selection is that underlies them remain open questions. Here, we discovered and analysed microgeographical patterns of genomic divergence in four European and Mediterranean conifers with widely differing life-history traits and ecological requirements (Abies alba MIll., Cedrus atlantica [Endl.] Manetti, Pinus halepensis Mill. and Pinus pinaster Aiton) by screening pairs from geographically close forest stands sampled along steep ecological gradients. We inferred patterns of genomic divergence by applying a combination of divergence outlier detection methods, demographic modelling, Approximate Bayesian Computation inferences and genomic annotation to genomic data. Surprisingly for such small geographical scales, we showed that selection is strong in all species but generally affects different loci in each. A clear signature of selection was systematically detected on a fraction of the genome, of the order of 0.1%-1% of the loci depending on the species. The novel modelling method we designed for estimating selection coefficients showed that the microgeographical selection coefficient scaled by population size (Ns) was 2-30. Our results convincingly suggest that selection maintains within-population diversity at microgeographical scales in spatially heterogeneous environments. Such genetic diversity is likely to be a major reservoir of adaptive potential, helping populations to adapt under fluctuating environmental conditions.

Genome-Wide Scans and Transcriptomic Analyses Characterize Selective Changes as a Result of Chlorantraniliprole Resistance in Plutella xylostella.

Pesticide resistance in insects is an example of adaptive evolution occurring in pest species and is driven by the artificial introduction of pesticides. The diamondback moth (DBM), Plutella xylostella (Lepidoptera: Plutellidae), has evolved resistance to various insecticides. Understanding the genetic changes underpinning the resistance to pesticides is necessary for the implementation of pest control measures. We sequenced the genome of six resistant and six susceptible DBM individuals separately and inferred the genomic regions of greatest divergence between strains using FST and θπ. Among several genomic regions potentially related to insecticide resistance, CYP6B6-like was observed with significant divergence between the resistant and susceptible strains, with a missense mutation located near the substrate recognition site (SRS) and four SNPs in the promoter. To characterize the relative effects of directional selection via insecticide tolerance (‘strain’) as compared to acute exposure to insecticide (‘treatment’), four pairwise comparisons were carried out between libraries to determine the differentially expressed genes. Most resistance-related differentially expressed genes were identified from the comparison of the strains and enriched in pathways for exogenous detoxification including cytochrome P450 and the ABC transporter. Further confirmation came from the weighted gene co-expression network analysis, which indicated that genes in the significant module associated with chlorantraniliprole resistance were enriched in pathways for exogenous detoxification, and that CYP6B6-like represented a hub gene in the “darkred” module. Furthermore, RNAi knock-down of CYP6B6-like increases P. xylostella sensitivity to chlorantraniliprole. Our study thus provides a genetic foundation underlying selection for pesticide resistance and plausible mechanisms to explain fast evolved adaptation through genomic divergence and altered gene expression in insects.

Studies on Genetic Variability, Divergence and Characters Associated with Yield Components in Rice

The current study was carried out to evaluate genetic factors such as Genotypic Coefficient of Variation (GCV), phenotypic coefficient of variation (PCV), heritability and genetic advance (GA) along with correlations, path coefficients and Genetic divergence from data collected on 22 rice genotypes. The results demonstrated significantly significant mean squares owing to genotypes for all variables investigated, demonstrating that there is adequate variation among genotypes and thus ample possibility for successful selection. Only seed yield per plant showed a high Phenotypic Coefficient of Variation (PCV). Moderate phenotypic coefficient of variation and Genotypic Coefficient of Variation (GCV) observed for number of tillers/plant, number of spikelets/panicle, flag leaf length, flag leaf width, number of filled grains/panicle,1000-grain weight and biological yield. High heritability and genetic advance as per cent of mean was observed for number of tillers/plant, number of spikelets/panicle, flag leaf length, flag leaf width, number of filled grains/panicle, 1000-grain weight, biological yield and seed yield per plant, indicating the effectiveness of direct selection for improvement of these traits. Panicle length,1000-grain weight and biological yield had recorded positive and significant association with seed yield per plant. The results on path analysis also revealed high and positive direct effect for biological yield followed by harvest index, days to 50% flowering, plant height, panicle length and number of spikelets/panicle and hence, these traits were identified as the most effective selection criteria for improvement of seed yield per plant in rice genotypes. The results on divergence analysis revealed that the genotypes were grouped into five clusters. Cluster I constituted maximum number of (10) genotypes. Maximum differences among the genotypes within the same cluster (intra-cluster) were shown by cluster IV (18.33) followed by cluster I, II, III. Cluster V showed zero intra -cluster distance. The genotypes contained in Clusters IV and V (20.20) displayed the greatest intercluster distance, indicating that they might be employed as parents in a future hybridization experiment.

