Developmental stability and pollination

A number of different insect species (ranging from Diptera, Lepidoptera and Coleoptera to Hymenoptera) have been shown to discriminate between small degrees of asymmetry when visiting flowers or flower-like models. Such preferences for symmetry may have an innate basis. Small degrees of bilateral or radial asymmetry of flowers are considered to represent a measure of developmental instability, since deviations from perfect symmetry reflect the inability to maintain developmental precision during ontogeny. Environmental factors causing increased asymmetry in leaves and flowers include radioactive radiation, ultraviolet radiation, excess artificial fertilizer, various pollutants, extreme saline conditions, herbivory and competition. Genetic factors that contribute to increased asymmetry in plants include homozygosity, hybridization, mutation and quantitative genetic differences among individuals. Insect preferences for symmetric flowers increase reproductive success of both pollen donors and recipients by affecting seed set and embryo abortion. The ability of insects to discriminate between flowers of superior and inferior quality is hypothesized to depend on the level of developmental instability of the perceptive apparatus of insects. Hence, asymmetry of insects may have consequences for plant reproductive success and mating patterns. Received: 18 November 1999 / Accepted: 15 December 1999     

Developmental origins of physical fitness: the Helsinki Birth Cohort Study

Background

Cardiorespiratory fitness (CRF) is a major factor influencing health and disease outcomes including all-cause mortality and cardiovascular disease. Importantly CRF is also modifiable and could therefore have a major public health impact. Early life exposures play a major role in chronic disease development. Our aim was to explore the potential prenatal and childhood origins of CRF in later life.

Methods/Principal Findings

This sub-study of the HBCS (Helsinki Birth Cohort Study) includes 606 men and women who underwent a thorough clinical examination and participated in the UKK 2-km walk test, which has been validated against a maximal exercise stress test as a measure of CRF in population studies. Data on body size at birth and growth during infancy and childhood were obtained from hospital, child welfare and school health records. Body size at birth was not associated with adult CRF. A 1 cm increase in height at 2 and 7 years was associated with 0.21 ml/kg/min (95% CI 0.02 to 0.40) and 0.16 ml/kg/min (95% CI 0.03 to 0.28) higher VO_2max, respectively. Adjustment for adult lean body mass strengthened these findings. Weight at 2 and 7 years and height at 11 years became positively associated with CRF after adult lean body mass adjustment. However, a 1 kg/m² higher BMI at 11 years was associated with −0.57 ml/kg/min (95% CI −0.91 to −0.24) lower adult VO_2max, and remained so after adjustment for adult lean body mass.

Conclusion/Significance

We did not observe any significant associations between body size at birth and CRF in later life. However, childhood growth was associated with CRF in adulthood. These findings suggest, importantly from a public point of view, that early growth may play a role in predicting adult CRF.     

Developmental stability in plants: Symmetries,stress and epigenesis

Plant developmental stability has received little attention in the past three or four decades. Here we review differences in plant and animal development, and discuss the advantages of using plants as experimental subjects in exploring developmental stability. We argue that any type of developmental invariant may be used to assess developmental stability and review the use of fluctuating asymmetry in studies of plant developmental stability. We also examine the use of deviations from translatory, radial, and self-symmetry as measures of developmental instability. The role of nonlinear dynamics and epigenesis in the production of the phenotype is also discussed.     

Developmental stability and genetic architecture: a comparison within and across thermal regimes in tadpoles

We investigated homogeneity of growth and development as indices of developmental stability in sibling tadpoles from two sampling regions of the common frog, Rana temporaria. One region is characterized by relatively warm breeding ponds with a short activity season (`north'), and one by relatively cool breeding ponds and a long activity season (`south'). Tadpoles from the two regions were raised in three different temperatures selected to mimic the natural variation throughout the range. The results show that (1) north tadpoles respond with a relatively greater increase in growth with increased temperature than south tadpoles, (2) mean growth rate and its coefficient of variation were negatively correlated in the temperature regime in which a population was primarily under selection in the wild, whereas no such correlation was found at temperatures more seldom encountered in the natural populations, (3) phenotypic and genetic correlations between morphological traits within individuals were positive and were relatively higher in north than south tadpoles in the warm treatment, but higher for south tadpoles in the cold treatment and (4) across thermal environments, south tadpoles showed significant genetic correlations, whereas the correlations for north tadpoles were not significantly different from zero. South tadpoles showed only positive genetic correlations (n=30), whereas 14 of 30 correlation coefficients were negative in north tadpoles. In conclusion, developmental stability for growth and morphometry was higher at `optimal' conditions and decreased at the tail ends of the reaction norms within regions, with marked differences reflecting selection history between regions.     

