Starfish use their eyes to stay close to home researchers find

first_img(Phys.org) —A starfish has an eye at the end of each arm. While scientists have known about the existence of these eyes for about two hundred years, until now, they haven’t been able to find out what starfish can see or what starfish use their eyes for. By performing morphological studies as well as behavioral experiments, Anders Garm and Dan-Eric Nilsson have discovered that starfish can see very low resolution images, and they use their eyes to avoid straying too far from their habitats. Their research appears in the Proceedings of the Royal Society B. This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. More information: Visual navigation in starfish: first evidence for the use of vision and eyes in starfish, Published 8 January 2014 DOI: 10.1098/rspb.2013.3011AbstractMost known starfish species possess a compound eye at the tip of each arm, which, except for the lack of true optics, resembles an arthropod compound eye. Although these compound eyes have been known for about two centuries, no visually guided behaviour has ever been directly associated with their presence. There are indications that they are involved in negative phototaxis but this may also be governed by extraocular photoreceptors. Here, we show that the eyes of the coral-reef-associated starfish Linckia laevigata are slow and colour blind. The eyes are capable of true image formation although with low spatial resolution. Further, our behavioural experiments reveal that only specimens with intact eyes can navigate back to their reef habitat when displaced, demonstrating that this is a visually guided behaviour. This is, to our knowledge, the first report of a function of starfish compound eyes. We also show that the spectral sensitivity optimizes the contrast between the reef and the open ocean. Our results provide an example of an eye supporting only low-resolution vision, which is believed to be an essential stage in eye evolution, preceding the high-resolution vision required for detecting prey, predators and conspecifics. Explore further © 2014 Phys.org Journal information: Proceedings of the Royal Society Bcenter_img Visual system of the starfish L. laevigata. (a) Linckia laevigata in its natural coral reef habitat at Akajima, Japan, where it feeds on detritus and algae. (b) As in other starfish species, the compound eye of L. laevigata is situated on the tip of each arm (arrowhead). It sits in the ambulaceral groove which continues to the top of the arm tip. (c) Lateral view of the compound eye, also called the optical cushion, which is sitting on the base of a modified tube foot. The eye has approximately 150 separate ommatidia with bright red screening pigment. (d) Frontal view of the compound eye showing its bilateral symmetry. (e) The tip of the arm seen from below. The view of the compound eye is obscured by a double row of modified black tube feet (arrow). (f) The arm tip seen straight from above. Note that the eye is again obscured from view by a modified black tube foot (arrow). (g) The compound eye (arrowhead) seen from 45° above horizontal in a freely behaving animal. When the animal is active, the modified black tube feet spread out to allow vision. (h) If the animal is disturbed, it closes the ambulaceral groove (broken line) at the arm tip and withdraws the modified tube feet. The compound eye is then completely covered, leaving the animal blind. Credit: doi: 10.1098/rspb.2013.3011 While previous research has already shown that starfish can distinguish between light and dark, scientists haven’t been sure if starfish can see images. Starfish don’t have brains. While they have compound eyes, like arthropods do, starfish eyes, unlike arthropod eyes, don’t have lenses. Previously, no one had ever seen a starfish use its eyes to navigate.Garm and Nilsson examined the eyes of the blue sea star (Linckia laevigata), a starfish that lives around coral reefs in the tropical Pacific and Indian Oceans. The researchers found that these starfish cannot distinguish colors, and because their eyes lack lenses, they can see only very crude, low resolution images. Blue sea stars also have very slow responses to light. The sea stars could not use their eyes to evade predators, find food or search for mates.Although starfish cannot detect small visual details, the placement of an eye on each arm gives them a large visual field. They can see large unmoving or slowly moving structures, such as the coral reefs that are their homes. Garm and Nilsson hypothesized that sea stars use their eyes to avoid straying too far from their coral reefs and becoming stranded on patches of sand, where they would be unable to find food and have no protection from predation. The researchers noted that while starfish cannot see colors, the ocean would appear light to them, while coral reefs would appear dark.To test their hypothesis, Garm and Nilsson placed starfish either one, two or four meters away from a coral reef. When they were one meter away, the starfish walked directly toward the reef. At four meters, they walked in random directions. Two meters, the distance at which the starfish would no longer be able to resolve the image of the reef, appeared to be the limit for successful navigation. The results were the same whether the reef was east-west facing or north-south facing. Blinded seas stars were lost even when they were only one meter away, and sighted ones couldn’t find their way back when they were one meter away on a moonless night. These results indicated that the sea stars were using their eyes to guide them.The researchers think the development of the ability to recognize habitats could have been one of the earliest stages in the evolution of vision. Citation: Starfish use their eyes to stay close to home, researchers find (2014, January 8) retrieved 18 August 2019 from https://phys.org/news/2014-01-starfish-eyes-home.html Seeing starfish: The missing link in eye evolution?last_img read more

