What is a cell?

posted by Sophia Tintori / on August 16th, 2010 / in Multicellularity

A couple of months ago Casey Dunn talked about animals that don’t have every one of the qualities we use to define something as an individual, and how those animals make us re-evaluate our definition: A member of a colony can be a descendant of a free living individual, but unable to live and interact with the world without the other members of the colony, making itself hard to pin down as an individual or a part of an individual. Similarly, sometimes the qualities that we associate with a cell don’t always come together in a tidy package.

In the plasmodial slime mold pictured on a piece of bark above, the organism’s body is large and complex enough to look like it’s made of many types of cells, but it is actually made up of just one long branching space. It has many nuclei within its one labyrinthine cell, with no walls or membranes separating them. The organism even has certain parts that look very different from other parts; there is a mat on the ground made of thin winding filaments, and then there are fruiting bodies that grow straight up into the air. This seems just like cellular differentiation in other creatures, but it is all coming from one cell.

Vaucheria (pictured below), the alga that is eaten by Elysia the photosynthesizing sea slug, is a similar story. Long and filamentous, the body has no cell walls between the many nuclei inside of it. One might think that the cytoplasm is simply viscous enough that the cell’s insides can stay put relatively well without walls, but cytoplasm has actually been seen streaming up and down the filaments, which are long enough to be spanning different microenvironments.

The upper photograph is slime mold on a piece of bark, peeled off the trees of Providence by Nick Jourjine, and photographed by Sophia Tintori. A really wonderful comprehensive set of drawings of slime molds can be found here. The bottom photograph is Vaucheria, photographed with a confocal microscope by Asya Rahlin and Harmony Lu. The sample was unstained, and so the green and red represent artifically colored autofluorescence. Nick, Asya and Harmony are ungraduates at Brown, and these photographs resulted from some of their work for Casey Dunn and Gary Wessels seminar on the origins of multicelularity and the evolution of the germ line. All photographs are published under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 license.

CreatureCast – Corals & Coloniality

posted by Sophia Tintori / on August 9th, 2010 / in Podcast (Student Contribution)

Here is a new video podcast from Lee Stevens, a rising junior at Brown University. In this episode Lee takes a closer look at corals. Corals tend to be known as home to a dynamic menagerie of animals, bacteria and plants, but the coral itself is also a pulsating community in it’s own right.

This video was produced by Lee Stevens, with music by Transient. It is released under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 license.

CreatureCast- Jellyfish Theater

posted by Sophia Tintori / on July 16th, 2010 / in Arthropods, Jellies, Parasites, Podcast, Symbiosis

In the vast ocean, without walls and far from the floor,  jellyfish can become drifting islands of activity. Creatures from far and wide will congregate on them to act out the ups and downs of life and death. Jellyfish have symbiotic relationships with living things of all sizes, from fish and shrimp that feed off them or off the pieces of food left between their tentacles, to single-celled photosynthesizing organisms that take shelter inside the cytoplasm of the jellyfish’s cells.

In this video, Trisha Towanda talks about one particular jellyfish, the fried egg jelly, and some of the other creatures that hang around it. There are moon jellies that the fried egg jelly eats. These moon jellies have little parasitic crustaceans on them called amphipods, which jump to the fried egg jelly while the moon jelly is being eaten. There are also crabs that ride around on the fried egg jelly, that are parasitic in their youth, but then grow to be helpful symbionts by eating off the little amphipods. This sort of coming of age story, where a symbiont’s relationship changes over its lifespan is an unusual one. Trisha put the pieces together by staring at them for hours and days and weeks when she was in Erik Thuessen‘s lab at Evergreen State College.

Many thanks to Trisha Towanda, who is now stationed in the Seibel lab at the University of Rhode Island. This video was edited and animated by Sophia Tintori, with an original score by local pop hero Amil Byleckie. It is released under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 license. Here is the paper Trisha wrote about the story.

