196,103 research outputs found
Cuttlefish camouflage:Blending in by matching background features
No full textCuttlefish are masters of camouflage and show a remarkable ability to hide in plain sight. A new study reveals how these animals translate visual information about their surroundings into effective camouflage patterns
Scorpionfish rapidly change colour in response to their background
No full textBackground: To facilitate background matching in heterogenous environments, some animals rapidly change body colouration. Marine predatory fishes might use this ability to hide from predators and prey. Here, we focus on scorpionfishes (Scorpaenidae), well-camouflaged, bottom-dwelling sit-and-wait predators. We tested whether Scorpaena maderensis and Scorpaena porcus adjust body luminance and hue in response to three artificial backgrounds and thereby achieve background matching. Both scorpionfish species are also red fluorescent, which could contribute to background matching at depth. Therefore, we tested whether red fluorescence is also regulated in response to different backgrounds. The darkest and the lightest backgrounds were grey, while the third background was orange of intermediate luminance. Scorpionfish were placed on all three backgrounds in a randomised repeated measures design. We documented changes in scorpionfish luminance and hue with image analysis and calculated contrast to the backgrounds. Changes were quantified from the visual perspective of two potential prey fishes, the triplefin Tripterygion delaisi and the goby Pomatoschistus flavescens. Additionally, we measured changes in the area of scorpionfish red fluorescence. Because scorpionfish changed quicker than initially expected, we measured luminance change at a higher temporal resolution in a second experiment. Results: Both scorpionfish species rapidly adjusted luminance and hue in response to a change of background. From prey visual perspective, scorpionfishes’ body achromatic and chromatic contrasts against the background were high, indicating imperfect background matching. Chromatic contrasts differed considerably between the two observer species, highlighting the importance of choosing natural observers with care when studying camouflage. Scorpionfish displayed larger areas of red fluorescence with increasing luminance of the background. With the second experiment, we showed that about 50% of the total luminance change observed after one minute is achieved very rapidly, in five to ten seconds. Conclusion: Both scorpionfish species change body luminance and hue in response to different backgrounds within seconds. While the achieved background matching was suboptimal for the artificial backgrounds, we propose that the observed changes were intended to reduce detectability, and are an essential strategy to camouflage in the natural environment
Scorpionfish adjust skin pattern contrast on different backgrounds
No full textThe two scorpionfish species Scorpaena maderensis and S. porcus are well camouflaged ambush predators that rapidly change body colouration to adjust to background colour in less than 1 min. We tested whether individuals of both species also adjust body pattern to that of the background. We placed fish on backgrounds of different pattern granularity and quantified the change in fish body pattern over 1 min. We used calibrated image analysis to analyse the patterns from the visual perspective of a prey fish species using a granularity (pattern energy) analysis and an image clustering approach. In our experiment, fish did not change their most contrasting pattern components as defined by the dominant marking size, but changed their average marking size. Moreover, fish responded with a change in pattern in contrast to the different experimental backgrounds, especially when compared to the acclimation phase. These results indicate that scorpionfish have one main pattern that can be adjusted by modulating its internal contrast. A reduction in pattern contrast could thereby improve background matching, while an increase could promote camouflage via disruptive colouration
Stealth and deception: Adaptive motion camouflage in hunting broadclub cuttlefish
No full textMaintaining camouflage while moving is a challenge faced by many predators. Some exploit background motion to hide while hunting, and others may use coloration and behavior to generate motion noise that impairs detection or recognition. Here, we uncover a unique form of motion camouflage, showing that broadclub cuttlefish pass dark stripes downward across their head and arms to disguise their hunting maneuvers. This "passing-stripe"display reduces the probability of response to predatory expanding stimuli by prey crabs in a lab-based experiment, is modulated according to approach speed during a hunt, and generates a motion pattern that is different from that of looming predators. This form of motion camouflage likely functions by overwhelming the threatening motion of the approaching predator with nonthreatening downward motion generated by the rhythmic stripes
AMČR - archeologický záznam M-201500045A
No full textStav: 3Označení: 464/2014Lokalizace/okolnosti: Santon
The contrast sensitivity function of a small cryptobenthic marine fish
No full textSpatial resolution is a key property of eyes when it comes to understanding how animals' visual signals are perceived. This property can be robustly estimated by measuring the contrast sensitivity as a function of different spatial frequencies, defined as the number of achromatic vertical bright and dark stripe pairs within one degree of visual angle. This contrast sensitivity function (CSF) has been estimated for different animal groups, but data on fish are limited to two freeswimming, freshwater species (i.e., goldfish and bluegill sunfish). In this study, we describe the CSF of a small marine cryptobenthic fish (Tripterygion delaisi) using an optokinetic reflex approach. Tripterygion delaisi features a contrast sensitivity that is as excellent as other fish species, up to 125 (reciprocal of Michelson contrast) at the optimal spatial frequency of 0.375 c/°. The maximum spatial resolution is instead relatively coarse, around 2.125 c/°. By comparing our results with acuity values derived from anatomical estimates of ganglion cells' density, we conclude that the optokinetic reflex seems to be adapted to process low spatial frequency information from stimuli in the peripheral visual field and show that small marine fish can feature excellent contrast sensitivity at optimal spatial frequency
AMČR - dokument M-TX-201900141
No full textStav: 3Popis: Tvarožná 2014 - Santon. Úpravy kaple panny Mari
AMČR - dokument M-TX-194602284
No full textStav: 3Popis: Fond Nevázané. Podle rukopisu I. L. Červinky.Lokalizace akce: Santon; trať U Lesa.Rok zahájení akce: 1937Rok ukončení akce: 193
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