Significant Additive Genetic Correlations Research Articles

Genetic and Environmental Factors Underlying Parallel Changes in Body Mass Index and Alcohol Consumption: A 36-Year Longitudinal Study of Adult Twins

Introduction: While the genetic and environmental underpinnings of body weight and alcohol use are fairly well-known, determinants of simultaneous changes in these traits are still poorly known. We sought to quantify the environmental and genetic components underlying parallel changes in weight and alcohol consumption and to investigate potential covariation between them. Methods: The analysis comprised 4,461 adult participants (58% women) from the Finnish Twin Cohort with four measures of alcohol consumption and body mass index (BMI) over a 36-year follow-up. Trajectories of each trait were described by growth factors, defined as intercepts (i.e., baseline) and slopes (i.e., change over follow-up), using latent growth curve modeling. Growth values were used for male (190 monozygotic pairs, 293 dizygotic pairs) and female (316 monozygotic pairs, 487 dizygotic pairs) same-sex complete twin pairs in multivariate twin modeling. The variances and covariances of growth factors were then decomposed into genetic and environmental components. Results: The baseline heritabilities were similar in men (BMI: h² = 79% [95% confidence interval: 74, 83]; alcohol consumption: h² = 49% [32, 67]) and women (h² = 77% [73, 81]; h² = 45% [29, 61]). Heritabilities of BMI change were similar in men (h² = 52% [42, 61]) and women (h² = 57% [50, 63]), but the heritability of change in alcohol consumption was significantly higher (p = 0.03) in men (h² = 45% [34, 54]) than in women (h² = 31% [22, 38]). Significant additive genetic correlations between BMI at baseline and change in alcohol consumption were observed in both men (rA = −0.17 [−0.29, −0.04]) and women (rA = −0.18 [−0.31, −0.06]). Non-shared environmental factors affecting changes in alcohol consumption and BMI were correlated in men (rE = 0.18 [0.06, 0.30]). Among women, non-shared environmental factors affecting baseline alcohol consumption and the change in BMI were inversely correlated (rE = −0.11 [−0.20, −0.01]). Conclusions: Based on genetic correlations, genetic variation underlying BMI may affect changes in alcohol consumption. Independent of genetic effects, change in BMI correlates with change in alcohol consumption in men, suggesting direct effects between them.

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.

Genetic variance of metabolomic features and their relationship with body weight and body weight gain in Holstein cattle1.

In recent years, metabolomics has been used to clarify the biology underlying biological samples. In the field of animal breeding, investigating the magnitude of genetic control on the metabolomic profiles of animals and their relationships with quantitative traits adds valuable information to animal improvement schemes. In this study, we analyzed metabolomic features (MFs) extracted from the metabolomic profiles of 843 male Holstein calves. The metabolomic profiles were obtained using nuclear magnetic resonance (NMR) spectroscopy. We investigated 2 alternative methods to control for peak shifts in the NMR spectra, binning and aligning, to determine which approach was the most efficient for assessing genetic variance. Series of univariate analyses were implemented to elucidate the heritability of each MF. Furthermore, records on BW and ADG from 154 to 294 d of age (ADG154-294), 294 to 336 d of age (ADG294-336), and 154 to 336 d of age (ADG154-336) were used in a series of bivariate analyses to establish the genetic and phenotypic correlations with MFs. Bivariate analyses were only performed for MFs that had a heritability significantly different from zero. The heritabilities obtained in the univariate analyses for the MFs in the binned data set were low (<0.2). In contrast, in the aligned data set, we obtained moderate heritability (0.2 to 0.5) for 3.5% of MFs and high heritability (more than 0.5) for 1% of MFs. The bivariate analyses showed that ~12%, ~3%, ~9%, and ~9% of MFs had significant additive genetic correlations with BW, ADG154-294, ADG294-336, and ADG154-336, respectively. In all of the bivariate analyses, the percentage of significant additive genetic correlations was higher than the percentage of significant phenotypic correlations of the corresponding trait. Our results provided insights into the influence of the underlying genetic mechanisms on MFs. Further investigations in this field are needed for better understanding of the genetic relationship among the MFs and quantitative traits.

