Testing Cheverud's conjecture for behavioral correlations and behavioral syndromes

Recent research regarding correlations among behaviors--under the labels of behavioral syndromes and animal personalities--has typically assumed that phenotypic correlations between behaviors are representative of underling genetic correlations. However, for behaviors, the concordance between phenotypic and genetic correlations has not been rigorously examined. I tested this assumption using published estimates and found phenotypic and genetic correlations to be strongly related but found that the average absolute difference between the two was quite high and similar to that observed in other traits. Using absolute differences as the sole criterion, phenotypic correlations do not reliably estimate the magnitude of genetic correlations for behaviors, which is problematic for behavioral syndrome researchers. However, phenotypic correlations explained 75% of the variation in genetic correlations and their sign was typically the same as that of genetic correlations. This suggests that phenotypic correlations between behaviors reliably estimate the direction of underling genetic relationships and provide considerable information regarding the magnitude of genetic correlations. Thus, if researchers are careful about the questions they ask, phenotypic correlations between behaviors can be informative regarding underling genetic correlations and their evolutionary implications.     

Analysis of embryo,cytoplasmic and maternal genetic correlations for seven essential amino acids in rapeseed meal (<Emphasis Type="Italic">Brassica napus</Emphasis> L.)

Genetic correlations of nutrient quality traits including lysine, methionine, leucine, isoleucine, phenylalanine, valine and threonine contents in rapeseed meal were analysed by the genetic model for quantitative traits of diploid plants using a diallel design with nine parents of Brassica napus L. These results indicated that the genetic correlations of embryo, cytoplasm and/or maternal plant have made different contribution to total genetic correlations of most pairwise nutrient quality traits. The genetic correlations among the amino acids in rapeseed meal were simultaneously controlled by genetic main correlations and genotype × environment (GE) interaction correlations, especially for the maternal dominance correlations. Most components of genetic main correlations and GE interaction correlations for the pairwise traits studied were significantly positive. Some of the pairwise traits had negative genetic correlations, especially between valine and other amino acid contents. Indirect selection for improving the quality traits of rapeseed meal could be expected in rape breeding according to the magnitude and direction of genetic correlation components.     

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.     

Cross prediction studies on spring barley

Summary Additive genetic, dominance genetic and environmental correlations between pairs of agronomically important characters in five spring barley crosses were calculated from estimates of the components of variance and covariance, obtained by Triple Test Cross analysis. Phenotypic correlations were calculated from the Triple Test Cross family means and compared to the additive genetic correlations. Phenotypic correlations were generally lower than the additive genetic correlations and, occasionally, of different sign. The highest phenotypic correlations between single plant yield and its components were found with number of tillers whereas these were the lowest additive genetic correlations, thousand grain weight giving the highest. High dominance genetic correlations were found between single plant yield and both grain number and thousand grain weight thus indirect early generation selection for single plant yield using these two characters would be ineffective. Additive and dominance genetic correlations confirm association of the erectoides dwarfing gene with low thousand grain weight and plant yield.     

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.     

新疆沙冬青AM和DSE真菌的空间分布

2012年6月从新疆阿图什市选取康苏、膘尔托阔依(阳)、膘尔托阔依(阴)和上阿图什4个样地,采集新疆沙冬青(Ammopiptanthus nanus)根围0—10、10—20、20—30、30—40和40—50cm5个土层土壤样品,研究了新疆沙冬青AM和DSE真菌定殖规律以及土壤因子的生态作用。结果表明,AM和DSE真菌平均总定殖率分别为83.2%和53.22%,说明AM和DSE真菌能与新疆沙冬青根系形成良好共生关系。AM和DSE真菌具有明显空间异质性,AM总定殖率最大值在20—30cm土层,样地间表现为康苏=上阿图什膘尔托阔依(阳)膘尔托阔依(阴);DSE土层间无规律性变化,样地间为膘尔托阔依(阳)膘尔托阔依(阴)康苏上阿图什。相关性分析表明,AM菌丝、泡囊和总定殖率与DSE定殖率极显著负相关,AM定殖强度与DSE菌丝和总定殖率显著负相关,丛枝定殖率与DSE菌丝和总定殖率极显著正相关,说明两者间存在生态位竞争。土壤速效P、总球囊霉素和酸性磷酸酶与AM总定殖率极显著正相关,pH与AM总定殖率显著负相关;脲酶与DSE极显著正相关,pH和碱解N与DSE显著负相关。     

THE DUAL ROLE OF SELECTION AND EVOLUTIONARY HISTORY AS REFLECTED IN GENETIC CORRELATIONS

The patterns of genetic correlations between a series of eye and antenna characters were compared among two sets of spring-dwelling and cave-dwelling populations of Gammarus minus. The two sets of populations originate from different drainages and represent two separate invasions of cave habitats from surface-dwelling populations. Matrix correlations, using permutation tests, indicated significant correlations both between populations in the same basin and from the same habitat. The technique of biplot, which allows for the simultaneous consideration of relationships between different genetic correlations and different populations, was used to further analyze the correlation structure. A rank-3 biplot indicated that spring and cave populations were largely differentiated by eye-antennal correlations, whereas basins were differentiated by both eye-antennal and antennal-antennal correlations. Eye-antennal correlations, which are likely to be subject to selection, were most similar within habitats, which are likely to have similar selective regimes.     

