Diameter asymmetry of porcine coronary arterial trees: structural and functional implications

The coronary vasculature is characterized by highly asymmetric diameters at bifurcations, which may be an important determinant of flow distribution. To facilitate accurate reconstruction of the coronary network for hemodynamic analysis, we introduce a statistical data set of the diameter asymmetry at bifurcations based on morphometric data of the porcine coronary arterial and venous trees. The bifurcation asymmetry data were represented by the diameter ratio of the daughters relative to mother vessel and by an area expansion ratio (AER) at each bifurcation. A novel asymmetry ratio matrix was introduced to describe the diameter asymmetry of daughters to mother vessels. The relations between AER and flow velocity, and asymmetry ratio matrix and flow distribution, were considered. The results indicate that the ratio of large daughter to mother vessel has a minimum value at order 5 (mean diameter of approximately 70 microm), whereas the ratio of small daughter to mother vessel decreases monotonically with increase in order number. The AER was found to be fairly uniform for larger vessels and to increase from order 5 toward the capillaries. At order 5, we observe a transition in asymmetric bifurcation pattern that may mark a hemodynamic transition from transmural to perfusion subnetworks. The functional implications of these structural transitions are considered.     

Review of the origin of asymmetry of biomolecules through weak interaction: latest developments

New results and discussions since 1977 are reviewed. It is stated that--excepting Kovács's crystallization experiments not yet repeated in independent laboratories--positive, unconfuted results do not exist. Considering also the results of the different amplification theories it seems to be very improbable that the weak interaction played any role in establishing the nearly complete asymmetry of biomolecules.     

Molecular chirality and the origin of life

In the living systems L-amino acids and D-sugars are found with almost no exceptions. Although all the molecular chirality must have been established prior to the emergence of life, the origin of the asymmetry of molecules is still an unsolved problem. The time of appearance of the asymmetry of molecules, therefore, was quite problematic during chemical evolution.Since Pasteur's discovery in 1848, a large number of works for solving this problem have been carried out on the basis of mathematics, physics or chemistry. All the proposals which put forth for breaking the symmetry are still considered to be too weak to explain the cause of obtaining the chiral purity as a result of the symmetry breaking of molecules. In order to expand our scope, new sources of the symmetry breaking of molecules should be considered.In this article, some approaches to the achiral-chiral transition are reviewed, which will give an idea for the origin of asymmetry of molecules.     

Ecological stress memory: Evidence in two out of seven species through the examination of the relationship between leaf fluctuating asymmetry and photosynthesis

Increased morphological fluctuating asymmetry is considered as an indication that the extent of a natural stress has surpassed the ability of the genotype to maintain the normal symmetry in the body plan. Young leaves can suffer by a variety of stresses, such as nutrient deficiencies, drought, heat and cold in combination with high light. Therefore, increased morphological fluctuating asymmetry in mature leaves may be considered as an ecological indicator of such environmental pressures. Hence, deviations from symmetry in a mature leaf may be a reminder of an adversity having occurred when the leaf was young and developing. We argued that a past stress may stigmatize future photosynthesis and we searched for correlations between leaf fluctuating asymmetry and photosynthetic parameters obtained from fast chlorophyll a fluorescence rise curves in mature leaves from seven tree species. The results were species-specific, with four species (Arbutus unedo, Cercis siliquastrum, Platanus orientalis and Populus alba) showing both maximum quantum yield of photosystem II and photosynthetic performance index (PI_total sensu Strasser) to be independent of the alleged juvenile stress, while in one species (Ceratonia siliqua) the two parameters were negatively correlated to leaf fluctuating asymmetry. Interestingly, in two species (Olea europaea and Pistacia lentiscus), higher leaf asymmetry was linked with lower risk of chronic photoinhibitory damage and higher photosynthetic capacity. An ‘ecological stress memory’ may be inferred for some species improving their tolerance to future adversities and global change.     