Shared Genetic Factors in the Co-Occurrence of Depression and Fatigue.

Depression and fatigue have previously been suggested to share an underlying genetic contribution. The present study aims to investigate and characterize the familiality and genetic relationship between depression and fatigue. The familiality of depression and fatigue was assessed by calculating relative risks, measured by the prevalence ratio, within 643 monozygotic (MZ) and 577 dizygotic (DZ) twin pairs. Bivariate twin modeling was utilized to assess the magnitude of shared heritability between depression and fatigue. Finally, the relationship between depression and fatigue was investigated using the co-twin control method, to determine whether the association is explained by causal or non-causal models. We observed an increased risk of fatigue in co-twins of probands with depression and increased risk of depression in co-twins of probands with fatigue. Higher risks were observed in MZ compared to DZ twin pairs, and bivariate heritability analyses indicated significant genetic components for depression and fatigue, with heritability estimates of 48% and 41%, respectively. Importantly, a significant additive genetic correlation of 0.71 [95% CI = 0.51-0.92) and bivariate heritability of 21% [95% CI = 10-35%] was observed between depression and fatigue. Furthermore, results from the co-twin control method indicate a non-causal genetic relationship that likely explains the association between depression and fatigue. Notably, the contribution of shared genetic factors remained significant, independent of the overlapping symptoms, indicating that the relationship between co-occurring depression and fatigue is primarily due to shared genetic factors rather than overlapping symptomatology.

Shared Genetic Factors Underlie Migraine and Depression.

Migraine frequently co-occurs with depression. Using a large sample of Australian twin pairs, we aimed to characterize the extent to which shared genetic factors underlie these two disorders. Migraine was classified using three diagnostic measures, including self-reported migraine, the ID migraine™ screening tool, or migraine without aura (MO) and migraine with aura (MA) based on International Headache Society (IHS) diagnostic criteria. Major depressive disorder (MDD) and minor depressive disorder (MiDD) were classified using the Diagnostic and Statistical Manual of Mental Disorders (DSM) criteria. Univariate and bivariate twin models, with and without sex-limitation, were constructed to estimate the univariate and bivariate variance components and genetic correlation for migraine and depression. The univariate heritability of broad migraine (self-reported, ID migraine, or IHS MO/MA) and broad depression (MiDD or MDD) was estimated at 56% (95% confidence interval [CI]: 53-60%) and 42% (95% CI: 37-46%), respectively. A significant additive genetic correlation (r G = 0.36, 95% CI: 0.29-0.43) and bivariate heritability (h 2 = 5.5%, 95% CI: 3.6-7.8%) was observed between broad migraine and depression using the bivariate Cholesky model. Notably, both the bivariate h 2 (13.3%, 95% CI: 7.0-24.5%) and r G (0.51, 95% CI: 0.37-0.69) estimates significantly increased when analyzing the more narrow clinically accepted diagnoses of IHS MO/MA and MDD. Our results indicate that for both broad and narrow definitions, the observed comorbidity between migraine and depression can be explained almost entirely by shared underlying genetically determined disease mechanisms.

Genetic factors involved in risk for methamphetamine intake and sensitization.

