Significant Additive Variance Research Articles

The adaptive potential of subtropical rainbowfish in the face of climate change: heritability and heritable plasticity for the expression of candidate genes.

Whilst adaptation and phenotypic plasticity might buffer species against habitat degradation associated with global climate change, few studies making such claims also possess the necessary and sufficient data to support them. Doing so requires demonstration of heritable variation in traits affecting fitness under new environmental conditions. We address this issue using an emerging aquatic system to study adaptation to climate change, the crimson‐spotted rainbowfish (Melanotaenia duboulayi), a freshwater species from a region of eastern Australia projected to be affected by marked temperature increases. Captive born M. duboulayi of known pedigree were used to assess the long‐term effects of contemporary and 2070‐projected summer temperatures on the expression of genes previously identified in a climate change transcriptomics (RNA‐Seq) experiment. Nearly all genes responded to increasing temperature. Significant additive genetic variance explained a moderate proportion of transcriptional variation for all genes. Most genes also showed broad‐sense genetic variation in transcriptional plasticity. Additionally, molecular pathways of candidate genes co‐occur with genes inferred to be under climate‐mediated selection in wild M. duboulayi populations. Together, these results indicate the presence of existing variation in important physiological traits, and the potential for adaptive responses to a changing thermal environment.

Additive genetic variance in polyandry enables its evolution, but polyandry is unlikely to evolve through sexy or good sperm processes.

Polyandry is widespread despite its costs. The sexually selected sperm hypotheses ('sexy' and 'good' sperm) posit that sperm competition plays a role in the evolution of polyandry. Two poorly studied assumptions of these hypotheses are the presence of additive genetic variance in polyandry and sperm competitiveness. Using a quantitative genetic breeding design in a natural population of Drosophila melanogaster, we first established the potential for polyandry to respond to selection. We then investigated whether polyandry can evolve through sexually selected sperm processes. We measured lifetime polyandry and offensive sperm competitiveness (P2 ) while controlling for sampling variance due to male×male×female interactions. We also measured additive genetic variance in egg-to-adult viability and controlled for its effect on P2 estimates. Female lifetime polyandry showed significant and substantial additive genetic variance and evolvability. In contrast, we found little genetic variance or evolvability in P2 or egg-to-adult viability. Additive genetic variance in polyandry highlights its potential to respond to selection. However, the low levels of genetic variance in sperm competitiveness suggest that the evolution of polyandry may not be driven by sexy sperm or good sperm processes.

Live fast die young life history in females: evolutionary trade-off between early life mating and lifespan in female Drosophila melanogaster.

The trade-off between survival and reproduction is fundamental to life history theory. Sexual selection is expected to favour a ‘live fast die young’ life history pattern in males due to increased risk of extrinsic mortality associated with obtaining mates. Sexual conflict may also drive a genetic trade-off between reproduction and lifespan in females. We found significant additive genetic variance in longevity independent of lifetime mating frequency, and in early life mating frequency. There was significant negative genetic covariance between these traits indicating that females from families characterized by high levels of multiple mating early in life die sooner than females that engage in less intense early life mating. Thus, despite heritable variation in both traits, their independent evolution is constrained by an evolutionary trade-off. Our findings indicate that, in addition to the well-known male-driven direct costs of mating on female lifespan (mediated by male harassment and harmful effects of seminal fluids), females with a genetic propensity to mate multiply live shorter lives. We discuss the potential role of sexual conflict in driving the evolutionary trade-off between reproduction and lifespan in Drosophila. More generally, our data show that, like males, females can exhibit a live fast die young life history strategy.

Quantitative genetics of migration-related traits in rainbow and steelhead trout.