INTRASPECIFIC VARIATION IN ANT SEX RATIOS AND THE TRIVERS-HARE HYPOTHESIS

We consider worker-controlled sex investments in eusocial Hymenoptera (ants in particular) and assume that relatedness asymmetry is variable among colonies and that workers are able to assess the relatedness asymmetry in their own colony. We predict that such “assessing” workers should maximize their inclusive fitness by specializing in the production of the sex to which they are relatively most related, i.e., colonies whose workers have a relatedness asymmetry below the population average should specialize in males, whereas colonies whose workers have a higher than average relatedness asymmetry should specialize in making females. Our argument yields the expectation that colony sex ratios will be bimodally distributed in ant populations where relatedness asymmetry is variable owing to multiple mating, worker reproduction, and/or polygyny. No such bimodality is expected, however, in ant species where relatedness asymmetry is known to be constant, or in cases where relatedness asymmetry is supposed to be irrelevant due to allospecific brood rearing under queen control, as in the slave-making ants. Comparative data on colony sex ratios in ants are reviewed to test the predictions. The data partly support our contentions, but are as yet insufficient to be considered as decisive evidence.     

Effects of colonization asymmetries on metapopulation persistence

Ocean currents, prevailing winds, and the hierarchical structures of river networks are known to create asymmetries in re-colonization between habitat patches. The impacts of such asymmetries on metapopulation persistence are seldom considered, especially rarely in theoretical studies. Considering three classical models (the island, the stepping stone and the distance-dependent model), we explore how metapopulation persistence is affected by (i) asymmetry in dispersal strength, in which the colonization rate between two patches differs in direction, and (ii) asymmetry in connectivity, in which the overall colonization pattern displays asymmetry (circulating or dendritic networks). Viability can be drastically reduced when directional bias in dispersal strength is higher than 25%. Re-colonization patterns that allow for strong local connectivity provide the highest persistence compared to systems that allow circulation. Finally, asymmetry has relatively weak effects when metapopulations maintain strong general connectivity.     

Heredity and the bimanual asymmetry of human finger and palm dermatoglyphs

An attempt has been made to study the effect of hereditary factors on the asymmetry of morpho-functional quantitative traits, in particular, finger and palm dermatoglyphs (24 indices). The results of examination of 140 twin pairs (83 monozygotic and 57 dizygotic) are presented. The hereditary effects have been found for ten traits when an account is taken of the asymmetry direction, and for nine traits when asymmetry direction is not considered.     

West Wind Drift revisited: testing for directional dispersal in the Southern Hemisphere using event-based tree fitting

Aim Recent studies suggest that if constrained by prevailing wind or ocean currents dispersal may produce predictable, repeated distribution patterns. Dispersal mediated by the West Wind Drift (WWD) and Antarctic Circumpolar Current (AAC) has often been invoked to explain the floristic similarities of Australia, South America and New Zealand. If these systems have been important dispersal vectors then eastward dispersal – from Australia to New Zealand and the western Pacific to South America – is expected to predominate. We investigate whether phylogenies for Southern Hemisphere plant groups provide evidence of historical dispersal asymmetry and more specifically whether inferred asymmetries are consistent with the direction of the WWD/AAC. Location Southern Hemisphere. Methods We assembled a data set of 23 published phylogenies for plant groups that occur in New Zealand, Australia and/or South America. We used parsimony‐based tree fitting to infer the number and direction of dispersals within each group. Observed dispersal asymmetries were tested for significance against a distribution of expected values. Results Our analyses suggest that dispersal has played a major role in establishing present distributions and that there are significant patterns of asymmetry in Southern Hemisphere dispersal. Consistent with the eastward direction of the WWD/ACC, dispersal from Australia to New Zealand was inferred significantly more often than in the reverse direction. No significant patterns of dispersal asymmetry were found between the western Pacific landmasses and South America. However, eastward dispersal was more frequently inferred between Australia and South America, while for New Zealand–South American events westward dispersal was more common. Main conclusions Our results suggest that eastward circumpolar currents have constrained the dispersal of plants between Australia and New Zealand. However, the WWD/ACC appear to have had less of an influence on dispersal between the western Pacific landmasses and South America. This observation may suggest that differences in dispersal mechanism are important – direct wind or water dispersal vs. stepping‐stone dispersal along the Antarctic coast. While our analyses provide useful preliminary insights into dispersal asymmetry in the Southern Hemisphere we will need larger data sets and additional methodological advances in order to test fully these dispersal patterns and infer processes from phylogenetic data.     