Lines of mice were created by selective breeding for the purpose of identifying genetic mechanisms that influence the magnitude of the selected trait and to explore genetic correlations for additional traits thought to be influenced by shared mechanisms. DNA samples from high and low methamphetamine-drinking (MADR) and high and low methamphetamine-sensitization lines were used for quantitative trait locus (QTL) mapping. Significant additive genetic correlations between the two traits indicated a common genetic influence, and a QTL on chromosome X was detected for both traits, suggesting one source of this commonality. For MADR mice, a QTL on chromosome 10 accounted for more than 50 % of the genetic variance in that trait. Microarray gene expression analyses were performed for three brain regions for methamphetamine-naïve MADR line mice: nucleus accumbens, prefrontal cortex, and ventral midbrain. Many of the genes that were differentially expressed between the high and low MADR lines were shared in common across the three brain regions. A gene network highly enriched in transcription factor genes was identified as being relevant to genetically determined differences in methamphetamine intake. When the mu opioid receptor gene (Oprm1), located on chromosome 10 in the QTL region, was added to this top-ranked transcription factor network, it became a hub in the network. These data are consistent with previously published findings of opioid response and intake differences between the MADR lines and suggest that Oprm1, or a gene that impacts activity of the opioid system, plays a role in genetically determined differences in methamphetamine intake.

Assessing genetic variation to improve stem straightness in Eucalyptus globulus

Stem straightness is an important trait for growers and processors of Eucalyptus globulus logs for solid-wood products. The aims of the study were to determine the extent of genetic variation in stem deviation from straightness in E. globulus and assess the utility of a six-point subjective scoring method as a selection criterion for stem straightness. Two E. globulus progeny trials, grown under solid-wood product regimes, were studied. At age 9 years (post-thinning), stem straightness was measured using both image analysis and a six-point subjective scale. Diameter at breast height (DBH; 1.3 m) was measured at both age 5 (pre-thinning) and age 9 years. Significant additive genetic variation was observed. Strong, positive and significant additive genetic correlations were observed between the stem straightness assessment methods and between DBH at ages 5 and 9 years. Significant positive genetic correlations were shown between subjectively scored stem straightness and DBH at both ages 5 and 9 years. The six-point subjective scoring method is a cost-effective selection criterion for stem straightness in E. globulus. The image measurement technique may be applied where objective estimates of stem straightness are required, for training purposes and to verify subjective scores.

Genetic variation in traits affecting sawn timber recovery in plantation-grown Eucalyptus nitens

& Introduction There is increasing interest in managing Eucalyptus nitens plantations for sawn timber production. & Aims This study aimed to determine the potential for genetic improvement of traits affecting green sawn board recovery in plantation-grown E. nitens. & Methods The study was undertaken on an E. nitens progeny trial. All trees were measured for diameter at breast height (DBH) and stem straightness, and 560 trees were selected for timber processing. Assessment was made of survival, log and green sawn board volume, log taper, and both upper and lower log end splitting. Genetic variation in and between these traits was estimated. & Results Geneticdifferencesamongracesweresignificantfor DBH at years 9 and 14, stem straightness, log taper and green sawn board volume. Within-race, narrow-sense heritabilities were significant for DBH, stem straightness, log volume, and both upper and lower log end splitting. Positive and significant additive genetic correlations were observed between DBH at all ages and survival, stem straightness and log volume. Significant adverse genetic correlations were shown between upper log end splitting and DBH at years 9 and 14. & Conclusion These findings showed that harvest-age stem straightness and log volume objective traits in E. nitens are amenable to genetic improvement and that selection for early-age DBH in breeding programmes should improve harvest-age survival, stem diameter and straightness, as well as log and green sawn board volume. However, these improvements are likely to be countered to some extent by increased end splitting of logs from larger trees.

