Genetic variation in competition traits at different ages and time periods and correlations with traits at field tests of 4-year-old Swedish Warmblood horses

For many years, the breeding value estimation for Swedish riding horses has been based on results from Riding Horse Quality Tests (RHQTs) of 4-year-olds only. Traits tested are conformation, gaits and jumping ability. An integrated index including competition results is under development to both get as reliable proofs as possible and increases the credibility of the indexes among breeders, trainers and riders. The objectives of this study were to investigate the suitability of competition data for use in genetic evaluations of horses and to examine how well young horse performance agrees with performance later in life. Competition results in dressage and show jumping for almost 40 000 horses from the beginning of the 1960s until 2006 were available. For RHQT data of 14 000 horses judged between 1988 and 2007 were used. Genetic parameters were estimated for accumulated competition results defined for different age groups (4 to 6 years of age, 4 to 9 years of age and lifetime), and for different birth year groups. Genetic correlations were estimated between results at RHQT and competitions with a multi-trait animal model. Heritabilities were higher for show jumping than dressage and increased with increasing age of the horse and amount of information. For dressage, heritabilities increased from 0.11 for the youngest group to 0.16 for lifetime results. For show jumping corresponding values increased from 0.24 to 0.28. Genetic correlations between competition results for the different age groups were highly positive (0.84 to 1.00), as were those between jumping traits at RHQT and competition results in show jumping (0.87 to 0.89). For dressage-related traits as 4-year-old and dressage competition results the estimated genetic correlations were between 0.47 and 0.77. We suggest that lifetime results from competitions should be integrated into the genetic evaluation system. However, genetic parameters showed that traits had changed during the over 35-year period covered due to the development of the sport, which needs to be considered in future genetic evaluations.     

Effects of long-time series of data on genetic evaluations for performance of Swedish Warmblood riding horses

For Swedish Warmblood sport horses, breeding values (BVs) are predicted using a multiple-trait animal model with results from competitions and young horse performance tests. Data go back to the beginning of the 1970s, and earlier studies have indicated that some of the recorded traits have changed through the years. The objective of this study was to investigate the effects of including all performance data or excluding the older ones compared to a bivariate model (BM) considering performance traits in early and late periods as separate traits. The bivariate approach was assumed to give the most correct BVs for the actual breeding population. Competition results in dressage and show jumping for almost 40 000 horses until 2006 were available. For riding horse quality test (RHQT), data of 14 000 horses judged between 1973 and 2007 were used. Genetic correlations of 0.69 to 1.00 were estimated between traits recorded at different time periods (RHQT data) or different birth year groups (competition data). A cross-validation study and comparison of BVs using different sets of data showed that most accurate and similar results were obtained when BVs were predicted from either the BM or the univariate model including all data from the beginning of the recording. We recommend using all data and applying the univariate model to minimise the computational efforts for genetic evaluations and for provision of reliable BVs for as many horses as possible.     

Multiple-trait selection for radiographic health of the limbs, conformation and performance in Warmblood riding horses

Information on 26 434 German Warmblood horses born between 1992 and 2001 was used for multivariate genetic analyses of radiographic health, conformation and performance traits to compare different modes of single- and multiple-trait selection of sires. Results of standardized radiological examinations of 5155 Hanoverian Warmblood horses, conformation evaluations from studbook inspections of 20 603 mares, and performance evaluations from mare performance tests and auction horse inspections of 16 098 horses were used for multivariate genetic analyses. Genetic parameters were estimated with restricted maximum likelihood (REML), and relative breeding values (RBV) were predicted with best linear unbiased prediction (BLUP) in multivariate linear animal models for four radiographic health traits, three conformation traits and five performance traits. Heritability estimates for osseous fragments in fetlock joints (OFF), osseous fragments in hock joints (OFH), deforming arthropathy in hock joints (DAH) and distinct radiographic findings in the navicular bones (DNB) ranged between 0.15 and 0.35 after transformation to the liability scale. Front limb conformation, hind limb conformation, withers height, walk, trot, canter, rideability and free jumping showed heritabilities between 0.09 and 0.49 and additive genetic correlations with OFF, OFH, DAH and DNB ranging between -0.53 and +0.52. Selection of sires was based on RBV or combinations of RBV, with selection for individual traits or traits from one of the three considered trait groups being considered as single-trait selection, and selection for traits from more than one trait group being considered as multiple-trait selection. The selection modes were compared by means of the expected selection response after one generation, calculated as the relative change in the prevalences of the radiographic findings or the mean conformation or performance scores in the offspring of the selected sires when compared with the offspring of all sires. The prevalences of OFF, OFH, DAH and DNB decreased by 30% to 57% after single-trait selection and 14% to 29% after multiple-trait selection, while mean conformation and performance scores increased by up to 4%. The results indicated that it is possible to simultaneously improve the radiographic health of the limbs, limb conformation, quality of gaits and rideability. However, genetic progress in free jumping ability and style could only be achieved by single- or multiple-trait selection with focus on jumping performance.     

