Estimates of heritability and correlations of morphometric traits in Clarkia (Onagraceae)

Summary Interspecific heritability values were estimated using parent-offspring regression analyses for 11 morphological traits differentiating Clarkia nitens and C. speciosa subsp. polyantha. Estimates ranged from near 0 for anther color and germination percentage, to 0.8 for calyx length and petal tip color. Phenotypic, genetic, and environmental correlation matrices were computed to determine the extent of interspecific correlations of traits. Cluster analyses of the genetic and environmental correlation matrices each resulted in three clusters of correlated traits; however, the clusters derived from the two matrices were different. The clusters produced by analysis of the environmental correlation matrix were similar to the factors obtained from principal component analysis of the phenotypic correlation matrix. Genetic correlations may result from strong linkage due to interspecific chromosomal differences.     

HOW SIMILAR ARE GENETIC CORRELATION STRUCTURES? DATA FROM MICE AND RATS

An integral assumption of many models of morphometric evolution is the equality of the genetic variance-covariance structure across evolutionary time. To examine this assumption, the quantitative-genetic aspects of morphometric form are examined for eight pelvic traits in laboratory rats (Rattus norvegicus) and random-bred ICR mice (Mus musculus). In both species, all traits are significantly heritable, and there are significant phenotypic and genetic correlations among traits, although environmental correlations among the eight traits are low. The size relations among the pelvic variables are isometric. Three matrix-permutation tests are used to examine similarity of phenotypic, genetic, and environmental covariance and correlation matrices within and between species. Independent patterns of morphometric covariation and correlation arise from genetic and environmental effects within each species and from environmental effects between species. The patterns of phenotypic and genetic covariation and correlation are similar within each species, and the phenotypic and genetic correlations are also similar between these species. However, genetic covariance matrices show no significant statistical association between species. It is suggested that the assumption of equality of genetic variance-covariance structures across divergent taxa should be approached with caution.     

QUANTITATIVE GENETICS OF SIZE,SHAPE, LIFE-HISTORY,AND FRUIT CHARACTERISTICS OF THE SEED HETEROMORPHIC COMPOSITE HETEROSPERMA PINNATUM. II. CORRELATION STRUCTURE

We have investigated phenotypic, environmental, within-population broad-sense genetic correlations and among-population genetic correlations for 17 traits in six populations of Heterosperma pinnatum Cav. (Compositae) grown in the greenhouse. The within-population genetic, environmental, and phenotypic correlations were somewhat similar while the among-population genetic correlations showed little correspondence to these. The different correlation matrices were compared to a hypothesis matrix, which predicted higher correlations for groups of functionally and developmentally related traits. The groups were seed and head traits, size and shape traits, and life history traits, with subgroups predicted to have still higher correlations. The phenotypic and environmental matrices corresponded well to the hypothesis matrix, the within-population broad-sense genetic matrix showed weaker, though still significant, correspondence, and the among-population genetic correlations showed no correspondence. Genetic correlations did not differ significantly among populations, though the power of these comparisons was low. Some particular genetic correlations are discussed as possible examples of adaptive correlations (e.g., a negative correlation between dispersal and dormancy) and as examples of developmental or physiological constraints including life-history tradeoffs.     

Evolution of phenotypic integration in Brassica (Brassicaceae)

Phenotypic integration is a necessary characteristic of living organisms that results from genetic, developmental, and functional relationships among traits. The nature of these relationships can be influenced by the environment. We examined patterns of phenotypic integration of six species of rapid cycling Brassica and of Raphanus sativus within a phylogenetic context. Specifically, we tested the hypothesis that hybrid species show intermediate levels of integration in morphological and life-history characters compared to their putative parentals. We used matrix correlation tests to examine if cytogenetic relationships or ecological similarities among species partially explained the patterns of phenotypic integration. There was a significant negative relationship between the ecological and cytogenetic matrices, suggesting that more closely related species were ecologically dissimilar. However, neither ecological nor cytogenetic matrices significantly explained differences among species in the pattern of their phenotypic correlations. Set correlation analysis indicated that important traits within the modules and the strength of the correlations within modules differed across species. We also found that there were a greater number of significant correlations between modules than within modules. Hybrid species were more integrated (had greater number of significant trait correlations) than either of their parents, both within and between modules. However, univariate analyses of character means of the hybrid species were not significantly different from the combined mean of their putative parents for 5, 6, or 7 of the 11 phenotypic characters (for Brassica napus, B. juncea and B. carinata, respectively); for the remaining characters, the hybrids were more similar to one of the parents.     