Rainbow trout (Oncorhynchus mykiss) exhibit remarkable life history diversity throughout their native range, and among the most evident is variation in migratory propensity. Although some populations and ecotypes will remain resident in freshwater habitats throughout their life history, others have the ability to undertake tremendous marine migrations. Those that migrate undergo a suite of behavioral, morphological, and physiological adaptations in a process called smoltification. We describe a quantitative genetic analysis of 22 growth, size, and morphological traits in addition to overall life history classification (resident or migrant) over the temporal process of smoltification in a large multi-generation experimental pedigree (n = 16,139) of migratory and resident rainbow trout derived from a wild population, which naturally segregates for migratory propensity. We identify significant additive genetic variance and covariance among the suite of traits that make up a component of the migratory syndrome in this species. Additionally, we identify high heritability estimates for the life history classifications and observe a strong negative genetic correlation between the migratory and resident life history trajectories. Given the large heritability estimates of all of the traits that segregate between migratory and resident rainbow trout, we conclude that these traits can respond to selection. However, given the high degree of genetic correlation between these traits, they do not evolve in isolation, but rather as a suite of coordinated characters in a predictable manner.

Investigating the influence of mineralogy and pore shape on the velocity of carbonate rocks: Insights from extant global data sets

Using a variety of recent public-domain data sets comprising porosity, velocity (P- and S-waves), and, in most cases, mineralogy and petrographic data, I created an extensive global data set and evaluated the importance of mineralogy and pore type on the elastic properties behavior of carbonate core plugs. Results from this investigation clearly illuminated the potential for overinterpreting elastic properties behavior as a function of pore type(s) when mineralogy was not explicitly included in the analysis. Rock-physics analysis using a combination of heuristic and theoretical models illustrated that mineralogy exerted a significant additional variation on velocity at a given porosity. Failure to account for mineralogy exacerbated inferences about the effect of pore type(s) made using a comparison of P-wave velocity to an inappropriate empirical model (Wyllie) that did not account for pore shape(s). In this analysis, extreme variability in carbonate velocity was observed in only portions of two data sets, when mineralogy was explicitly considered and robust models that accounted for inclusion (pore) shape were used. Results from this analysis resulted in a recommended workflow, including a rock-physics template and dry-rock modulus diagnostics, for the evaluation of lab-based carbonate rock-physics data. The workflow was amenable to further integration with well-based data and other core-based petrophysical measurements (e.g., electrical properties).

Genetic analysis of yield and yield related attributes in Brassica napus

Diallel analysis in Rapeseed (Brassica napus L.) was carried out during 2011-2012 at The University of Agriculture, Peshawar to estimate the pattern of inheritance and heritability for important traits. During 2010-2011 four contrasting genotypes of Brassica napus. viz. G2, G4, G6 and G9 were crossed in a diallel manner and in the following season (2011-2012) all the F1 hybrids along with parents were evaluated under field condition in a randomized complete block design. Highly significant (P ≤ 0.01) differences were observed for plant height, primary branches plant -1 , seeds pod -1 , pods plant -1 , weight of 1000 seed, seed weight plant -1 . Additive-dominance model was fully adequate for plant height, primary branches plant -1 , pods plant -1 , seeds pod -1 , whereas for the rest of the traits it was partially adequate. Diallel analysis showed significant additive (a) and dominance (b) variances for all parameters. Genetic parameters estimation showed significant and higher magnitude of dominance component for all the studied traits. Graphical analysis showed overdominance for all of the parameters. The value of average degree of dominance for plant height (1.858), primary branches plant -1 (4.355), pods plant -1 (3.704), seeds pod -1 (2.417), 1000 seed weight (3.995) and seed weight plant -1 (1.852) also indicated the presence of overdominance gene action controlling these yield attributes, as it was greater than one. Low narrow (0.16-0.31) and broad (0.81-0.96) sense heritabilities were estimated for all the studied parameters, suggesting the low value of additive gene action and genetic potential for the improvement of such traits through selection in later generations.

The evolution and adaptive potential of transcriptional variation in sticklebacks--signatures of selection and widespread heritability.