In situ wood quality assessment in Douglas-fir

The genetic control and phenotypic and genotypic correlations among wood density, modulus of elasticity, height, diameter, and volume were assessed using 967 trees representing 20 unrelated 32-year-old coastal Douglas-fir full-sib families growing on four (spaced and pruned vs. control) comparable test sites. Generally, no significant differences were observed between treatments, indicating their limited effect at assessment time. Family effect did not differ for the growth traits; however, significant differences were observed for wood density and both in situ methods (drilling resistance and acoustic velocity). Growth and wood quality attributes, individually, produced high and positive phenotypic and genetic correlations; however, high and negative correlations were observed between individual variables belonging to the two suites of attributes. Individual tree heritabilities were low for growth (0.04 to 0.08) and modest to high for wood quality attributes (0.14 to 0.68). The observed heritabilities and phenotypic and genotypic correlations imply modest to strong genetic control; however, they operated in opposing direction. The significant and consistent genetic correlations between the in situ methods and wood density and stiffness support their use as a non-destructive and economic assessment approach. The reliability of the in situ assessments was verified through cumulative pith-to-bark wood density assessment, resulting in inconsistent genetic and phenotypic correlations for early growth years. These latter findings imply that caution should be used in employing these in situ techniques as early screening tools in breeding programs.     

Pig peripheral blood mononuclear leucocyte subsets are heritable and genetically correlated with performance

Indicator traits used to select pigs for increased resistance to infection or improved health must be heritable and, preferably, be associated with improved performance. We estimated the heritability of a range of immune traits and their genetic and phenotypic correlations with growth performance. We measured immune traits on 589 pigs and performance on 1941 pigs from six farms, three of which were classified as 'high health status' (i.e. specific pathogen-free) and three were of lower health status. All pigs were apparently healthy. Immune traits were total white blood cells (WBC), and peripheral blood mononuclear leucocyte (PBML) subsets positive for CD4, CD8α, gamma delta (γδ) T cell receptor, CD11R1 (natural killer cell marker), B cell and monocyte markers at the start and the end of standard growth performance tests. At both time points, all immune traits were moderately to highly heritable except for CD8α+ cells. At end of test, heritability estimates (h2) (±s.e.) were 0.18 (±0.11) for total WBC count. For PBML subset proportions, the heritabilities were 0.52 (±0.14) for γδ TCR+ cells, 0.62 (±0.14) for CD4+ cells, 0.44 (±0.14) for CD11R1+ cells, 0.58 (±0.14) for B cells and 0.59 (±0.14) for monocytes. Farm health status affected the heritabilities for WBC, being substantially higher on lower health status farms, but did not have consistent effects on heritabilities for the PBML subsets. There were significant negative genetic correlations between numbers and proportions of various PBML subsets and performance, at both start and end of test. In particular, the proportion of PBML cells that were CD11R1+ cells, at end of test, was strongly correlated with daily gain (rg = -0.72; P < 0.01). There were also weaker but significant negative phenotypic correlations between PBML subsets measured at end of test and performance, for γδ+ T cells, CD8α+, CD11R1+ cells, B cells or monocytes. Phenotypic correlations with daily gain were generally lower at the start of test than at the end of test. These results show that most of the major pig PBML subsets are heritable, and that systemic levels of several of these PBML subsets are genetically negatively correlated with performance. This approach provides a basis for using immune trait markers when selecting boars that can produce higher-performing progeny.     