Common genetic influences underlie comorbidity of migraine and endometriosis

We examined the co-occurrence of migraine and endometriosis within the largest known collection of families containing multiple women with surgically confirmed endometriosis and in an independent sample of 815 monozygotic and 457 dizygotic female twin pairs. Within the endometriosis families, a significantly increased risk of migrainous headache was observed in women with endometriosis compared to women without endometriosis (odds ratio [OR] 1.57, 95% confidence interval [CI]: 1.12-2.21, P=0.009). Bivariate heritability analyses indicated no evidence for common environmental factors influencing either migraine or endometriosis but significant genetic components for both traits, with heritability estimates of 69 and 49%, respectively. Importantly, a significant additive genetic correlation (r(G) = 0.27, 95% CI: 0.06-0.47) and bivariate heritability (h(2)=0.17, 95% CI: 0.08-0.27) was observed between migraine and endometriosis. Controlling for the personality trait neuroticism made little impact on this association. These results confirm the previously reported comorbidity between migraine and endometriosis and indicate common genetic influences completely explain their co-occurrence within individuals. Given pharmacological treatments for endometriosis typically target hormonal pathways and a number of findings provide support for a relationship between hormonal variations and migraine, hormone-related genes and pathways are highly plausible candidates for both migraine and endometriosis. Therefore, taking into account the status of both migraine and endometriosis may provide a novel opportunity to identify the genes underlying them. Finally, we propose that the analysis of such genetically correlated comorbid traits can increase power to detect genetic risk loci through the use of more specific, homogenous and heritable phenotypes.

Heritable Variation in the Sex Pheromone of the Almond Moth, Cadra cautella

The sex pheromone of the female almond moth, Cadra cautella, constitutes a highly variable signal. Age and period of the L/D cycle had significant effects on the variation in titers of (Z,E)-9,12-tetradecadienyl acetate (Z9,E12-14:Ac) and (Z)-9-tetradecenyl acetate (Z9-14:Ac) and the ratio of Z9,E12-14:Ac to Z9-14:Ac. Across age classes, minimum and maximum mean titers (ng +/- SE) of Z9,E12-14:Ac and Z9-14:Ac ranged from 8.7 +/- 0.46 to 21 +/- 1.0 and from 2.0 +/- 0.14 to 2.9 +/- 0.15, respectively; the mean ratio of Z9,E12-14:Ac to Z9-14:Ac ranged from 5.2 +/- 0.21 to 11 +/- 0.40. The titers of Z9,E12-14:Ac and Z9-14:Ac and the ratio of Z9,E12-14:Ac to Z9-14:Ac were highest at the onset of the scotophase and lowest at the onset of the photophase. Similarly, the titer of Z9,E12-14:Ac and the ratio of Z9,E12-14:Ac to Z9-14:Ac were highest in females sampled 1 d postemergence and declined over all age classes. The titer of Z9-14:Ac increased from day 1 to day 2, and then declined to levels equivalent to day 1. Analysis of pupal and adult mass demonstrated a positive correlation (r = 0.874, P < 0.001); however, the titer of neither Z9,E12-14:Ac or Z9-14:Ac nor the ratio of Z9,E12-14:Ac to Z9-14:Ac were significantly correlated with pupal mass. Age-related variations in pheromone titer and ratios were heritable. The narrow-sense heritability of the observed variation in 1-d-old females, 1 hr into the scotophase is 1.2 +/- 0.32, 0.75 +/- 0.24, and 0.46 +/- 0.17 for the titer of Z9,E12-14:Ac and Z9-14:Ac and the ratio of Z9,E12-14:Ac to Z9-14:Ac, respectively. A significant additive genetic correlation was observed between that of Z9,E12-14:Ac and Z9-14:Ac, but not between that of either Z9,E12-14:Ac or Z9-14:Ac and the ratio of Z9,E12-14:Ac to Z9-14:Ac. The results of the genetic analyses suggest that the traits of titer of Z9,E12-14:Ac and Z9-14:Ac have a greater potential to respond to selection than the trait of ratio of Z9,E12-14:Ac to Z9-14:Ac.

