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.

Tube vision

posted by S. Zachary Swartz / on March 17th, 2010 / in Echinoderms, locomotion, optics

As a student of science, I love how even something close to home can take me completely by surprise. I study sea urchin development, and yet until recently I had no idea that urchins can see. I find this fascinating because they do not have eyes, at least not as I typically think of them. I first learned of this at a talk about feet, of all things. Feet may be the organs by which urchins largely experience their world. Sea urchins have hundreds of feet: thin, muscular tubes with suction cups at the ends. In the video below, you can see how their combined action allows the animal to move (slowly). The role of the tube foot goes beyond locomotion, however.

Urchins have many of the same genes that are associated with vision in other animals. But they don’t have anything that resemble eyes. Instead, these genes are expressed most in the tube feet and short appendages called pedicellariae. It’s been long recognized that sea urchins are light sensitive. Specifically, they tend to move away from it. Trickier, though, is determining how sensitive they are. Are sea urchins reacting to the presence or absence of light, or do they actually have spatial perception? Recent work by Blevins and Johnsen (2004) and Yerramilli and Johnsen (2009) suggests the latter. In these experiments, urchins would react to the presence of dark targets that looked like nice holes to crawl into in their tank. But they only recognized them if they were above a certain size, implying that their visual perception has a resolution of that certain size, and that they’re not just recognizing simple light or dark cues.

So urchins can move in relation to where the dark shapes are, and they have these photoreceptor genes in their feet. But a photoreceptor alone won’t provide spatial information. A creature needs a way to screen out light coming from the sides of the photoreceptors, and only recognize light coming directly at it, so that each photoreceptor is getting a unique reading. Then it can use those readings to get a sense of the differences between the different spaces in front of each receptor. Where does sea urchins’ resolution come from? It’s possible that their spines block out all light except that which is directly in front of any given photoreceptor. When combined, all of the photoreceptors—on the tube feet, pedicellariae, and probably the shell itself—may function as a giant compound eye like that of an insect, with each receptor only seeing what’s in front of it. And if fact, it turns out that the resolution of sea urchin vision actually correlates well with the spacing between their spines. The resolution is modest, but enough to allow for some complex behavior, helping them seek shelter, locate food, or flee from predators. Sea urchins lack a central nervous system or anything resembling a brain, so I find it amazing that they are able to process spatial information.

Videos and photographs taken by Adrian Reich of the Wessel lab. The top photo shows the wandering tube feet of the sea urchin Strongylocentrotus purpuratus. Next down is a video of S. purpuratus moving, then an image of the tube feet of S. purpuratus and its sea star relative Patria miniata. The bottom photo is a close up on P. miniata.

CreatureCast – Diving for Jellies

posted by Sophia Tintori / on March 3rd, 2010 / in History, Jellies, Podcast, Siphonophores

Here in the Dunn lab, siphonophores are our favorite animal and the focus of much of our research.

Dr. Phil Pugh is a good friend of the lab, and he also happens to have described more new species of siphonophores than anyone who has ever lived. In the video below, he describes what it’s like to come across a siphonophore in the deep sea with a submarine. What looks like one long body in this video is actually a free-swimming colony of clones — many genetically identical bodies that are all attached. But each body in the group isn’t just like its neighbor. They each do a specific job for the colony. Some individuals will swim, some will catch food, and some will reproduce.

More on siphonophore biology can be found in papers here and here. But we’ll talk about all that later — for now, just take a look.

Footage courtesy of the Bioluminescence lab at the Monterey Bay Aquarium Research Institute. Music graciously provided by Raf Spielman of The Golden Hours. Edited by Sophia Tintori. This podcast is published under a Creative Commons Attribution Non-Commercial No Derivatives 3.0 license.

Royal jellies

posted by Sophia Tintori / on February 17th, 2010 / in History, Jellies

Emperor Hirohito was a man who wore many hats. Most famously, he was Japan’s head of state during World War Two. As emperor, he was the stoic and elegant embodiment of Japan. But he was also a family man, a poet, and a marine biologist.

Hirohito had the Imperial Biological Laboratory built for him when he was 24, which was substantially upgraded three years later when he became the emperor. It contrasted the rest of the Imperial Household in the plainness and usefulness of its furniture. Plain furniture, such as a trash bin made out of a trophy elephant leg.