Axolotls and the French Intervention

posted by Sophia Tintori / on July 15th, 2010 / in Uncategorized

Léon-Eugène Méhédin was a photo-journalist in the mid 1800s. After documenting the Crimean War, the Italian Campaign of Napoleon III, and taking pictures in Egypt and Nubia for a photographic encyclopedia, he traveled to Mexico with the French Expeditionary Forces. There he claims to have discovered the ruins of Xochicalco. He took papier machê molds and many photographs, all of which were reported to have been too artistic to be of any scientific value, and have never been seen since. Upon their return from Mexico, the French Expeditionary Forces brought 34 funny mexican salamander-like animals back to give to the Natural History Museum of Paris.

These animals, called axolotls, were first seen as a scientific oddity; they spend their whole lives looking like the larval state of a salamander, but they become sexually mature and can reproduce without metamorphosing into the adult form. In 1863, Méhédin gave 6 of these animals (and then one more, a few years later) to a local biologist named August Duméril, who started breeding them and enthusiastically sharing thousands of them with his colleagues all over Europe.

Since then axolotls have become one of developmental biology‘s model organisms, mostly because they are easy to raise, their embryos are large and transparent, and axolotls can regenerate their limbs and heart. In that same time, the original populations of wild axolotls, which live solely in the lakes in and near Mexico City, have dwindled to the point of near-extinction.  The vast majority of axolotls alive today are being bred in developmental biology labs across the globe. Most individuals can be traced back to two of those 7 axolotls from Méhédin in the 1860s.

Above is a video of a some axolotls captured by Stefan Siebert, a post-doc in the Dunn lab. It was edited by Sophia Tintori, and is released under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 license. Thanks to Dr. Nadine Piekarski for telling us about their ancestry.

More Budding Jelly Babies

posted by Sophia Tintori / on July 1st, 2010 / in Development, Jellies, lab, lifecycles

We found more jellyfish being born in our lab this week!

Rebecca Helm, a Dunn lab graduate student, left a couple of bowls of salt water and hydroids out on the table overnight, instead of the refrigerator where they usually live at around 50 or 60 degrees fahrenheit. The next day she came in and found them doing this:

This particular animal is called Podocoryna carnea. Like most jellies and close relatives of jellies, it has a pretty elaborate life cycle. This one involves a free swimming jellyfish, and a larva that swims around then lands on the back of a hermit crab’s shell. Then the larva metamorphoses into a polyp, which buds more polyps, growing into a whole colony on the crab’s back. The colony is made up of lots of polyps that are all connected and share fluid through a web of tubes that circulate partially digested food. Some members of this colony will eventually bud new swimming jellyfish.

The video at the top is of one of the colonies we have growing in our lab. These polyps were given to us by friends, but they can also be collected from hermit crabs at the beach, then grafted onto slides. They seem to grow well on slides, and slides are much easier to take care of then crabs.

Some of the polyps in the video have pink balls growing around the top. These are the buds that will mature to become free-swimming jellyfish. If you look closely, you can see jellies of all stages of maturity growing, including some that are ready to break free. After they swim off they will continue growing. We’ll try to follow up on how that goes.

Video by Sophia Tintori, life cycle drawing by Perrin Ireland, both released under a Creative Commons Attribution-Noncommercial-Share Alike license. Thanks to Diane Bridge and Neil Blackstone for the Podocoryna colonies. Check out this earlier post of the other polyps we saw budding jellyfish in our lab.

Salty Pups

posted by Sophia Tintori / on June 23rd, 2010 / in Chordates, Extremophiles

In Death Valley, life can be difficult.  One might think that such a dry area would be a bad place for fish to live, and it is. But that is exactly why it is such a great habitat for this particular fish, Cyprinodon salinus, as well as the other desert pupfishes.

