AFP
Nov. 19, 2008 -- Biologists on Wednesday explained how the larvae of marine zooplankton can see with just two cells, using what is believed to be the world's simplest vision system.
Zooplankton are tiny creatures such as copepods and krill that drift in the ocean's water columns, swimming up from the depths towards the light in order to graze on marine plants called phytoplankton near the surface.
This movement, called phototaxis, is the biggest biomass displacement in the world.
In a study published by the British-based journal Nature, European scientists looked at the larvae of the marine ragworm Platyneris dumerilii to try to explain how plankton are able to do the phototaxis trick.
The larva has just two eye cells, consisting of a pigment cell and a light-sensitive cell, say the investigators.
The cells are unable to form images but enable the plankton to sense the difference between light and dark and send appropriate signals to its swimming mechanism, say the investigators.
First, the pigment cell absorbs light and casts a shadow over the photoreceptor cell. The shape of the shadow varies according to the position of the light source.
The photoreceptor cell then converts this light signal into electricity, sending it in a signal along a nerve that connects to a band of cells endowed with thin hairs, called cilia, that beat to displace water.
The basic but effective system could explain how the very first eyes in evolution may have worked, say the team from the European Molecular Biology Laboratory (EMBL) and the Max Planck Institute.
"For a long time, nobody knew how the animals do phototaxis with their simple eyes and nervous system," said EMBL's Detlev Arendt.
"We assume that the first eyes in the animal kingdom evolved for exactly this purpose. Understanding phototaxis thus unravels the first steps of eye evolution."
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AFP
Nov. 17, 2008 -- Scientists have discovered for the first time a menagerie of perfectly intact marine microorganisms trapped in tree resin at least 100 million years ago, according to a new study.
The unexpected find in the Charente region of southwestern France pushes back by at least 20 million years the period when a type of single-cell algae called diatoms are known to have appeared on Earth, said the study.
It also creates a mystery: how did sea creatures wind up trapped in a glob of resinated amber that oozes out of trees?
The most likely scenario, the scientists concluded, is that the forest producing the amber was very near the coast, and that the tiny organisms -- which also included primitive plankton -- were either carried inland by strong winds or flood waters during a storm.
"This discovery will deepen our understanding of these lost marine species as well as providing precious data about the coastal environment of western France during the Cretaceous Period," which spanned from 145 to 65 million years ago, the researchers said in a statement.
It also challenges certain theories about the evolution of these organisms, and vindicates the research of molecular geneticists, said Jean-Paul Saint Martin, a scientist at the National History Museum in Paris and a co-author of the study.
Using "molecular clocks," biochemists move backward in time to figure out at what point in the evolutionary process certain plant and animal species split off into different branches.
"We had no record of these microorganisms over a period of 20 million years. These fossils have filled that void in the most extraordinary manner," Saint Martin told AFP.
The study, carried out in collaboration with the National Center for Scientific Research in Strasbourg, was published in the Proceedings of the National Academy of Sciences.
