A few carnivals have popped up:
Also, Mendel’s Garden #6 is looking for submissions — it will be hosted at The Voltage Gate tomorrow!
Pharyngula
Evolution, development, and random biological ejaculations from a godless liberal
A few carnivals have popped up:
Also, Mendel’s Garden #6 is looking for submissions — it will be hosted at The Voltage Gate tomorrow!
We are all familiar with the idea that there are strikingly different kinds of eyes in animals: insects have compound eyes with multiple facets, while we vertebrates have simple lens eyes. It seems like a simple evolutionary distinction, with arthropods exhibiting one pattern and vertebrates another, but the story isn’t as clean and simple as all that. Protostomes exhibit a variety of different kinds of eyes, leading to the suggestion that eyes have evolved independently many times; in addition, eyes differ in more than just their apparent organization, and there are some significant differences at the molecular level between our photoreceptors and arthropod photoreceptors. It’s all very confusing.
There has been some recent press (see also this press release from the EMBL) about research on a particular animal model, the polychaete marine worm, Platynereis dumerilii, that is resolving the confusion. The short answer is that there are fundamentally two different kinds of eyes based on the biology of the cell types, and our common bilaterian ancestor had both—and the diversity arose in elaborations on those two types.
Everyone knows the story of Konrad Lorenz and his goslings, right? It was a demonstration of imprinting: when young animals are exposed to a stimulus at a critical time, they can fix on it; Lorenz studied this phenomenon in geese, which if they saw him shortly after hatching, would treat him like their mother, following him around on his walks. Similarly, many animals seem to experience sexual imprinting, where they acquire the sexual preferences that will be expressed later on.
I just ran across a charming short letter about imprinting in cephalopods, and somehow the story seems so appropriate. Imprint a young, freshly hatched cuttlefish on something, and they don’t treat it like Mom, and they don’t later want to mate with it—they want to eat it. Lorenz was lucky he was working on birds rather than cephalopods.
The experiment is straightforward. Cuttlefish normally prefer to eat shrimp over crab. If, the day after hatching, small crab are put in the tank with the hatchlings for at least two hours, and then removed (the crabs are not eaten), then 3 days later when tested again, the cuttlefish will prefer to kill and eat crabs over shrimp. The procedure is very specific: they have to be exposed to crab for at least two hours, within 2 hours after sunrise on their first day after hatching.
The paper has a good, succinct description of why many animals would have this mechanism:
Precocial animals, like domestic
chicks and cuttlefish, which are
independent within hours of hatch
or birth and which receive no
posthatch parental care have
two options for acquisition of
information: bring it into the world
with you (unlearned preferences
for food, sexual partners and so on)
or pick up the information as you go
(trial and error learning). Imprinting
allows something in between:
a certain degree of flexibility in
response, useful for learning
information for which the timing is
likely to be predictable—food
seen in first few hours of life,
sibling/parents seen during
juvenile stages—but in which
specifying the exact details of
the experience is not useful.
An evil man could think of many nefarious things to do with this bit of information, I think.
Healy SD (2006)Imprinting: seeing food and eating it. Curr Biol.16(13):R501-502.
Stop it! Some misguided people are killing stingrays in apparent retribution for the death of Steve Irwin.
A fisheries department official says up to ten of the normally docile fish have been found dead and mutilated on Australia’s eastern coast since Steve Irwin was killed by one last week. At least two had their tails lopped off.
As the article goes on to say, this is the antithesis of what a conservationist like Irwin would have wanted.
I’ve been tinkering with a lovely software tool, the 3D Virtual Embryo, which you can down download from ANISEED (Ascidian Network of In Situ Expression and Embryological Data). Yes, you: it’s free, it runs under Java, and you can get the source and versions compiled for Windows, Linux, and Mac OS X. It contains a set of data on ascidian development—cell shapes, gene expression, proteins, etc., all rendered in 3 dimensions and color, and with the user able to interact with the data, spinning it around and highlighting and annotating. It’s beautiful!
Unfortunately, as I was experimenting with it, it locked up on me several times, so be prepared for some rough edges. I’m putting it on my list of optional labs for developmental biology—3-D visualization of morphological and molecular data is one of those tools that are going to be part of the future of embryology, after all—but it isn’t quite reliable enough for general student work. At least not in my hands, anyway. If one of my students were to work through the glitches and figure out how to avoid them, though, it could be a useful adjunct to instruction in chordate development.
If you want to play with it, I’ll give you a quick overview of what’s going on in the dataset. A paper by Munro et al. has used these kinds of data to summarize key events in the transformation of a spherical ball of cells into an elongate, swimming tadpole larva.
I got this email from Alan Kazlev, one of the main fellows working on the Palaeos website (a very useful paleontological resource), which I had previously reported as going offline. Plans are afoot to bring it back, and the answer seems to be to wikify it and build it anew, with a more distributed set of contributors. How Web 2.0! I’ve included the full email below the fold if you’d like more details.
Life is cruel and brutal, I guess.
Ya Ya, a seven-year-old panda and new mother of twins, “appeared tired” when nursing the younger cub in a patch of grass, the paper said.
Her head sagged, her paws separated and her baby fell to the ground next to her. The panda then rolled on to her side and crushed her baby beneath her.
I remember that chronic exhaustion when our kids were piping hot and fresh from the uterus, too.
Every week, someone finds something that reminds them of me, and they send it off in an email. I think that every day someone strolls through a fish market and the PZ-spot in their brain lights up like a Tesla coil, triggering odd associations that can only be relieved by grounding them out in an email message. Some examples are below the fold.
The latest issue of Science has a fascinating article on Exotic Earths—it contains the results of simulations of planet formation in systems like those that have been observed with giant planets close to their stars. The nifty observation is that such simulations spawn lots of planets that are in a habitable zone and that are very water-rich.
Dynamics of Cats has a better summary than I could give, and it leads in with this lovely illustration of an hypothetical alien organism on one of these hot water worlds.
The only thing cooler than a cephalopod has to be a tentacled alien cephalopodoid. There’s a high-res version of that image at Dynamics of Cats—and I’ve got a new desktop picture.
Perusable blogaliciousness for your Friday morning:
The Hairy Museum of Natural History has put out a call for submissions to the Tangled Bank, with an early deadline. If you want a shot at maybe seeing your link with a custom illustration, send it in by Sunday evening. He’ll try to accept stuff up through Tuesday, but make life easy on the guy, OK?
