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.