Coefficient Of Additive Genetic Variation Research Articles

Genetic diversity, heritability, and estimated breeding values for growth of domesticated Asian seabass Latescalcarifer from Thailand

To establish a new breeding program, genetic diversity of five domesticated populations and two commercial stocks of Asian seabass (Lates calcarifer) were examined. Moderate levels of genetic diversity based on microsatellite polymorphism were found. The number of alleles per locus (NA) was 3.429–11.571. Observed (Ho) and expected (He) heterozygosities were 0.416–0.772 and 0.423–0.805. FST and genetic heterogeneity analysis revealed significant genetic differences of most pairwise comparisons (P < 0.001). Genetic distance between populations was 0.000–0.703. Phylogenetic analysis divided examined populations to two genetic stocks; A: DOF-Chachoengsao 2, DOF-Songkhla, and DOF-Trang and B: Commercial Farm 1 (Phuket) and Commercial Farm 2 (Chachengsao), DOF-Chachoengsao 1 and DOF-Krabi. The base population (G0, 51 families) was established from crosses between these founder populations. Heritability and estimated breeding values (EBVs) for growth in G0 families were evaluated at 519 day post hatch (dph, mean body weight = 616.64 ± 266.80 g, N = 1655). The heritability (h2) for growth of L. calcarifer in this study was 0.386 ± 0.020. The additive genetic coefficient of variation was 28% indicating high potential of genetic improvement for growth in this population. The distribution of EBVs showed high variation both between and within families. Fish exhibiting high EBVs (SATREPS-DOF-G0-hEBVs) clustered with a phylogenetic clade A while the SATREPS-DOF-G0-lEBVs group was phylogenetically allocated to clade B. Genetic selection with +1SD criteria is expected to achieve genetic gain of 28.5% per generation. The information on genetic diversity and EBVs estimates allows efficient implementation of our ongoing breeding program of L. calcarifer.

Low interspecific variation and no phylogenetic signal in additive genetic variance in wild bird and mammal populations

AbstractEvolutionary adaptation through genetic change requires genetic variation and is a key mechanism enabling species to persist in changing environments. Although a substantial body of work has focused on understanding how and why additive genetic variance (VA) differs among traits within species, we still know little about how they vary among species. Here we make a first attempt at testing for interspecific variation in two complementary measures of VA and the role of phylogeny in shaping this variation. To this end, we performed a phylogenetic comparative analysis using 1822 narrow‐sense heritability (h2) for 68 species of birds and mammals and 378 coefficients of additive genetic variance (CVA) estimates for 23 species. Controlling for within‐species variation attributable to estimation method and trait type, we found some interspecific variation in h2 (~15%) but not CVA. Although suggestive of interspecific variation in the importance of non‐(additive) genetic sources of variance, sample sizes were insufficient to test this hypothesis directly. Additionally, although power was low, no phylogenetic signal was detected for either measure. Hence, while this suggests interspecific variation in VA is probably small, our understanding of interspecific variation in the adaptive potential of wild vertebrate populations is currently hampered by data limitations, a scarcity of CVA estimates and a measure of their uncertainty in particular.

Classifying coefficients of genetic variation and heritability for Eucalyptus spp.

The objective of this study was to establish classification ranges for genetic and additive genetic coefficients of variation, as well as for broad and narrow sense heritability, as a function of growth and wood quality traits for Eucalyptus spp. We conducted statistical analyses to determine differences in this classification the types of coefficients used. The selected studies that met the inclusion criteria, 58 presented genetic variation coefficients (448 data points) and 53 presented heritability coefficients (423 data points). To descriptive statistics and the Shapiro-Wilk test, we confirmed that it was necessary to separate coefficients and traits into groups. Inconsistencies for growth traits were observed, confirming the influence of experimental error, indirect estimation methods, and environmental effects on coefficient estimates. We recommend the use of the classification tables included in this literature review to interpret results in studies so as to standardize the classification of coefficients of genetic variation and heritability.