Non-consecutive versus consecutive footstrikes as an equivalent method of assessing gait asymmetry

Asymmetry of gait is often studied to characterize populations and assess the efficacy of treatment protocols. However, despite the continuous nature of gait, many studies have made comparisons between data from non-consecutive footstrikes. This is typically considered a limitation of these studies. However, if gait characteristics are sufficiently repeatable within a side, consecutive footstrikes may not be necessary to properly describe the asymmetry between sides. Therefore, one purpose of this study was to compare asymmetry values calculated from consecutive and non-consecutive footstrikes. Additionally, the variability of gait within and between sides was compared to assess the repeatability and distinctiveness of the characteristics on each side. The results suggest that kinetic and kinematic asymmetry can be assessed from either consecutive or non-consecutive footstrikes. Further, the patterns of movement tend to be sufficiently consistent within a side, such that the variability within a side is much lower than the variability between sides. However, there may be some variables, or populations, that exhibit high within-side variability. Several trials of consecutive footstrikes may be a better way to characterize asymmetry of those variables.     

Bite Force Performance,Fluctuating Asymmetry and Antisymmetry in the Mandible of Inbred and Outbred Wild-Derived Strains of Mice (<Emphasis Type="Italic">Mus musculus domesticus</Emphasis>)

Developmental instability, as measured by fluctuating asymmetry is generally considered to increase with genetic and environmental stresses. Few studies have, however, addressed the role of asymmetry in altering organism performance. Here, we measured bite force performance in three strains of inbred and outbred mice derived from wild ancestors. We quantified size and shape directional, and fluctuating asymmetry, as well as inter-individual variation of their mandibles using geometric morphometrics. We also developed a way to estimate shape antisymmetry, to filter it out of the fluctuating asymmetry component. Contrary to our expectations, we found no significant link between bite force and asymmetry levels. Inbreeding did not produce any clear and significant increase or decrease in neither inter-individual variance, nor fluctuating asymmetry. Furthermore, fluctuating asymmetry levels were unrelated to inter-individual variance levels, although these two types of variation affected the same areas of the mandible. We did not highlight any impact of inbreeding depression on bite force. Fluctuating asymmetry was reduced in the mandible, which we argue may be linked to its functional relevance. We found some significant but very reduced antisymmetry possibly linked to lateralization. This lateralization did not relate to any bite force difference. Our results show that neither inbreeding, nor asymmetry (combining fluctuating, directional asymmetry and antisymmetry) significantly affect bite force performance in mice, and that despite affecting the same morphological regions, developmental stability and canalization are independent.     

Polymorphisms for purely cytoplasmically inherited traits in bisexual plants

It is shown that cytoplasm polymorphisms transmitted only by the ovules can be maintained without gene-cytoplasmic interactions. The necessary prerequisites are asymmetry of the plasmotypes in production of ovules and pollen (sexual asymmetry), incomplete and frequency-dependent fertilization efficiency and differential selfing rates. These factors can generate the negative frequency dependence of cytoplasmic fitnesses required for a stable polymorphism. The model considered allows also for facultative fixation of either of two plasmotypes and, thus, may produce all of the dynamical characteristics known for nuclear selection with two alleles at one locus.

Strong sexual asymmetry, which probably occurs frequently in bisexual plants, may facilitate stable cytoplasmic polymorphisms. However, these polymorphisms may also endanger survival of the whole population in the absence of nuclear interactions. Gene-cytoplasmic interactions avoid this risk and, at the same time, utilize the advantages of sexual asymmetry in maintaining genetic polymorphisms.