Developmental stability,sexual selection and speciation

Fluctuating asymmetry occurs when an individual is unable to undergo identical development of an otherwise bilaterally symmetric trait on both sides of its body. Since both sides of a bilaterally symmetric trait are the result of the actions of a single genome, fluctuating asymmetry represents an epigenetic measure of the sensitivity of development to stress. Different morphological traits may show a direct relationship between their functional importance and their degree of developmental canalization. This may explain why some characters show high degrees of fluctuating asymmetry, and why these characters more often become exaggerated secondary sexual ornaments. The degree of fluctuating asymmetry is generally larger in small marginal populations living in novel environments, and this will particularly lead to relatively large degrees of asymmetry in the least developmentally canalized traits. More stringent selection against heterozygotes in marginal populations may further break down developmental stability and linkage groups which would lead to increased genetic variance. Females may prefer to mate with males having large, but relatively symmetric morphological characters, because it is more difficult to make large traits (a good genes argument), a large trait is more easily perceived (a sensory bias preference), and because symmetry signals ability to cope with stress (a good genes argument). The low degree of developmental stability and the large amount of genetic variance in secondary sexual characters in small, marginal populations could set the scene for rapid development of divergence and speciation in marginal populations.     

Developmental variability and stability in continuous-time host-parasitoid models

Insect host-parasitoid systems are often modeled using delay-differential equations, with a fixed development time for the juvenile host and parasitoid stages. We explore here the effects of distributed development on the stability of these systems, for a random parasitism model incorporating an invulnerable host stage, and a negative binomial model that displays generation cycles. A shifted gamma distribution was used to model the distribution of development time for both host and parasitoid stages, using the range of parameter values suggested by a literature survey. For the random parasitism model, the addition of biologically plausible levels of developmental variability could potentially double the area of stable parameter space beyond that generated by the invulnerable host stage. Only variability in host development time was stabilizing in this model. For the negative binomial model, development variability reduced the likelihood of generation cycles, and variability in host and parasitoid was equally stabilizing. One source of stability in these models may be aggregation of risk, because hosts with varying development times have different vulnerabilities. High levels of variability in development time occur in many insects and so could be a common source of stability in host-parasitoid systems.     

Selection in yeast I: Assessing genetic stability and relative fitness of commercial yeasts

Summary The potential for changes in allele frequencies in yeast populations by selection was examined. Cells from the wine yeastSaccharomyces cerevisiae (strain Montrachet) were grown over a large number of generations using two different culturing techniques, each with two variations: serial transfers on WLN agar plates with and without UV irradiation, and continuous culture in autoclaved and in filter-sterilized grape must. A low frequency of variant isozyme patterns was found in samples taken at the end of the experiment. Growth rates in must and on agar plates were also examined, and it was found that all samples were faster-growing than the original strain, to varying degrees. Applications for the selection system developed are discussed.     

Developmental biology of the pancreas: A comprehensive review

Pancreatic development represents a fascinating process in which two morphologically distinct tissue types must derive from one simple epithelium. These two tissue types, exocrine (including acinar cells, centro-acinar cells, and ducts) and endocrine cells serve disparate functions, and have entirely different morphology. In addition, the endocrine tissue must become disconnected from the epithelial lining during its development. The pancreatic development field has exploded in recent years, and numerous published reviews have dealt specifically with only recent findings, or specifically with certain aspects of pancreatic development. Here I wish to present a more comprehensive review of all aspects of pancreatic development, though still there is not a room for discussion of stem cell differentiation to pancreas, nor for discussion of post-natal regeneration phenomena, two important fields closely related to pancreatic development.     

Developmental and reproductive fitness of Orius laevigatus (Hemiptera: Anthocoridae) reared on factitious and artificial diets

The developmental and reproductive fitness of the polyphagous predator Orius laevigatus (Fieber) (Hemiptera: Anthocoridae) was compared on two factitious foods and four artificial diets. Adults fed factitious foods (Ephestia kuehniella Zeller eggs and Artemia franciscana Kellogg cysts) performed better than those fed artificial diets. Among the artificial diets, a diet composed of liver and ground beef scored better than meridic diets based on egg yolk. Within the egg yolk-based artificial diets, the developmental fitness varied proportionally with the amount of egg yolk present in the diet. A food switching experiment, in which nymphs and adults of the predator were fed either E. kuehniella eggs or an egg yolk-based artificial diet, showed that the impact of adult food on reproductive capacity was greater than that of nymphal food. An optimal adult food was able to wholly compensate for deficiencies incurred by an inferior artificial diet in the nymphal stage. A strong correlation was found between oocyte counts, lifetime oviposition, and the number of eggs laid after 8 d. A rapid dissection assay may thus be effective to reliably and economically assess the fitness of O. laevigatus as a function of the diet. This method also may prove useful as part of quality assurance procedure for commercially produced predators.     