Changes of genetic variances and heritability by effect of selection in a Mexican local variety of Squash

A local variety of squash (Cucurbita pepo L.), ‘Round Zuchinni’ type from Los Reyes Acatlixhuayan State of México, México, was simultaneously evaluated and selected. The objective was to study effect of selection on genetic variance and heritability. Additive genetic variance decreased in seven of nine traits studied: fruit height (79.93 %); fruit weight (65.72 %); fruit width (60.91 %); flesh thickness (57.66 %); flesh color (43.70 %); dry weight of seed (39.54 %); flesh flavor (16.60 %); except in width and seed length traits where it increased 63.40 % and 0.81 %, respectively. Only weight of seed had dominance genetic variance. The coefficient of additive genetic variance (CVA) fluctuated from 9.4 to 61.7 % in the first cycle, and from 9.4 to 51.8 % in the second cycle of selection-evaluation among traits. Heritability diminished in seven from nine characters. In general, the estimated genetic variances (additive and dominance) and heritability decreased as a result of combined selection of falf sib families.

Long-term storage shapes ejaculate traits in a monogamous stingless bee (Scaptotrigona aff. depilis)

The influence of long-term storage on the evolution of social insect male ejaculates remains a puzzle. Here, we studied the influence of sperm storage on male ejaculates in the stingless bee Scaptotrigona aff. depilis, a species where queens mate with a single male and thus do not trigger sperm competition. We estimated quantitative genetic parameters by sampling males from six colonies and two consecutive generations (n = 172). Heritability for sperm length was lower than heritability estimates for other traits. Coefficients of additive genetic variance (CVa) suggest sperm viability and sperm counts are under directional selection, sperm length under stabilizing selection, and male size under weak selection. Both genetic and phenotypic correlations were weak and not significant, indicating independent trait evolution. Overall, our findings provide evidence of selection acting on social insect ejaculates and bring insights for stingless bee breeding programs.

Parámetros genéticos de la población Gema de tomate de cáscara (Physalis ixocarpa Brot. ex Horm.)

The Gema population of the husk tomato (Physalis ixocarpa Brot. ex Horm.) is the result of selection towards very large fruit from F1 of the intervarietal crossing of Verde Puebla and CHF1-Chapingo. After six selection cycles, genetic variance and heritability are likely to have decreased, which could make genetic improvement difficult. The aim of this study was to determine (through heritability [ĥ2], the coefficient of additive genetic variation [CVA] and the additive genetic correlation) whether it is possible to continue with the genetic improvement of the Gema population. Four quantitative traits were studied in 200 families, obtained from the Gema population, under a randomized complete block experimental design with three replications and 22 plants per experimental unit. The CVA ranged from 18.08 to 29.32 %, and the ĥ2 fluctuated between 32.03 and 44.14 %. The highest ĥ2 was found in yield per plant, whose 1-α confidence interval for ĥ2 was estimated to be between 29.2 and 56.3 % (α = 0.05). High, positive and significant additive genetic correlations were found between number of fruits per plant and yield per plant. Therefore, it is possible to obtain significant advances by selection in the Gema variety. The greatest gain could be obtained for yield per plant and number of fruits, with emphasis on the first trait.

Associating REML/BLUP and pedigree in developing sweet pepper (Capsicum annuum L.) progenies resistant to bacterial spot

Associating desirable agronomic characters of sweet peppers and resistance to bacterial spot (BS) has been challenging plant breeders, especially when seeking durable resistance. In this work, we select BS resistant progenies with desirable agronomic characteristics by mixed model. F2:3 plants derived from sixty F2 individuals from crosses between pure lines UENF 2285 (susceptible) × UENF 1381 (resistant) were phenotyped. For BS resistance assessment, 1320 seedlings were inoculated with Xanthomonas euvesicatoria in greenhouse. The progress of the disease on seedlings was evaluated by using a score scale, with values from one to five, for eleven consecutive days. With the values of the Area Under Disease Progress Curve (AUDPC), the components of variance were estimated, and the genetic values for resistance to bacterial spot predicted. Resistant seedlings were cultivated in the field for agronomic characters phenotyping. The average rank index was used to select promising offspring. The coefficient of additive genetic variation (12.97–32.57%) confirmed the existence of genetic variability in the population. The progeny-mean heritability was of high magnitude (80–97%), and narrow sense heritability had average magnitude (17–65%), which indicates desirable gains with the selection of individual plants. The accuracy of the selection was above 80% for all studied traits. The predicted genetic value for AUDPC was negative and the genetic gain was null; in contrast, for the IP variable and morphoagronomic characters, the predicted genetic gain was high. Thirty-three percent of promising segregation lines were selected, which should originate new pure line type sweet pepper cultivars resistant to BS.