He would steal away every Saturday afternoon and most Thursdays when he could, to his lab where he would meet with other biologists to identify and describe the species that they had dredged up from the surrounding waters. He had a gentle touch when working in the field. If collecting from a colony of polyps, he would take only a small bit of each colony and would put the rock carefully back in place, so as to let the rest thrive.

After the war he published 32 books of plates, describing some 23 new species of ascidians, 7 new species of crabs, 8 new species of starfish, and 6 new species of pycnogonids. He conducted the first comprehensive survey of the biodiversity of Sagami Bay, but he was particularly well versed in the tiny tentacled polyps that grew on the sea floor, called hydrozoans. All of his work was published under the name ‘Hirohito Emperor of Japan.’

At the top is a photo of Emperor Hirohito with his wife, whose hat is making her look a bit like a hydrozoan herself. Next down is Emperor Hirohito in the Imperial Laboratory, from E. J. H. Corner’s article about Hirohito’s scientific career. Below that is an illustration of a nudibranch (left) from Opisthobranchia of Sagami Bay (1949), and an illustration of a coral (right) from The Hydrocorals and Scleractinian Corals of Sagami Bay (1968), by Hirohito Emperor of Japan. Below is a photo of Emperor Hirohito in Kurume, also in 1949.

Solar Powered Sea Slugs

posted by Freya Goetz / on February 8th, 2010 / in molluscs, Symbiosis

The slug pictured above, Elysia chlorotica, is a symbiont thief.

Elysia chlorotica eats the alga Vaucheria litorea but does not digest it. The slug cuts open algal filaments and sucks out the contents, transferring the living chloroplasts to its own tissue. Chloroplasts are organisms that have lived symbiotically within plant cells for many millions of years. They harness energy from the sun, which they give to the plant or alga cell they live within. Most animals digest the chloroplasts entirely when they eat plants, but not Elysia. By keeping the chloroplasts intact and transferring them to its own tissue, Elysia allows them to continue photosynthesizing, producing energy for the slug. The slug can then live for months without eating as long as sunlight is available, and can maintain the same chloroplasts for its entire adult life. This is an extremely unique relationship between an animal and plant symbionts.

Many other animals form associations with photosynthetic organisms. Corals such as the one depicted below have a symbiosis with multiple single-celled organisms called zooxanthellae. This is a multiple-level symbiosis because corals house the entire chloroplast-containing zooxanthellae cells within their tissue. This is different from Elysia chlorotica, who has cut out the middleman — instead of incorporating entire  cells, it only retains the chloroplasts.

The upper photograph (of Elysia chowing down) was taken by Nicholas E. Curtis and Ray Martinez. The second photograph is courtesy of Mary S. Tyler, and was the cover of PNAS when this paper was published. The lower picture is the coral Porites as photographed by Casey Dunn. You can watch two amazing videos of the slugs in action, here and here, both of which were included in the PNAS paper.

CreatureCast – Picky Females

posted by Sophia Tintori / on January 14th, 2010 / in lifecycles, Podcast

A couple of weeks ago the Dunn lab went out after work, and we got to talking. There’s this thing that usually happens whenever we get together after a day in the lab or field– being a group where everyone focuses in one way or another on the diversity and evolution of reproduction and development, we start to tell stories about how animals reproduce. Someone mentions some surprising tidbit of reproductive biology they recently heard, and that sets it off. Then someone else remembers a weirder story, and tells it. This spurs someone else’s memory, and so on, and then I start feeling overwhelmed.

Well, this time we got caught up on the issue of female choosiness. It takes more energy and resources to make an egg packed with resources, or to raise offspring, or to carry a baby inside the womb, than it does to make sperm. This often leads females to be more selective about their mates than males are. We started talking about ways in which female choosiness manifests itself; sometimes through behavior, sometime through anatomy, and sometimes at the level of the cell. And then sometimes it is all for naught.

In this episode of CreatureCast Rebecca Helm, a graduate student in the Dunn Lab, recounts a few short stories about the many levels of reproductive selection.

Editing and animation by Sophia Tintori. We Want To Be Old by Bird Names. Photos of bowers by Mila Zinkova and Peter Halasz. Duck story from the research of Richard Prum and Patricia Brennan. Video of the inside of a comb jelly egg by Christian Sardet, Danielle Carré and Christian Rouviere, from the BioMarCell group. This video is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.