Study of developmental homeostasis: From population developmental biology and the health of environment concept to the sustainable development concept

The study of the indices of developmental homeostasis in natural populations leads to the definition of the fundamentals of population developmental biology, which is associated with the assessment of the nature of phenotypic diversity and the mechanisms of population dynamics and microevolutionary changes. Characterization of environmental quality based on the assessment of population status by developmental homeostasis determines the fundamentals of the health of environment concept. The use of the ideas of developmental homeostasis and the health of environment in the studies of homeostatic mechanisms of biological systems of different levels (from the organism and population to the community and ecosystem) is promising. This gives new opportunities for understanding the mechanisms that provide sustainability and their ratio at different levels as well as for the characterization of ontogenetic stability significance. The notion of developmental homeostasis, or homeorhesis, is promising for the elaboration of the ecological and biological basics of sustainable development.     

Estimate of cytogenetic homeostasis in natural populations of some small murid rodents]

Cytogenetic homeostasis in natural populations under natural conditions and anthropogenic stress was estimated according to the frequency of chromosome aberrations in somatic cells for six species of small mammals. Cytogenetic homeostasis was disturbed under the stress effect of increased density during population cycles, at the ecological periphery, and in the case of environmental chemical and radiation contamination. Cytogenetic homeostasis disturbances were related to changes in other indices of homeostasis, such as developmental stability and immune status, suggesting the use of the cytogenetic approach for estimating the general state of individuals in natural populations.     

Estimate of Cytogenetic Homeostasis in Natural Populations of Some Small Murid Rodents

Cytogenetic homeostasis in natural populations under natural conditions and anthropogenic stress was estimated according to the frequency of chromosome aberrations in somatic cells for six species of small mammals. Cytogenetic homeostasis was disturbed under the stress effect of increased density during population cycles, at the ecological periphery, and in the case of environmental chemical and radiation contamination. Cytogenetic homeostasis disturbances were related to changes in other indices of homeostasis, such as developmental stability and immune status, suggesting the use of the cytogenetic approach for estimating the general state of individuals in natural populations.     

Morphogenetic approach to estimation of health of environment: Study of developmental stability

The study of the developmental stability in natural populations is a promising direction of population developmental biology, which opens new possibilities for estimation of the nature of the observed phenotypic diversity and understanding the mechanisms of population dynamics and microevolutionary transformations. This direction of the studies allows one to approach the estimation of the condition of natural populations. A special analysis of possible changes in the developmental stability indicators under different anthropogenic effects allows one to characterize this approach as one of the main within the methodology of the health of environment estimation based on the organism condition characteristics by the developmental homeostasis. The approach seems promising for the estimation and monitoring of the condition of natural populations of different species as well as for the environmental quality estimation.     

Fluctuating asymmetry of meristic traits: an isofemale line analysis in an invasive drosophilid, <Emphasis Type="Italic">Zaprionus indianus</Emphasis>

Metric (e.g., body size) and meristic (e.g., bristle number) traits are of general use in quantitative genetic studies, and the phenotypic variance is subdivided into a genetic and a non-genetic environmental component. The non-genetic variance may have two origins: a common garden effect between individuals and a developmental instability within the same individual. Developmental instability may be studied by considering the fluctuating asymmetry (FA) between the two sides of the body. The isofemale line technique is a convenient method for investigating the architecture of natural populations but has been rarely implemented for investigating FA. In this paper, we use this experimental design for analyzing four meristic traits in eight populations of the cosmopolitan Zaprionus indianus. A study of the correlation between left and right side of each line revealed that almost 90% of the variability was due to a developmental noise, while a much higher correlation among the means of the lines from the same population was observed. A slight trend toward a directional asymmetry was observed: more thoracic bristles on the left side. Four kinds of indices, scaled or non-scaled to the mean were used for comparing the different traits. Unscaled values (mean absolute values or standard deviation of each line) revealed a linear increase with the means. Interestingly the results of ovariole number were included in the same regression. With the scaled indices (mean absolute divided by each individual value or stadard deviation devided by the mean), the differences among traits were considerably decreased, but still remained significant. The mean FA of the various traits were not correlated, suggesting that each trait harbors its own developmental stability. The CVs of FA were high with a magnitude similar to those of the trait themselves, slightly less than 10%. Finally, even with the isofemale line design, which is a powerful means for unravelling slight genetic variations, we did not to find any clear indication of a genetic component of FA under the optimal environmental conditions used in this study.     