Conditions for positive and negative correlations between fitness and heterozygosity in equilibrium populations.

The past decades have witnessed extensive efforts to correlate fitness traits with genomic heterozygosity. While positive correlations are revealed in most of the organisms studied, results of no/negative correlations are not uncommon. There has been little effort to reveal the genetic causes of these negative correlations. The positive correlations are regarded either as evidence for functional overdominance in large, randomly mating populations at equilibrium, or the results of populations at disequilibrium under dominance. More often, the positive correlations are viewed as a phenomenon of heterosis, so that it cannot possibly occur under within-locus additive allelic effects. Here we give exact genetic conditions that give rise to positive and negative correlations in populations at Hardy-Weinberg and linkage equilibria, thus offering a genetic explanation for the observed negative correlations. Our results demonstrate that the above interpretations concerning the positive correlations are not complete or even necessary. Such a positive correlation can result under dominance and potentially under additivity, even in populations where associated overdominance due to linked alleles at different loci is not significant. Additionally, negative correlations and heterosis can co-occur in a single population. Although our emphasis is on equilibrium populations and for biallelic genetic systems, the basic conclusions are generalized to non-equilibrium populations and for multi-allelic situations.     

Analysis of phenotypic correlations of human psychophysiological traits

Twin data analysis provides the estimates of genetic and environmental components of correlations within groups of skin potential reactions (SPR) and the evoked responses (ER) characters. Two-thirds of the total SPR correlations are significant, 74% of them being based on the strong genetic relationships. So, the genetic mechanisms of the SPR seem to be very general and independent of ecological quality of the stimulus (its neutrality/aversiveness). There are few significant ER correlations (25.4%) and only 35.7% of these developed from the high genetic correlations. Some ER correlations (i. e. correlations of the amplitude of P3 wave) are determined by common between-family ("cultural") environmental factors.     

Intra- and Inter-Plant Level Correlations among Floral Traits in <Emphasis Type="Italic">Iris Gracilipes</Emphasis> (Iridaceae)

Although the sizes of individual flowers within one plant vary, few studies to date have investigated correlations among floral traits at the intra-plant level. Variations of the pleiotropic genes or linkage disequilibrium of genes, those have been said to create larger correlations between some combinations of traits than others at the inter-plant level, cannot predict intra-plant level correlations. In this study, correlations between several combinations of floral traits, including the number and volume of pollen grains and ovules, were investigated at both intra- and inter-plant levels in Iris gracilipes. The pattern of intra-plant level correlations was similar to that of inter-plant level correlations with some exceptions; correlations between functionally related traits tended to be larger than others at both levels. For example, correlations between sepal and petal size, and between petaloid style and filament length were large at both levels. This may be explained by the genetic and the developmental relationships between some combinations of traits, rather than by (co)variations of the peculiar properties of the individual plants such as genetic variations. Co-ordinat`ing editor: X. Pico     

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.     

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.     

Competition among herbivores of Solanum carolinense as a constraint on the evolution of host-plant resistance

Interspecific competition (or facilitation) between herbivores sharing a host plant species can result in negative (or positive) correlations in damage levels, independent of a plant’s genetic covariance in resistance to the herbivores. Just like genetic correlations in resistance to herbivory, these “environmental correlations” in damage may affect the evolution of resistance in the host plant. In a field study of 960 ramets and 40 genets of the herbaceous plant Solanum carolinense, I looked for evidence of such environmental correlations in damage caused by 11 species of herbivores, including 10 insects and 1 mammal. There were 28 significant correlations in damage levels between species (21 negative and 7 positive) after plant genetic influences on resistance were statistically removed. Negative environmental correlations were more likely between species that fed upon the same type of plant organs than between those that fed on different types of organs, and the magnitudes of the correlations were inversely proportional to the abundance of the organ types. Taken together, these results offer strong evidence that competition is largely responsible for the pattern of environmental correlations in damage. Environmental correlations were just as common as genetic correlations in resistance, but the environmental correlations tended to be lower in magnitude, were more likely to be negative, and were more evenly spread out among the herbivore community than the genetic correlations. Damage levels by all 11 species were negatively correlated with damage by at least one other species. Thus the selective advantage a plant would receive from increased resistance any of these herbivores would be partially negated by increased damage by competing herbivores. As a result, competition has the potential to be an important constraint on the evolution of resistance in S. carolinense.     