QUANTITATIVE GENETICS OF THE WING COLOR PATTERN IN THE BUCKEYE BUTTERFLY (PRECIS COENIA AND PRECIS EVARETE): EVIDENCE AGAINST THE CONSTANCY OF G

Models for the evolution of continuously varying traits use heritabilities, genetic correlations, and the G -matrix to quantify the genetic variation upon which selection acts. Given estimates of these parameters, it is possible to predict the long-term effects of selection, infer past selective forces responsible for observed differences between populations or species, and distinguish the effects of drift from selection. Application of these methods, however, requires the unproven assumption that the G -matrix remains constant from one generation to the next. This study examines the assumption of constancy for the wing pattern characteristics of two sibling species of butterflies, Precis coenia and P. evarete (Lepidoptera: Nymphalidae). Quantitative genetic parameters were estimated from parent-offspring regression. Two approaches were taken to test the null hypothesis of equality between species. First, pairwise tests between corresponding elements of G and between heritabilities and genetic correlations for the two species were constructed. Second, a modification of Bartlett's modified likelihood-ratio test was used to test for equality between the G -matrices. The matrix test failed to detect any between species differences. In contrast, pairwise comparision revealed significant differences. Thus, it appears that constancy cannot be assumed at the species level in quantitative genetic studies. In particular, the assumption of constancy was violated for the trait with the greatest difference in mean phenotype.     

Genetics of crossbred sow longevity

The aim of this study was to estimate genetic parameters for longevity from Swedish crossbred sows to investigate the possibilities of selecting for this trait. Data were collected from 16 commercial piglet-producing herds, on crossbred (Landrace × Yorkshire) sows farrowing in the period 1 January 2001 to 31 December 2004. The data set with records on 10 373 sows was split into two sets according to the breed of the sire, i.e. Landrace sires (LS) or Yorkshire sires (YS). Removal hazard during productive life (PL) was analysed with survival analysis, using a sire model. Stayability from first to second litter (STAY12), stayability from first to third litter (STAY13), length of productive life (LPL) and lifetime production (LTP) were analysed with linear models, using an animal model. Females after the worst sire had 1.7 times higher (progeny of LS) and 2.4 times higher (progeny of YS) risk of removal than females after the best sire. Heritability for PL was estimated at 0.06 (LS) and 0.12 (YS). The heritabilities for the linear longevity traits ranged from 0.03 to 0.08. Genetic correlations between the four linear longevity traits were all high and positive (0.6 to 1.0), as were the phenotypic correlations (0.5 to 0.8). The correlations (Spearman rank) between the sire's estimated breeding values for all the five longevity traits were all significant (P < 0.001) and moderate to strong in both data sets. Estimated breeding value (EBV) correlations between the five longevity traits and traits included in the present Swedish breeding evaluation (Quality Genetics (QG)) were significant in a few cases. Significant and favourable EBV correlations were found between age at first farrowing and both STAY12 and STAY13 (-0.20 and -0.31), as well as between litter weight at 3 weeks and LPL and LTP (0.13 to 0.20). Significant and unfavourable EBV correlations were found between age at 100 kg and STAY12 (0.32), as well as between the exterior conformation score from testing station and PL (-0.20). The level of the estimated heritabilities for longevity indicates that genetic improvement of sow longevity would be possible. However, overall, there was no strong indirect selection for sow longevity with the current Swedish breeding evaluation (QG).     

Genetic and phenotypic correlations among size-related traits, and heritability variation between body parts in Drosophila buzzatii

Recent studies have shown that body size is a heritable trait phenotypically correlated with several fitness components in wild populations of the cactophilic fly Drosophila buzzatii. To obtain further information on size-related variation, heritabilities as well as genetic and phenotypic correlations among size-related traits of several body parts (head, thorax and wings) were estimated. The study was carried out on an Argentinean natural population in which size-related selection was previously detected. The genetic parameters were estimated using offspring-parent regressions (105 families) in the laboratory G₂ generation of a sample of wild flies. The traits were also scored in Wild-Caught Flies (WCF). Laboratory-Reared Flies (LRF) were larger and less variable than WCF. Although heritability estimates were significant for all traits, heritabilities were higher for thorax-wing traits than for head traits. Phenotypic and genetic correlations were all positive. The highest genetic correlations were found between traits which are both functionally and developmentally related. Genetic and phenotypic correlations estimated in the lab show similar correlation patterns (r = 0.49; TP = 0.02, Mantel's test). However, phenotypic correlations were found to be typically larger in WCF than in LRF. The genetic correlation matrix estimated in the relatively homogeneous lab environment is not simply a constant multiplicative factor of the phenotypic correlation matrix estimated in WCF. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic parameters for direct and maternal effects on body weights of Draa goats

