The eye is considered to have developed at rather quick pace during the ‘Cambrian explosion’, 540 million years ago.Charles Drawin always wondered how natural selection could have led to the development of an organ as complex as the eye and with a common origin, in so many different kinds of animals. A group of Scientists led by Detlev Arendt, in EMBL,Germany have found how the primitive sea creature, zooplankton, respond to light that marks an early stage in the development of the eye. Larvae of marine invertebrates – worms, sponges, jellyfish - have the simplest eyes that exist consisting of only two cells: a photoreceptor cell and a pigment cell. These are called “eye spots” resembling the proto eyes suggested by Charles Darwin. According to Charles Darwin Proto eyes are the first eyes to appear in animal evolution.

These eye spots cannot form any image but only sense direction of light and this ability is crucial for phototaxis – the swimming towards light exhibited by many zooplankton larvae. Detlev is of opinion that the first eyes in the animal kingdom evolved for exactly this purpose and hence understanding phototaxis will unravels the first steps of eye evolution.”

Studying the larvae of the marine ragworm Platynereis dumerilii, the scientists found that a nerve connects the photoreceptor cell of the eyespot and the cells that bring about the swimming motion of the larvae.

Caption: The larvae of marine ragworm Platynereis dumerilii have the simplest eyes that exist. They resemble the first eyes that developed in animal evolution and allow the larvae to navigate guided by light.

Credit: EMBL

The photoreceptor detects light and converts it into an electrical signal that travels down its neural projection, which makes a connection with a band of cells endowed with cilia. These cilia - thin, hair-like projections - beat to displace water and bring about movement.

Shining light selectively on one eyespot changes the beating of the adjacent cilia. The resulting local changes in water flow are sufficient to alter the direction of swimming, computer simulations of larval swimming show.

The second eyespot cell, the pigment cell, confers the directional sensitivity to light. It absorbs light and casts a shadow over the photoreceptor. The shape of this shadow varies according to the position of the light source and is communicated to the cilia through the signal of the photoreceptor.

“Platynereis can be considered a living fossil,” says Gáspár Jékely, former member of Arendt’s lab who now heads a group at the MPI for Developmental Biology, “it still lives in the same environment as its ancestors millions of years ago and has preserved many ancestral features. Studying the eyespots of its larva is probably the closest we can get to figuring out what eyes looked like when they first evolved.”

It is likely that the close coupling of light sensor to cilia marks an important, early landmark in the evolution of animal eyes. Many contemporary marine invertebrates still employ the strategy for phototaxis.

Reference:

Mechanism of phototaxis in marine zooplankton.
Jékely G, Colombelli J, Hausen H, Guy K, Stelzer E, Nédélec F, Arendt D.
Nature. 2008 Nov 20;456(7220):395-9.

The research training program Graduiertenkolleg 1104 (From Cells to Organs: Molecular Mechanisms of Organogenesis) is a DFG-funded research program joining developmental biologists in the Faculty of Biology, the Faculty of Medicine,and the Max-Planck- Institute of Immunobiology in Freiburg with the aim to create an innovative training program for graduate students.

In the Department of Molecular Embryology at the Institute of Anatomy and Cell Biology, we offer a GRK1104-funded PhD position to study the development of blood vessels. The project will include experimental work in chick embryos to study the molecular regulation of the recruitment of smooth muscle cells to the developing aorta. We seek a candidate with a solid background in molecular biology and strong interest in developmental biology. Applications including complete CV, description of
previous research experience, motivation, and at least two references should be sent to :
PD Dr. Martin Scaal
Department of Molecular Embryology
Institute of Anatomy and Cell Biology
University of Freiburg
Albertstr. 17
79104 Freiburg
Germany
For further information please contact martin.scaal@anat.uni-freiburg.de
The position will be available from 01.01.2009.

Image Credit : Flickr / Loligense

Drosophila ,which played a significant role in understanding many complex biological process is well on the way of solving another major puzzle.Species of Drosophila lay eggs outside in the environment , which develops and transforms into first instar larvae in about 24 hours time. UC San Diego biologists have discovered a species from the islands of Seychelles, often lay larvae instead of eggs. Understanding the development of this species might provide us with some clues how animals switch from laying eggs to live birth ?

Currently we have complete genome sequence data of 12 species of Drosophila and the species which lays larvae directly is one among them. Studying the genes which are differentially expressed might help us understand why females of this species, and not others, can retain their fertilized eggs until they are ready to hatch. Eggs laid by this species takes only around 2 hours to hatch when compared to 24 hours for other species.The Seychelles flies also lay larger eggs — nearly double the average volumes found for the other species — and their ovaries have fewer threadlike structures called ovarioles in which insect eggs mature before fertilization.