Genetic and Phenotypic Correlations Between Feather Pecking Behavior, Stress Response, Immune Response, and Egg Quality Traits in Laying Hens

The objective of the current study was to estimate genetic and phenotypic correlations among feather pecking (FP) behavior and stress response, immune response, and egg quality parameters. These traits have been measured in an F2 cross, coming from a cross between a high and a low FP line of laying hens. Heritabilities (h2) of stress response (32 wk), primary immune response to keyhole limpet hemocyanin (KLH) (36 wk) and Mycobacterium butyricum (39 wk), and egg quality parameters (35, 44, and 50 wk of age) were calculated. The h2 was 0.05 ± 0.05 (SE) for stress response, 0.15 ± 0.07 for antibody response to KLH, and 0.08 ± 0.06 for antibody response to M. butyricum. The h2 for egg quality traits were in the range of 0.12 to 0.30. Significant phenotypic correlations were found between gentle FP in adult hens and stress response, egg weight at 44 and 50 wk, and egg deformation at 50 wk. Significant additive genetic correlations were found between severe FP in adult hens and antibody response to KLH (0.79 ± 0.35), and between ground pecking in adult hens and egg deformation at 50 wk (0.63 ± 0.26), and between ground pecking and eggshell strength at 35, 44, and 50 wk of age (-0.86 ± 0.29, -0.81 ± 0.20, -0.76 ± 0.24, respectively).

Herencia de la tolerancia al calor de la habichuela de origen Andino

Los cultivares de habichuela (Phaseolus vulgaris L.) para el Caribe necesitan un mayor nivel de tolerancia al calor. El objetivo principal de esta investigación fue estudiar la herencia de tolerancia al calor de una población Andina. Se realizaron experimentos de campo durante un período de dos años para evaluar el comportamiento de 81 líneas del cruzamiento 'DOR 303/Indeterminate Jamaica Red'. Durante el verano, PR9919-116 y PR9919-168 produjeron rendimientos de semilla significativamente mayor que 'Indeterminate Jamaica Red', el progenitor con tolerancia al calor. Las heridabilidades en el sentido estrecho para rendimiento de semilla por planta, número de vainas por planta y número de semilla por vaina fue de baja a intermedia en magnitud, con un rango de 0.16 hasta 0.62. Estos valores de heridabilidad sugieren que la evaluación para la tolerancia al calor debe realizarse utilizando líneas avanzadas en ensayos con repeticiones. Las correlaciones genéticas aditivas entre el rendimiento de semilla por planta y el número de vainas por planta y el peso de 100 semillas fueron positivas y significativas. Además, las correlaciones entre el peso de 100 semillas y el número de vainas por planta fueron significativas y positivas. Debido a las altas correlaciones genéticas aditivas entre el peso de 100 semillas y el rendimiento de semilla por planta y las altas heridabilidades en el sentido estrecho para el peso de 100 semillas, la selección indirecta para mayor tamaño de semilla podría ser utilizada para seleccionar para tolerancia al calor. La línea PR9920-13 produjo el mayor rendimiento promedio en el invierno y fue la tercera en rendimiento promedio en las siembras del verano. Sin embargo, el comportamiento de las otras líneas en los ensayos sugiere que la selección para rendimiento de semilla en el invierno no garantiza la identificación de líneas de habichuela con alto rendimiento en el verano. La selección para adaptación a ambientes de alta temperatura requiere la evaluación de líneas de habichuela durante el verano. Los promedios de porcentaje de viabilidad de polen de las líneas tolerantes al calor fueron significativamente mayores que los promedios de las líneas sensitivas a alta temperatura. Solamente una línea, PR9920-171 combinó la tolerancia de calor de Indeterminate Jamaica Red con la resistencia al mosaico dorado amarillo de DOR 303.