Genetic Improvement of Sawn-Board Stiffness and Strength in Scots Pine (Pinus sylvestris L.).

Given an overall aim of improving Scots pine structural wood quality by selective tree breeding, we investigated the potential of non-destructive acoustic sensing tools to accurately predict wood stiffness (modulus of elasticity, MOE) and strength (modulus of rupture, MOR) of sawn boards. Non-destructive measurements of wood density (DEN), acoustic velocity (VEL) and MOE were carried out at different stages of wood processing chain (standing trees, felled logs and sawn boards), whilst destructively measured stiffness and strength served as benchmark traits. All acoustic based MOE and VEL estimates proved to be good proxies (rA > 0.65) for sawn-board stiffness while MOETREE, VELHIT and resistograph wood density (DENRES) measured on standing trees and MOELOG and VELFAK measured on felled logs well reflected board strength. Individual-tree narrow-sense heritability () for VEL, MOE and MOR were weak (0.05–0.26) but were substantially stronger for wood density (0.34–0.40). Moreover, additive genetic coefficients of variation for MOE and MOR were in the range from 5.4% to 9.1%, offering potential targets for exploitation by selective breeding. Consequently, selective breeding based on MOETREE, DENRES or stem straightness (STR) could improve several structural wood traits simultaneously.

Genetic parameters of growth and quality traits in open-pollinated silver birch progeny tests

Genetic parameters of growth and stem quality traits were estimated for open-pollinated silver birch Roth progenies in Latvia at the age of 10 and 14 years. Tree height and stem volume were found to be under strong genetic control at both inventories (narrow-sense heritabilities varied from 0.41 to 0.66). Mainly low heritabilities were found for stem defects, yet genetic control of branch diameter, stem straightness and overall stem quality varied from low to high depending on study site. High additive genetic coefficient of variation was found for stem volume (25.3–32.5%). Genetic correlations among growth traits were strong and positive (0.90–0.99). Mainly weak genetic correlations between growth and quality traits implied simultaneous improvement. Still, strong negative correlations between branch angle and stem straightness might result in enlarged knot size for straighter logs. The genetic age-age correlations were strong. Weak genotype by environment interaction and stability of best genotypes over different sites was indicated by strong genetic correlations between trials. Each growth or quality trait alone showed substantial improvement in terms of estimated genetic gain (up to 62% over trial mean for stem volume). Therefore, selection index combining both growth and stem quality may be developed.Betula pendula

Sex differences in the genetic architecture of aggressiveness in a sexually dimorphic spider.

Sex differences in the genetic architecture of behavioral traits can offer critical insight into the processes of sex‐specific selection and sexual conflict dynamics. Here, we assess genetic variances and cross‐sex genetic correlations of two personality traits, aggression and activity, in a sexually size‐dimorphic spider, Nuctenea umbratica. Using a quantitative genetic approach, we show that both traits are heritable. Males have higher heritability estimates for aggressiveness compared to females, whereas the coefficient of additive genetic variation and evolvability did not differ between the sexes. Furthermore, we found sex differences in the coefficient of residual variance in aggressiveness with females exhibiting higher estimates. In contrast, the quantitative genetic estimates for activity suggest no significant differentiation between males and females. We interpret these results with caution as the estimates of additive genetic variances may be inflated by nonadditive genetic effects. The mean cross‐sex genetic correlations for aggression and activity were 0.5 and 0.6, respectively. Nonetheless, credible intervals of both estimates were broad, implying high uncertainty for these estimates. Future work using larger sample sizes would be needed to draw firmer conclusions on how sexual selection shapes sex differences in the genetic architecture of behavioral traits.

