A small step for lungfish, a big step for the evolution of walking
The African lungfish (Protopterus annectens) displays primitive walking behavior in controlled studies. Credit: Yen-Chyi Liu/University of Chicago
The African lungfish (Protopterus annectens) displays primitive walking behaviors in controlled conditions. Credit: Yen-Chyi Liu/University of Chicago
The eel-like body and scrawny "limbs" of the African lungfish would appear to make it an unlikely innovator for locomotion. But its improbable walking behavior, newly described by University of Chicago scientists, redraws the evolutionary route of life on Earth from water to land.
December 12, 2011
Extensive video analysis, published in the Proceedings of the National Academy of Sciences, reveal that the African lungfish can use its thin pelvic limbs to not only lift its body off the bottom surface but also propel itself forward. Both abilities were previously thought to originate in early tetrapods, the limbed original land-dwellers that appeared later than the lungfish's ancestors.
The observation reshuffles the order of evolutionary events leading up to terrestriality, the adaptation to living on land. It also suggests that fossil tracks long believed to be the work of early tetrapods could have been produced instead by lobe-finned ancestors of the lungfish.
"In a number of these trackways, the animals alternate their limbs, which suggested that they must have been made by tetrapods walking on a solid substrate," said Melina Hale, PhD, associate professor of Organismal Biology and Anatomy. "We've found that aquatic animals with fundamentally different morphologies and that aren't tetrapods could potentially make very similar track patterns."
Lungfish are a popular pet in the paleontological community, treasured for their unique evolutionary heritage.
"The lungfish is in a really great and unique position in terms of how it is related to fishes and to tetrapods," said Heather King, a graduate student and lead author of the study. "Lungfish are very closely related to the animals that were able to evolve and come out of the water and onto land, but that was so long ago that almost everything except the lungfish has gone extinct."
While anecdotes and rumors circulated within the scientific community about the alleged walking behavior of these strange fish, nobody looked systematically at the biomechanics of their locomotion. An African lungfish (Protopterus annectens) kept in the laboratory of study co-author Michael Coates inspired King to study the species' ability to walk on its unusually thin limbs.
King and her colleagues designed a special tank in which the motions of lungfish could be videotaped from the side and below for in-depth analysis. The videos revealed that lungfish commonly use their hind, or pelvic, limbs to elevate their body off the surface and propel themselves forward. Though the forelimbs look similar to the hindlimbs, they were not involved in locomotion, the authors found.
"This is all information we can only get from a living animal," King said. "Because if you were just to look at the bones, like you would with a fossil, you might not ever know these motions could occur."
Lungfish also demonstrated both "bounding" motions, where both limbs moved at once, and "walking," marked by alternating limbs. Coupled with the ability of the lungfish to fully rotate the limb and place each subsequent footfall in front of the joint, the motion suggests that similar creatures would have been capable of producing some of the fossil tracks credited to tetrapods.
"It's tempting to attribute alternating impressions to something like the footfalls of an early tetrapod with digits, and yet here we've got good evidence that living lungfish can leave similar sequences of similar gait," said Coates, PhD, professor of Organismal Biology and Anatomy. "The fin or limb use thought to be unique to tetrapods is actually more general."
The lungfish's ability to use its thin limbs to support its body may be helped by the reduced demands of gravity underwater, the authors proposed. By filling its lungs with air, the lungfish may increase the buoyancy of its front end, enabling the scrawny hindlimbs to lift the entire body off the ground.
"If you showed me the skeleton of this creature and asked me to make a bet on whether it walks or not, I would have bet it couldn't," said co-author Neil Shubin, PhD, Robert R. Bensley Professor of Organismal Biology and Anatomy. "Their fins seem like the furthest thing from walking appendages possible. But it shows what's possible in an aquatic medium where you don't have to support yourself with gravity."
The discovery suggests that many of the developments necessary for the transition from water to land could have occurred long before early tetrapods, such as Tiktaalik, took their first steps on shore. Lobe-finned ancestors of the lungfishes as well as tetrapods could have evolved hindlimb propulsion and the ability to walk on the substrate at the bottom of a lake or marsh millions of years before limbs with digits and land-dwelling animals appeared.
"This shows us — pardon the pun — the steps that are involved in the origin of walking," Shubin said. "What we're seeing in lungfish is a very nice example of how bottom-walking in fish living in water can easily come about in a very tetrapod-like pattern."
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More information: The paper, "Behavioral evidence for the evolution of walking and bounding before terrestriality in sarcopterygian fishes [ http://www.pnas.org/content/early/2011/12/08/1118669109 ]," will be published in the online Early Edition of Proceedings of National Academy of Sciences the week of December 12, 2011.
Movie S2. This movie shows the lungfish P. annectens locomoting underwater in ventral view. Note that the pelvic fins begin by alternating, then make a discrete transition to a synchronous gait. This movie corresponds to Figs. 1B and 2 B and D. Each square of the grid in this movie is 1 cm.