Mice selected for a high basal metabolic rate evolved larger guts but not more efficient mitochondria.

Intra-specific variation in both the basal metabolic rate (BMR) and mitochondrial efficiency (the amount of ATP produced per unit of oxygen consumed) has profound evolutionary and ecological consequences. However, the functional mechanisms responsible for this variation are not fully understood. Mitochondrial efficiency is negatively correlated with BMR at the interspecific level but it is positively correlated with performance capacity at the intra-specific level. This discrepancy is surprising, as theories explaining the evolution of endothermy assume a positive correlation between BMR and performance capacity. Here, we quantified mitochondrial oxidative phosphorylation activity and efficiency in two lines of laboratory mice divergently selected for either high (H-BMR) or low (L-BMR) levels of BMR. H-BMR mice had larger livers and kidneys (organs that are important predictors of BMR). H-BMR mice also showed higher oxidative phosphorylation activity in liver mitochondria but this difference can be hypothesized to be a direct effect of selection only if the heritability of this trait is low. However, mitochondrial efficiency in all studied organs did not differ between the two lines. We conclude that the rapid evolution of BMR can reflect changes in organ size rather than mitochondrial properties, and does not need to be accompanied obligatorily by changes in mitochondrial efficiency.

Characterization of the Genetic Variability in Rice (Oryza sativa L.) and its Assessment Using Principal Component Analysis (PCA)

Present investigation was conducted to estimate genetic parameters such as Genotypic Coefficient of Variation (GCV), Phenotypic Coefficient of Variation (PCV), heritability and Genetic Advance (GA) along with correlations, path coefficients, Genetic divergence and Principal Component Analysis (PCA) from data collected on 21 rice genotypes. The results revealed highly significant mean squares due to genotypes for all traits studied, indicating the existence of sufficient variation among the genotypes and therefore an ample scope for effective selection. High PCV, GCV, heritability and genetic advance as per cent of mean was observed for 1000-grain weight, seed yield per plant, and harvest index, indicating the effectiveness of direct selection for improvement of these traits. Thousand grain weight and harvest index had recorded positive and significant association with seed yield per plant. The results on path analysis also revealed high and positive direct effect for harvest index followed by flag leaf width, days to 50% flowering, days to maturity, plant height, panicle length, number of filled grains/panicle, number of spikelets/panicle and hence, these traits were identified as the most effective selection criteria for improvement of seed yield per plant in rice genotypes. The results on divergence analysis revealed that the genotypes were grouped into five clusters. Cluster I constituted maximum number of (17) genotypes. Maximum differences among the genotypes within the same cluster (intra-cluster) were shown by cluster I (18.33) followed by cluster II, III, IV, V showed zero intra -cluster distance. Cluster III and V (37.41) showed maximum inter cluster distance, suggesting that the genotypes constituted in these clusters may be used as parents for future hybridization programme. Principal Component Analysis (PCA) was utilized to estimate the relative contribution of various traits for total variability. Five components were found to possess eigen value more than 1.00. The PC1, PC2, PC3, PC4 and PC5 contributed 31.2, 14.5, 12.6, 10.5 and 10.1 per cent of variability. Together, they accounted for 78.9% of the variability of the genotypes used in the study has revealed the traits contributing for the variation.

Assessment of genetic variability and trait association for yield and its components in bi-parental early segregating generation of maize

The present investigation was carried out to understand the co-efficients of variation, heritability, genetic advance, correlation co-efficient and path analysis in F2 population of maize.The study comprised of 303 F2 progeny plants, parents and F1of the cross, CM 111 × DHKN 509 evaluatedunder un-replicated trial during Rabi 2020-21. The observations were recorded for ten traits viz., days to tasseling, days to silking, anthesis-silking interval, plant height, ear height, ear girth, number of kernels per row, pith weight, shelling per cent and grain yield per plantin all the F2 progeny plants and ten plants each from parents and F1 and noticed wide variation among the traits studied in the F2 population.The extent of phenotypic and co-efficient of variation was higher than genotypic co-efficient of variation for all the traits studied. High PCV and GCV was recorded for anthesis-silking interval, number of kernels per row, pith weight and grain yield per plant. High heritability coupled with high genetic advance over mean were observed for anthesis-silking interval, number of kernels per row, pith weight and grain yield per plant suggesting that these traits are governed by additive gene action and can be improved through simple selection. Positive and significant association with grain yield was recorded with number of kernels per row, pith weight, cob girth and shelling per cent. Days to tasseling and anthesis-silking interval exhibited highest direct positive effect on grain yield per plant followed by pith weight and shelling per cent indicating the effectiveness of direct selection, whereas direct negative effects were recorded by days to silking and ear height indicating the effectiveness of indirect selection.