Genetic parameters for reproductive, longevity and lifetime production traits in Bísaro pigs

The Bísaro pig has gained popularity in recent years reflecting the success of the conservation program. Nevertheless, no data is available for animal genetic evaluation in this breed. Therefore, this study aimed to estimate genetic parameters and trends for reproduction related traits in Bísaro pigs. Through a restricted maximum likelihood procedure applied to mixed linear models, 27,844 farrowing records, from 1995 to 2017, were used to analyse total number of pigs born per litter (NBT), number of pigs born alive (NBA), number of stillborn (NSB), number of pigs weaned per litter (NBW), age at first farrowing (AFF), farrowing interval (FIT), length of productive life (LPL), lifetime number of litters (LNL), lifetime pig production (LTP) and lifetime efficiency (LTP365). The heritability estimates for litter size traits were low and ranged from 0.007 ± 0.004 to 0.015 ± 0.006. Differently, the heritabilities for traits related to longevity and lifetime production traits were higher (0.078 ± 0.026 to 0.121 ± 0.030). AFF registered the highest heritability value (0.345 ± 0.028). NSB and FIT presented high values of additive genetic coefficient of variation (0.177 and 0.271) in contrast with low heritability estimates (0.007 ± 0.004 and 0.002 ± 0.005). Very tight genetic correlations were found between NBT and NBA (0.968), NBW and NBT (0.974), and NBW and NBA (0.945). Weak genetic correlations were found between both NBT and NSB (0.352) and between NBA and NSB (0.107). Longevity and lifetime production traits presented high positive genetic correlations (0.811–0.969) and moderate to high phenotypic correlations (0.266–0.946). No major genetic changes were registered over time for most of the analysed traits, except for AFF and LPL, having registered an overall decrease of mean estimated breeding values (21.3 and 17.5) and negative genetic trends of −0.6 and −0.4 (P < 0.001), respectively.

Genetic control of intra-annual height growth in 6-year-old Norway spruce progenies in Latvia

Coupling growth with periods of favourable weather conditions minimizes risks of frost damage and maximizes annual height increment. The phenology of the formation of height increment is therefore a trait related to the adaptability of trees to annual weather fluctuations. Strong genetic control of the timing of the onset and cessation of shoot elongation has been reported for Norway spruce, but little is known about its fluctuations that occur during the growth period. The strength of the genetic control of the height growth rate was assessed for young (6 years old) Norway spruce progenies originating from six open-pollinated stands from two local provenance regions. In 2010, the length of the growing period for the studied trees was ca. 60 days. Trees from the more continental provenance region, which had later onset and cessation of height growth (by ca. 2.5 days), exhibited slightly lower increments (by ca. 1%). Accordingly, the provenance region had a significant effect on height growth at the beginning and end of the growing period. Nevertheless, considerable genetic control of the growth rate was found throughout the entire growing period (particularly at the beginning and cessation, ha2 ≥ 0.20), except for a week-long interval around mid-summer (ha2 = 0.07). Similarly, the coefficient of additive genetic variation suggested that breeding could be applied for the improvement of height growth intensity throughout the season. The phenotypic correlations between weekly growth rates and tree height (before growth) were mostly non-significant, suggesting varying mechanisms of control, hence possibility for simultaneous improvement of the traits by breeding.