Genetic,phenotypic, and environmental correlations in black medic,Medicago lupulina L., grown in three different environments

We have investigated the relationship between phenotypic and genetic correlations among a large number of quantitative traits (36) in three different environments in order to determine their degree of disparity and whether phenotypic correlations could be substituted for their genetic counterparts whatever the environment. We also studied the influence of the environment on genetic and phenotypic correlations. Twenty accessions (full-sib families) ofMedicago luPulina were grown in three environments. In two of these two levels of environmental stress were generated by harvesting plants at flowering and by growing plants in competition with barley, respectively. A third environment, with no treatment, was used as a control with no stress. Average values of pod and shoot weight indicate that competition induces the highest level of stress. The genetic and phenotypic correlations among the 36 traits were compared. Significant phenotypic correlations were obtained easily, while there was no genetic variation for 1 or the 2 characters being correlated. The large positive correlation between the genetic and phenotypic correlation matrices indicated a good proportionality between genetic and phenotypic correlations matrices but not their similarity. In a given environment, when only those traits with a significant genetic variance were taken into account, there were still differences between genetic and phenotypic correlations, even when levels of significance for phenotypic correlations were lowered. Consequently, it is dangerous to substitute phenotypic correlations for genetic correlations. The number of traits that showed genetic variability increased with increasing environmental stress, consequently the number of significant genetic correlations also increased with increasing environmental stress. In contrast, the number of significant phenotypic correlations was not influnced by the environment. The structures of both phenotypic and genetic matrices, however, depended on the environment, and not in the same way for both matrices.     

Relationships among ontogenetic,static, and evolutionary allometry

The relationship between ontogenetic, static, and evolutionary levels of allometry is investigated. Extrapolation from relative size relationships in adults to relative growth in ontogeny depends on the variability of slopes and intercepts of ontogenetic vectors relative to variability in length of the vector. If variability in slopes and intercepts is low relative to variability in length, ontogenetic and static allometries will be similar. The similarity of ontogenetic and static allometries was tested by comparing the first principal component, or size vector, for correlations among 48 cranial traits in a cross-sectional ontogenetic sample of rhesus macaques from Cayo Santiago with a static sample from which all age- and sex-related variation had been removed. The vector correlation between the components is high but significantly less than one while two of three allometric patterns apparent in the ontogenetic component are not discernable in the static component. This indicates that there are important differences in size and shape relationships among adults and within ontogenies. Extrapolation from intra- or interspecific phenotypic allometry to evolutionary allometry is shown to depend on the similarity of genetic and phenotypic allometry patterns. Similarity of patterns was tested by comparing the first principal components of the phenotypic, genetic, and environmental correlation matrices calculated using standard quantitative genetic methods. The patterns of phenotypic, genetic, and environmental allometry are dissimilar; only the environmental allometries show ontogenetic allometric patterns. This indicates that phenotypic allometry may not be an accurate guide to patterns of evolutionary change in size and shape.     

Heritabilities,social environment effects and genetic correlations of social behaviours in a cooperatively breeding vertebrate