Evidence implicating differential gene expression as a significant driver of evolutionary novelty continues to accumulate, but our understanding of the underlying sources of variation in expression, both environmental and genetic, is wanting. Heritability in particular may be underestimated when inferred from genetic mapping studies, the predominant “genetical genomics” approach to the study of expression variation. Such uncertainty represents a fundamental limitation to testing for adaptive evolution at the transcriptomic level. By studying the inheritance of expression levels in 10,495 genes (10,527 splice variants) in a threespine stickleback pedigree consisting of 563 individuals, half of which were subjected to a thermal treatment, we show that 74–98% of transcripts exhibit significant additive genetic variance. Dominance variance is also prevalent (41–99% of transcripts), and genetic sources of variation seem to play a more significant role in expression variance in the liver than a key environmental variable, temperature. Among-population comparisons suggest that the majority of differential expression in the liver is likely due to neutral divergence; however, we also show that signatures of directional selection may be more prevalent than those of stabilizing selection. This predominantly aligns with the neutral model of evolution for gene expression but also suggests that natural selection may still act on transcriptional variation in the wild. As genetic variation both within- and among-populations ultimately defines adaptive potential, these results indicate that broad adaptive potential may be found within the transcriptome.

Estimates of direct and indirect effects for early juvenile survival in captive populations maintained for conservation purposes: the case of Cuvier's gazelle.

Together with the avoidance of any negative impact of inbreeding, preservation of genetic variability for life-history traits that could undergo future selective pressure is a major issue in endangered species management programmes. However, most of these programmes ignore that, apart from the direct action of genes on such traits, parents, as contributors of offspring environment, can influence offspring performance through indirect parental effects (when parental genotype and phenotype exerts environmental influences on offspring phenotype independently of additive genetic effects). Using quantitative genetic models, we estimated the additive genetic variance for juvenile survival in a population of the endangered Cuvier's gazelle kept in captivity since 1975. The dataset analyzed included performance recording for 700 calves and a total pedigree of 740 individuals. Results indicated that in this population juvenile survival harbors significant additive genetic variance. The estimates of heritability obtained were in general moderate (0.115–0.457) and not affected by the inclusion of inbreeding in the models. Maternal genetic contribution to juvenile survival seems to be of major importance in this gazelle's population as well. Indirect genetic and indirect environmental effects assigned to mothers (i.e., maternal genetic and maternal permanent environmental effects) roughly explain a quarter of the total variance estimated for the trait analyzed. These findings have major evolutionary consequences for the species as show that offspring phenotypes can evolve strictly through changes in the environment provided by mothers. They are also relevant for the captive breeding programme of the species. To take into account, the contribution that mothers have on offspring phenotype through indirect genetic effects when designing pairing strategies might serve to identify those females with better ability to recruit, and, additionally, to predict reliable responses to selection in the captive population.

Mapping and Expression of Candidate Genes for Development Rate in Rainbow Trout (Oncorhynchus mykiss).

Development rate has important implications for individual fitness and physiology. In salmonid fishes, development rate correlates with many traits later in life, including life-history diversity, growth, and age and size at sexual maturation. In rainbow trout (Oncorhynchus mykiss), a quantitative trait locus for embryonic development rate has been detected on chromosome 5 across populations. However, few candidate genes have been identified within this region. In this study, we use gene mapping, gene expression, and quantitative genetic methods to further identify the genetic basis of embryonic developmental rate in O. mykiss Among the genes located in the region of the major development rate quantitative trait locus (GHR1, Clock1a, Myd118-1, and their paralogs), all were expressed early in embryonic development (fertilization through hatch), but none were differentially expressed between individuals with the fast- or slow-developing alleles for a major embryonic development rate quantitative trait locus. In a follow-up study of migratory and resident rainbow trout from natural populations in Alaska, we found significant additive variation in development rate and, moreover, found associations between development rate and allelic variation in all 3 candidate genes within the quantitative trait locus for embryonic development. The mapping of these genes to this region and associations in multiple populations provide positional candidates for further study of their roles in growth, development, and life-history diversity in this model salmonid.

