Who is the woman in your relationship?

June 14, 2009

For some, it’s a bitter fight. Check out this video of two flatworms mating!

The first one who gets stabbed by the other’s penis will become the mother, and both are struggling with gusto and determination for the fatherhood.

Hat tip: Deep Sea News.

A single-cell organism that communicates using light signals

April 7, 2009

Some multicellular organisms emit light in a conspicuous way. Fireflies carry beacons that shine in the night, and some deep-sea fishes use phosphorescent appendages to attract prey. However, the information content in these light emissions is probably no greater than “I am here”, or possibly “I am moving in a certain direction with a certain velocity”.

A few days ago, a paper appeared in PLoS One showing that the unicellular organism paramecium caudatus uses light signals of a specific wavelength to communicate. These signals influence the proliferation rate of the protozoa and imply that they not only have a sense of vision, but also a signal-generating organ, and an apparatus to translate the visual input into a representation of its environment, which in turn guides the organism’s behaviour.

Paramecium caudatum. Image borrowed from A Blog Around the Clock.

Paramecium caudatum. Image borrowed from A Blog Around the Clock.

I found this story through the most interesting Neurotypical blog, written by a neuroscientist who starts off almost apologetically by saying that this has nothing to do with neuroscience. I beg to differ.

Although the paramecium possesses no nervous system, it clearly has all the necessary faculties for information processing of the kind with which neuroscience concerns itself. It is not the substrate that determines the dynamics of an information processing system, but the structure and organisation of the network.

Check out the post by Neurotypical, as well as the the original paper, it’s open access!

Lungs – what are they really good for? More on lungless amphibians

March 27, 2009

ResearchBlogging.org This is a follow-up on yesterday’s post, which discussed a lungless frog species recently discovered on Borneo. Victor H. Hutchison has written a comment in the journal Current Biology that highlights a few interesting concepts.

Sometimes I give an introductory lecture on the histology of the human lung to undergraduates in our department. I invariably start off by asking the students what the organ is good for, and I always get the same two answers: Gas exchange and barrier function. I never realised that there is a third function in many animals, although it’s obvious when you think of it: flotation. As a submarine can regulate its buoyancy by filling tanks with either water or air, so can many amphibians regulate theirs with their lungs.

Hutchison explains that amphibians may be particularly susceptible to losing their lungs because they have rather inefficient breathing dynamics. Apparently, they cannot breathe by changing the volume of the thorax with muscles, like we do. Instead, thay have to force air into the lungs by a swallowing motion. Then, because of the higher pressure built up in the lungs, expiration takes place when they open their mouths again. Further factors that contribute to the redundacy of lungs are a higher body surface area to volume ratio, a permeable skin with capillaries growing into the epidermis (unlike ours, which stop in the underlying dermis), and low metabolic rates due to cold temperatures.

A unifying trait for the previously known lungless salamanders and the recently discovered lungless frog is that they live in cold streams. Hutchison therefore proposes that the loss of lungs helps keep these animals on the bottom, preventing them from being swept away by the water. He does not mention that gas exchange will be much more efficient in moving water than in a still-standing pond, but this seems an obvious observation to me.

Some amphibians have reduced lungs while still retaining the capacity to use them. One example is the Titicaca frog (Telmatobius culeus). This animal lives in high-altitude waters in the Andean mountains. Normally, these frogs stay underwater and use their many skin folds for gas echange. These folds have very superficial blood vessels and are ventilated by a “bobbing” motion. In addition, the frog’s blood is very rich in hemoglobin.

Titicaca frog. Image from Hutchison's paper.

Titicaca frog. Image from Hutchison's paper.

Hutchison remarks that there are probably more lungless frog species with specimens sitting around in museums of natural history, that have never been dissected. Perhaps these museums would be helped by a small CT scanner? (More likely perhaps, they would be helped by people with an interest in going through their vast collections and cataloguing them.)

Full reference:
HUTCHISON, V. (2008). Amphibians: Lungs’ Lift Lost Current Biology, 18 (9) DOI: 10.1016/j.cub.2008.03.006

Breathing in the bitter cold: lungless frogs and a fish without erythrocytes

March 26, 2009

ResearchBlogging.orgToday I stumbled upon two blog posts that really capture some of the beauty of the diverse adaptations in nature.

Random Biology writes about creatures living in cold waters. Water can carry oxygen at a far greater density at lower temperatures. This simple phenomenon, combined with the slower metabolism of cold tissues, has made it possible for certain salamanders to get along fine without lungs. All their breathing occurs through the skin.

In a recent paper in Current Biology, David Bickford and two colleagues describe the same phenomenon in a frog! It’s called Barbourula kalimantanensis, and lives in Borneo. Interestingly, it has apparently retained the lining of the lungs and thoracic cavity, called the mesothelium.

Barbourula kalimantanensis. Image from the paper by Bickford et al.

Barbourula kalimantanensis. Image from the paper by Bickford et al.

In a still more fascinating post, Biochemical Soul describes a fish with a new way of dealing with freezing temperatures. Or several, actually. It is the Channichthyidae family of icefishes, which live in Antarctic waters that are often below freezing point (but still liquid, of course, because of their salinity). These fishes have no hemoglogin, and consequently no red blood cells. They also lack myoglobin, the related molecule that stores oxygen in muscle cells. They rely instead on the greater oxygen-carrying capacity of their cold blood. With no erythrocytes, the viscosity of the blood decreases, which helps circulation. And to compensate for the lack of oxygen carriers in the blood, they have a 4-5 times increased stroke volume of the heart. This was originally described in 2006 by Thomas J. Near and coworkers in an open-access paper in Molecular Biology and Evolution.

Icefish. Image from the paper by Near et al.

Icefish. Image from the paper by Near et al, referenced below.

Cool stuff! (Don’t excuse the pun.)

Full references:
BICKFORD, D., ISKANDAR, D., & BARLIAN, A. (2008). A lungless frog discovered on Borneo Current Biology, 18 (9) DOI: 10.1016/j.cub.2008.03.010
Near, T. (2006). A Genomic Fossil Reveals Key Steps in Hemoglobin Loss by the Antarctic Icefishes Molecular Biology and Evolution, 23 (11), 2008-2016 DOI: 10.1093/molbev/msl071

I can see through your forehead!

February 24, 2009

Well, what to make of this? The Zooillogix blog alerts me to a new report on the barreleye, a bizarre deep-sea fish. It has recessed its eyes quite deep underneath the skin of the forehead, which is completely translucent! Over the mouth are two small dots that look like eyes, but are in fact nostrils of a sort.

Check out this video:

Deep sea news has more coverage.