Genetic parameters and (co)variance components were estimated for weights at birth and at 30, 90 and 180 days of age for Draa goat maintained at Ouarzazate station over a period of 18 years (1988–2005). Records of 1498 kids, the progeny of 46 sires and 404 dams were used in the study. Analyses were carried out by restricted maximum likelihood. Six different animal models including or ignoring maternal genetic or permanent environmental effects were fitted for all traits. The Model 2 with only permanent environmental maternal effects seemed most suitable. Estimates of direct heritability from this model were 0.16 for birth weight and 0.07, 0.11 and 0.11 for weights at 30, 90 and 180 days, respectively. Maternal heritability estimates varied from 0.00 to 0.24 for all traits according to the model used (Models 4–6). Bivariate analysis by Model 2 was also used to estimate genetic correlations between traits. The estimates of genetic and phenotypic correlations among weights were positive and intermediate to high in value. Despite the low estimated heritabilities of body weight traits of Draa goat, there is a small genetic variability that may be exploited to improve growth performance.     

Simultaneous estimation of daily weight and feed intake curves for growing pigs by random regression

In this study, random regression models were used to estimate covariance functions between feed intake and BW in boars from the two breeds: the Norwegian Landrace and the Norwegian Duroc. In total, 1476 animals of the Norwegian Landrace breed and 1300 animals of the Norwegian Duroc breed had registrations on daily feed intake and growth from 54 to 180 days of age. Random regressions on the Legendre polynomials of age were used to describe genetic and permanent environmental curves in BW (up to the second order) and feed intake (up to the first order) for both the breeds. Heritabilities on BW increased over time for the Landrace (0.18 to 0.24), but were approximately constant for the Duroc (0.33 to 0.35). Average heritabilities for feed intake were approximately the same in both the breeds (0.09 to 0.11), and the estimates decreased over time, most pronounced in Duroc. On the basis of the current data, daily feed intake was seemingly controlled by the same genetic factors throughout the test period for Duroc; however, for Landrace, genetic correlations between test days decreased with increasing distance in time. For BW, the genetic correlations between test days were in general high, and did not go below 0.8 for any of the two breeds in this study. For both feed intake and BW, permanent environmental correlations between start and end of the test were reduced with increasing difference in days, most pronounced in Duroc. This study indicates that weight of the animal at the end of the test was more closely genetically correlated to feed intake of earlier periods compared with later periods of growth for both the breeds. This may be explained by the fact that BW is the cumulative growth of an individual, which is likely to be heavily affected by the feed intake during the most intense growth period.     

Biochemical polymorphism in relation to performance in horses

Summary Investigations on relationships between biochemical polymorphism and variation in quantitative traits are of interest from the perspectives of both theoretical quantitative genetics and practical animal breeding. This subject was studied by using racing performance records of more than 25,000 horses of the Swedish Trotter breed born in the period 1970–1979. For all horses data on six blood group and nine electrophoretic loci were available. Two different performance traits were investigated. A racing performance index value was calculated for all individuals which had started in at least five races. Horses which had not started at all or less than five times were pooled in an unstarted class and the proportion of started horses was analysed as an all-or-none trait. The relationships between the marker genes and these two performance traits were analysed statistically by using linear models. Analysis within sires revealed a very highly significant association between variation at the serum esterase locus (Es) and the proportion of started horses. In addition, four weakly significant associations were found. A striking feature of the highly significant association involving the esterase locus was that the effect of different alleles showed a good fit to an additive genetic model as the value of each heterozygous type was intermediate to the two corresponding homozygotes. In addition to the association tests, the possibility of genetic linkage between marker genes and genes affecting performance was tested as well as the influence on performance of heterozygosity at marker loci. No significant relationships were revealed in these latter tests.     