Genetic variation and the potential response to selection on leaf traits after habitat degradation in a long-lived cycad

Rapid evolution may be common in human-dominated landscapes where environmental changes are severe. We used phenotypic selection analyses and a marker-based method to estimate genetic variances and covariances to predict the potential response to selection in populations of a long-lived cycad recently exposed to drastic environmental changes. Patterns of selection in adult fecundity showed that different traits were under directional selection in subpopulations from native-undisturbed habitats and the novel degraded-forest habitat. Plants from a native-habitat subpopulation tend to maximize fitness through larger leaf area or smaller specific leaf area (SLA). In contrast, larger leaf production increased fitness in a degraded-habitat subpopulation, and canopy openness appears to be a major agent of selection for this trait. Leaf production and SLA showed significant additive genetic variance and no genetic trade-offs with examined traits, suggesting that these traits can respond to selection. Directional selection coefficients and heritability values were large, therefore significant phenotypic changes between subpopulations in few generations are possible. These results suggest that recent environmental change can result in strong directional selection in subpopulations of this cycad, and that these subpopulations have the potential to diverge at the genetic level in leaf traits after anthropogenic habitat degradation.

Combining ability analysis for yield and protein content in bread wheat (Triticum aestivum)

The experiment was conducted with 10 parents and their 45 F1s (half diallel) during crop seasons (2008/09 and 2009/10) under normal and heat-stress environment to find out combining ability effects. The analysis of variance showed highly significant differences for all the traits at genotypic level under both normal and heat-stress environment. The significant additive variance (D) and dominance variance (H1) indicated that, expression of these traits is controlled by both additive and non-additive gene action. Among the parents, there was asymmetrical distribution of positive and negative dominant genes and preponderance of over-dominance gene action for all the traits under both the environment. Estimates of narrow-sense heritability were higher for days to 50% flowering; days to maturity; plant height and spike length. Our results also indicated that only three parents (HD 2285 for grain filling duration and thousand grains weight; PBW 373 for the days to maturity and plant height and UP 2425 for number of tillers and grain yield) had favorable general combining ability (GCA) effects under normal sown environment. While under heat-stress environment, cultivar HD 2285 showed highest GCA effect for days to 50% flowering, grain filling duration and thousand grain weight; HD 2733 for plant height and protein content; and PBW 373 for number of tillers and grain yield. Five cross combinations showed contrasting favorable specific combining ability (SCA) effect for more than one trait under both normal and heat-stress environment. Attempting combinations involving parents with high GCA for desirable yield components could be useful. The traits showing more than 35 percent narrow-sense heritability could be rewarding for further improvement of grain yield and protein content in wheat (Triticum aestivum L.).

The Geographic Dispersion of Google Search and the Market Reaction to Earnings Announcements

We examine the impact of distance on investor search behavior, and the effect of geographic dispersion of investor search on the stock market response around earnings announcements. We find significant “local bias” in Internet search behavior. While more visible firms have more geographically dispersed search, there is significant additional variation in search dispersion. Motivated by theories of network effects and psychological distance, we predict and find that firms with a higher geographic dispersion of search experience higher abnormal trading volume, lower abnormal bid-ask spreads, and larger earnings response coefficients at the time of earnings announcements, as well as weaker post-earnings-announcement drift. These results hold both cross-sectionally and when examining changes in dispersion or propensity-score matched pairs. In addition, path analysis suggests that both network effects and investor psychology are significant drivers of the return results. Overall, our results suggest that geographic proximity affects search, and that firms with more geographically dispersed search experience better market responses to earnings announcements.