Social animals interact frequently with conspecifics, and their behaviour is influenced by social context, environmental cues and the behaviours of interaction partners, allowing for adaptive, flexible adjustments to social encounters. This flexibility can be limited by part of the behavioural variation being genetically determined. Furthermore, behaviours can be genetically correlated, potentially constraining independent evolution. Understanding social behaviour thus requires carefully disentangling genetic, environmental, maternal and social sources of variations as well as the correlation structure between behaviours. Here, we assessed heritability, maternal, common environment and social effects of eight social behaviours in Neolamprologus pulcher, a cooperatively breeding cichlid. We bred wild‐caught fish in a paternal half‐sibling design and scored ability to defend a resource against conspecifics, to integrate into a group and the propensity to help defending the group territory (“helping behaviour”). We assessed genetic, social and phenotypic correlations within clusters of behaviours predicted to be functionally related, namely “competition,” “aggression,” “aggression‐sociability,” “integration” and “integration‐help.” Helping behaviour and two affiliative behaviours were heritable, whereas there was little evidence for a genetic basis in all other traits. Phenotypic social effects explained part of the variation in a sociable and a submissive behaviour, but there were no maternal or common environment effects. Genetic and phenotypic correlation within clusters was mostly positive. A group's social environment influenced covariances of social behaviours. Genetic correlations were similar in magnitude but usually exceeding the phenotypic ones, indicating that conclusions about the evolution of social behaviours in this species could be provisionally drawn from phenotypic data in cases where data for genetic analyses are unobtainable.     

Big and beautiful? Quantitative genetic parameters for appearance of large rainbow trout

A quantitative genetic analysis of body condition, body shape, skin colour and spottiness of large, farmed rainbow trout Oncorhynchus mykiss showed that the traits can be modified through selective breeding. This was indicated by their high heritabilities ( h ² = 0·46–0·61 on the underlying liability scale and 0·29–0·50 on the observed scale). Correlations calculated using linear models showed that skin colour and the amount of spots displayed positive phenotypic ( r _P = 0·33) and genetic correlations ( r _A = 0·83), the relationship being advantageous for the genetic improvement of the traits. Body shape and condition factor displayed disadvantageous correlations with body mass at both ages, the genetic correlations between the traits ranging from 0·36 to 0·57. It was concluded that there are no strong genetic constraints for the genetic improvement of appearance, the only limitation being that rapidly growing fish become rotund.     

The genetic architecture of correlations among growth‐related traits and male age at maturation in rainbow trout

Heritabilities and genetic correlations among growth‐related traits of two cultured strains (Rainbow Springs and Spring Valley) of rainbow trout Oncorhynchus mykiss were estimated using restricted maximum likelihood methods with a three‐generation pedigree. Heritability was high (>0·50 ± 0·03) for body mass and condition factor but moderate (0·35 ± 0·04) for age at sexual maturity in males. Body mass and age at sexual maturation were phenotypically correlated in the families of one experimental strain, Rainbow Springs, and had a positive genetic correlation (0·26 ± 0·03) across families from both test strains (Rainbow Springs and Spring Valley). This indicates that faster growing individuals were more likely to mature at 2 years of age than slower growing individuals in the two hatchery strains investigated. Microsatellite markers of body mass quantitative tract loci (QTL) were reconfirmed as being located on linkage groups B, G, N, 5 and new markers on Oi were detected. Some QTL effects were restricted to specific sampling dates suggesting temporal expression of QTL. QTL for condition factor were limited to linkage group G in both strains. Three suggestive QTL for precocious maturation mapped to similar regions as those for body mass in the Rainbow Springs families while no associations were evident in the Spring Valley families. The results suggest that these regions may play a role in the basis for genetic and phenotypic correlations between body mass and precocious maturation in this species.     

A COMPARISON OF GENETIC AND PHENOTYPIC CORRELATIONS

Genetic variances and correlations lie at the center of quantitative evolutionary theory. They are often difficult to estimate, however, due to the large samples of related individuals that are required. I investigated the relationship of genetic- and phenotypic-correlation magnitudes and patterns in 41 pairs of matrices drawn from the literature in order to determine their degree of similarity and whether phenotypic parameters could be used in place of their genetic counterparts in situations where genetic variances and correlations cannot be precisely estimated. The analysis indicates that squared genetic correlations were on average much higher than squared phenotypic correlations and that genetic and phenotypic correlations had only broadly similar patterns. These results could be due either to biological causes or to imprecision of genetic-correlation estimates due to sampling error. When only those studies based on the largest sample sizes (effective sample size of 40 or more) were included, squared genetic-correlation estimates were only slightly greater than their phenotypic counterparts and the patterns of correlation were strikingly similar. Thus, much of the dissimilarity between phenotypic- and genetic-correlation estimates seems to be due to imprecise estimates of genetic correlations. Phenotypic correlations are likely to be fair estimates of their genetic counterparts in many situations. These further results also indicate that genetic and environmental causes of phenotypic variation tend to act on growth and development in a similar manner.     