Directional Selection of Microbial Community Reduces Propionate Accumulation in Glycerol and Glucose Anaerobic Bioconversion Under Elevated pCO2.

Volatile fatty acid accumulation is a sign of digester perturbation. Previous work showed the thermodynamic limitations of hydrogen and CO2 in syntrophic propionate oxidation under elevated partial pressure of CO2 (pCO2). Here we study the effect of directional selection under increasing substrate load as a strategy to restructure the microbial community and induce cross-protection mechanisms to improve glucose and glycerol conversion performance under elevated pCO2. After an adaptive laboratory evolution (ALE) process, viable cell density increased and predominant microbial groups were modified: an increase in Methanosaeta and syntrophic propionate oxidizing bacteria (SPOB) associated with the Smithella genus was found with glycerol as the substrate. A modest increase in SPOB along with a shift in the predominance of Methanobacterium toward Methanosaeta was observed with glucose as the substrate. The evolved inoculum showed affected diversity within archaeal spp. under 5 bar initial pCO2; however, higher CH4 yield resulted from enhanced propionate conversion linked to the community shifts and biomass adaptation during the ALE process. Moreover, the evolved inoculum attained increased cell viability with glucose and a marginal decrease with glycerol as the substrate. Results showed differences in terms of carbon flux distribution using the evolved inoculum under elevated pCO2: glucose conversion resulted in a higher cell density and viability, whereas glycerol conversion led to higher propionate production whose enabled conversion reflected in increased CH4 yield. Our results highlight that limited propionate conversion at elevated pCO2 resulted from decreased cell viability and low abundance of syntrophic partners. This limitation can be mitigated by promoting alternative and more resilient SPOB and building up biomass adaptation to environmental conditions via directional selection of microbial community.

Direct effects of selection on aboveground biomass contrast with indirect structure-mediated effects of complementarity in a subtropical forest.

Understanding the multiple biotic and abiotic controls of aboveground biomass (AGB) is important for projecting the consequences of global change and to effectively manage carbon storage. Although large-scale studies have identified the major environmental and biological controls of AGB, drivers of local-scale variation are less well known. Additionally, involvement of multiple causal paths and scale dependence in effect sizes potentially confounds comparisons among studies differing in methodology and sampling grain. We tested for scale dependence in evidence supporting selection, complementarity and environmental factors as the main determinants of AGB variation over a 50ha study extent in subtropical China, modelling this at four sampling grains (0.01, 0.04, 0.25 and 1ha). At each grain, we used piecewise structural equation models to quantify the direct and indirect effects of environmental (topographic and edaphic properties) and forest attributes (structure, diversity and functional traits) on AGB, while controlling for spatial autocorrelation. Direct scale-invariant effects on AGB were evident for structure and community-mean traits, supporting dominance of selection effects. However, diversity had strong indirect effects on AGB via forest structure, particularly at larger sampling grains (≥ 0.25ha), while direct effects only emerged at the smallest grain size (0.01ha). The direct and indirect effects of edaphic and topographic factors were also important for explaining both forest attributes and AGB across all scales. Although selection effects appeared to be more influential on ecosystem function, ignoring indirect causal pathways for diversity via structural attributes risks overlooking the importance of complementarity on ecosystem functioning, particularly as sampling grain increases.

Hybrid Incompatibilities and Transgressive Gene Expression Between Two Closely Related Subspecies of Drosophila.

Genome-wide assays of expression between species and their hybrids have identified genes that become either over- or underexpressed relative to the parental species (i.e., transgressive). Transgressive expression in hybrids is of interest because it highlights possible changes in gene regulation linked to hybrid dysfunction. Previous studies in Drosophila that used long-diverged species pairs with complete or nearly complete isolation (i.e., full sterility and partial inviability of hybrids) and high-levels of genome misregulation have found correlations between expression and coding sequence divergence. The work highlighted the possible effects of directional selection driving sequence divergence and transgressive expression. Whether the same is true for taxa at early stages of divergence that have only achieved partial isolation remains untested. Here, we reanalyze previously published genome expression data and available genome sequence reads from a pair of partially isolated subspecies of Drosophila to compare expression and sequence divergence. We find a significant correlation in rates of expression and sequence evolution, but no support for directional selection driving transgressive expression in hybrids. We find that most transgressive genes in hybrids show no differential expression between parental subspecies and used SNP data to explore the role of stabilizing selection through compensatory mutations. We also examine possible misregulation through cascade effects that could be driven by interacting gene networks or co-option of off-target cis-regulatory elements.