Research shows collision created Chelyabinsk asteroid

first_img Citation: Research shows collision created Chelyabinsk asteroid (2014, May 23) retrieved 18 August 2019 from https://phys.org/news/2014-05-collision-chelyabinsk-asteroid.html (Phys.org) —On February 15 2013, an asteroid exploded about 30 kilometers above Chelyabinsk, Russia. The explosion, shared on video around the world, was the Earth’s second largest recorded airburst. By analyzing fragments of the meteorite that fell to Earth, Shin Ozawa at Tohoku University in Sendai, Japan and colleagues determined that the asteroid formed when a parent asteroid collided with another asteroid and then broke apart. The research appears in Scientific Reports. © 2014 Phys.org Insight into space collisions from Chelyabinsk fireball More information: Jadeite in Chelyabinsk meteorite and the nature of an impact event on its parent body, Scientific Reports 4, Article number: 5033 DOI: 10.1038/srep05033AbstractThe Chelyabinsk asteroid impact is the second largest asteroid airburst in our recorded history. To prepare for a potential threat from asteroid impacts, it is important to understand the nature and formational history of Near-Earth Objects (NEOs) like Chelyabinsk asteroid. In orbital evolution of an asteroid, collision with other asteroids is a key process. Here, we show the existence of a high-pressure mineral jadeite in shock-melt veins of Chelyabinsk meteorite. Based on the mineral assemblage and calculated solidification time of the shock-melt veins, the equilibrium shock pressure and its duration were estimated to be at least 3–12 GPa and longer than 70 ms, respectively. This suggests that an impactor larger than 0.15–0.19 km in diameter collided with the Chelyabinsk parent body at a speed of at least 0.4–1.5 km/s. This impact might have separated the Chelyabinsk asteroid from its parent body and delivered it to the Earth. Journal information: Scientific Reportscenter_img (a) The host-rock showing an equilibrated chondrite texture. (b) A shock-melt vein cutting through the host-rock. The two white dotted lines represent the boundaries between them. (c) Coarse-grained fragments and fine-grained matrix in a shock-melt vein. (d) Enlarged view of the area shown by the white rectangular in (c). Needle-like and skeletal-rhombic crystals of jadeite occur with feldspathic glass. Ol = olivine, En = enstatite, Di = diopside, Fsp = albitic feldspar, Me = Fe–Ni metal, Tro = troilite, Chr = chromite, SMV = shock-melt vein, Mtx = matrix of shock-melt vein, Jd = jadeite, Gl = feldspathic glass. Credit: Scientific Reports 4, Article number: 5033 doi:10.1038/srep05033 When an asteroid, 17 to 20 meters in diameter, burst over the south of Chelyabinsk city, in Russia’s southern Ural region, it generated shockwaves that injured more than 1000 people and damaged many buildings. Unlike many other Near Earth Objects (NEOs), the Chelyabinsk asteroid had a well-recorded trajectory, and it left fragments on the Earth. This gave scientists a unique opportunity to study its formation.Previous studies of the asteroid’s fragments had shown they contain shock-melt veins, which form when heat and pressure from an impact cause materials in a section of an asteroid to melt. Eventually, shock-melt veins lose heat to cooler surrounding rock and solidify, forming glassy structures.Ozawa’s team examined the shock-melt veins in the Chelyabinsk fragments and found they contain the mineral jadeite, which forms under extremely high pressure. Some terrestrial rocks and meteorites contain jadeite. However, when the team examined the jadeite from the Chelyabinsk meteorite under an electron microscope, they found the mineral had a unique composition and structure that indicated it had crystallized very rapidly.By calculating the rate at which the jadeite must have solidified, the team were able to determine that the asteroid must have formed when a parent asteroid collided with a second asteroid, which was at least 150 meters in diameter and moving at a relative speed of 0.4 to 1.5 kilometers per second. A previous study of the isotopes in the meteorite had shown that a collision could have occurred up to 290 million years ago. The jadeite would have formed as the result of this collision, as the mineral would not have survived a later impact. Earlier calculations had shown that asteroids in the main asteroid belt have lifetimes of less than 10 million years. The researchers think the Chelyabinsk asteroid broke off from its parent after the collision and moved into an orbital resonance less than 10 million years ago. It then fell into an orbit crossing that of the Earth.The research increases our understanding of how NEOs form and evolve. It shows that NEOs, which have the potential to strike the Earth, can survive much longer than previously believed. This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Explore furtherlast_img read more

COACH Daniel Anderson has been forced to change hi

first_imgCOACH Daniel Anderson has been forced to change his Exiles team take on England in the opening match of the International Origin Series at Langtree Park on Saturday June 16 (6.45pm).Due to injuries to Brett Hodgson (Warrington Wolves) and Setaimata Sa (Catalan Dragons), the Exiles have drafted in Hull KR’s Shannon McDonnell.McDonnell takes Hodgson’s place at full-back while David Fa’alogo of Huddersfield Giants moves from the bench to take the number 13 shirt, meaning all yesterday’s named interchange players are now in the match day squad.The Exiles have also drafted in Widnes Vikings player Patrick Ah Van as 18th man.Wigan Warriors’ experienced half-back Thomas Leuluai will captain the side.The Exiles:Shannon McDonnell; Joel Monaghan, Sia Soliola, Daryl Millard, Francis Meli; Thomas Leuluai, Scott Dureau; Tony Puletua, Lance Hohaia, Jeff Lima, Willie Manu, Trent Waterhouse, David Fa’alogo.Subs from: Anthony Laffranchi, Antonio Kaufusi, David Faiumu, Epalahame Lauaki, Patrick Ah Van.Tickets for the opening fixture at Langtree Park, St Helens, on Saturday June 16 (6.45pm) cost from £18 (£9 concessions) for standing and £21 (£10 concessions) seating. Details are here.last_img read more