The principle of the energy minimum in ontogeny and the channeling of developmental processes

The principle of minimum of energy in ontogenesis has been formulated on the basis of data concerning age changes in energetic metabolism, as well as the influence of ecological factors on this process. According to this principle the smallest expenditures of energy are observed in the zone of the most favorable developmental conditions. The minimal level of energetic metabolism at every developmental stage that corresponds to the most stable state of organism is treated as homeostasis and the developmental stability is treated as homeorrhesis. Regulation mechanisms of energetic metabolism during ontogenesis and under the influence of environmental factors are analyzed.     

How accurate is the phenotype? – An analysis of developmental noise in a cotton aphid clone

Background  

The accuracy by which phenotype can be reproduced by genotype potentially is important in determining the stability, environmental sensitivity, and evolvability of morphology and other phenotypic traits. Because two sides of an individual represent independent development of the phenotype under identical genetic and environmental conditions, average body asymmetry (or "fluctuating asymmetry") can estimate the developmental instability of the population. The component of developmental instability not explained by intrapopulational differences in gene or environment (or their interaction) can be further defined as internal developmental noise. Surprisingly, developmental noise remains largely unexplored despite its potential influence on our interpretations of developmental stability, canalization, and evolvability. Proponents of fluctuating asymmetry as a bioindicator of environmental or genetic stress, often make the assumption that developmental noise is minimal and, therefore, that phenotype can respond sensitively to the environment. However, biologists still have not measured whether developmental noise actually comprises a significant fraction of the overall environmental response of fluctuating asymmetry observed within a population.     

Quantitative genetic analysis of responses to larval food limitation in a polyphenic butterfly indicates environment‐ and trait‐specific effects

Different components of heritability, including genetic variance (V_G), are influenced by environmental conditions. Here, we assessed phenotypic responses of life‐history traits to two different developmental conditions, temperature and food limitation. The former represents an environment that defines seasonal polyphenism in our study organism, the tropical butterfly Bicyclus anynana, whereas the latter represents a more unpredictable environment. We quantified heritabilities using restricted maximum likelihood (REML) procedures within an “Information Theoretical” framework in a full‐sib design. Whereas development time, pupal mass, and resting metabolic rate showed no genotype‐by‐environment interaction for genetic variation, for thorax ratio and fat percentage the heritability increased under the cool temperature, dry season environment. Additionally, for fat percentage heritability estimates increased under food limitation. Hence, the traits most intimately related to polyphenism in B. anynana show the most environmental‐specific heritabilities as well as some indication of cross‐environmental genetic correlations. This may reflect a footprint of natural selection and our future research is aimed to uncover the genes and processes involved in this through studying season and condition‐dependent gene expression.     

DEVELOPMENTAL STABILITY, DISEASE AND MEDICINE

Developmental stability reflects the ability of a genotype to undergo stable development of a phenotype under given environmental conditions. Deviations from developmental stability arise from the disruptive effects of a wide range of environmental and genetic stresses, and such deviations are usually measured in terms of fluctuating asymmetry and phenodeviants. Fluctuating asymmetry is the most sensitive indicator of the ability to cope with stresses during ontogeny. There is considerable evidence that developmental stability, and especially fluctuating asymmetry, is a useful measure of phenotypic and genetic quality, because it covaries negatively with performance in multiple fitness domains in many species, including humans. It is proposed that developmental stability is an important marker of human health. Our goal is to initiate formally the integration of the sciences of evolutionary biology, developmental biology and medicine. We believe that this integrative framework provides a significant addition to the growing field of Darwinian medicine. The literature linking developmental stability and disease in humans is reviewed. Recent biological theoretical treatments pertaining to developmental stability are applied to a range of human health issues such as genetic diseases, ageing and survival, subfertility, abortion, child maltreatment by parents, cancer, infectious diseases, physiological and mental health, and physical attractiveness as a health certification.     

Evolution of genetic potential

Organisms employ a multitude of strategies to cope with the dynamical environments in which they live. Homeostasis and physiological plasticity buffer changes within the lifetime of an organism, while stochastic developmental programs and hypermutability track changes on longer time-scales. An alternative long-term mechanism is "genetic potential"--a heightened sensitivity to the effects of mutation that facilitates rapid evolution to novel states. Using a transparent mathematical model, we illustrate the concept of genetic potential and show that as environmental variability decreases, the evolving population reaches three distinct steady state conditions: (1) organismal flexibility, (2) genetic potential, and (3) genetic robustness. As a specific example of this concept we examine fluctuating selection for hydrophobicity in a single amino acid. We see the same three stages, suggesting that environmental fluctuations can produce allele distributions that are distinct not only from those found under constant conditions, but also from the transient allele distributions that arise under isolated selective sweeps.     