Genetic gain for rice yield in rainfed environments in India.

The complexity of genotype × environment interactions under drought reduces heritability, which determines the effectiveness of selection for drought tolerance and development of drought tolerant varieties. Genetic progress measured through changes in yield performance over time is important in determining the efficiency of breeding programmes in which test cultivars are replaced each year on the assumption that the new cultivars will surpass the older cultivars. The goal of our study was to determine the annual rate of genetic gain for rice grain yield in a drought-prone rainfed system in a series of multi-environment trials conducted from 2005 to 2014 under the Drought Breeding Network of Indian sites in collaboration with the International Rice Research Institute (IRRI). Our results show a positive trend in grain yield with an annual genetic yield increase of about 0.68 % under irrigated control, 0.87 % under moderate reproductive stage drought stress and 1.9 % under severe reproductive stage drought stress due to breeding efforts. The study also demonstrates the effectiveness of direct selection for grain yield under both irrigated control as well as managed drought stress screening to improve yield in typical rainfed systems. IRRI's drought breeding programme has exhibited a significant positive trend in genetic gain for grain yield over the years under both drought stress as well as favorable irrigated control conditions. Several drought tolerant varieties released from the programme have outperformed the currently grown varieties under varied conditions in the rainfed environments on farmers' fields.

Genetic variability, correlation and path-coefficient studies among Persian walnut (Juglans regia) genotypes

The present study was conducted during 2015 and 2016 at ICAR-CITH, Rangreth, Srinagar to corroborate genetic variability among walnut genotypes and determine the potential traits for selection of superior genotypes. Genetic variability in any crop is a pre-requisite to initiate the breeding programme for the selection of superior entries over the existing cultivars. The efficiency of selection largely depends upon the magnitude of the genetic variability present in the plant population. Thus, large genetic variability offers better scope for the crop improvement. The experimental material comprised 136 walnut genotypes. Nut samples of each genotype were collected randomly in five replications and each replication consisted of five nuts. Quantitative traits were recorded as per walnut descriptors developed by IPGRI. The highly significant differences (P = 0.01) existed between genotypes for the nut and kernel traits studied. The range of some economically important traits varied widely for nut weight (6.08–24.23 g), kernel weight (3.30–11.16 g), and kernel recovery (36.27–60.19 %). The estimates of GCV and PCV were very high for nut weight (25.07, 26.05 respectively) and kernel weight (23.59, 25.35 respectively) indicating the importance of these traits in selection of superior genotypes. Trait association analysis also revealed mutual relationships and degree of interrelationships among all the nut and kernel traits. Thus, ample genetic variability observed among the studied genotypes for nut and kernel traits indicated effectiveness of direct selection for improvement of these commercially important traits.

English

Maize is one of the high priority crops to feed the ever increasing population in Africa, however, its production limited by shortage of high yielding variety coupled with biotic and abiotic stresses. The study was initiated to evaluate the heterotic performances of the F1 hybrids over the standard checks (Kolba and Jibat). Fifty entries consists 48 F1 single crosses developed from 24 inbred lines and 2 testers using line x tester design and two commercial check hybrids used in the study. The experiment was conducted using alpha lattice design with two replications at Ambo and Holeta Agricultural Research Center. Analysis of variance revealed existence of significant genetic variation among genotypes for all studied traits except for plant aspect. Location x entry interaction for most of the traits was not significant which suggests hybrid performance was consistent across tested locations. The magnitude of standard heterosis over Kolba and Jibat for grain yield ranged from -40.31 (L13 x T1) to 32.44% (L23 x T1). Cross L23 x T1 exhibited maximum standard heterosis (32.44%) over Kolba and Jibat for grain yield followed by L11 x T1 (22.18%). Positive and significant genotypic, phenotypic correlation coefficient were recorded for yield with plant height (rg=48** and rp=40**), ear height, ear per plant, number of kernels per row, ears length, ear diameter and number of kernel rows per ear. Number of ears per plan (1.08) had the highest positive direct effect on grain yield followed by ear diameter (0.95), number of kernels per row and number of kernel rows per ear indicating the effectiveness of direct selection. Finally, crosses with high standard heterosis for yield and yield components could be used for developing high yielding maize hybrids in the future maize breeding program. Key words: Heterosis, Hybrid, correlation, path analysis.

