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 algae. Corals such as the one depicted below have a symbiosis with single celled algae called zooxanthellae. This is many-layered symbiosis because corals house the entire chloroplast-containing algal cells within their tissue. This is different from Elysia chlorotica who has cut out the middle man– instead of incorporating entire algal 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.
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.
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.
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.
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.
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.
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.
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.
Our own lifecycles are pretty simple. Making babies requires sex. Sex creates offspring with new unique combinations of genes. Many organisms are also capable of asexual reproduction, which doesn’t involve sex (as the name implies) and involves only one parent. In most types of asexual reproduction, genes aren’t reshuffled and the offspring are genetic clones of their parent.
Unlike ourselves, many species have lifecycles that combine both sexual and asexual reproduction. Take the moon jelly, for example. Moon jellies, also known as Aureliaaurita, are perhaps the quintessential jellyfish, with a typical umbrella-like medusa that travels on ocean currents. There is more to their lifecyle, though, than this swimming organism. The swimming medusa does use sex to make babies—but the babies don’t grow directly into swimming medusae. Medusae release their eggs and sperm into the water and these combine to form a zygote (the fertilized egg). The zygote then develops into a planula larva. The planula eventually sinks to the ocean floor and develops into a polyp, an organism that looks nothing like a medusa. Polyps are attached to the ocean floor, usually on a rock or other hard surface, and stay in one place their whole life. They have a mouth surounded by tentacles, just like the more familiar polyps of sea anemones and Hydra. These polyps, however, are incapable of having sex—they cannot make eggs and sperm. Instead, they reproduce asexually. They can asexually produce other polyps, but they can also asexually produce miniature medusae called ephyra. These are pinched off from the polyp’s mouth as if they were a stack of plates, with the most mature medusa on top. The ephyra then swim away, grow into mature medusae, and complete the lifecycle.
This installment of CreatureCast is the first of several contributions that were done as final projects by undergraduate students in Casey Dunn’s Bio0410 Invertebrate Zoology class at Brown University. In episode 3 sophomore Lee Stevens discusses how comb jellies move the same way that many single-celled organisms do, which is remarkable given how much bigger comb jellies are.
We have managed to create a huge memorial to human waste at a location that is remote from everyday human activity. In 2008 the predicted existence of a floating mass of pelagic plastic, a giant Garbage Patch, was confirmed in the stable waters of the North Atlantic gyre where plastic debris is accumulating over an area estimated to be twice the size of Texas.
Anna Hepler is a sculptor based in Portland, Maine. The subject of Hepler’s work is often the way a multitude of interlocked entities form a shape or a flock, spreading through space. On learning about the Garbage Patch, she incorporated it in a project for one of her first large scale installations. In January 2009 she spent a week together with eight assistants sowing together discarded plastic from a Portland recycling center. Once stitched together, the plastic nets formed a giant boat hull hanging from the walls and ceiling of the Center of Maine Contemporary Art in Rockport.
An extended article about the project can be found here. Also, Hepler will be recreating this piece in the Portland Museum of Art in 2010 under the title ‘The Great Haul’.