- A Small Step for Lungfish, a Big Step for the Evolution of Walking The eel-like body and scrawny "limbs" of the African lungfish would appear to make it an unlikely innovator for locomotion. But its improbable walking behavior, newly described by University of Chicago scientists, redraws the evolutionary route of life on Earth from water to land. http://www.sciencedaily.com/releases/2011/12/111212153117.htm
Reference Behavioral evidence for the evolution of walking and bounding before terrestriality in sarcopterygian fishes PNAS December 12, 2011, doi: 10.1073/pnas.1118669109 http://www.pnas.org/content/early/2011/12/08/1118669109
Abstract Tetrapods evolved from sarcopterygian fishes in the Devonian and were the first vertebrates to colonize land. The locomotor component of this transition can be divided into four major events: terrestriality, the origins of digited limbs, solid substrate-based locomotion, and alternating gaits that use pelvic appendages as major propulsors. As the sister group to tetrapods, lungfish are a morphologically and phylogenetically relevant sarcopterygian taxon for understanding the order in which these events occurred. We found that a species of African lungfish (Protopterus annectens) uses a range of pelvic fin-driven, tetrapod-like gaits, including walking and bounding, in an aquatic environment, despite having a derived limb endoskeleton and primitively small, muscularly supported pelvis. Surprisingly, given these morphological traits, P. annectens also lifts its body clear of the substrate using its pelvic fins, an ability thought to be a tetrapod innovation. Our findings suggest that some fundamental features of tetrapod locomotion, including pelvic limb gait patterns and substrate association, probably arose in sarcopterygians before the origin of digited limbs or terrestriality. It follows that the attribution of some of the nondigited Devonian fossil trackways to limbed tetrapods may need to be revisited.
Supporting Information Video
- Movie S1. This movie shows the lungfish Protopterus annectens locomoting underwater in ventral view. Note that the pelvic fins alternate, and the pectoral fins do not move rhythmically. This movie corresponds to Figs. 1A and 2 A and C. Each square of the grid in this movie is 1 cm. http://www.pnas.org/content/suppl/2011/12/09/1118669109.DCSupplemental/sm01.avi
- Movie S2. This movie shows the lungfish P. annectens locomoting underwater in ventral view. Note that the pelvic fins begin by alternating, then make a discrete transition to a synchronous gait. This movie corresponds to Figs. 1B and 2 B and D. Each square of the grid in this movie is 1 cm. http://www.pnas.org/content/suppl/2011/12/09/1118669109.DCSupplemental/sm02.avi
- Movie S3. This movie shows the lungfish P. annectens locomoting underwater in simultaneous lateral and ventral views. In lateral view, the lifting of the body is evident, as is the range of motion of the pelvic fin, including movement in front of and above the articulation with the body. Each square of the grid in this movie is 1 cm. http://www.pnas.org/content/suppl/2011/12/09/1118669109.DCSupplemental/sm03.avi
- Movie S4. This movie shows the lungfish P. annectens locomoting underwater in simultaneous lateral and ventral views. Here we show an example of the effectiveness of the pelvic fins in lifting the body. Each square of the grid in this video is 1 cm. http://www.pnas.org/content/suppl/2011/12/09/1118669109.DCSupplemental/sm04.avi
Nearly Extinct Bird Blown Out of Nest During Storm: Rescuers Lend a Hand
by Laura Simpson .. December 15, 2011 .. 11:00 pm .. 7 comments
Written by the Saint Francis of Assisi Foundation of Zarzal, Colombia
During a windstorm, a very rare Coclí pigeon .. http://www.care2.com/causes/the-guerrilla-pigeon-feeders-of-paris.html .. fell out of his nest perched at the top of a tall palm tree. We made him comfortable in a special cage, and because his beak was slightly injured, we hand-fed him carefully with small worms for the next week.
When he was able to eat on his own, we at the Foundation made contact with the firemen who came with their very long ladders and were able to put him right back up in his nest, where his parents and sibling were anxiously awaiting his return.
We were very pleased to have been able to do this successfully, because this bird which is indigenous to our area has been hunted almost to extinction — in fact, it has already been placed on the extinct list. To our knowledge, in the last seven years only 38 baby birds have been born and we are hoping that they will re-populate other rural areas as well as ours. More photos of the rescued Coclí pigeon. .. http://animalrescuechase.com/rescue_showcase/story.php?id=610
'Intelligent' slime able to navigate its way out of maze
Toshiyuki Nakagaki, professor of Future University Hakodate Photo: SHINGO ITO/AFP/Getty Images
A Japanese scientist is exploring the power of slime mould in an attempt to uncover the key to intelligence.
