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.

Spicules and droplets

posted by Erwin Keustermans / on January 4th, 2010 / in Science & Art

When I was a kid and colour television was rare, people would shrug away the need for it saying that the only good reason for having a colour set would be marine documentaries.

But it’s not only the colours and optics that are different, also form and movement are part of the experience. Life in water is different in shape, structure and kinetics. Evolution in a marine environment makes creatures that are very different from ground- or air-bound life. Wentworth D’Arcy Thompson, a Victorian scientist, set out to demonstrate the mathematical and physical aspects of under water biological processes in his book “On Growth and Form” (1917). For marine life that would be gravity, pressure, scale, osmosis, and buoyancy.

I mention the book here because it is very readable, even for the layman, and even after more than 90 years. Without reading it I probably would not have realized why it is such a smart idea for the artist/filmmaker Saskia Olde Wolbers to use liquids. Olde Wolbers’ stories are told in voice-over while showing seemingly unrelated going-ons in submersed sets that are smaller than life-size. She fills these with – next to more recognizable props – fluids of different densities .  And that definitely makes for an uncanny visual experience.

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But even without knowing the precise techniques used, you feel somehow that those are the particular optics and physics at work in this shot from her 2003 film “Interloper”.

Reading on Saskia Olde Wolbers can be found in Tyler Green’s art blog. An interview  about a video that relates to the Three Gorges dam. Olde Wolbers’ images at Maureen Paley Gallery. The image shown courtesy of Maureen Paley Gallery.

CreatureCast – Pattern Shifting Snails

posted by Sophia Tintori / on December 29th, 2009 / in molluscs, Podcast (Student Contribution), Science & Art

This is the fourth of four contributions from undergraduates in Casey Dunn’s Bio0041 Invertebrate Zoology class. This episode is inspired by the fascinating behavior of the flamingo tongue snail, Cyphoma gibbosum, which is described in further detail in Casey Dunn’s earlier post.

Video, music, and narration by Chris Vamos. This podcast is licensed under a Creative Commons Attribution-Noncommercial-No Deriviatives 3.0 United States License.

CreatureCast – Comb Jellies

posted by Sophia Tintori / on December 21st, 2009 / in Comb Jellies, Podcast (Student Contribution)

This is the third of four contributions from undergraduates in Casey Dunn’s Bio0041 Invertebrate Zoology class. In this episode, Daniella Prince describes the many wonders of comb jellies.

Video by Daniella Prince, with music by Ben Esposito. This podcast is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.

Stack of plates in action

posted by Sophia Tintori / on December 17th, 2009 / in Development, Jellies, lab, lifecycles

Look what we caught happening in our refrigerator.

While doing a fridge clean-out in the Dunn Lab, graduate student Rebecca Helm took a look at a forgotten bowl of Chrysaora colorata polyps from our friends Chad Widmer and Wyatt Patry at the Monterey Bay Aquarium. These creatures were left over from an RNA extraction we had done earlier for the Cnidarian Tree of Life Project, and were hidden in the back of the fridge, despite the labs strict ‘no pets’ rule.

Upon inspection, Rebecca noticed that the polyps were strobilating! This is a spectacular type of asexual reproduction, which is explained in more depth in Perrin Ireland’s post on the scyphozoan life cycle.

In this video, a polyp has pinched off into a stack of plate-like discs, called ephyrae. When they pop off of the end of the polyp, they each become a free swimming individual, and a direct clone of the parent polyp. Each ephyra will mature into adult bell-shaped jellyfish. Even before they break away from the poly, they are strongly pulsating as they flex their newly developed swimming muscles before birth.

Video by R. Helm and S. Siebert.

CreatureCast – Marine Worms

posted by Sophia Tintori / on December 16th, 2009 / in Annelids, Podcast (Student Contribution)

This installment of CreatureCast is the second of several contributions that were done as final projects by undergraduate students in Casey Dunn’s Invertebrate Zoology class at Brown University. In episode 4, sophomore Noah Rose delves into the bottom half of the circle of life, where dead things decompose and elements that can then be incorporated into other living organisms are liberated. Noah discusses how the many-legged worms we tend to think of as fish bait impact this process.

This podcast is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License. The video and sound work was done by Noah Rose, with music by Noah Rose.