MHC class I expression dependent on bacterial infection and parental factors in whitefish embryos (Salmonidae)

Ecological conditions can influence not only the expression of a phenotype, but also the heritability of a trait. As such, heritable variation for a trait needs to be studied across environments. We have investigated how pathogen challenge affects the expression of MHC genes in embryos of the lake whitefish Coregonus palaea. In order to experimentally separate paternal (i.e. genetic) from maternal and environmental effects, and determine whether and how stress affects the heritable variation for MHC expression, embryos were produced in full-factorial in vitro fertilizations, reared singly, and exposed at 208 degree days (late-eyed stage) to either one of two strains of Pseudomonas fluorescens that differ in their virulence characteristics (one increased mortality, while both delayed hatching time). Gene expression was assessed 48 h postinoculation, and virulence effects of the bacterial infection were monitored until hatching. We found no evidence of MHC class II expression at this stage of development. MHC class I expression was markedly down-regulated in reaction to both pseudomonads. While MHC expression could not be linked to embryo survival, the less the gene was expressed, the earlier the embryos hatched within each treatment group, possibly due to trade-offs between immune function and developmental rate or further factors that affect both hatching timing and MHC expression. We found significant additive genetic variance for MHC class I expression in some treatments. That is, changes in pathogen pressures could induce rapid evolution in MHC class I expression. However, we found no additive genetic variance in reaction norms in our study population.

Genetic variation underlies temperature tolerance of embryos in the sea urchinHeliocidaris erythrogramma armigera

Ocean warming can alter natural selection on marine systems, and in many cases, the long-term persistence of affected populations will depend on genetic adaptation. In this study, we assess the potential for adaptation in the sea urchin Heliocidaris erythrogramma armigera, an Australian endemic, that is experiencing unprecedented increases in ocean temperatures. We used a factorial breeding design to assess the level of heritable variation in larval hatching success at two temperatures. Fertilized eggs from each full-sibling family were tested at 22°C (current spawning temperature) and 25°C (upper limit of predicted warming this century). Hatching success was significantly lower at higher temperatures, confirming that ocean warming is likely to exert selection on this life-history stage. Our analyses revealed significant additive genetic variance and genotype-by-environment interactions underlying hatching success. Consistent with prior work, we detected significant nonadditive (sire-by-dam) variance in hatching success, but additionally found that these interactions were modified by temperature. Although these findings suggest the potential for genetic adaptation, any evolutionary responses are likely to be influenced (and possibly constrained) by complex genotype-by-environment and sire-by-dam interactions and will additionally depend on patterns of genetic covariation with other fitness traits.

Heritability of life‐history traits in the spruce budworm

AbstractThe heritability of life‐history traits is of particular importance for insects that are very dependent on host conditions. Severe defoliation caused by the spruce budworm negatively impacts its food source, which in turn imposes environmental constraints on the insect. The heritability of those traits can help elucidate this species' evolutionary process. Heritability also helps identify which traits exhibit significant additive variance and can be key to understanding natural selection effects. Individuals were reared under laboratory conditions over three generations on an artificial diet. Heritability was estimated by parent–offspring regression. Fertility and fecundity demonstrated significant heritability followed by larval development, while pupal mass showed minimal heritable variation. These results suggest an important percent of additive variance in life‐history traits. This study contributes to our understanding of the relationship of this forest pest to its environmental conditions. This study also reveals an important genetic architectural structure of life‐history traits in the spruce budworm.

Heritability of sperm length and adult shell size in the land snail Arianta arbustorum (Linnaeus, 1758)