Local Adaptation and Genetics of Acid-Stress Tolerance in the Moor Frog, Rana arvalis

As potential to adapt to environmental stress can be essential for population persistence, knowledge on the genetic architecture of local adaptation is important for conservation genetics. We investigated the relative importance of additive genetic, dominance and maternal effects contributions to acid stress tolerance in two moor frog (Rana arvalis) populations originating from low and neutral pH habitats. Experiments with crosses obtained from artificial matings revealed that embryos from the acid origin population were more tolerant to low pH than embryos from the neutral origin population in embryonic survival rates, but not in terms of developmental stability, developmental and growth rates. Strong maternal effect and small additive genetic contributions to variation were detected in all traits in both populations. In general, dominance contributions to variance in different traits were of similar magnitude to the additive genetic effects, but dominance effects outweighed the additive genetic and maternal effects contributions to early growth in both populations. Furthermore, the expression of additive genetic variance was independent of pH treatment, suggesting little additive genetic variation in acid stress tolerance. The results suggest that although local genetic adaptation to acid stress has taken place, the current variation in acid stress tolerance in acidified populations may owe largely to non-genetic effects. However, low but significant heritabilities (h ² 0.07–0.22) in all traits – including viability itself – under a wide range of pH conditions suggests that environmental stress created by low pH is unlikely to lower moor frog populations' ability to respond to selection in the traits studied. Nevertheless, acid conditions could lower populations' ability to respond to selection in the long run through reduction in effective population size.     

Environmental and genetic cues in the evolution of phenotypic polymorphism

Phenotypic polymorphism is a consequence of developmental plasticity, in which the trajectories of developing organisms diverge under the influence of cues. Environmental and genetic phenotype determination are the two main categories of polymorphic development. Even though both may evolve as a response to varied environments, they are traditionally regarded as fundamentally distinct phenomena. They can however be joined into a single framework that emphasizes the parallel roles of environmental and genetic cues in phenotype determination. First, from the point of view of immediate causation, it is common that phenotypic variants can be induced either by environmental or by allelic variation, and this is referred to as gene-environment interchangeability. Second, from the point of view of adaptation, genetic cues in the form of allelic variation at polymorphic loci can play similar roles as environmental cues in providing information to the developmental system about coming selective conditions. Both types of cues can help a developing organism to fit its phenotype to selective circumstances. This perspective of information in environmental and genetic cues can produce testable hypotheses about phenotype determination, and can thus increase our understanding of the evolution of phenotypic polymorphism.     

HOW STABLE ‘SHOULD’ EPIGENETIC MODIFICATIONS BE? INSIGHTS FROM ADAPTIVE PLASTICITY AND BET HEDGING

Although there is keen interest in the potential adaptive value of epigenetic variation, it is unclear what conditions favor the stability of these variants either within or across generations. Because epigenetic modifications can be environmentally sensitive, existing theory on adaptive phenotypic plasticity provides relevant insights. Our consideration of this theory suggests that stable maintenance of environmentally induced epigenetic states over an organism's lifetime is most likely to be favored when the organism accurately responds to a single environmental change that subsequently remains constant, or when the environmental change cues an irreversible developmental transition. Stable transmission of adaptive epigenetic states from parents to offspring may be selectively favored when environments vary across generations and the parental environment predicts the offspring environment. The adaptive value of stability beyond a single generation of parent–offspring transmission likely depends on the costs of epigenetic resetting. Epigenetic stability both within and across generations will also depend on the degree and predictability of environmental variation, dispersal patterns, and the (epi)genetic architecture underlying phenotypic responses to environment. We also discuss conditions that favor stability of random epigenetic variants within the context of bet hedging. We conclude by proposing research directions to clarify the adaptive significance of epigenetic stability.     

Rapid divergence of genetic variance-covariance matrix within a natural population

The matrix of genetic variances and covariances (G matrix) represents the genetic architecture of multiple traits sharing developmental and genetic processes and is central for predicting phenotypic evolution. These predictions require that the G matrix be stable. Yet the timescale and conditions promoting G matrix stability in natural populations remain unclear. We studied stability of the G matrix in a 20-year evolution field experiment, where a population of the cosmopolitan parthenogenetic soil nematode Acrobeloides nanus was subjected to drift and divergent selection (benign and stress environments). Selection regime did not influence the level of absolute genetic constraints: under both regimes, two genetic dimensions for three life-history traits were identified. A substantial response to selection in principal components structure and in general matrix pattern was indicated by three statistical methods. G structure was also influenced by drift, with higher divergence under benign conditions. These results show that the G matrix might evolve rapidly in natural populations. The observed high dynamics of G structure probably represents the general feature of asexual species and limits the predictive power of G in phenotypic evolution analyses.     