GENETIC RELATIONSHIPS BETWEEN GRAIN YIELD AND YIELD COMPONENTS IN A SYNTHETIC MAIZE POPULATION AND THEIR IMPLICATIONS IN SELECTION

The synthetic maize population 316PO2 was subjected to genetic correlation analyses between grain yield, yield components and morphological traits. The purpose was to enable estimates to be made of the advantage of using selection indices compared with selection based on grain yield only, and if that advantage was present, to choose enough simple selection indices for practical use. Selection indices were constructed out of four traits highly significantly correlated with grain yield, in addition to yield itself. Grain yield exhibited a highly significant additive genetic correlation with ear diameter (ra=0.588**), kernels row-1(ra=0.643**), ears plant-1(ra=0.871**) and ear height (ra=0.427**). The most efficient index was Index No. 14 (R.E.I12345= 108.83%), which included all four traits and grain yield. Index No. 3, one of the simplest forms of index, including only ears plant-1 and grain yield, showed slightly less relative efficiency (R.E.I35=107.24%) than Index No. 14. Using this simple form of index with two characters (Index No. 3) could improve the efficiency of selection for grain yield. The estimated advantage from its use is 179.6 kg/selection cycle for grain yield over selection based only on grain yield.

Genetic parameters for growth traits in Suffolk and Polypay sheep

Genetic parameters for growth traits in Suffolk and Polypay sheep were estimated using U.S. National Sheep Improvement Program data. Records on 12,814 Suffolks from 65 flocks and 9,028 Polypays from 39 flocks were used. Heritability ( h 2) estimates for weaning weights (WW) at 30, 60, 90, and 120 d in Suffolks were 0.16, 0.14, 0.21, and 0.55, respectively; h 2 for WW at 30, 60, and 90 d in Polypay were 0.07, 0.08, and 0.07. For postweaning gain (PWG), h 2 for models with and without maternal effects were 0.14 and 0.21, respectively, in Suffolk and 0.13 and 0.22, respectively, in Polypay. Maternal effects (additive+permanent environmental) accounted for 16 to 23% of variation in WW through 90 d of age but for 6% or less of the variation in 120-d WW and PWG. Correlations between WW at different ages were uniformly high. Postweaning gain had significant additive genetic correlations with WW at 30 d (1.00) and 60 d (0.69) in Suffolks but was not significantly correlated with 60 d WW in Polypay (0.41). Residual correlations between WW and PWG were small and not significant. Evidence for a modest antagonistic relationship between additive direct and maternal effects on WW was observed in both breeds.

Genetic relationship between measures of HDL phenotypes and insulin concentrations.

We used data from the San Antonio Family Heart Study to determine the HDL correlates of the insulin resistance syndrome (IRS), as reflected by insulin concentrations in nondiabetic subjects. We measured insulin concentrations both in the fasting state and 2 hours after a glucose challenge (2-hour insulin) and we assessed seven aspects of HDL phenotype, including size and concentration of both lipid and protein components. Measurements were obtained from 1202 nondiabetic members of 42 families. Initial quantitative genetic analyses revealed that a substantial portion of phenotypic variation in the nine variables was due to genes (heritabilities, h2, ranged from 0.32 to 0.47). We then conducted a series of bivariate genetic analyses, which indicated that there were significant additive genetic correlations (ie, pleiotropy) between the two measures of insulin and five of seven HDL measures tested, including concentrations of HDL cholesterol (fasting insulin only) and triglyceride, and HDL size distributions of apoAI, apoAII, and cholesterol; concentrations of apoAI and apoAII were not genetically related to either insulin measure. Increased insulin levels were associated with relatively smaller HDL phenotypes, and considering a similar association with small, dense LDLs, this finding suggests a common effect of insulin resistance on particle size distributions for these lipoproteins. Thus, these results suggest the existence of genes that pleiotropically influence variation in both HDLs and insulin levels and therefore contribute to the clustering of proatherogenic traits in the IRS.