Sperm length varies considerably, both between and within species, but the evolutionary implications of this variation are poorly understood. Sexual selection on sperm length requires a significant additive genetic variance, but few studies have actually measured this. Stylommatophoran gastropods have extraordinarily long sperm. However, the extent of intraspecific variation has rarely been examined. Here we present the first estimates of heritability of sperm length in the land snail Arianta arbustorum using two complementary approaches (one-parent –offspring regression and full-sibling split design). We also examined whether sperm length is influenced by the shell size of the snail and estimated heritability of shell size. Sperm delivered by the same individuals in 2–4 matings over two reproductive seasons did not differ in length, indicating a high repeatability of this trait. Offspring of 10 families were kept at three temperatures (11, 15 and 208C) to examine the influence of different environmental conditions on sperm length and adult shell breadth. Independent of shell breadth, sperm length was affected by temperature but not by family of origin (the variance component associated with family was not significantly different from zero), while adult shell breadth was influenced by temperature and family of origin. Higher temperatures resulted in shorter sperm, but larger shells. The heritability of sperm length derived from the two different approaches (one-parent –offspring regression: h 2 + SE ¼ 0.52+ 0.55; full-sibling split design: H 2 + SE ¼ 20.19+ 0.28) suggests relatively little genetic variation in this trait in the studied population. In contrast, the heritability of adult shell breadth indicates a strong genetic effect (mother –offspring regression, h 2 + SE ¼ 0.90+ 0.33). The heritability (h 2 + SE) of adult shell breadth obtained from the father –offspring regression was 0.18+ 0.42, i.e. five times smaller than that of the mother –offspring regression, suggesting a maternal effect on shell size.

A SELDI mass spectrometry study of experimental autoimmune encephalomyelitis: sample preparation, reproducibility, and differential protein expression patterns

BackgroundExperimental autoimmune encephalomyelitis (EAE) is an autoimmune, inflammatory disease of the central nervous system that is widely used as a model of multiple sclerosis (MS). Mitochondrial dysfunction appears to play a role in the development of neuropathology in MS and may also play a role in disease pathology in EAE. Here, surface enhanced laser desorption ionization mass spectrometry (SELDI-MS) has been employed to obtain protein expression profiles from mitochondrially enriched fractions derived from EAE and control mouse brain. To gain insight into experimental variation, the reproducibility of sub-cellular fractionation, anion exchange fractionation as well as spot-to-spot and chip-to-chip variation using pooled samples from brain tissue was examined.ResultsVariability of SELDI mass spectral peak intensities indicates a coefficient of variation (CV) of 15.6% and 17.6% between spots on a given chip and between different chips, respectively. Thinly slicing tissue prior to homogenization with a rotor homogenizer showed better reproducibility (CV = 17.0%) than homogenization of blocks of brain tissue with a Teflon® pestle (CV = 27.0%). Fractionation of proteins with anion exchange beads prior to SELDI-MS analysis gave overall CV values from 16.1% to 18.6%. SELDI mass spectra of mitochondrial fractions obtained from brain tissue from EAE mice and controls displayed 39 differentially expressed proteins (p≤ 0.05) out of a total of 241 protein peaks observed in anion exchange fractions. Hierarchical clustering analysis showed that protein fractions from EAE animals with severe disability clearly segregated from controls. Several components of electron transport chain complexes (cytochrome c oxidase subunit 6b1, subunit 6C, and subunit 4; NADH dehydrogenase flavoprotein 3, alpha subcomplex subunit 2, Fe-S protein 4, and Fe-S protein 6; and ATP synthase subunit e) were identified as possible differentially expressed proteins. Myelin Basic Protein isoform 8 (MBP8) (14.2 kDa) levels were lower in EAE samples with advanced disease relative to controls, while an MBP fragment (12. 4kDa), likely due to calpain digestion, was increased in EAE relative to controls. The appearance of MBP in mitochondrially enriched fractions is due to tissue freezing and storage, as MBP was not found associated with mitochondria obtained from fresh tissue.ConclusionsSELDI mass spectrometry can be employed to explore the proteome of a complex tissue (brain) and obtain protein profiles of differentially expressed proteins from protein fractions. Appropriate homogenization protocols and protein fractionation using anion exchange beads can be employed to reduce sample complexity without introducing significant additional variation into the SELDI mass spectra beyond that inherent in the SELDI- MS method itself. SELDI-MS coupled with principal component analysis and hierarchical cluster analysis provides protein patterns that can clearly distinguish the disease state from controls. However, identification of individual differentially expressed proteins requires a separate purification of the proteins of interest by polyacrylamide electrophoresis prior to trypsin digestion and peptide mass fingerprint analysis, and unambiguous identification of differentially expressed proteins can be difficult if protein bands consist of several proteins with similar molecular weights.

