The Experts below are selected from a list of 4962 Experts worldwide ranked by ideXlab platform

Browman Howard - One of the best experts on this subject based on the ideXlab platform.

  • Glass eels (Anguilla anguilla) imprint the magnetic Direction of tidal currents from their juvenile estuaries
    'Springer Science and Business Media LLC', 2019
    Co-Authors: Cresci Alessandro, Durif Caroline, Paris, Claire B., Shema, Steven D., Skiftesvik, Anne Berit, Browman Howard
    Abstract:

    The European eel (Anguilla anguilla) hatches in the Sargasso Sea and migrates to European and North African freshwater. As glass eels, they reach estuaries where they become pigmented. Glass eels use a tidal phase-dependent magnetic Compass for orientation, but whether their magnetic Direction is innate or imprinted during migration is unknown. We tested the hypothesis that glass eels imprint their tidal-dependent magnetic Compass Direction at the estuaries where they recruit. We collected 222 glass eels from estuaries flowing in different cardinal Directions in Austevoll, Norway. We observed the orientation of the glass eels in a magnetic laboratory where the magnetic North was rotated. Glass eels oriented towards the magnetic Direction of the prevailing tidal current occurring at their recruitment estuary. Glass eels use their magnetic Compass to memorize the magnetic Direction of tidal flows. This mechanism could help them to maintain their position in an estuary and to migrate upstream.publishedVersio

  • Glass eels (Anguilla anguilla) imprint the magnetic Direction of tidal currents from their juvenile estuaries
    2019
    Co-Authors: Cresci Alessandro, Durif Caroline, Paris, Claire B., Shema, Steven D., Skiftesvik, Anne Berit, Browman Howard
    Abstract:

    The European eel (Anguilla anguilla) hatches in the Sargasso Sea and migrates to European and North African freshwater. As glass eels, they reach estuaries where they become pigmented. Glass eels use a tidal phase-dependent magnetic Compass for orientation, but whether their magnetic Direction is innate or imprinted during migration is unknown. We tested the hypothesis that glass eels imprint their tidal-dependent magnetic Compass Direction at the estuaries where they recruit. We collected 222 glass eels from estuaries flowing in different cardinal Directions in Austevoll, Norway. We observed the orientation of the glass eels in a magnetic laboratory where the magnetic North was rotated. Glass eels oriented towards the magnetic Direction of the prevailing tidal current occurring at their recruitment estuary. Glass eels use their magnetic Compass to memorize the magnetic Direction of tidal flows. This mechanism could help them to maintain their position in an estuary and to migrate upstream

Randolf Menzel - One of the best experts on this subject based on the ideXlab platform.

  • way finding in displaced clock shifted bees proves bees use a cognitive map
    Proceedings of the National Academy of Sciences of the United States of America, 2014
    Co-Authors: James F Cheeseman, Craig D Millar, Uwe Greggers, Konstantin Lehmann, Matthew D M Pawley, C R Gallistel, Guy R Warman, Randolf Menzel
    Abstract:

    Mammals navigate by means of a metric cognitive map. Insects, most notably bees and ants, are also impressive navigators. The question whether they, too, have a metric cognitive map is important to cognitive science and neuroscience. Experimentally captured and displaced bees often depart from the release site in the Compass Direction they were bent on before their capture, even though this no longer heads them toward their goal. When they discover their error, however, the bees set off more or less directly toward their goal. This ability to orient toward a goal from an arbitrary point in the familiar environment is evidence that they have an integrated metric map of the experienced environment. We report a test of an alternative hypothesis, which is that all the bees have in memory is a collection of snapshots that enable them to recognize different landmarks and, associated with each such snapshot, a sun-Compass–referenced home vector derived from dead reckoning done before and after previous visits to the landmark. We show that a large shift in the sun-Compass rapidly induced by general anesthesia does not alter the accuracy or speed of the homeward-oriented flight made after the bees discover the error in their initial postrelease flight. This result rules out the sun-referenced home-vector hypothesis, further strengthening the now extensive evidence for a metric cognitive map in bees.