Host plant effects on the genetic variation and correlations in the individual performance of the Gypsy Moth

1. Quantitative genetic analysis of variation in host-use ability was performed in an extremely polyphagous species – the Gypsy Moth. Various life-history traits were investigated by applying a split-family two-environment experimental design, where 30 full-sibling families were reared on oak and Locust Tree leaves.
2. Feeding on Locust Tree leaves decreased preadult viability, prolonged development time, decreased pupal mass both in males and females, and decreased reproductive effort in females.
3. The majority of broad-sense heritabilities did not change across host plants.
4. Significant expression of genetic variation in diet breadth was observed for development time and pupal mass both in males and females, but not for female reproductive effort traits. The heritabilities of plasticities were, on average, lower than heritabilities of the traits themselves.
5. The majority of genetic correlations between the host plants were significantly positive. The only trade-off was found between reciprocal value of reproductive index and the average mass of a fertilized egg within oak. This means that selection for the decrease in relative reproductive investment (under starvation during gradation) will be followed by laying larger eggs. Given that the Gypsy Moth has a cyclic population dynamics, this negative genetic correlation could have a role in maintaining genetic variability in this species.     

Genetic variation of ecophysiological traits in two gynodioecious species of Schiedea (Caryophyllaceae)

Evolution of dimorphic breeding systems may involve changes in ecophysiological traits as well as floral morphology because of greater resource demands on females. Differences between related species suggest that ecophysiological traits should be heritable, and species with higher female frequencies should show greater sexual differentiation. We used modified partial diallel crossing designs to estimate narrow-sense heritabilities and genetic correlations of sex-specific ecophysiological and morphological traits in closely related gynodioecious Schiedea salicaria (13% females) and Schiedea adamantis (39% females). In S. salicaria, hermaphrodites and females differed in photosynthetic rate and specific leaf area (SLA). Narrow-sense heritabilities were significant for stomatal conductance, SLA and inflorescence number in hermaphrodites, and for SLA and inflorescence number in females. Schiedea adamantis had no sexual dimorphism in measured traits; stomatal conductance, stem number and inflorescence number were heritable in females, and stem number was heritable in hermaphrodites. In both species, significant genetic correlations of traits between sexes were rare, indicating that traits can evolve independently in response to sex-differential selection. Significant genetic correlations were detected between certain traits within sexes of both species. Low heritability of some ecophysiological traits may reflect low additive genetic variability or high phenotypic plasticity in these traits.     

Genetic analysis of kinematic traits at the trot in Lusitano horse subpopulations with different types of training

The possibility of using quantitative kinematic traits as indirect selection criteria for sport performance could be beneficial to perform an early genetic evaluation of the animals. The genetic parameters for objectively measured kinematic traits under field conditions have been estimated for the first time, in order to potentially use these traits as indicators of gait quality in future selection of the Lusitano breed. The repeatability within three different types of training (dressage, bullfighting and untrained) was also discussed. A total of 176 males (4 to 14 years old) were recorded at trot in hand using a 3D videographic system. The speed and 10 kinematic traits were studied (one temporal, two linear and seven angular variables). The genetic parameters of the kinematic variables were estimated using VCE software. The heritability estimates were moderate to high (0.18 to 0.53). The stride length and the forelimb angular variables presented the highest heritabilities (0.49 to 0.53), whereas the hindlimb angular variables revealed the lowest values (0.18 to 0.40). More than half of the genetic correlations were moderately to highly positive (mostly 0.20 to 0.70; up to 0.88 between hindlimb traits). The dressage and bullfighting groups presented the highest repeatabilities (over 0.6) in the majority of the traits, maybe because of the acquired gait regularity expected in animals subjected to specific training, and suggesting a greater influence of the individuals over the kinematic traits studied in these two subpopulations than in the untrained subpopulation. The longer swing phase duration and the larger range of motion of the elbow, hock and pelvis joints observed in the dressage group may indicate a better gait quality of this group, according to FEI (International Equestrian Federation) standards. The bullfighting and untrained groups were more similar to each other in terms of kinematic traits. Selection of young horses for characteristics such as stride length and the hindlimbs traits can apparently contribute to further genetic improvement of the performance of Lusitano breed.     