Genetic variation in resistance to Uromycladium acaciae fungus, growth, gummosis, and stem form in Acacia mearnsii populations

A new epidemic disease caused by the rust fungus Uromycladium acaciae emerged in 2013/2014 causing defoliation, branch, and stem deformations in plantations of Acacia mearnsii (black wattle) in South Africa. This study investigated the level of genetic resistance to the rust fungus Uromycladium acaciae in six progeny tests from two different trial series. A total of 269 open pollinated families of different levels of improvement, ranging from wild selections to fourth cycle generations were included in the study. Families originated from land race subpopulations of South Africa and from Australian provenances. Rust severity was assessed across all the trials at 6 months of age. In the rust screening trials, different measures of rust incidence were assessed at 6, 12, and 17 months, as well as tree height and mirid damage at 12 months. In the progeny trial series, tree height, stem defects, and gummosis were measured at 36 months. Results suggested that rust incidence is under moderate genetic control at the family level. The coefficient of additive genetic variation was large (59.4%) for the disease incidence. The family mean heritability for rust disease was $$ {h}_{fm}^2=0.48\pm 0.16 $$ in the progeny trial series, whereas it was $$ {h}_{fm}^2=0.33\pm 0.06 $$ in the rust screening trials. Among the rust assessment methods, 6-month rust incidence (yes/no) assessment produced higher heritability estimates. With some exceptions, Australian provenances from low altitude sites along the eastern coast of Victoria and the south east coast of New South Wales showed high tolerance to rust, better growth, low gummosis incidence but poor stem form. All the South African sources showed high rust susceptibility and had average or below average growth, gummosis incidence, and stem form. For rust disease improvement, the South African material should be avoided and the best existing Australian families should be used for further breeding. In addition, new seed sources from Australia should be infused to the breeding program in order to increase the genetic diversity while increasing genetic gain for the rust, gummosis, and growth.

Moderate heritability and low evolvability of sperm morphology in a species with high risk of sperm competition, the collared flycatcher Ficedula albicollis

Spermatozoa represent the morphologically most diverse type of animal cells and show remarkable variation in size across and also within species. To understand the evolution of this diversity, it is important to reveal to what degree this variation is genetic or environmental in origin and whether this depends on species' life histories. Here we applied quantitative genetic methods to a pedigreed multigenerational data set of the collared flycatcher Ficedula albicollis, a passerine bird with high levels of extra-pair paternity, to partition genetic and environmental sources of phenotypic variation in sperm dimensions for the first time in a natural population. Narrow-sense heritability (h2 ) of total sperm length amounted to 0.44±0.14 SE, whereas the corresponding figure for evolvability (estimated as coefficient of additive genetic variation, CVa ) was 0.02±0.003 SE. We also found an increase in total sperm length within individual males between the arrival and nestling period. This seasonal variation may reflect constraints in the production of fully elongated spermatozoa shortly after arrival at the breeding grounds. There was no evidence of an effect of male age on sperm dimensions. In many previous studies on laboratory populations of several insect, mammal and avian species, heritabilities of sperm morphology were higher, whereas evolvabilities were similar. Explanations for the differences in heritability may include variation in the environment (laboratory vs. wild), intensity of sexual selection via sperm competition (high vs. low) and genetic architecture that involves unusual linkage disequilibrium coupled with overdominance in one of the studied species.

Evolutionary potential varies across populations and traits in the neotropical oak Quercus oleoides.

Heritable variation in polygenic (quantitative) traits is critical for adaptive evolution and is especially important in this era of rapid climate change. In this study, we examined the levels of quantitative genetic variation of populations of the tropical tree Quercus oleoides Cham. and Schlect. for a suite of traits related to resource use and drought resistance. We tested whether quantitative genetic variation differed across traits, populations and watering treatments. We also tested potential evolutionary factors that might have shaped such a pattern: selection by climate and genetic drift. We measured 15 functional traits on 1322 1-year-old seedlings of 84 maternal half-sib families originating from five populations growing under two watering treatments in a greenhouse. We estimated the additive genetic variance, coefficient of additive genetic variation and narrow-sense heritability for each combination of traits, populations and treatments. In addition, we genotyped a total of 119 individuals (with at least 20 individuals per population) using nuclear microsatellites to estimate genetic diversity and population genetic structure. Our results showed that gas exchange traits and growth exhibited strikingly high quantitative genetic variation compared with traits related to leaf morphology, anatomy and photochemistry. Quantitative genetic variation differed between populations even at geographical scales as small as a few kilometers. Climate was associated with quantitative genetic variation, but only weakly. Genetic structure and diversity in neutral markers did not relate to coefficient of additive genetic variation. Our study demonstrates that quantitative genetic variation is not homogeneous across traits and populations of Q. oleoides. More importantly, our findings suggest that predictions about potential responses of species to climate change need to consider population-specific evolutionary characteristics.

