Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Eye Evolution: A Snapshot In Time

04.06.2014

Larvae of the marine bristle worm Platynereis dumerilii orient themselves using light.

Early in their development, these larvae swim towards the light to use surface currents for their dispersal. Older larvae turn away from the light and swim to the sea floor. Scientists of the Max Planck Institute for Developmental Biologyhave discovered that this change in the behavioural response to light is coupled to different neuronal systems underlying the eyes.


Bristle worm Platynereis dumerilii

Nadine Randel / Max Planck Institute for Developmental Biology


Model of a bristle worm (Platynereis dumerilii)

Nadine Randel / Max Planck Institute for Developmental Biology

The scientists have reconstructed the first neuronal map of a visual system, from the input of the light stimulus up to the behavioural reaction. Using this neuronal map, the biologists can glimpse the evolution of vision.

Phototaxis, the movement towards or away from a light source, is widespread among marine invertebrate larvae. During their development, many larvae switch from positive (movement towards light) to negative phototaxis. The underlying mechanism of phototaxis has to date only been described for the early larval stage of Platynereis dumerilii.

Later in their development, the larvae develop additional eyes. With these new eyes comes the ability to switch between positive and negative phototaxis. “Instead of only swimming towards the light, the larvae often display negative phototaxis and swim away from the light”, said Gáspár Jékely, head of the research group “Neurobiology of Marine Zooplankton”.

During the first two days of their life, the offspring of the bristle worm has the simplest eyes on the planet: On each side of the tiny head is a single photoreceptor cell together with one shading pigment cell. In 2008, Jékely and his co-workers from the European Molecular Biology Laboratory (EMBL) in Heidelberg discovered that this photoreceptor cell is directly connected to the larval driving engine, a band of cilia, a collar directly located below the headregion. When light hits the photoreceptor cell, larvae propel ahead in spirals, always towards the source of the stimulus.

However, after 3 days of development, these simple larval eyes no longer mediate phototaxis.. At this stage, two pairs of more sophisticated eyes appear on the upper side of the head – the precursors of the adult eyes. These new eyes consist of several photoreceptor cells, a pigment cup and even a simple lens. Moreover, a simple neuronal network develops that processes and transduces light stimuli.

The scientists in Jékely’s team studied this neuronal network in a greater detail using an electron-microscope. In a detailed map of the visual neuronal network of a 3 day old larva they identified 71 neurons that are connected by more than 1000 neuronal connections, so-called synapses. The scientists found that the light signal is still transmitted to the cilia, but now it also reaches the larval body musculature. Moreover, the eyes from the two body sides are also connected at the neuronal level.

“We could show with behavioural experiments that the light stimulus activates the body musculature in such a way that it causes the larva to turn away from the light”, says Nadine Randel, first author of the study. During the experiment, the 3 day old larvae swam in a transparent container and were illuminated only from one side. As a result, the larvae bent their body and swam in a curve away from the light.

The scientists also pharmacologically blocked the neuronal communication between photoreceptor cells and musculature. Although these treated animals could still swim normally, they no longer reacted to the light source.

The neuronal connections between the eyes on either side of the body are required for spatial resolution. Additionally, the scientists could identify certain neurons, which block the signal of the photoreceptor cell from the opposite sides of the larva. “This enhances the contrast between light and dark and improves phototaxis”, explains Randel.

For the first time, the developmental biologists from Tübingen describe a complete neuronal network of a simple visual system from the stimulus to the behavioral output. They also further gained deeper insights into the evolution of eyes. The simple eyes, which mediate phototaxis in the early larva, consist of two cells corresponding to Charles Darwin's idea of the “proto-eye”, the precursor of all existing eyes. The four eyes which appear in the 3 day old larva represent an advanced form of this proto-eye principle.

“It is as if we could observe several steps of eye evolution in a single animal”, says Jékely. “We think that the first eyes probably evolved to perform phototaxis – later, eyes evolved that could recognize objects”.

Probably, the first simple eyes in evolution could merely discriminate a bright from a dark field. Such eyes might nonetheless represent the starting point for the evolution of more complex visual systems, as for example the human eyes.

Original Publication:
Nadine Randel, Albina Asadulina, Luis A. Bezares- Calderón, Csaba Verasztó. Elisabeth A. Williams, Markus Conzelmann, Réza Shahidi, Gáspár Jékely: Neuronal connectome of a sensory-motor circuit for visual navigation. eLife 2014;10.7554/eLife.02730

Weitere Informationen:

http://tuebingen.mpg.de/en/homepage/detail/eye-evolution-a-snapshot-in-time.html

Nadja Winter | Max-Planck-Institut

Further reports about: Bristle worm Evolution eyes larvae musculature photoreceptor stimulus

More articles from Life Sciences:

nachricht Tracking the American Woodcock
28.07.2015 | University of Arkansas, Fayetteville

nachricht Possible Path Toward First Anti-MERS Drugs
28.07.2015 | American Crystallographic Association (ACA)

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Superfast fluorescence sets new speed record

Plasmonic device has speed and efficiency to serve optical computers

Researchers have developed an ultrafast light-emitting device that can flip on and off 90 billion times a second and could form the basis of optical computing.

Im Focus: Unlocking the rice immune system

Joint BioEnergy Institute study identifies bacterial protein that is key to protecting rice against bacterial blight

A bacterial signal that when recognized by rice plants enables the plants to resist a devastating blight disease has been identified by a multi-national team...

Im Focus: Smarter window materials can control light and energy

Researchers in the Cockrell School of Engineering at The University of Texas at Austin are one step closer to delivering smart windows with a new level of energy efficiency, engineering materials that allow windows to reveal light without transferring heat and, conversely, to block light while allowing heat transmission, as described in two new research papers.

By allowing indoor occupants to more precisely control the energy and sunlight passing through a window, the new materials could significantly reduce costs for...

Im Focus: Simulations lead to design of near-frictionless material

Argonne scientists used Mira to identify and improve a new mechanism for eliminating friction, which fed into the development of a hybrid material that exhibited superlubricity at the macroscale for the first time. Argonne Leadership Computing Facility (ALCF) researchers helped enable the groundbreaking simulations by overcoming a performance bottleneck that doubled the speed of the team's code.

While reviewing the simulation results of a promising new lubricant material, Argonne researcher Sanket Deshmukh stumbled upon a phenomenon that had never been...

Im Focus: NASA satellite camera provides 'EPIC' view of Earth

A NASA camera on the Deep Space Climate Observatory (DSCOVR) satellite has returned its first view of the entire sunlit side of Earth from one million miles away.

The color images of Earth from NASA's Earth Polychromatic Imaging Camera (EPIC) are generated by combining three separate images to create a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

3rd Euro Bio-inspired - International Conference and Exhibition on Bio-inspired Materials

23.07.2015 | Event News

Clash of Realities – International Conference on the Art, Technology and Theory of Digital Games

10.07.2015 | Event News

World Conference on Regenerative Medicine in Leipzig: Last chance to submit abstracts until 2 July

25.06.2015 | Event News

 
Latest News

Possible Path Toward First Anti-MERS Drugs

28.07.2015 | Life Sciences

Smart Hydrogel Coating Creates “Stick-slip” Control of Capillary Action

28.07.2015 | Materials Sciences

Are Fish Getting High on Cocaine?

28.07.2015 | Ecology, The Environment and Conservation

VideoLinks
B2B-VideoLinks
More VideoLinks >>>