  • encoding spatial information in the waggle dance
    The Journal of Experimental Biology, 2005
    Co-Authors: Rodrigo J. De Marco, Randolf Menzel
    Abstract:

    Apis mellifera bees execute waggle dances to recruit other bees to desirable food sources. Several components of the waggle dance are correlated with the Direction of and the distance to food. Moreover, recruits use the spatial information encoded in the dance to locate the signalled food. However, although dance communication has been studied extensively, little is known about how the dancers combine the Compass (Direction) and the odometric (distance) information they acquire during the foraging flight. In the present study, we analysed the encoding of spatial information in the waggle dance by manipulating the navigational information provided to dancing bees. To this end, we took advantage of the bees' visually driven odometer. We found that the waggle dance basically encodes information on the distance gauged during the outbound (hive-to-food) flight. However, it does not necessarily refer to a global vector based on path integration of the outbound flight. Whenever the Direction connecting the subjective food location and the hive does not match the Direction of the global vector, dancers refer to a Direction close to that of the shortcut connecting the actual food location and the hive. Moreover, in our experiments, this Direction was close to that of the inbound (food-to-hive) flight, indicating that landmark-based information is computed during the inbound flight and that it may strongly affect the encoding of Directional information in the waggle dance. Moreover, we found that the bees' experience of the terrain modulates the encoding of spatial information in the waggle dance, suggesting that interactions between path integration and visual landmarks are computed in the context of dance communication.

Frederic Baret - One of the best experts on this subject based on the ideXlab platform.

  • estimates of plant density of wheat crops at emergence from very low altitude uav imagery
    Remote Sensing of Environment, 2017
    Co-Authors: Xiuliang Jin, Shouyang Liu, Frederic Baret, Matthieu Hemerle, Alexis Comar
    Abstract:

    Abstract Plant density is useful variable that determines the fate of the wheat crop. The most commonly used method for plant density quantification is based on visual counting from ground level. The objective of this study is to develop and evaluate a method for estimating wheat plant density at the emergence stage based on high resolution imagery taken from UAV at very low altitude with application to high throughput phenotyping in field conditions. A Sony ILCE α5100L RGB camera with 24 Mpixels and equipped with a 60 mm focal length lens was flying aboard an hexacopter at 3 to 7 m altitude at about 1 m/s speed. This allows getting ground resolution between 0.20 mm to 0.45 mm, while providing 59–77% overlap between images. The camera was looking with 45° zenith angle in a Compass Direction perpendicular to the row Direction to maximize the cross section viewed of the plants and minimize the effect of the wind created by the rotors. Agisoft photoscan software was then used to derive the position of the cameras for each image. Images were then projected on the ground surface to finally extract subsamples used to estimate the plant density. The extracted images were first classified to separate the green pixels from the background and the rows were then identified and extracted. Finally, image object (group of connected green pixels) was identified on each row and the number of plants they contain was estimated using a Support Vector Machine whose training was optimized using a Particle Swarm Optimization. Three experiments were conducted in Greoux, Avignon and Clermont sites with some variability in the sowing dates, densities, genotypes, flight altitude, and growth stage at the time of the image acquisition. The application of the method on the 270 samples available over the three sites provides a RMSE and relative RMSE on estimates of 34.05 plants/m 2 and 14.31% with a bias of 9.01 plants/m 2 . However, differences in performances were observed between the three sites, mostly related to the growth stage at the time of the flight. Plants should have between one to two leaves when images are taken. Further, a specific sensitivity analysis shows that the ground resolution of the images should be better than 0.40 mm. Finally, the repeatability of the method is good especially when images are taken from similar observational geometries. The current limits and possible improvements of the method proposed are finally discussed.

  • gai estimates of row crops from downward looking digital photos taken perpendicular to rows at 57 5 zenith angle theoretical considerations based on 3d architecture models and application to wheat crops
    Agricultural and Forest Meteorology, 2010
    Co-Authors: Frederic Baret, B De Solan, Raul Lopezlozano, Marie Weiss
    Abstract:

    Abstract This study describes a technique to estimate green area index (GAI) of row crops from gap fraction measurements at 57.5° perpendicular to the row using downward looking digital photos. This particular Directional configuration makes the gap fraction independent from leaf angle distribution and minimizes leaf clumping when plants overlap within the row and when rows overlap from this particular Direction which is the case for several crops including wheat, maize, sorghum, sunflower and soybean. This was demonstrated from generic row crop canopy architecture models. Additional simulations over realistic 3D scenes of wheat crop allowed to calibrate the following equation relating the gap fraction ( Po (57.5°)) to GAI for this particular Directional configuration: Po (57.5°) =  e −0.824· GAI . This relationship appears very robust across development stages, cultivars and variations due to environmental conditions. When comparing with the situation where leaves are randomly distributed, performances degrade significantly, demonstrating that some residual clumping ( Ω  = 0.89) has to be accounted for. Field experiments were conducted over wheat crops using colour digital photos taken at 57.5° zenith angle from above in a Compass Direction perpendicular to the rows. The corresponding gap fraction was computed after image segmentation based on the three colours. The equation derived from wheat architecture model simulations was then used to estimate GAI. Comparison with destructive GAI field measurements shows very good performances with a relative RMSE of 12%. GAI values estimated with this technique were also showing a good consistency with LAI2000 PAI (plant area index) estimates. However, systematic biases between the two estimates were observed, due to canopy elements at the bottom of the canopy not sampled by the instrument because of the height of the LAI2000 sensor, as well as accounting for the residual clumping in the proposed method. These results suggest that this GAI estimation method is very efficient over wheat crops from emergence up to flowering independently from possible architecture variation due to genotype or environmental condition differences. Possible extension to other crops is discussed.