Milk metabolites and their genetic variability

The composition of milk is crucial to evaluate milk performance and quality measures. Milk components partly contribute to breeding scores, and they can be assessed to judge metabolic and energy status of the cow as well as to serve as predictive markers for diseases. In addition to the milk composition measures (e.g., fat, protein, lactose) traditionally recorded during milk performance test via infrared spectroscopy, novel techniques, such as gas chromatography-mass spectrometry, allow for a further analysis of milk into its metabolic components. Gas chromatography-mass spectrometry is suitable for measuring several hundred metabolites with high throughput, and thus it is applicable to study sources of genetic and nongenetic variation of milk metabolites in dairy cows. Heritability and mode of inheritance of metabolite measurements were studied in a linear mixed model approach including expected (pedigree) and realized (genomic) relationship between animals. The genetic variability of 190 milk metabolite intensities was analyzed from 1,295 cows held on 18 farms in Mecklenburg-Western Pomerania, Germany. Besides extensive pedigree information, genotypic data comprising 37,180 single nucleotide polymorphism markers were available. Goodness of fit and significance of genetic variance components based on likelihood ratio tests were investigated with a full model, including marker- and pedigree-based genetic effects. Broad-sense heritability varied from zero to 0.699, with a median of 0.125. Significant additive genetic variance was observed for highly heritable metabolites, but dominance variance was not significantly present. As some metabolites are particularly favorable for human nutrition, for instance, future research should address the identification of locus-specific genetic effects and investigate metabolites as the molecular basis of traditional milk performance test traits.

Genotypic and ecological effects on leafiness of red clover (Trifolium pratense L.)

The objective of this experiment was to: 1) examine the degree of influence of hereditary factors and conditions of growth (region of cultivation, season of growth and type of cultivation) on the phenotypic variance of leafiness in breeding populations of red clover; 2) quantify heritability and experimental variances in order to assess the opportunities for red clover breeding for improved leafiness. Five genotypes of red clover (four synthetic breeding populations and variety Sofia 52) were screened in the study. Among the factors studied as environmental variables, the season of growth had the strongest effect on the leafiness of red clover. In second vegetation of the life cycle of plants there was a significant additive genetic variance (hns 2 = 0.31) of the trait of leaf proportion in the fresh forage and the recurrent phenotypic selection for this criterion could be used in the breeding for leafiness in this species. It can be concluded from the results in this experiment that a higher degree of heritable genetic variation of leafiness must be searched for in connection with the variation of additional characteristics - thickness of stems, rates of formation and growth of stems, growth features related to regrowth (secondary growth) and age of sward (plants) and probably to persistence of genotypes.

Estimates for the heritability of growth of Mytilus edulis

13 half-sib families and 39 full-sib families of Mytilus edulis were established with the balance nest design in which each male mated with three females and the artificial fertilization technique.The shell height and length of each family were measured in 2,3,5,6 months.The heritability of the growth was estimated using the full-sib families theories.The results show that the maternal genetic variance component estimates are all significantly greater than those of paternal ones of each growth trait(P0.05).The female genetic variance components have significant maternal effects(P0.05),suggesting that the large non-additive genetic effects could not be differentiated from the available data,so the heritability of paternal half-sib families estimates in the narrow sense were precise unbiased estimator.The shell height heritability of paternal half-sib families estimates are 0.29,0.85,0.84,0.87 respectively.The shell length heritability are 0.27,0.87,0.86,0.85 respectively,during 2,3,5,6 months.There were significant additive genetic variance of the growth and different heritability of shell height and shell length,indicating that there is a great potential genetic improvement for the growth of M.edulis using the selective breeding.