Heritability of hemostasis phenotypes and their correlation with type 2 diabetes status in Mexican Americans

Hypercoagulation often occurs in type 2 diabetes, suggesting pleiotropy of the genes that influence disease liability and hemostasis-related phenotypes. To better understand the relationship between hemostasis and diabetes, we first used maximum-likelihood methods to estimate the relative contribution of additive genetic, measured environmental, and shared household effects to the normal variance of 16 hemostasis-related traits in 813 individuals participating in the San Antonio Family Heart Study. We estimated moderate to high heritabilities (0.20-0.60) for each phenotype. Von Willebrand factor (VWF), thrombin activatable fibrinolysis inhibitor, activated protein C (APC) ratio, factor V, and prothrombin time had heritabilities greater than 0.50. The correlation between type 2 diabetes status and the hemostasis-related traits was then partitioned into genetic and environmental components using bivariate variance-components methods. Significant (p < or = 0.05) positive genetic correlations (0.37-0.51) occurred with factors II and VIII, VWF, total protein S (tPS), and tissue factor pathway inhibitor. Significant negative genetic correlations were estimated for activated partial thromboplastin time (-0.49) and APC ratio (-0.38). By contrast, significant environmental correlations occurred only with factor II (-0.40) and tPS (-0.31). Our results suggest that genes are important contributors to the normal variation in hemostasis-related traits and that genes influencing hemostasis-related traits pleiotropically influence diabetes risk.     

Genetic and environmental analysis of dystocia and stillbirths in draft horses

Genetic parameters and environmental factors were estimated for foaling ease (FE) and stillbirths (SBs) in four breeds of draft horses based on 11 229, 38 877, 35 764 and 13 274 FE and SB scores recorded between 1998 and 2010 for Ardennais (A), Breton (B), Comtois (C) and Percheron (P), respectively. Incidences for the three FE categories were: easy or without help 91.0% (A) to 95.4% (B), difficult 3.4% (B) to 7.1% (A) and intervention of a veterinarian 1.1% (B) to 1.9% (A). The frequency of SB ranged between 5.4% (B) and 9.4% (A). A multiple-trait threshold animal model was used that included the effects of sex of foal, region, month, year of foaling, combined maternal age and parity, direct genetic, maternal genetic and permanent environments. Estimates were obtained using Markov Chain Monte Carlo Gibbs sampling. The most unfavourable effect was first parity, which decreased the probability of easy foaling to 78.6% for A and 88.3% for B. Interaction with age showed that the risk for first foaling for mares aged 3 years was higher than at 4 or 5 to 9 years. This was also observed for SB with an increased probability of SB at first foaling of 17.9% (A) or 9.6% (B). The most unfavourable month was found to be the most frequent month for foaling (April) and not the most demanding months weather-wise (winter). For FE, direct heritabilities were A 0.27 (0.06), B 0.14 (0.03), C 0.18 (0.03) and P 0.18 (0.04), and maternal heritabilities were A 0.25 (0.06), B 0.19 (0.04), C 0.12 (0.03) and P 0.21 (0.06). Genetic correlations between direct and maternal genetic effects were A −0.29 (0.14), B −0.39 (0.12), C −0.09 (0.14) and P −0.54 (0.17). For SB, direct heritabilities were A 0.52 (0.09), B 0.42 (0.04), C 0.28 (0.04) and P 0.39 (0.05), and maternal heritabilities were A 0.25 (0.05), B 0.10 (0.02), C 0.07 (0.02) and P 0.14 (0.02). Genetic correlations between direct and maternal genetic effects were A −0.85 (0.06), B −0.63 (0.06), C −0.64 (0.11) and P −0.69 (0.06). Direct genetic correlations between FE and SB traits were A 0.60 (0.10), B 0.58 (0.10), C 0.36 (0.10) and P 0.29 (0.15). Maternal genetic correlations between FE and SB traits were A 0.67 (0.10), B 0.47 (0.13), C 0.28 (0.15) and P 0.39 (0.15). These estimates are posterior means of the Gibbs samples and are within the upper limits of comparable results reported in cattle.     