A reconciliation of inclusive fitness and personal fitness approaches: a proposed correcting term for the inclusive fitness formula

Hamilton implicitly defined the inclusive fitness of an individual as the number of genomes, identical by descent to its own, but not in its own body, which owe their existence to expression of genes in said individual. Hamilton regarded inclusive fitness as the true metric of evolutionary success and the thin- maximized by selection. Williams, Stern and Orlove either claimed this property for mean reproductive success, or stated that expected reproductive success equals expected inclusive fitness. These statements are reconciled if a correcting term is added to Hamilton's inclusive fitness formula.This change completely accounts for inclusive fitness in personal fitness terminology. The use of ? in place of r renders the new formula exact. This has less numerical impact than the addition of the correcting term to begin with, but helps show inclusive fitness theory holds exactly.     

Developmental roles of heparan sulfate proteoglycans: a comparative review in Drosophila,mouse and human

In recent years, progress in the fields of development and proteoglycan biology have produced converging evidence of the role of proteoglycans in morphogenesis. Numerous studies have demonstrated that proteoglycans are involved in several distinct morphogenetic pathways upon which they act at different levels. In particular, proteoglycans can determine the generation of morphogen gradients and be required for their signal transduction. The surface of most cells and the extracellular matrix are decorated by heparan sulfates which are the most common glycosaminoglycans, normally present as heparan sulfate proteoglycans. Considerable structural heterogeneity is generated in proteoglycans by the biosynthetic modification of their heparan sulfate chains as well as by the diverse nature of their different core proteins. This heterogeneity provides an impressive potential for protein-protein and protein-carbohydrate interactions, and can partly explain the diversity of proteoglycan involvement in different morphogenetic pathways. In this review, we summarize the current knowledge about mutations affecting heparan sulfate proteoglycans that influence the function of growth factor pathways essential for tissue assembly, differentiation and development. The comparison of data obtained in Drosophila, rodents and humans reveals that mutations affecting the proteoglycan core proteins or one of the biosynthetic enzymes of their heparan sulfate chains have profound effects on growth and morphogenesis. Further research will complete the picture, but current evidence shows that at the very least, heparan sulfate proteoglycans need to be counted as legitimate elements of morphogenetic pathways that have been maintained throughout evolution as determinant mechanisms of pattern formation.     

Developmental stability and predation success in an insect predator-prey system

I investigated the relationships among developmental stability(as measured by individual bilateral asymmetry values), twomeasures of locomotory performance and predation success inan insect predator-prey system. In this system yellow dungfliesScathophaga stercoraria preyed upon houseflies Musca domesticainlaboratory-controlled conditions. There was no relationshipbetween locomotion and absolute asymmetry or mean size of twomorphological traits (fourth longitudinal wing vein, forelegtibia) in either species. Analysis of single predation trialsindicated that locomotion performance and trait size are notassociated with the probability of predation. However, Muscathat were captured had tibia that were more asymmetric thanMusca that survived. Similarly, Scathophaga that were successfulpredators had more symmetric forelegs than unsuccessful predators.There was no relationship between predation and wing vein asymmetry,which may indicate the importance of terrestrial-based predatoryavoidance tactics in this system. There were no relationshipsbetween morphology or locomotion with predation latency, preyhandling times, or the number of times a prey "escaped" froma predator. The mechanisms behind the relationship between tibiaasymmetry and predation success are discussed. This is the firstexperiment to reveal direct evidence for selection for symmetric,developmentally stable individuals through differential predation     

Habitat fragmentation effects on fitness of plant populations – a review

Habitat fragmentation threatens the survival of many species and local populations. Habitat fragmentation has two major consequences: populations become more isolated and are reduced in size. Small compared with large populations have increased extinction risks because of different types stochasticity (e.g. genetic drift) and inbreeding, which can negatively affect the fitness of individuals or populations. Habitat fragmentation may also change the abiotic conditions of the surrounding landscape, which influences biotic interactions. This review gives an introduction to the theory of the effects of habitat fragmentation on mean fitness of plant populations. It intends to help bridge the gap between conservation biologists and conservation practitioners. The paper shortly introduces basic concepts of population biology, demography and genetics and cites relevant and new literature. Special attention is given to more common plant species, which have attracted far less conservation attention than rare species.     