The salt creeks and pools of the California desert evaporate quickly, making their salinity change day by day. In the winter some creeks will be essentially freshwater, while in the hottest parts of the summer the water can become twice as salty as the ocean. Because the desert pupfish can handle this kind of fluctuation, which would kill most of the rest of us, they usually get the creek to themselves, with no other competing fish.

Some desert pupfishes in South America even live in ponds that dry up entirely during the summer. They lay their eggs in the mud before it dries, then when the rain starts to fall again, the population is reconstituted and the eggs begin to hatch.

This past March, while visiting Death Valley with his family, Casey Dunn, the principle investigator of our lab at Brown University, visited a salt water creek and found these pupfish spinning around each other while mating. The females are the smaller ones, and they lay one egg at a time. A male will swim up next to her, they will both curve their bodies into an S shape, the female drops an egg into the male’s fin, he fertilizes the egg, then drops it on the floor of the creek. In this clip the males are tagging off, each taking turns fertilizing eggs as they come out of the females.

This video is released under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 license. Thanks to Maria Dzul for pointing me towards some information about desert pupfish. Here is a paper about pupfish and the fluctuating salinity of their water, here is a description of C. macularius‘ mating behavior, and here is a nice book about California fish, which might be at your local library.

Centerless Self

posted by Sophia Tintori / on June 15th, 2010 / in Arthropods, Development, Platyhelminthes

The sense that the self exists somewhere close to the brain or heart is an intuitive one for humans. It also seems to apply to most of the animals we regularly encounter, even when they can regrow parts of their body. When a crayfish gets into a tight spot and loses one of its claws, the part of the crayfish with the head will regrow the lost claw, but the claw won’t regrow a body and head.

For many animals, though, there is no such essential center of the organism. When a flatworm gets its tail cut off, both the tail and head will fill in the missing parts and make two whole flatworms that are clones of each other. Its body is arranged such that there isn’t a single part of the animal that can be identified as the core.

Here is a bit of footage taken by Stephanie Spielman, an undergraduate in Casey Dunn and Gary Wessel’s seminar on the evolution of multicellularity at Brown University. The clip features the flatworm Dugesia tigrina swimming around the Dunn lab. It is released under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 license. The crawfish video is from Day at the River (1928), a video from DeVry School Films, Inc., which is under public domain.

How do krill grow?

posted by Lisa Roberts / on June 4th, 2010 / in Arthropods, Development, lifecycles, Podcast, Science & Art

Early last year, at the Australian Antarctic Division (AAD), I saw an unusual sight: the birth of a live Antarctic krill, Euphausia superba.
The newborn appeared on a video screen that projected the view of a camera poised over a petri dish. A tremulous form emerged from its egg with its legs beating furiously!
This event began a continuing conversation with krill research leader, So Kawaguchi.
Back in my Sydney studio, I worked with So’s words and images. He explained (by email) how krill grow, and sent me diagrams by John Kirkwood to work with. I also found data sets online of how krill appendages move (Uwe Kils). Piano music was improvised by an 11 year old friend, Sophie Green.
This is the first of some animations that I am making to more fully describe this elusive and most important creature.
Krill are central to the marine life food web. Their health is endangered as a result of oceans becoming more acidic (as carbon increasingly enters the atmosphere and then dissolves into the water).
A new research project at the AAD is to record changes in normal krill development in increasingly acid water. Next month (June 2010) I return to the AAD krill nursery to find out more about this research.
I will also record So Kawaguchi describe what he has identified as a circling krill mating dance. What a fine gesture of continuity!

This video is released by Lisa Roberts under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 license. More animations can be found at AntarcticAnimation.com.

Bone Boring Worms

posted by Perrin Ireland / on May 25th, 2010 / in Annelids, Development, lifecycles

In 2002, while out roaming the depths in Monterey Bay Canyon with the remote operated vehicle (ROV) Tiburon, MBARI scientist Robert Vrijenhoek stumbled upon a whale carcass on the ocean floor, and noticed that it had its own little ecosystem. When a whale has died, its skeleton drops to the ocean floor, creating a habitat island in the depths. Creatures apparently gather from far and wide to use the whale carcass’ nutrients and living space.

