Search results for "symmetry"
showing 10 items of 3576 documents
Impact of sewage pollution on two species of sea urchins in the Mediterranean Sea (Cortiou, France): radial asymmetry as a bioindicator of stress.
2015
9 pages; International audience; BackgroundThe surroundings of the Cortiou sewage are among the most polluted environments of the French Mediterranean Sea (Marseilles, France). So far, no studies have precisely quantified the impact of pollution on the development of organisms in this area.MethodsWe used a fluctuating asymmetry (FA) measure of developmental instability (DI) to assess environmental stress in two species of radially symmetric sea urchins (Arbacia lixula and Paracentrotus lividus). For six sampling sites (Cortiou, Riou, Maire, East Maire, Mejean, and Niolon), levels of FA were calculated from continuous and discrete skeletal measures of ambulacral length, number of pore pairs …
Pollination biology in Roepera (Zygophyllaceae): How flower structure and shape influence foraging activity
2019
The foraging behavior of bees is a complex phenomenon that depends on numerous physical features of flowers. Of particular importance are accessibility of floral rewards, floral proportions, symmetry and orientation. The flowers of Roepera are characterized by the presence of staminal scales (SS), which play an important role in nectar protection. We studied two species of Roepera with different symmetry and flower orientation, which are mainly visited by honeybees (Apis mellifera). We aimed to show how the foraging behavior of honey bees is affected by the function of SS, floral symmetry and orientation. The foraging behavior was documented by video photography. Handling time, access to ne…
Symmetry breaking in mass-recruiting ants: extent of foraging biases depends on resource quality.
2016
Abstract The communication involved in the foraging behaviour of social insects is integral to their success. Many ant species use trail pheromones to make decisions about where to forage. The strong positive feedback caused by the trail pheromone is thought to create a decision between two or more options. When the two options are of identical quality, this is known as symmetry breaking, and is important because it helps colonies to monopolise food sources in a competitive environment. Symmetry breaking is thought to increase with the quantity of pheromone deposited by ants, but empirical studies exploring the factors affecting symmetry breaking are limited. Here, we tested if (i) greater …
Insecticide residues in cotton soils of Burkina Faso and effects of insecticides on fluctuating asymmetry in honey bees (Apis mellifera Linnaeus).
2011
8 pages; International audience; Four insecticides (acetamiprid, cypermethrin, endosulfan and profenofos) are used quarterly in the cotton-growing areas of Burkina Faso, West Africa. These insecticides were investigated in soils collected from traditionally cultivated and new cotton areas. Also, the effects of insecticide exposure on the developmental instability of honey bees, Apis mellifera, were explored. In soil samples collected three months after insecticide treatments, endosulfan and profenofos concentrations varied in the range of 10-30μgkg(-1) in the traditionally cultivated zones and 10-80μgkg(-1) in the new cotton zones, indicating a pollution of agricultural lands. However, only…
Heterozygosity-fitness correlations in adult and juvenile Zenaida Dove, Zenaida aurita.
2013
10 pages; International audience; Understanding how fitness is related to genetic variation is of crucial importance in both evolutionary ecology and conservation biology. We report a study of heterozygosity-fitness correlations in a wild, noninbred population of Zenaida Doves, Zenaida aurita, based on a sample comprising 489 individuals (382 adults and 107 juveniles) typed at 13 microsatellite loci, resulting in a data set comprising 5793 genotypes. In both adults and juveniles, and irrespective of sex, no evidence was found for an effect of either multilocus or single-locus heterozygosity on traits potentially related to fitness such as foraging tactic, competitive ability, and fluctuatin…
Honeybees prefer novel insect-pollinated flower shapes over bird-pollinated flower shapes
2019
AbstractPlant–pollinator interactions have a fundamental influence on flower evolution. Flower color signals are frequently tuned to the visual capabilities of important pollinators such as either bees or birds, but far less is known about whether flower shape influences the choices of pollinators. We tested European honeybee Apis mellifera preferences using novel achromatic (gray-scale) images of 12 insect-pollinated and 12 bird-pollinated native Australian flowers in Germany; thus, avoiding influences of color, odor, or prior experience. Independent bees were tested with a number of parameterized images specifically designed to assess preferences for size, shape, brightness, or the number…
Graph Filtering of Time-Varying Signals over Asymmetric Wireless Sensor Networks
2019
In many applications involving wireless sensor networks (WSNs), the observed data can be modeled as signals defined over graphs. As a consequence, an increasing interest has been witnessed to develop new methods to analyze graph signals, leading to the emergence of the field of Graph Signal Processing. One of the most important processing tools in this field is graph filters, which can be easily implemented distributedly over networks by means of cooperation among the nodes. Most of previous works related to graph filters assume the same connection probability in both link directions when transmitting an information between two neighboring nodes. This assumption is not realistic in practice…
Making sense of crises: the implications of information asymmetries for resilience and social justice in disaster-ridden communities
2017
New information and communication technologies (ICT) have enabled communities to collect and share information and tap into a network of peers in unprecedented ways. For more than a decade, informa...
Modelling load-transmission mechanisms in axially loaded RC columns retrofitted with steel jackets
2018
The use of steel jacketing technique is a common practice for retrofitting existing reinforced concrete (RC) columns, as it allows increasing load-carrying capacity and ductility of the member. When the external jacket has no-end connections – i.e. the jacket is indirectly loaded- the load sustained by the column is transferred from the inner RC core to the external jacket through shear stresses along the contact surface. The assessment of this mechanism is quite complex, due to the marked non-linear behaviour of constituent materials and to the calibration of a proper shear stress-relative slip constitutive law of the concrete-to-steel interface. In this paper, a step-by-step analytical ap…
Trochoidal motion and pair generation in skyrmion and antiskyrmion dynamics under spin-orbit torques
2018
Magnetic skyrmions are swirling magnetic spin structures that could be used to build next-generation memory and logic devices. They can be characterized by a topological charge that describes how the spin winds around the core. The dynamics of skyrmions and antiskyrmions, which have opposite topological charges, are typically described by assuming a rigid core. However, this reduces the set of variables that describe skyrmion motion. Here we theoretically explore the dynamics of skyrmions and antiskyrmions in ultrathin ferromagnetic films and show that current-induced spin–orbit torques can lead to trochoidal motion and skyrmion–antiskyrmion pair generation, which occurs only for either the…