Henrik Mouritsen - One of the best experts on this subject based on the ideXlab platform.

  • a visual pathway links brain structures active during magnetic Compass orientation in migratory birds
    PLOS ONE, 2007
    Co-Authors: Dominik Heyers, Martina Manns, Harald Luksch, Onur Gunturkun, Henrik Mouritsen
    Abstract:

    The magnetic Compass of migratory birds has been suggested to be light-dependent. Retinal cryptochrome-expressing neurons and a forebrain region, “Cluster N”, show high neuronal activity when night-migratory songbirds perform magnetic Compass orientation. By combining neuronal tracing with behavioral experiments leading to sensory-driven gene expression of the neuronal activity marker ZENK during magnetic Compass orientation, we demonstrate a functional neuronal connection between the retinal neurons and Cluster N via the visual thalamus. Thus, the two areas of the central nervous system being most active during magnetic Compass orientation are part of an ascending visual processing stream, the thalamofugal pathway. Furthermore, Cluster N seems to be a specialized part of the visual wulst. These findings strongly support the hypothesis that migratory birds use their visual system to perceive the reference Compass Direction of the geomagnetic field and that migratory birds “see” the reference Compass Direction provided by the geomagnetic field.

Cresci Alessandro - One of the best experts on this subject based on the ideXlab platform.

  • Glass eels (Anguilla anguilla) imprint the magnetic Direction of tidal currents from their juvenile estuaries
    'Springer Science and Business Media LLC', 2019
    Co-Authors: Cresci Alessandro, Durif Caroline, Paris, Claire B., Shema, Steven D., Skiftesvik, Anne Berit, Browman Howard
    Abstract:

    The European eel (Anguilla anguilla) hatches in the Sargasso Sea and migrates to European and North African freshwater. As glass eels, they reach estuaries where they become pigmented. Glass eels use a tidal phase-dependent magnetic Compass for orientation, but whether their magnetic Direction is innate or imprinted during migration is unknown. We tested the hypothesis that glass eels imprint their tidal-dependent magnetic Compass Direction at the estuaries where they recruit. We collected 222 glass eels from estuaries flowing in different cardinal Directions in Austevoll, Norway. We observed the orientation of the glass eels in a magnetic laboratory where the magnetic North was rotated. Glass eels oriented towards the magnetic Direction of the prevailing tidal current occurring at their recruitment estuary. Glass eels use their magnetic Compass to memorize the magnetic Direction of tidal flows. This mechanism could help them to maintain their position in an estuary and to migrate upstream.publishedVersio

  • Glass eels (Anguilla anguilla) imprint the magnetic Direction of tidal currents from their juvenile estuaries
    2019
    Co-Authors: Cresci Alessandro, Durif Caroline, Paris, Claire B., Shema, Steven D., Skiftesvik, Anne Berit, Browman Howard
    Abstract:

    The European eel (Anguilla anguilla) hatches in the Sargasso Sea and migrates to European and North African freshwater. As glass eels, they reach estuaries where they become pigmented. Glass eels use a tidal phase-dependent magnetic Compass for orientation, but whether their magnetic Direction is innate or imprinted during migration is unknown. We tested the hypothesis that glass eels imprint their tidal-dependent magnetic Compass Direction at the estuaries where they recruit. We collected 222 glass eels from estuaries flowing in different cardinal Directions in Austevoll, Norway. We observed the orientation of the glass eels in a magnetic laboratory where the magnetic North was rotated. Glass eels oriented towards the magnetic Direction of the prevailing tidal current occurring at their recruitment estuary. Glass eels use their magnetic Compass to memorize the magnetic Direction of tidal flows. This mechanism could help them to maintain their position in an estuary and to migrate upstream