Comparison of genetic parameters between optimal and marginal populations of oriental sweet gum on adaptive traits

Genetic parameters of 9 oriental sweetgum (Liquidambar orientalis Mill.) populations were estimated at a common garden test. Open-pollinated seeds were collected from 16-27 families for each population. The common garden test was established in 2009 using a randomized complete block design in 25 blocks with single tree plot, with each block included 223 families. Breast height diameter, height and crown diameter were measured at the age of five. The purpose of study was to compare the genetic parameters of optimal and marginal populations and to assess the findings for genetic conservation. The study revealed significant variability in all traits evaluated. In variance components, variation among populations was three times higher than that of families. Individual heritability estimates for breast height diameter, height and crown diameter pooled across the whole dataset (marginal and optimal populations) were 0.21 ± 0.04, 0.27 ± 0.04 and 0.11 ± 0.03 and additive genetic coefficients of variation were 13.4%, 9.1% and 7.1%, respectively. Individual heritability estimates for breast height diameter, height and crown diameter in marginal and optimal populations were 0.27 ± 0.10, 0.19 ± 0.08 and 019 ± 0.08 and 0.19 ± 0.04, 0.29 ± 0.05 and 0.09 ± 0.03, respectively. Additive genetic coefficients of variation for breast height diameter, height and crown diameter were 16.7%, 8.3% and 10.8% in marginal and 12.8%, 9.1% and 6.2% in optimal populations, respectively. While breast height diameter and crown diameter were more heritable for marginal populations, height was more heritable for optimal populations. These findings are discussed in terms of genetic conservation of oriental sweet gum.

Alternative somatic cell count traits exploitable in genetic selection for mastitis resistance in Italian Holsteins

The aim of the present study was to characterize alternative somatic cell count (SCC) traits that could be exploited in genetic selection for mastitis resistance. Data were from 66,407 first-parity Holsteins in 404 herds. Novel SCC traits included average somatic cell score (SCS, log-transformation of SCC) in early lactation (SCS_150), standard deviation of SCS of the entire lactation (SCS_SD), the presence of at least one test-day (TD) SCC >400,000 cells/mL in the lactation, and the ratio of number of TD SCC >400,000 cells/mL to total number of TD in the lactation. Novel traits and lactation-mean SCS (SCS_LM) were analyzed using linear mixed or logistic regression models, including month of calving, year of calving, number of TD, and milk yield as fixed effects, and herd and residual as random terms. A multitrait linear animal model was applied to a random subset of 152 herds (n = 22,695 cows) to assess heritability of and genetic correlations between SCC traits. Alternative SCC traits were affected by the environmental factors included in the model; in particular, results suggested a seasonal effect and a tendency toward an improvement of the udder health status in the last years. Association was also found between novel SCC traits and milk production. Alternative SCC traits exhibited coefficients of additive genetic variation that were similar to or larger than that of traditional SCS_LM. Heritability of novel SCC traits was smaller than heritability of SCS_LM (0.126 ± 0.014), ranging from 0.044 ± 0.008 (SCS_SD) to 0.087 ± 0.010 (SCS_150). Genetic correlations between SCC traits ranged from 0.217 ± 0.096 (SCS_150 and SCS_SD) to 0.969 ± 0.010 (SCS_LM and SCS_150). Alternative SCC traits exhibited additive genetic variation that is potentially exploitable in breeding programs of Italian Holstein population to improve resistance to mastitis.