The effect of lead on fitness components and developmental stability in Drosophila subobscura

We analyzed the developmental time, egg-to-adult viability, and developmental stability (fluctuating wing size asymmetry) in Drosophila subobscura, maintained for six generations on different concentrations of lead. Development time is significantly affected by generation and lead concentration, but interaction of these factors is not a significant source of variability for this fitness component. Generation and the interaction generation x concentration of lead significantly affect egg-to-adult viability. Levene's test of heterogeneity of variance showed that variability of FA is not significant in any of the samples. Within both lead concentrations females showed significantly higher FA indices for the wing width than males. Within sexes, a significantly higher FA was found only in females for wing width FA between the control and the lower concentration of lead. The results show that if strong relationship between FA and the studied fitness components exists, it results in a stronger selection of unstable genotypes under lead as a stress factor and, consequently, FA needs to be used with caution as a biomarker in natural populations under environmental stress.     

Developmental plasticity of HPA and fear responses in rats: a critical review of the maternal mediation hypothesis

Developmental plasticity of HPA and fear responses in rats has been proposed to be mediated by environment-dependent variation in active maternal care. Here, we review this maternal mediation hypothesis based on the postnatal manipulation literature and on our own recent research in rats. We show that developmental plasticity of HPA and fear responses in rats cannot be explained by a linear single-factor model based on environment-dependent variation in active maternal care. However, by adding environmental stress as a second factor to the model, we were able to explain the variation in HPA and fear responses induced by postnatal manipulations. In this two-factor model, active maternal care and environmental stress (as induced, e.g., by long maternal separations or maternal food restriction) exert independent, yet opposing, effects on HPA reactivity and fearfulness in the offspring. This accounts well for the finding that completely safe and stable, as well as, highly stressful maternal environments result in high HPA reactivity and fearfulness compared to moderately challenging maternal environments. Furthermore, it suggests that the downregulation of the HPA system in response to stressful maternal environments could reflect adaptive developmental plasticity based on the increasing costs of high stress reactivity with increasingly stressful conditions. By contrast, high levels of environmental stress induced by environmental adversity might constrain such adaptive plasticity, resulting in non-adaptive or even pathological outcomes. Alternatively, however, developmental plasticity of HPA and fear responses in rats might be a function of maternal HPA activation (e.g., levels of circulating maternal glucocorticoid hormones). Thus, implying a U-shaped relationship between maternal HPA activation and HPA reactivity and fearfulness in the offspring, increasing maternal HPA activation with increasing environmental adversity would explain the effects of postnatal manipulations equally well. This raises the possibility that variation in active maternal care is an epiphenomenon, rather than a causal factor in developmental plasticity of HPA and fear responses in rats. Developmental plasticity of HPA and fear responses in rats and other animals has important implications for the design of animal experiments and for the well-being of experimental animals, both of which depend on the exact underlying mechanism(s). Importantly, however, more naturalistic approaches are needed to elucidate the adaptive significance of environment-dependent variation of HPA reactivity and fearfulness in view of discriminating between effects reflecting adaptive plasticity, phenotypic mismatch and pathological outcomes, respectively.     

Developmental stability covaries with genome-wide and single-locus heterozygosity in house sparrows

Fluctuating asymmetry (FA), a measure of developmental instability, has been hypothesized to increase with genetic stress. Despite numerous studies providing empirical evidence for associations between FA and genome-wide properties such as multi-locus heterozygosity, support for single-locus effects remains scant. Here we test if, and to what extent, FA co-varies with single- and multilocus markers of genetic diversity in house sparrow (Passer domesticus) populations along an urban gradient. In line with theoretical expectations, FA was inversely correlated with genetic diversity estimated at genome level. However, this relationship was largely driven by variation at a single key locus. Contrary to our expectations, relationships between FA and genetic diversity were not stronger in individuals from urban populations that experience higher nutritional stress. We conclude that loss of genetic diversity adversely affects developmental stability in P. domesticus, and more generally, that the molecular basis of developmental stability may involve complex interactions between local and genome-wide effects. Further study on the relative effects of single-locus and genome-wide effects on the developmental stability of populations with different genetic properties is therefore needed.     

Developmental genetics and homology: a hierarchical approach

New advances in developmental genetics are providing a bridge to connect the study of development and evolution. The successful integration of these fields, however, is dependent on having a clear understanding of the concept of homology. Therefore, developmental genetic data must be placed within the context of the comparative method to provide insight into the evolutionary and developmental origins of traits. The comparative analysis of traits derived from several hierarchical levels (genes, gene expression patterns, embryonic origins and morphology) can potentially reveal scenarios of developmental integration, opportunity and constraint. Moreover, this approach has implications for resolving modern controversies surrounding the concept of homology.