A quantitative genetic test of adaptive decoupling across metamorphosis for locomotor and life-history traits in the pacific tree frog, Hyla regilla

Metamorphosis is assumed to be beneficial because it can break developmental links between traits in the different phases of a complex life-cycle and thereby allow larval and adult phases to adapt independently. I tested the prediction that correlations between the larval and adult phases are smaller than within stages. I estimated phenotypic and additive genetic variances and correlations for tadpole swimming speed, frog jump distance, body size, and larval period in a single population of the Pacific tree frog, Hyla regilla. These traits are known or reasonably assumed to be important for survival in this and other anuran species from temporary ponds. Only the three size variables were affected by sire identity. Heritabilities for locomotor performance, larval period, and size-independent performance were low (0.00-0.23) and not significant. Body size measurements showed somewhat higher and statistically significant heritabilities (0.24-0.34). Most traits were phenotypically correlated. On average, phenotypic correlations were larger between phases than within phases (0.41 vs. 0.28). Genetic correlations involving body-size traits were positive and large, and average within- and between-phase genetic correlation coefficients were identical (0.81). These results do not support the adaptive decoupling hypothesis, and they indicate that a paucity of additive genetic variation is a likely constraint on the evolution of traits measured for this population.     

Positive genetic correlations among major life-history traits related to ecological success in the aphid Myzus persicae

Life-history theory is based on the assumption that evolution is constrained by trade-offs among different traits that contribute to fitness. Such trade-offs should be evident from negative genetic correlations among major life-history traits. However, this expectation is not always met. Here I report the results of a life-table experiment designed to measure the broad-sense heritabilities of life-history traits and their genetic correlations in 19 different clones of the aphid Myzus persicae from Victoria, Australia. Most individual traits, as well as fitness calculated as the finite rate of increase from the life table, exhibited highly significant heritabilities. The pattern of genetic correlations revealed absolutely no evidence for life-history trade-offs. Rather, life histories were arranged along an axis from better to worse. Clones with shorter development times tended to have larger body sizes, higher fecundities, and larger offspring. The fitness of clones estimated from the life table in the laboratory tended to be positively associated with their abundance in the field. Fitness also increased significantly with heterozygosity at the seven microsatellite loci that were used to distinguish clones and estimate their frequencies in the field. I discuss these findings in light of a recent proposition that positive genetic correlations among life-history traits for which trade-offs are expected can be explained by genetic variation for resource acquisition ability that is maintained in populations by a cost of acquisition, and I propose ways to test for such a cost in M. persicae.     

Genetic basis of variation in morphological and life-history traits of a wild population of pink salmon

Understanding the genetic basis of phenotypic variation is essential for predicting the direction and rate of phenotypic evolution. We estimated heritabilities and genetic correlations of morphological (fork length, pectoral and pelvic fin ray counts, and gill arch raker counts) and life-history (egg number and individual egg weight) traits of pink salmon (Oncorhynchus gorbuscha) from Likes Creek, Alaska, in order to characterize the genetic basis of phenotypic variation in this species. Families were created from wild-caught adults, raised to the fry stage in the lab, released into the wild, and caught as returning adults and assigned to families using microsatellite loci and a growth hormone locus. Morphological traits were all moderately to highly heritable, but egg number and egg weight were not heritable, suggesting that past selection has eliminated additive genetic variation in egg number and egg weight or that there is high environmental variance in these traits. Genetic correlations were similar for nonadjacent morphological traits and adjacent traits. Genetic correlations predicted phenotypic correlations fairly accurately, but some pairs of traits with low genetic correlations had high phenotypic correlations, and vice versa, emphasizing the need to use caution when using phenotypic correlations as indices of genetic correlations. This is one of only a handful of studies to estimate heritabilities and genetic correlations for a wild population.     

Laboratory Estimates of Heritabilities and Genetic Correlations in Nature

A lower bound on heritability in a natural environment can be determined from the regression of offspring raised in the laboratory on parents raised in nature. An estimate of additive genetic variance in the laboratory is also required. The estimated lower bounds on heritabilities can sometimes be used to demonstrate a significant genetic correlation between two traits in nature, if their genetic and phenotypic correlations in nature have the same sign, and if sample sizes are large, and heritabilities and phenotypic and genetic correlations are high.