Patterns of phenotypic covariation and correlation in modern humans as viewed from morphological integration

Proportionality of phenotypic and genetic distance is of crucial importance to adequately focus on population history and structure, and it depends on the proportionality of genetic and phenotypic covariance. Constancy of phenotypic covariances is unlikely without constancy of genetic covariation if the latter is a substantial component of the former. If phenotypic patterns are found to be relatively stable, the most probable explanation is that genetic covariance matrices are also stable. Factors like morphological integration account for such stability. Morphological integration can be studied by analyzing the relationships among morphological traits. We present here a comparison of phenotypic correlation and covariance structure among worldwide human populations. Correlation and covariance matrices between 47 cranial traits were obtained for 28 populations, and compared with design matrices representing functional and developmental constraints. Among-population differences in patterns of correlation and covariation were tested for association with matrices of genetic distances (obtained after an examination of 10 Alu-insertions) and with Mahalanobis distances (computed after craniometrical traits). All matrix correlations were estimated by means of Mantel tests. Results indicate that correlation and covariance structure in our species is stable, and that among-group correlation/covariance similarity is not related to genetic or phenotypic distance. Conversely, genetic and morphological distance matrices were highly correlated. Correlation and covariation patterns were largely associated with functional and developmental factors, which probably account for the stability of covariance patterns.     

Phylogenetic analysis of correlation structure in stalk-eyed flies (Diasemopsis,Diopsidae)

Morphological divergence among species may be constrained by the pattern of genetic variances and covariances among traits within species. Assessing the existence of such a relationship in nature requires information on the stability of intraspecific correlation and covariance structure and the correspondence of this structure to the pattern of evolutionary divergence within a lineage. Here, we investigate these issues for nine morphological traits and 15 species of stalk-eyed flies in the genus Diasemopsis. Within-species matrices for these traits were generated from phenotypic data for all the Diasemopsis species and from genetic data for a single Diasemopsis species, D. dubia. The among-species pattern of divergence was assessed by calculating the evolutionary correlations for all pairwise combinations of the morphological traits along the phylogeny of these species. Comparisons of intraspecific matrices reveal significant similarity among all species in the phenotypic correlations matrices but not the covariance matrices. In addition, the differences in correlation structure that do exist among species are not related to their phylogenetic placement or change in the means of the traits. Comparisons of the phenotypic and phylogenetic matrices suggest a strong relationship between the pattern of evolutionary change among species and both the intraspecific correlation structure and the stability of this structure among species. The phenotypic and the phylogenetic matrices are significantly similar, and pairs of traits whose intraspecific correlations are more stable across taxa exhibit stronger coevolution on the phylogeny. These results suggest either the existence of strong constraints on the pattern of evolutionary change or a consistent pattern of correlated selection shaping both the phenotypic and phylogenetic matrices. The genetic correlation structure for D. dubia, however, does not correspond with patterns found in the phenotypic and phylogenetic data. Possible reasons for this disagreement are discussed.     

A preliminary investigation of allozyme genetic variation and population geographical structure in Aphanius fasciatus from Italian brackish-water habitats

A total of 150 individuals from Aphanius fasciatus from coastal brackish-water habitats was analysed by allozyme electrophoresis to collect data on its genetic variation. From 22 enzymes, 43 putative enzyme-coding loci were resolved, 12 of which were polymorphic at P_0·99 level. Only one of the 31 probability tests showed a significant departure from the Hardy-Weinberg equilibrium. Aphanius fasciatus showed low levels of genetic polymorphism, with expected heterozygosity values ranging from 0·027 (S.E.=0·013) to 0·064 ( s.e. =0·023). Nei's genetic distances between populations ranged from 0·002 to 0·042. Weir & Cockerham F -statistics showed high levels of genetic heterogeneity among populations (jackknifed θ=0·302, s.e. =0·045) and estimates of N _m were < 1, indicating restricted gene flow. Significant positive correlation between genetic distance and geographical distance matrices, detected by Mantel's test ( g =1·941; P 0·001), is consistent with the prediction that the species is genetically structured by isolation-by-distance.     