Authors think that Live birth could result from changes to the male reproductive strategy as well. Proteins found in the semen of the well-known lab fruit fly, Drosophila melanogaster, stimulate egg laying in the female. A modification of these signals could be responsible for the switch.One other fly , Drosophila yakuba, also occasionally laid larvae instead of eggs, and their eggs also hatched fairly quickly, most in under 14 hours.

These results are published in journal of evolutionary biology.

Reference:

T. A. Markow, S. Beall, L. M. Matzkin.
Egg size, embryonic development time and ovoviviparity in Drosophila species. Journal of Evolutionary Biology, 2008; DOI: 10.1111/j.1420-9101.2008.01649.x

Achim Paululat’s lab in Department of Zoology & Developmental Biology, Osnabrück-Germany worked out the first developmental study on Wing Hearts in Drosophila melanogaster. One of key area of research in Achim paululat’s lab is to understand Heart development in fruit fly and Search for genes specifically expressed in Heart led to the transcription factor Hand, which played a vital role in deciphering the developmental pattern of Wing hearts.

Circulatory system ensures that metabolites from fat bodies are supplied to all cells, carries wastes material to excretory organs and also ensures immunity against harmful organisms.Insects have a simple, open circulatory system. The circulatory system consists of a dorsal vessel running across the length of the body and can be divided into posterior Heart and anterior Aorta.The open space of the body is called the hemocoel and hemocoel is filled with hemolymph. Apart from proper Heart insects posses auxiliary pulsatile hearts present at the base of the antennae, legs and wings, which ensures regular hemolymph flow through these narrow appendages.

In Drosophila, the wing hearts consist of two bilateral muscular pumps of unknown origin.Recent work from the lab of Achim paululat show that the wing hearts originate from eight embryonic progenitor cells arising in two pairs in parasegments 4 and 5.
The progenitors cells of wing hearts consists of Even-skipped positive pericardial cells (EPC) ,similar to classical heart however the difference lies in the subsequent loss of expression of NK gene Tinman .This is critical step in the development of wing hearts as gain of expression of Tinman in wing hearts progenitors completely inhibit organ formation resulting in severe wing phenotype and adults flies are unable to fly.This result indicates that wing hearts are necessary for the normal wing morphogenesis and function.

Reference:

The Drosophila wing hearts originate from pericardial cells and are essential for wing maturation.

Tögel M, Pass G, Paululat A.

Dev Biol. 2008 Jun 1;318(1):29-37.

A nice animation has been prepared by Larry Keeley, Professor Emeritus of Entomology,Department of Entomology,Texas A&M University to help students understand better about the complex process of physiological process of insects.His webpage also have some other interesting animations and sure worth visit.

Insect organization : Structure and function - Animation of Larry Keeley

Heard about the exhibition of paintings by Apes? I thought it could be some brush strokes here and there on canvas but i was shocked to see the skill of these great Apes,which are on display in Iowa.In fact Apes are pretty good at this art and might compete well with humans.If you don’t believe me ,then check out the exhibition at Des Moines, Iowa for yourself.Some magnificent work created by Great Ape Trust of Iowa’s resident orangutans and bonobos was a complete sell out

Critically endangered peace loving bonobos
Originally uploaded by kjdrill

at a Des Moines coffeehouse , raising nearly $10,000 for great ape conservation efforts in the countries where the endangered species remain in the wild.These Apes also give a title to their painting ,giving researchers more insight into their intelligence.

Art created by Apes is not something new ,way back in 1950’s a chimpanzee named Congo produced about 400 drawings and paintings over a three-year period beginning in 1956.

The money raised by this exhibit will help Great Ape trust is protecting four great Apes,which are on the brink of extinction. The numbers from last estimate for bonobos, chimpanzees and gorillas in Africa, and orangutans in Asia are not encouraging and hence these fabulous work by Apes might go a long way in saving their species from extinction.

Orangutang
Originally uploaded by edebell

These great paintings are still on display at Zanzibar’s Coffee Adventure, 2723 Ingersoll Ave., Des Moines, till 25 November.Since the opening of gallery in 1993 Zanzibar has displayed work of many local artists ,but according to owner Julie McGuire ,The work by orangutans Azy, Knobi and Allie and bonobos Kanzi, Panbanisha and Nathan has been a sensation with her regular customers and some new ones drawn to Zanzibar’s by the unique art exhibit.

“We’ve had a couple of exhibits that have virtually sold out,, “but nothing at this speed. It’s very rare for a show to sell out completely.”-” McGuire

Links to great Ape trust:

Slideshow & Stories Behind the Ape Art Pieces

Great Ape Trust