Decorrelation of Neural-Network Activity by Inhibitory Feedback

Correlations in spike-train ensembles can seriously impair the encoding of information by their spatio-temporal structure. An inevitable source of correlation in finite neural networks is common presynaptic input to pairs of neurons. Recent studies demonstrate that spike correlations in recurrent neural networks are considerably smaller than expected based on the amount of shared presynaptic input. Here, we explain this observation by means of a linear network model and simulations of networks of leaky integrate-and-fire neurons. We show that inhibitory feedback efficiently suppresses pairwise correlations and, hence, population-rate fluctuations, thereby assigning inhibitory neurons the new role of active decorrelation. We quantify this decorrelation by comparing the responses of the intact recurrent network (feedback system) and systems where the statistics of the feedback channel is perturbed (feedforward system). Manipulations of the feedback statistics can lead to a significant increase in the power and coherence of the population response. In particular, neglecting correlations within the ensemble of feedback channels or between the external stimulus and the feedback amplifies population-rate fluctuations by orders of magnitude. The fluctuation suppression in homogeneous inhibitory networks is explained by a negative feedback loop in the one-dimensional dynamics of the compound activity. Similarly, a change of coordinates exposes an effective negative feedback loop in the compound dynamics of stable excitatory-inhibitory networks. The suppression of input correlations in finite networks is explained by the population averaged correlations in the linear network model: In purely inhibitory networks, shared-input correlations are canceled by negative spike-train correlations. In excitatory-inhibitory networks, spike-train correlations are typically positive. Here, the suppression of input correlations is not a result of the mere existence of correlations between excitatory (E) and inhibitory (I) neurons, but a consequence of a particular structure of correlations among the three possible pairings (EE, EI, II).     

A family study of anthropometric traits in a Punjabi community: I. Introduction and familial correlations

Data on 40 anthropometric measurements from 144 nuclear families in Chandigarh, India, are presented. Most families contain a pair of monozygotic or dizygotic twins, one or more singleton siblings, and their parents. Familial correlations for age-sex standardized, normalized measurements are estimated by maximum likelihood for marital, parent-child, sibling, and twin pairs. Heterogeneity tests for sex-specific subtype correlations male-male, male-female, female-female) indicate that the sex of the relative plays no significant role in the magnitude of the familial correlations except for maternal effects and differences among male and female twin pairs for a few of the variables. Marital correlations are high for body measurements, but not for head or face variables. Twin correlations seem to indicate a higher level of heritability than correlations from other family members.     

Joint distribution of z transformations estimated from the same sample

When correlations are estimated by maximum likelihood method from the same sample, Fisher's z transformations of the correlations (as well as the sample correlations themselves) are shown to be asymptotically distributed as multivariate normal with appropriate mean and dispersion matrix.     

THE EFFECT OF A VARIABLE ENVIRONMENT ON THE GENETIC CORRELATION STRUCTURE IN A FIELD CRICKET

The evolutionary trajectory of a trait depends not only on the presence of genetic variation, but also on the pattern of genetic correlations (r_g) among traits. Genetic correlations are most easily measured under homogeneous, controlled laboratory conditions, whereas natural populations typically experience a higher degree of environmental variability. The effect of environmental variability on genetic correlations in the cricket, Gryllus pennsylvanicus, was studied by measuring genetic correlations within and between two environments differing in levels of environmental heterogeneity. Within-environment r_g among morphological traits measured in the homogeneous laboratory environment were found to be reliable predictors of r_g measured in the experimental field environment. Laboratory measures of r_g involving life-history traits, though, were not found to reflect the same correlations measured in the heterogeneous environment. A significant negative genetic correlation between fecundity and developmental time was found in the field environment, yet was not detectable when measured in the laboratory. Phenotypic correlations may be obtained much more easily than genetic correlations, but their usefulness in evolutionary inference depends on the pattern of similarity between the two correlations. A comparison of genetic and phenotypic correlations revealed a close match between the two measures for morphological traits, but revealed only broad similarities when considering life-history traits. Male-female genetic correlations between morphological traits were high (all r_g > 0.73) and were consistently higher in the field environment than in the laboratory. The genetic correlations between the sexes in developmental time followed the same trend, but the male-female genetic correlation of gonad weights was low in both environments. Across-environment correlations were found to be strong for morphological traits and for gonad weight, whereas the genetic expression of developmental time was found to be dependent on the environment in which the crickets were raised.     

Genetic correlations, tradeoffs and environmental variation

Negative genetic correlations among traits are often used as evidence for tradeoffs that can influence evolutionary trajectories in populations. While there may be evidence for negative correlations within a particular environment, genetic correlations can shift when populations encounter different environmental conditions. Here we review the evidence for these shifts by focusing on experiments that have examined genetic correlations in more than one environment. In many studies, there are significant changes in correlations and these can even switch sign across environments. This raises questions about the validity of deducing genetic constraints from studies in one environment and suggests that the interaction between environmental conditions and the expression of genetic covariation is an important avenue for future work.     

Influence of degree correlations on network structure and stability in protein-protein interaction networks

Background  

The existence of negative correlations between degrees of interacting proteins is being discussed since such negative degree correlations were found for the large-scale yeast protein-protein interaction (PPI) network of Ito et al. More recent studies observed no such negative correlations for high-confidence interaction sets. In this article, we analyzed a range of experimentally derived interaction networks to understand the role and prevalence of degree correlations in PPI networks. We investigated how degree correlations influence the structure of networks and their tolerance against perturbations such as the targeted deletion of hubs.