TAS2R20 variants confer dietary adaptation to high-quercitrin bamboo leaves in Qinling giant pandas.

Sensitivity to bitter tastes provides animals with an important means of interacting with their environment and thus, influences their dietary preferences. Genetic variants encoding functionally distinct receptor types contribute to variation in bitter taste sensitivity. Our previous study showed that two nonsynonymous sites, A52V and Q296H, in the TAS2R20 gene are directionally selected in giant pandas from the Qinling Mountains, which are speculated to be the causative base‐pair changes of Qinling pandas for the higher preference for bamboo leaves in comparison with other pandas. Here, we used functional expression in engineered cells to identify agonists of pTAS2R20 (i.e., giant panda's TAS2R20) and interrogated the differences in perception in the in vitro responses of pTAS2R20 variants to the agonists. Our results show that pTAS2R20 is specifically activated by quercitrin and that pTAS2R20 variants exhibit differences in the sensitivity of their response to the agonist. Compared with pTAS2R20 in pandas from other areas, the receptor variant with A52V and Q296H, which is most commonly found in Qinling pandas, confers a significantly decreased sensitivity to quercitrin. We subsequently quantified the quercitrin content of the leaves of bamboo distributed in the Qinling Mountains, which was found to be significantly higher than that of the leaves of bamboo from panda habitats in other areas. Our results suggest that the decreased sensitivity to quercitrin in Qinling pandas results in higher‐quercitrin‐containing bamboo leaves to be tasting less bitter to them and thus, influences their dietary preference. This study illustrates the genetic adaptation of Qinling pandas to their environments and provides a fine example of the functional effects of directional selection in the giant panda.

Sorghum Hybrids for Low‐Input Farming Systems in West Africa: Quantitative Genetic Parameters to Guide Hybrid Breeding

ABSTRACTThe development of sorghum [Sorghum bicolor (L.) Moench] hybrids with Guinea‐race parents is a promising approach to increase yields in West Africa (WA). There is heretofore no quantitative genetic information about the genetic value of new hybrids and their parents, or about the efficiency of alternative selection methods for targeting yield performance under the predominantly low‐input, P‐deficient production conditions. This study aims to estimate the heterosis levels attainable by new Guinea‐race hybrids and the combining abilities of the current suite of parents with partial‐ to full‐Guinea‐race backgrounds of contrasting geographic origins, and to determine the effectiveness of direct selection under low‐P (LP) relative to indirect selection under high‐P (HP) conditions. Single‐cross hybrids were evaluated in 2015 and 2016 for yield under both LP and HP conditions at two locations in Mali. The hybrid yields were substantially superior to farmers’ local Guinea‐race varieties, with 20 to 80% higher means in both LP and HP environments. Average midparent and better‐parent heterosis estimates were, respectively, 78 and 48% under HP, and 75 and 42% under LP. Direct selection for yield under LP was predicted to be 20 to 60% more effective than indirect selection under HP conditions. The combining ability estimates provided initial insights into the potential benefit of germplasm from more eastern and humid regions of WA for developing a restorer pool distinct and complementary to the female pool from Mali and surrounding countries. Substantial yield superiorities of hybrids over local varieties suggested that a hybrid breeding strategy based on Guinea germplasm could help improve WA smallholder farmers’ livelihood.

Sex‐specific selection on plant architecture through “budget” and “direct” effects in experimental populations of the wind‐pollinated herb, Mercurialis annua

Sexual selection may contribute to the evolution of plant sexual dimorphism by favoring architectural traits in males that improve pollen dispersal to mates. In both sexes, larger individuals may be favored by allowing the allocation of more resources to gamete production (a "budget" effect of size). In wind-pollinated plants, large size may also benefit males by allowing the liberation of pollen from a greater height, fostering its dispersal (a "direct" effect of size). To assess these effects and their implications for trait selection, we measured selection on plant morphology in both males and females of the wind-pollinated dioecious herb Mercurialis annua in two separate experimental common gardens at contrasting density. In both gardens, selection strongly favored males that disperse their pollen further. Selection for pollen production was observed in the high-density garden only, and was weak. In addition, male morphologies associated with increased mean pollen dispersal differed between the two gardens, as elongated branches were favored in the high-density garden, whereas shorter plants with longer inflorescence stalks were favored in the low-density garden. Larger females were selected in both gardens. Our results point to the importance of both a direct effect of selection on male traits that affect pollen dispersal, and, to a lesser extent, a budget effect of selection on pollen production.