Effect of low stressful temperature on genetic variation of five quantitative traits in Drosophila melanogaster

A half-sib analysis was used to investigate genetic variation for three morphological traits (thorax length, wing length and sternopleural bristle number) and two life-history traits (developmental time and larva-to-adult viability) in Drosophila melanogaster reared at a standard (25 degrees C) and a low stressful (13 degrees C) temperature. Both phenotypic and environmental variation showed a significant increase under stressful conditions in all traits. For estimates of genetic variation, no statistically significant differences were found between the two environments. Narrow heritabilities tended to be higher at 13 degrees C for sternopleural bristle number and viability and at 25 degrees C for wing length and developmental time, whereas thorax length did not show any trend. However, the pattern of genetic variances and evolvability indices (coefficient of genetic variation and evolvability), considered in the context of literature evidence, indicated the possibility of an increase in additive genetic variation for the morphological traits and viability and in nonadditive genetic variation for developmental time. The data suggest that the effect of stressful temperature may be trait-specific and this warns against generalizations about the behaviour of genetic variation under extreme conditions.     

Genetic diversity, clonality and sexuality in Toxoplasma gondii

The majority of Toxoplasma gondii strains from a variety of human and animal sources have been grouped into three highly clonal but closely related lineages. The low occurrence of nucleotide differences among the three predominant lineages and their unusual dimorphic allelic composition suggest that they have arisen from a recent common ancestry. Less than 1% of the previously studied strains contain unique genotypes and high divergence of DNA sequence, and therefore are considered 'exotic' or 'atypical' strains. The seemingly low genetic diversity in T. gondii may have been underestimated because most parasite strains in previous studies were collected from human patients and domestic animals in North America and Europe. To investigate the genetic diversity of T. gondii, we analysed parasite strains isolated from remote geographical regions by multilocus microsatellite sequencing and phylogenetic analysis. The genetic diversity indices, the molecular analysis of microsatellite genotypes and the constructed phylogram considered together suggest that the global T. gondii population is highly diversified and not characteristic of a clonal organism. The most parsimonious hypothesis is that T. gondii presents a complex population structure with a mix of clonal and sexual propagation as a function of the environmental conditions. The comparison between domestic strains data on one hand and wild strains data on the other hand is in favour of more frequent sexual recombinations in wild environment even though Toxoplasma subpopulation in human and domestic animals is largely clonal.     

Extreme temperatures increase the deleterious consequences of inbreeding under laboratory and semi-natural conditions

The majority of experimental studies of the effects of population bottlenecks on fitness are performed under laboratory conditions, which do not account for the environmental complexity that populations face in nature. In this study, we test inbreeding depression in multiple replicates of inbred when compared with non-inbred lines of Drosophila melanogaster under different temperature conditions. Egg-to-adult viability, developmental time and sex ratio of emerging adults are studied under low, intermediate and high temperatures under laboratory as well as semi-natural conditions. The results show inbreeding depression for egg-to-adult viability. The level of inbreeding depression is highly dependent on test temperature and is observed only at low and high temperatures. Inbreeding did not affect the developmental time or the sex ratio of emerging adults. However, temperature affected the sex ratio with more females relative to males emerging at low temperatures, suggesting that selection against males in pre-adult life stages is stronger at low temperatures. The coefficient of variation (CV) of egg-to-adult viability within and among lines is higher for inbred flies and generally increases at stressful temperatures. Our results contribute to knowledge on the environmental dependency of inbreeding under different environmental conditions and emphasize that climate change may impact negatively on fitness through synergistic interactions with the genotype.     

遗传多样性的取样策略

合理取样是生物多样性有效保护、利用和研究所面临的最基本问题 ,它在很大程度上受到植物自身的生物学特性、环境条件和取样目的的影响。遗传多样性的取样策略是指对一定地理分布范围内的生物个体取样时 ,使样本具有代表性和包含尽可能多的遗传变异的最佳取样方法 ,包括了取样数目 (一个给定区域的居群数和一个居群的个体数 )以及取样方式。包括“哈迪 温伯格平衡 (Hardy WeinbergEquilibrium)”定律在内的居群遗传学基本原理是研究取样策略的理论基础 ,在此基础上可以对居群内的取样个体数及应获取的居群数进行理论计算 ,同时还可以根据物种居群的遗传结构特点和环境条件的异质性来决定取样的方式。因此 ,应该依据研究对象本身的特点和取样的目的来确定某一特定区域的居群取样数 ,以及某一居群内的样本数及取样方式。