Scientists have categorized four stages of whale carcass ecosystems- first the “mobile scavengers” show up, such as sharks, crabs, hagfish. These guys pick away at what luscious meat remains. Snails, slugs and worms show up next to make use of the nutrient-rich poo (in science speak, “organically rich sediment”) the larger scavengers have left behind. The third stage is comprised of animals that rely on hydrogen sulfide gas emitted from the decomposing bones and organic sediments. These animals, like vesicomyid clams, depend on symbiotic bacteria that live inside their cells to make energy for the animal from sulfur based compounds. Free-living bacteria that also live off sulfur form in mats that coat the bones. The final stage of a whale bone’s community succession is the reef stage, when most of the nutrients the whale bone can provide have been exhausted, and the minerals remaining in the bone provide a surface for suspension and filter feeders, who rely on the ocean currents to bring food their way.

When Vrijenhoek and his colleagues were at depth checking out whalebone world, they noticed little red worms that they were unable to identify all over the remaining whalebones. They collected a sample and send the worms to worm expert Greg Rouse, who informed them they had discovered a new species. Related to tube worms that live at the mouths of hydrothermal vents, Osedax grow at their longest to be about the length of your index finger, and as thick as a pencil. Penetrating deep into the marrow cavities of the whalebones are their elaborate root systems. These roots house bacteria that help the worms extract and digest nutrients from the bone, as they lack stomachs and digestive tubes.

Perhaps most bizarre and enticing about the Osedax worm is that all the worms the scientists first discovered appeared to be reproductive females, with no males in sight. Eventually they found the tiny males living in tubes along the female’s trunk. An Osedax female essentially has a harem of up to fourteen males that do nothing else but provide sperm for the eggs she produces. Osedax males feed for their entire lives on yolk provisioned by the egg from which they hatched, like forty year olds living at home on Mom’s meatloaf. The males look strikingly similar to Osedax larva, suggesting that they are larva in arrested development that began producing sperm.

Most of the eggs exiting the female are already fertilized. But how do those little guys lying along her trunk scoot their sperm up to catch the eggs as they’re on the way out? And how, then, do larvae being flung into the dark beyond know whether to become male or female? It could be possible that sex determination depends on whether a larva lands on bone or lands on another female. Perhaps similar to hydrothermal vent worms, a juvenile becomes a male if it lands on a female and she releases a chemical, enticing it into her little harem, to do her reproductive bidding.

A Tale of Two Nuclei

posted by Rebecca Helm / on May 16th, 2010 / in Development, Fungi, lifecycles

Mushrooms may look mundane, but they’ve got a lot going on underneath the surface.  In animals, each cell in a body contains one nucleus, and each nucleus has 2 copies of the genome, one from the mother, and one from the father, which fused at fertilization. Unlike in animals, where the nuclei of the egg and sperm quickly join after the cells combine, the nuclei in mushroom cells stay separate. The reason for the difference boils down to the particular way fungi have sex.

Frisky fungi creep through the soil with long filaments.  These moldy structures occupy the spaces between dirt, and allow the organisms to digest organic matter.  They’re also great for mating. Fungi spend much of their lives with only a single nucleus.  Except, that is, when two filaments cross paths.

When two lonely filaments find each other, the cells at the tip of the filaments fuse, and form new structures that have two nuclei per cell. This cell with two nuclei takes on a life of it’s own and divides many times to form a mushroom.  Each mushroom cell contains a copy of each of the parent nucleus.  The nuclei only fuse in the mushroom gills (pictured), just prior to the formation of mushrooms spores, which are then carried away by the breeze, off to seed the next generation of fungi.

Photographs of the basidiomycete Agaricus bisporus by Rebecca Helm.