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.

Be still its beating heart

posted by Sophia Tintori / on May 6th, 2010 / in molluscs

This animal is not the most agile swimmer in the sea. It’s called Nautilus, and it is closely related to cuttlefish and snails. But it swims backwards and often bumps into things.

Thankfully, it has a thick shell, and can retreat into it to avoid predators. And it also dives down deep into the sea during the day when it’s not feeding. The longer it spends inside its shell, though, the harder it is to get oxygen, and levels can get dangerously low if it has to wait for a long time without any new water flowing by. While we might try to hold our breath at those depths, Nautilus holds its heart. Nautilus slows its metabolism down, and it can hold its blood in its enlarged vena cava, spacing out its heart beat to once every one or two minutes.

Sea turtles, also fantastic divers, have a similar mechanism of energy conservation. The deeper they go, and colder the waters get around them, the slower their heart beats, going down to two or three times a minute and slowing their energy use to one tenth of what they would normally use on the shore.

Photographs graciously provided by Adrian Reich of the Wessel lab at Brown University. Thanks to Brad Seibel, our favorite mollusc exercize physiologist, for his help fact-checking. More about Nautilus metabolism can be found here.

CreatureCast – Sea Stars

posted by Sophia Tintori / on April 30th, 2010 / in Echinoderms, Podcast (Student Contribution)

[podcast]http://creaturecast.org/uploads/Pisaster1.mp3[/podcast]

Here is another student contribution to the CreatureCast series, by Nathaniel Chu. Nathaniel is a sophomore at Brown University, and was in Casey Dunn’s Invertebrate Zoology course last fall. In this audio piece, Nathaniel talks (and sings) about sea stars, from their run-in with the oyster industry in the early 1900’s, to their profound influence on that stretch of land between high tide and low tide, known as the intertidal zone.

Also featured are the voices of Dr. Chris Harley from the University of British Columbia, and Dr. Mark Bertness of Brown University.

This podcast is published under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 license. Photograph by Dr. D. Gordon E. Robertson. If you’d like, you can download this podcast here.

Seeing the invisible

posted by Erwin Keustermans / on April 22nd, 2010 / in Science & Art

Although we prefer pictures to represent reality as it is, that is often not the case. Images are made using digital filtering, pseudo-colours and polarised light.  Scientific subjects are isolated, prepared, sliced and coated. So what is shown is often outside the range of immediate perception. But instead of mistrusting the pictures, we find that it adds an extra element of fascination. We trust scientific images to reveal the invisible.

Adam Fuss is a contemporary photographer whose pictures work within this range of conventions. In this photograph of what appears to be a snake on the surface of the water, we are allowed to see the underlying physics of the way the animal moves. The waves emanate elegantly from the points in the cycle that the snake places pressure on the water around it.

Pictures courtesy of Cheim and Read gallery, New York. On the topic of photography and science, last year the San Francisco Museum of Modern Art staged an exhibiton about the history of modern science and photography: “Brought to Light Photography and the Invisible, 1840-1900“.There is a beautiful catalogue still in print.

CreatureCast – Individuality

posted by Sophia Tintori / on April 8th, 2010 / in Development, Jellies, Podcast, Siphonophores

Last month we posted a video of a siphonophore (one of the Dunn lab’s favorite animals) swimming freely in the ocean. In this next installment of CreatureCast, Casey Dunn describes how siphonophores help us question what we think of as an individual.

There are different ways to think of individuality. Individuality can refer to function- whether an organism operates and interacts with the world as a unit. A fish is a functional individual, but so is an ant colony. Individuality can refer to evolutionary descent. In this respect our liver is not an individual, there was no ancestral free-living livers out there that our liver is descended from. But our mitochondria are individuals in this sense. They evolved from free-living bacteria that became incorporated into other cells. Individuality can also refer to the process of evolution. In this sense an individual is any entity that has the properties necessary for evolution by natural selection- it reproduces and has variable heritable properties that influence the chances of survival. This could be a free living cell, a cell in a body, an entire multicellular organism, and even groups of organisms in some cases.

All of these definitions of individuality are in alignment in most of the organisms we are familiar with. A bird, a rose bush, and a fly are all individuals as functional entities, according to their ancestry, and as units of selection. This makes it easy to get lulled into thinking of individuality as a monolithic property.

A siphonophore colony is a functional individual. But a siphonophore colony is made up of many parts that are each equivalent to free living organisms such as sea anemones and “true” jellyfish. So by the evolutionary descent definition it is a collection of individuals. The colony as a whole is acted upon by natural selection, making it an individual in the sense of the process of evolution. But it is entirely unclear whether natural selection can act on the parts within the colony, as it does on our own cells when we get cancer, since we don’t know about the heritability between the parts of the colony.

Siphonophores, by forcing us to disentangle what we mean when we call something an individual, help us understand the evolutionary origins of individuality. These different aspects of individuality don’t necessarily evolve at the same time, and one or more of them can even be lost. Organisms like siphonophores provide glimpses of these different combinations of individuality.

Most of the stills are plates from the first papers describing siphonophores. They were published from the mid 1800’s to the early 1900’s by Henry Bryant Bigelow, Ernst Haeckel, and Karl Vogt.

The song New Homes is by Lucky Dragons, the siphonophore video is from Dr. Steve Haddock at MBARI, the podcast was produced by Sophia Tintori, and the video is published under a Creative Commons Attribution Non-Commercial Share Alike 3.0 license.

Hitching a ride

posted by Christopher Laumer / on March 27th, 2010 / in Arthropods, Parasites, Symbiosis

When collecting bugs out in the field, it can be easy to get more than one bargained for. Many flies, beetles, and other mobile beasties such as the harvestman shown above (Megalopsalis sp. from New Zealand) find themselves regular host to hitchhikers of arachnid origin: the five orangish globules nestled among the bases of this unfortunate individual’s limbs are parasitic mites hunkered down for the long haul.

Indeed, many tens of thousands of mite species spend their early lives attached to a host, slowly drawing nutrition from its internal fluids until they become large enough to drop off wherever their hosts have carried them, where they begin life as free-living adults. However, these parasitic freeloaders aren’t the only kind of tenants one will find on harvestmen; there are also diverse sorts of more benign bedfellows who climb aboard with no appreciable harm to their unwitting ride.

One group of these tag-alongs is the pseudoscorpions – distant relatives of true scorpions, living secretive lives in forest soil and tree bark – which many would doubtless find abjectly terrifying… if they ever got larger than a few millimeters. Below, you can see a pseudoscorpion hanging for dear life onto the leg of another Megalopsalis. There are reports of pseudoscorpions waiting eagerly around a flower for a bee pollinator to grab onto, or clustering around the pupal bores of flies just before the airborne adult emerges. The traditional interpretation of this behavior suggests that climbing aboard larger, more mobile animals is an adaptation meant to transport these tinier critters to a wider range of habitats. Others, however, have suggested that perhaps pseudoscorpions simply grab onto whatever passes by them in the hopes that they might be able to eat it.

Strangely enough, even pseudoscorpions can bear hitchhikers, as the parasitic mites on this neobisiid I collected during field work in Alabama attest (gray bugs next to the greenish dots). It’s hard not to be reminded of the poet Jonathan Swift’s famous verses:

“The vermin only teaze and pinch
Their foes superior by an inch.
So, naturalists observe, a flea
Has smaller fleas that on him prey,
And these have smaller still to bite ’em,
And so proceed ad infinitum.”

First three photographs by Gonzalo Giribet. Last photograph by Christopher Laumer.