Search results for "DIRECTION"
showing 10 items of 343 documents
Negative frequency-dependent selection of sexually antagonistic alleles in Myodes glareolus.
2011
Sexually antagonistic genetic variation, where optimal values of traits are sex-dependent, is known to slow the loss of genetic variance associated with directional selection on fitness-related traits. However, sexual antagonism alone is not sufficient to maintain variation indefinitely. Selection of rare forms within the sexes can help to conserve genotypic diversity. We combined theoretical models and a field experiment with Myodes glareolus to show that negative frequency-dependent selection on male dominance maintains variation in sexually antagonistic alleles. In our experiment, high-dominance male bank voles were found to have low-fecundity sisters, and vice versa. These results show …
Rapid assessment of female preference for male size predicts subsequent choice of spawning partner in a socially monogamous cichlid fish.
2011
5 pages; International audience; Although size-assortative mating in convict cichlids, Amatitliana nigrofasciata, is supposed to result from mutual mating preference for larger individuals, female choice in relation to male size remains ambiguous. We revisited the evidence for directional preference for larger males in female convict cichlids using a classical two-way choice apparatus in which each female could decide to spend time in front of a small male or a large one. We found evidence for female preference for large males, as assessed from association preference during a 4-hour period following encounter. Furthermore, females decided to spawn in front of the initially preferred male mo…
Female mate choice in convict cichlids is transitive and consistent with a self-referent directional preference
2013
10 pages; International audience; INTRODUCTION: One of the most important decisions that an animal has to make in its life is choosing a mate. Although most studies in sexual selection assume that mate choice is rational, this assumption has not been tested seriously. A crucial component of rationality is that animals exhibit transitive choices: if an individual prefers option A over B, and B over C, then it also prefers A over C. RESULTS: We assessed transitivity in mate choice: 40 female convict cichlids had to make a series of binary choices between males of varying size. Ninety percent of females showed transitive choices. The mean preference index was significantly higher when a female…
Spatial heterogeneity of spring phytoplankton in a large tropical reservoir: could mass effect homogenize the heterogeneity by species sorting?
2018
Reservoirs are river–lake hybrid ecosystems characterized by a marked longitudinal zonation and variable flushing rates depending on the use of stored waters. The structure of their phytoplankton is therefore subjected to the interplay between the environmental conditions of the different zones (species sorting) and the strength of the unidirectional flow (mass effect). The spatial distribution of spring phytoplankton was investigated in a tropical reservoir across its different zones. Phytoplankton displayed heterogeneous spatial patterns from the turbulent, nutrient-rich riverine zones to the relatively stable lacustrine zone. The analysis of this spatial heterogeneity revealed the relati…
Modelling vertical and lateral seed bank movements during mouldboard ploughing
2000
Abstract The vertical distribution of weed seeds in the soil is of fundamental importance because seedling emergence depends on seed depth. The lateral displacement of the earth during mouldboard ploughing contributes to the dispersal of the weeds inside the tilled field. In order to model vertical and lateral seed displacements during ploughing, an existing model describing soil particle movements for different ploughing characteristics (depth and width) and soil structures was tested on a multilocal field trial. The trials were carried out in 1996 and 1997 and comprised two soil textures and three soil structures; tillage was performed with a mouldboard plough at varying ploughing widths …
Size does matter — the eco-evolutionary effects of changing body size in fish
2020
Body size acts as a proxy for many fitness-related traits. Body size is also subject to directional selection from various anthropogenic stressors such as increasing water temperature, decreasing dissolved oxygen, fisheries, as well as natural predators. Changes in individual body size correlate with changes in fecundity, behaviour, and survival and can propagate through populations and ecosystems by truncating age and size structures and changing predator–prey dynamics. In this review, we will explore the causes and consequences of changing body size in fish in the light of recent literature and relevant theories. We will investigate the central role of body size in ecology by first discu…
Rotation estimation and vanishing point extraction by omnidirectional vision in urban environment
2012
International audience; Rotation estimation is a fundamental step for various robotic applications such as automatic control of ground/aerial vehicles, motion estimation and 3D reconstruction. However it is now well established that traditional navigation equipments, such as global positioning systems (GPSs) or inertial measurement units (IMUs), suffer from several disadvantages. Hence, some vision-based works have been proposed recently. Whereas interesting results can be obtained, the existing methods have non-negligible limitations such as a difficult feature matching (e.g. repeated textures, blur or illumination changes) and a high computational cost (e.g. analyze in the frequency domai…
Omnidirectional vision for UAV: applications to attitude, motion and altitude estimation for day and night conditions
2012
International audience; This paper presents the combined applications of omnidirectional vision featuring on its application to aerial robotics. Omnidirectional vision is first used to compute the attitude, altitude and motion not only in rural environment but also in the urban space. Secondly, a combination of omnidirectional and perspective cameras permits to estimate the altitude. Finally we present a stereo system consisting of an omnidirectional camera with a laser pattern projector enables to calculate the altitude and attitude during the improperly illuminated conditions to dark environments. We demonstrate that omnidirectional camera in conjunction with other sensors is suitable cho…
Visual contact with catadioptric cameras
2015
Abstract Time to contact or time to collision (TTC) is utmost important information for animals as well as for mobile robots because it enables them to avoid obstacles; it is a convenient way to analyze the surrounding environment. The problem of TTC estimation is largely discussed in perspective images. Although a lot of works have shown the interest of omnidirectional camera for robotic applications such as localization, motion, monitoring, few works use omnidirectional images to compute the TTC. In this paper, we show that TTC can be also estimated on catadioptric images. We present two approaches for TTC estimation using directly or indirectly the optical flow based on de-rotation strat…
Visual tracking with omnidirectional cameras: an efficient approach
2011
International audience; An effective technique for applying visual tracking algorithms to omni- directional image sequences is presented. The method is based on a spherical image representation which allows taking into account the distortions and nonlinear resolution of omnidirectional images. Experimental results show that both deterministic and probabilistic tracking methods can effectively be adapted in order to robustly track an object with an omnidirectional camera.