     

Patterns of humeral asymmetry among Late Pleistocene humans

Human humeral diaphyseal asymmetry in midshaft and mid-distal rigidity is assessed through the Late Pleistocene in samples of late archaic (Neandertal) and early modern humans. It is considered with respect to directionality (handedness), levels of asymmetry, body size and sexual differences. The overall Late Pleistocene sample indicates a right-handed preference in frequencies (right: 74.8%, left: 15.0%, ambiguous: 10.3%), which are similar to those of recent human samples. Average levels of humeral asymmetry are elevated relative to Holocene samples through all but the small Middle Paleolithic modern human and eastern Eurasian late Upper Paleolithic samples. Humeral asymmetry is especially high among the males relative to the females, and the possibility of a division of labor between uni-manual tasks (mostly male) and bi-manual tasks (mostly female) is considered. At the same time, there is a general pattern of increased asymmetry with larger body size, but it remains unclear to what extent it reflects body size versus sexual effects on bilateral humeral loading. There do not appear to have been substantial changes in humeral asymmetry through time, indicating a continuity of similar manual behavioral patterns through the Late Pleistocene, despite considerable changes in technology through the Late Pleistocene.     

Directional asymmetry reversal of male copulatory organs in chafer beetles (Coleoptera: Scarabaeidae): implications on left–right polarity determination in insect terminalia

During large‐scale examinations of male genitalia for taxonomic studies of Sericini chafers (Coleoptera: Scarabaeidae), we have found that reversals of directed left–right (LR) asymmetry in male copulatory organs are compared to other insects not common. However, such inversions do occur occasionally and they must be considered a significant ‘source of error’ in taxonomic studies. Our data indicate asymmetry reversal of male genitalia affects only the abdominal segments (genitalia) as changes in asymmetric structures of the head and thorax were not observed. Based on these observations, we believe that this partial abdominal LR asymmetry reversal of terminalia could be due to a local change in the polarity determining LR patterning in the growth zone of posterior abdominal segments as development of these segments begins.     

Loss of membrane phospholipid asymmetry during activation of blood platelets and sickled red cells; mechanisms and physiological significance

Membrane phospholipid asymmetry is considered to be a general property of biological membranes. Detailed information is presently available on the non-random orientation of phospholipids in red cell- and platelet membranes. The outer leaflet of the lipid bilayer membrane is rich in choline-phospholipids, whereas amino-phospholipids are abundant in the inner leaflet. Studies with blood platelets have shown that these asymmetries are not maintained when the cells are activated in various ways. Undoing the normal asymmetry of membrane phospholipids in activated blood cells is presumably mediated by increased transbilayer movement of phospholipids. This process, which leads to increased exposure of negatively charged phosphatidylserine at the outer surface, plays an important physiological role in local blood clotting reactions. A similar phenomenon occurs in sickled red cells. Phospholipid vesicles breaking off from reversibly sickled cells contribute similarly to intravascular clotting in the crisis phase of sickle cell disease.The loss of membrane phospholipid asymmetry in activated platelets seems to be strictly correlated with degradation of cytoskeletal proteins by endogenous calpain. It is remarkable that membrane phospholipid asymmetry can be (partly) restored when activated platelets are treated with reducing agents. This leads to disappearance of phosphatidylserine from the outer leaflet where it was previously exposed during cell activation. These observations will be discussed in relation to two mechanisms which have been recognized to play a role in the regulation of membrane phospholipid asymmetry; i.e. the interaction of aminophospholipids to cytoskeletal proteins, and the involvement of a phospholipid-translocase catalyzing outward-inward transbilayer movement of amino-phospholipids.     