Comparison of quantitative genetic parameters between two natural populations of a selfing plant species, Medicago truncatula Gaertn.

 In this paper we compare mean values, heritability estimates, coefficient of genetic variation, and genetic correlations among several fitness components of two natural populations of a selfing plant species, Medicago truncatula L. It is shown that the population that had been found most polymorphic for molecular markers in a previous study was also the most variable for quantitative characters. Depending on the traits, the larger heritabilities in this population were due to either larger coefficients of genetic variances or smaller coefficients of environmental variances. Whereas genetic and phenotypic correlation matrices were very similar within each population, they were quite different between populations. In particular, although a positive correlation between age and size at maturity was found in both populations, the correlation between age at maturity and reproductive success was negative in the more variable population (late flowering plant, with a larger size at flowering, produced fewer pods), whereas no correlation was observed in the less variable population. We suggest that while in the less variable population all individuals have a high reproductive effort, several strategies coexist in the more variable population, with some early-flowering genotypes showing a high reproductive effort and other late-flowering genotypes showing a larger competitive ability through increased vegetative growth. Received: 25 June 1996 / Accepted: 11 October 1996     

Multivariate structure of human populations: sedentary versus migrants

The rate change of gene frequency in a population subject to emigration obviously depends on differences in the effective reproductive size (and resulting random genetic drift effects) between emigrants and natives. An important additional force may be the different selection pressures of the original and the new environment into which the population penetrates. Discrete traits and monolocus systems have been studied in many natural populations of various species. However, knowledge about the migration influence on quantitative, i.e. polygenic, characters is very limited. The present study set out to answer the following biological questions: (1) Does migration induce changes in sets of phenotypic, genetic and environmental correlations? (2) If so, are these changes expressed in levels and/or structure of the correlation matrices? Data on 20 anthropometric traits in 305 Mexican families [129 families from Mexico (sedentary population) and 176 families living in Texas (migrant population)] were used for analysis. The curves of distribution and average values of phenotypic, genetic and environmental correlations remained unchanged between the two populations. However, qualitatively (i.e., as far as the agreement between matrix compositions is concerned), all three matrices changed significantly. The phenotypic correlations appear to be the most highly canalized, the correspondence between the two matrices being 62.1%. The environmental matrices had the highest variation, and although 26.3% of the correlations were in agreement, this was statistically nonsignificant. The most important finding in the present study was the relatively low correspondence between the two genetic matrices (35.6%). We suggest that these changes were provoked by preselection (i.e., by a nonrandom sample) of migrating individuals.     

Non‐consumptive effects of predation: does perceived risk strengthen the genetic integration of behaviour and morphology in stickleback?

Predators can shape genetic correlations in prey by altering prey perception of risk. We manipulated perceived risk to test whether such non‐consumptive effects tightened behavioural trait correlations in wild‐caught stickleback from high‐ compared to low‐risk environments due to genetic variation in plasticity. We expected tighter genetic correlations within perceived risk treatments than across them, and tighter genetic correlations in high‐risk than in low‐risk treatments. We identified genetic variation in plasticity, with genetic correlations between boldness, sociality, and antipredator morphology, as expected, being tighter within treatments than across them, for both of two populations. By contrast, genetic correlations did not tighten with exposure to risk. Tighter phenotypic correlations in wild stickleback may thus arise because predators induce correlational selection on environmental components of these traits, or because predators tighten residual correlations by causing environmental heterogeneity that is controlled in the laboratory. Our study places phenotypic integration firmly into an ecological context.     