Quantitative genetics of juvenile hormone esterase, juvenile hormone binding and general esterase activity in the cricket Gryllus assimilis

Heritabilities and genetic, environmental and phenotypic correlations were estimated for two endocrine traits (juvenile hormone esterase (JHE) and juvenile hormone binding (JHB) activity) and one non-endocrine trait (general esterase activity (GE)) in the cricket Gryllus assimilis. Genetic parameters were estimated in three stages of the last stadium as well as in the entire last stadium. Significant additive genetic heritabilities were observed for each trait for activities pooled over all developmental stages. For JHE and JHB, significant heritabilities were also observed within most developmental stages. This indicates that these endocrine features have sufficient genetic variability during most periods of the last stadium to respond rapidly to selection. Significant phenotypic correlations were observed in eight of nine pairwise comparisons between the three traits in the three stages. Significant additive genetic correlations were observed between JHE and JHB and between JHE and GE for activities pooled over all developmental stages. Nearly all phenotypic and additive genetic correlations between the same trait in different developmental stages were significant. This indicates that these three traits are highly intercorrelated and should evolve in concert. Of particular note is the positive phenotypic and genetic correlation between JHE and JHB which suggests that these two traits may be coordinately regulated and may function in concert to reduce the JH titre. This is, to our knowledge, the first quantitative-genetic analysis of hormonal features of an insect.

Quantitative-Genetic Analysis of Temperature Regulation in Mus domesticus. IV. Pleiotropy and Genotype-by-Environment Interactions

The heritabilities of, and genetic correlations among, several traits related to thermoregulation in house mice were examined in a randomly bred population. The traits studied comprised aspects of morphology, behavior, and physiology. Effects of the environment, both internal and external, on the phenotypic expression and genetic architecture of the traits were considered. Genotype-by-environment interactions of two kinds were found to be important. The external environment had an effect on the expression of genetic influences on behavioral thermoregulation, with shifts in the ambient temperature causing a significant change in heritability. The internal environment affected genetic variation in physiological thermoregulation, with significant differences being found in the heritability of body temperature between males and females. Phenotypic dimorphisms were poor predictors of sex differences at the genetic level. Morphological characters were phenotypically the most dimorphic, but genotypically the least dimorphic; body temperature showed the reverse relationship. Significant additive genetic correlations were found between several of the traits. These were highest for pairs of similar characters, for example, body weight at different ages and nesting behavior at different temperatures. The correlation between morphological and behavioral aspects of temperature regulation was also significant. Physiological aspects of thermoregulation could evolve essentially as independent characters, but behavior and morphological traits would be expected to evolve in concert. The relevance of these results to general predictive theories is discussed. In particular, the assumption of no genotype-by-environment interactions could be misleading, and the occurrence of such interactions is likely to be troublesome when selection pressures fluctuate or differ qualitatively in males and females. Furthermore, genetic correlations between traits can pose a major difficulty, even when the traits vary as much as aspects of behavior and morphology. We conclude that a greater amount of empirical information is needed for a wider range of traits on both genotype-by-environment interactions and additive genetic correlations, and that such information must be incorporated into predictions of specific evolutionary adaptations.

Genetic variation in tissue cultures of red clover

Design II matings were made among randomly selected clones of 'Arlington' red clover (Trifolium pratense L.). Progeny were evaluated in vitro on two regeneration media for callus growth and differentiation. Additive genetic variance was a significant source of variability for nearly all traits evaluated, including somatic embryogenesis. In vitro traits, such as rapid callus growth, colony vascularization, root initiation, chlorophyll production and embryogenesis were highly heritable and should respond to breeding and selection. Dominance genetic variance was significant for only a few in vitro characters. Maternal and cytoplasmic factors were significant primarily in the early subcultures. Highly significant additive genetic correlation of performance on two regeneration media was found. A population selected on one of the regeneration media for such characteristics as improved plantlet regeneration, rapid callus growth, long term colony viability or the frequency of root initiation should show correlated improvement on the other medium. No significant differences for embryogenesis were attributable to differences in the regeneration media used. Furthermore, no interaction of additive genetic effects with regeneration media were observed. These data indicate that improvement in the frequency of plantlet regeneration from callus of red clover could effectively be achieved by breeding and selection for embryogenic types.