Application of Molecular Marker Assayed Paternity in a White Clover Breeding Program

The use of molecular tools, coupled with improvements in paternity assignment computation, offer breeders a cost‐effective and readily implementable breeding tool to improve the rate of genetic gain in forages. Molecular marker paternity assays may improve genetic gain in white clover (Trifolium repens L.) half‐sib family breeding programs by utilizing a larger coefficient of additive genetic variation. To evaluate the potential to improve breeding outcomes by use of a molecular marker paternity assay in allotetraploid white clover (2n = 4x = 32), seven single‐locus, homoeologue‐specific simple sequence repeat markers were genotyped and analyzed on 1277 half‐sib progeny and their 20 parents from a polycross pollinated by bumble bees (Bombus sp.). Paternity was assigned to 88.9% of progeny using a likelihood algorithm implemented in Cervus. Estimates of additive genetic variances from multisite, space‐planted field experiments established in perennial ryegrass (Lolium perenne L.) were used to predict selection responses. Joint maternal and molecular‐marker‐assayed paternal half‐sib family selection offered improved theoretical selection gains relative to conventional maternal half‐sib family selection for herbage yield and trifoliate center leaflet width. The estimated selection responses based on empirical parameters demonstrated the theoretical wisdom of incorporating molecular‐marker‐assayed paternity in white clover breeding programs as an effective tool to improve selection responses per cycle of selection.

Heritable Micro-environmental Variance Covaries with Fitness in an Outbred Population of Drosophila serrata.

The genetic basis of stochastic variation within a defined environment, and the consequences of such micro-environmental variance for fitness are poorly understood . Using a multigenerational breeding design in Drosophila serrata, we demonstrated that the micro-environmental variance in a set of morphological wing traits in a randomly mating population had significant additive genetic variance in most single wing traits. Although heritability was generally low (<1%), coefficients of additive genetic variance were of a magnitude typical of other morphological traits, indicating that the micro-environmental variance is an evolvable trait. Multivariate analyses demonstrated that the micro-environmental variance in wings was genetically correlated among single traits, indicating that common mechanisms of environmental buffering exist for this functionally related set of traits. In addition, through the dominance genetic covariance between the major axes of micro-environmental variance and fitness, we demonstrated that micro-environmental variance shares a genetic basis with fitness, and that the pattern of selection is suggestive of variance-reducing selection acting on micro-environmental variance.

Genetic Parameters and Prediction of Breeding Values in Switchgrass Bred for Bioenergy

Estimating genetic parameters is an essential step in breeding by recurrent selection to maximize genetic gains over time. This study evaluated the effects of selection on genetic variation across two successive cycles (C1 and C2) of a ‘Summer'x‘Kanlow’ switchgrass (Panicum virgatum L.) population. Two progeny tests were planted in 2007 and 2011 near Mead, NE and respectively analyzed for 2 and 4 yr. Each test was a randomized complete block design, with four replicates of 34 halfsib families in single‐row plots of 10 seedlings in C1 and with three replicates of 111 halfsib families in single‐row plots of five seedlings in C2. The C2 test included C0, C1, and parental populations for comparison. Multivariate mixed linear models revealed ample additive genetic variation for dry matter yield (DMY), Klason lignin (KL), and predicted ethanol yield (ETOH) in both cycles, with heritability ranging from 0.40±0.18 to 0.5±0.14 at the family level, from 0.22±0.17 to 0.36±0.22 at the individual level, and from 0.25 to 0.31 within family in C1. Matching values in C2 were: from 0.42±0.09 to 0.63±0.07, from 0.10±0.07 to 0.34±0.13, and from 0.12 to 0.48. More opportunity exists to improve DMY, with a coefficient of additive genetic variation of 11 to 32%, than KL (3–5%) or ETOH (3–6%). The traits were properly aligned for joint improvement for high DMY and reduced KL in C1, owing to favorable genetic correlations (rA=−0.33±0.11) and each having respective rA of 0.60±0.05 and −0.62±0.07 with ETOH. In C2, the rA between DMY and KL (−0.19±0.10) or ETOH (0.04±0.04) decreased towards zero, and that between KL and ETOH was moderately less negative (−0.35±0.15). These results suggest a strong genetic basis for improvement of the traits and monitoring of their patterns every cycle to find the proper weights that maximize the breeding goal of designing the ideal bioenergy switchgrass.