The Fluid–Mosaic model of cell membranes: A brief introduction,historical features,some general principles,and its adaptation to current information

The Fluid–Mosaic Membrane (FMM) model was originally proposed as a general, nanometer-scale representation of cell membranes (Singer and Nicolson, 1972). The FMM model was based on some general principles, such as thermodynamic considerations, intercalation of globular proteins into a lipid bilayer, independent protein and lipid dynamics, cooperativity and other characteristics. Other models had trimolecular structures or membrane globular lipoprotein units. These latter models were flawed, because they did not allow autonomous lipids, membrane domains or discrete lateral dynamics. The FMM model was also consistent with membrane asymmetry, cis- and trans-membrane linkages and associations of membrane components into multi-molecular complexes and domains. It has remained useful for explaining the basic organizational principles and properties of various biological membranes. New information has been added, such as membrane-associated cytoskeletal assemblies, extracellular matrix interactions, transmembrane controls, specialized lipid-protein domains that differ in compositions, rotational and lateral mobilities, lifetimes, functions, and other characteristics. The presence of dense, structured membrane domains has reduced significantly the extent of fluid-lipid membrane areas, and the FMM model is now considered to be more mosaic and dense than the original proposal.     

Axis determination in C. elegans: initiating and transducing polarity.

The anterior-posterior axis in Caenorhabditis elegans is determined by the sperm and leads to the asymmetric localisation of PAR (partitioning-defective) proteins, which are critical for polarity. New findings demonstrate that sperm asters play a critical role and suggest models for how PAR asymmetry is established. In addition, studies of blastomere fate determination and heterotrimeric G proteins have started to uncover how initial polarity may be translated into the asymmetric distribution of maternal proteins and the control of spindle position.     

Fluctuating asymmetry in antlers of fallow deer (Dama dama): the relative roles of environmental stress and sexual selection

Antler lengths were recorded of a total of 250 male fallow deer (Dama dama (L)). Animals sampled were from marked populations where the majority of individuals were of known age. Asymmetry in antler length was normally distributed with a mean not significantly different from zero, confirming that differences in length between the antler pair constitute a true fluctuating asymmetry (FA). We found no clear relationship between the degree of asymmetry in antler length of an individual male and either population density or actual body mass. We did, however, detect a significant relationship between asymmetry and deviation from maximum cohort bodyweight. If deviation from maximum weight within a cohort may be considered some index of competitive success or increasing environmental stress, this may suggest that asymmetry in antler length relates in some way to developmental stress suffered by the individual concerned. The degree of asymmetry recorded in antler length also showed a significant decline with animal age, with antlers of animals of 2 years or older showing significantly greater symmetry. This is consistent with a hypothesis that despite continued competition for resources, there is a changing balance of selection pressure as animals reach maturity, with increased pressure from sexual selection requiring males to produce significantly more symmetrical ornaments.     

Sex-dependent structural asymmetry of the medial habenular nucleus of the chicken brain

Summary An investigation of structural asymmetry in the avian brain was conducted on the epithalamic medial habenular nucleus of the chicken. Twelve male and ten female two-day-old chickens were used for a morphometric evaluation of asymmetry. The medial habenular nucleus was measured from paraffin-wax-embedded, 8 m-thick sections by use of a semiautomatic image analyser. The volumes of the right and left medial habenula of each animal were statistically analysed (within animal experimental design). The right medial habenula in males showed significant group asymmetry. In contrast, females failed to demonstrate group bias in favour of either hemisphere. However, individual females were lateralised, with either a larger right or left medial habenula. Although individuals of both sexes were lateralised, there was no significant sex difference in volume in either the right or left medial habenula.We propose that sex-linked structural asymmetry may be influenced by steroid hormonal effects in the central nervous system, and that such asymmetry could be more prevalent in the non-mammalian vertebrate brain than previously considered.     

The preference for movement direction in a T-maze in planarians

Characteristics of spatial orientation in T-maze were studied in 1768 Planaria of following types: Dugesia tigrina (sexless and sexual race), Dugesia lugubris, Ijmia tenuis, Bdellacephala punctata. It was shown that from one third to one half of individuals were characterized by asymmetry of movement direction preference. The preference of right turning was typical for Dugesia tigrina; Dugesia lugubris, Ijmia tenuis, Bdellacephala punctata preferred left turning. The asymmetry described is considered as a primitive form of species functional asymmetry.