Genetic and environmental correlation and path coefficient analysis of fruit yield per bush and other traits in black currants (Ribes nigrum L.)

Twenty-five F1 hybrid families of black currants (Ribes nigrum L.) originating from diallel crosses of five cultivars were assessed. Phenotypic correlation coefficient between full-sib family means (rFS), genetic correlation coefficient between full-sib family expected values (rG) and the environmental correlation were estimated on the basis of two years of observations for 12 quantitative characteristics studied. Evident repeatability of correlations in both years was proved. A considerable consistency between the values of genetic and phenotypic correlation coefficients was also observed. Coefficients of phenotypic and environmental correlation were significant for many pairs of traits. Most of the significant environmental correlation coefficients were found for the same pairs of characteristics for which phenotypic correlation coefficients were significant. This shows that genetic and environmental factors affected similar traits. Fruit yield expressed the largest number of significant correlations with other traits. Path coefficient analysis indicated that plant and berry size were the main factors influencing directly fruit yield in both years. It was proved that the number and length of one-year-old shoots via bush size had very large indirect effects on fruit yield per plant.     

Phenotypic and Genetic Effects of Contrasting Ethanol Environments on Physiological and Developmental Traits in Drosophila melanogaster

A central problem in evolutionary physiology is to understand the relationship between energy metabolism and fitness-related traits. Most attempts to do so have been based on phenotypic correlations that are not informative for the evolutionary potential of natural populations. Here, we explored the effect of contrasting ethanol environments on physiological and developmental traits, their genetic (co)variances and genetic architecture in Drosophila melanogaster. Phenotypic and genetic parameters were estimated in two populations (San Fernando and Valdivia, Chile), using a half-sib family design where broods were split into ethanol-free and ethanol-supplemented conditions. Our findings show that metabolic rate, body mass and development times were sensitive (i.e., phenotypic plasticity) to ethanol conditions and dependent on population origin. Significant heritabilities were found for all traits, while significant genetic correlations were only found between larval and total development time and between development time and metabolic rate for flies of the San Fernando population developed in ethanol-free conditions. Posterior analyses indicated that the G matrices differed between ethanol conditions for the San Fernando population (mainly explained by differences in genetic (co)variances of developmental traits), whereas the Valdivia population exhibited similar G matrices between ethanol conditions. Our findings suggest that ethanol-free environment increases the energy available to reduce development time. Therefore, our results indicate that environmental ethanol could modify the process of energy allocation, which could have consequences on the evolutionary response of natural populations of D. melanogaster.     

ADAPTIVE GENETIC VARIATION IN GROWTH AND DEVELOPMENT OF TADPOLES OF THE HYBRIDOGENETIC RANA ESCULENTA COMPLEX

The distribution and proportion of the sexual species Rana lessonae to the hemiclonal hybrid R. esculenta among natural habitats suggests that these anurans may differ in adaptive abilities. I used a half-sib design to partition phenotypic and quantitative genetic variation in tadpole responses at two food levels into causal variance components. Rana lessonae displays strong phenotypic variation across food levels. Growth rate is strictly determined by environmental factors and includes weak maternal effects. Larval period and body size at metamorphosis both contain moderate levels of additive genetic variance. The sire x food interactions and the lack of environmental correlations indicate that adaptive phenotypic plasticity is present in both of these traits. In contrast, R. esculenta displays less phenotypic variation across food levels, especially for larval period. Variation in body size at metamorphosis is underlain by genetic variation as shown by high levels of additive genetic variance, yet growth rate and larval period are not. Significant environmental correlations between larval period at high food level and growth, larval period, and body size at low food, indicate phenotypic plasticity is absent. A positive phenotypic correlation between body size at metamorphosis and larval period for R. lessonae at both food levels suggests a trade-off between growing large and metamorphosing quickly to escape predation or pond drying. The lack of a similar correlation for R. esculenta at the high food level suggests it may be less constrained. Different levels of adaptive genetic variation among larval traits suggest that the sexual species and the hybridogenetic hemiclone differ in their abilities to cope with temporally and spatially heterogeneous environments.