By Danielle Demetriou in Tokyo 11:23AM GMT 29 Dec 2011
Toshiyuki Nakagaki, a professor at Future University Hakodate, northern Japan, cultivates the slime in petri dishes and has discovered how the brainless organism is capable of finding its way out of a maze.
The brainless organism is able to “organise” its cells to create the most direct route through a maze in order to reach a source of food, according to his studies.
The findings highlight how slime mould possesses information processing abilities shared by humans which are more sophisticated than the most advanced computers, according to Professor Nakagaki.
"Humans are not the only living things with information-processing abilities," he said. "Simple creatures can solve certain kinds of difficult puzzles. If you want to spotlight the essence of life or intelligence, it's easier to use these simple creatures."
Slime mould, a monocellular being that lives on rotting leaves and does not possess a brain, may not be the obvious subject of scientific research in relation to intelligence.
However, Professor Nakagaki is one of a growing number of scientists examining the information-professing capabilities of slime as a potential key to designing biocomputers of the future capable of solving complex problems.
Previous research has shown how slime moulds become inactive when “stressed” due to changes in temperature or humidity and are subsequently able to “remember” and anticipate such situations reoccurring.
In another experiment, slime mould successfully formed the pattern of a railway system similar to the complex human-designed railroad networks of the Kanto region of Japan.
Atsushi Tero, from Kyushu University, southern Japan, who conducted the research, believes that the intelligence skills possessed by slime mould networks could potentially be used in the future design of transport systems or electric transmission lines.
"Computers are not so good at analysing the best routes that connect many base points because the volume of calculations becomes too large for them," he said.
"But slime moulds, without calculating all the possible options, can flow over areas in an impromptu manner and gradually find the best routes.”
Zoologger: Unique life form is half plant, half animal
Crazy mixed-up microorganism (Image: Øjvind Moestrup/The Journal of Eukaryotic Microbiology)
14:34 13 January 2012 by Michael Marshall
Species: Mesodinium chamaeleon Habitat: seawater around Scandinavia and North America, chowing down on a new generation of slaves
Many animals transform themselves almost beyond recognition in the course of their lives. Caterpillars become butterflies and tadpoles become frogs, and if we couldn't watch them do so we might not even suspect that the two stages were the same creature.
Spectacular as these shifts are, they are only shape-shifting. A tadpole and a frog are both animals, so both must take in food from their surroundings.
Not so Mesodinium chamaeleon. This newly discovered single-celled organism is a unique mixture of animal and plant.
Plant pals
M. chamaeleon is a ciliate – a kind of single-celled animal covered in hundreds of tiny "hairs" called cilia. It was discovered in Nivå bay in Denmark by Øjvind Moestrup of the University of Copenhagen, also in Denmark, and his team. Other specimens have since been found off the coasts of Finland and Rhode Island.
Ciliates using their hair-like cilia to motor around rapidly in water. Most get their food by eating other organisms, rather than by synthesising the nutrients themselves. This marks them as quite animal-like.
Some Mesodinium species are different, though. They engulf other microorganisms, generally algae called cryptomonads. The two then form a partnership: the algae produce sugars by photosynthesis, while the Mesodinium protects them and carries them around.
Such hybrid organisms are animals and plants at the same time. One such species, M. rubrum, only eats red algae and is often found in the algal blooms that form the famous red tides.
These hybrids play merry hell with our attempts to classify organisms into neat groups. "The division between plants and animals is collapsing completely," Moestrup says. Instead, many microorganisms may be animal and plant at once, or switch between the two, like M. rubrum.
The new M. chamaeleon breaks yet another barrier. It is halfway between a pure animal and a hybrid.
Red and green
M. chamaeleon takes in algal cells, just like M. rubrum, but it doesn't keep them permanently. Nor does it digest them immediately, as a hungry animal-like organism might. Instead, the cells remain intact for several weeks before being broken down, during which time they keep producing sugar by photosynthesis. M. chamaeleon also changes colour depending on whether it is hosting red or green algae or both.
"It is quite unusual," says Moestrup. Other Mesodinium species either retain their captured cells for ages or digest them immediately.
The ability to take in other cells and put them to work is called endosymbiosis, and is one of the most important inventions in the history of life. Some 2 billion years ago, a single cell swallowed a bacterium and used it as an energy source. The descendants of the enslaved bacterium eventually became the mitochondria that now power all complex cells, including ours. Without endosymbiosis, there wouldn't be any multicellular life.
While the first endosymbiosis may have been a lucky chance, the process now seems to be common, at least among the more complex single-celled organisms. Some are so good at taking in cells that over the years they have switched symbionts. "It happens quite regularly," Moestrup says.
M. chamaeleon may offer a snapshot of how endosymbiosis developed: the organism is still on the road from simply eating other cells to keeping them alive within itself.
Journal reference: The Journal of Eukaryotic Microbiology, DOI: 10.1111/j.1550-7408.2011.00593.x
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