Retractable spots

posted by Casey Dunn / on September 7th, 2009 / in molluscs

cyphoma

The marine snail Cyphoma gibbosum browses on the polyps of soft corals (top). It appears to have a brightly spotted shell, but when disturbed the spots begin to move (middle) and then retract within the white shell, along with the rest of the animal (bottom). This is possible because the spots are not part of the shell at all. They are patterns on the thin mantle tissue that extends out of the shell opening and up around the snail’s back. Photos by Casey Dunn.

Evolution by co-option

posted by S. Zachary Swartz / on August 20th, 2009 / in Development

Onthophagus taurus

In the course of evolution organisms sometimes acquire completely new and sometimes dramatic features, like horns or new appendages.  The evolutionary origins of new structures are much more difficult to study than modifications to existing ones.  One approach, however, is to study the development of newly arisen structures in as many different species as possible.  The genome does not code for a body plan directly; rather, it encodes genes that coordinate the process of development.  Development is a series of events that pattern a fertilized egg into a multicellular organism. The timing and spatial organization of gene function in an embryo is therefore central to creating body structure.  Again and again it has been seen that new structures don’t necessarily mean new genes; the development of many new structures is controlled by previously existing genes that have been deployed in new contexts. The use of existing genes for a new purpose is called co-option.

A recent study by Moczek et al. provides fresh detail on the development of new structures in a particularly interesting group of animals. Many species of beetle possess rather gaudy horns on their heads and thoraxes. Horns are not modified mouthparts or limbs; they exist in addition to a full set of these other structures.  Certain limb genes, though, are turned on in the horns.  These genes, distal-less, dachshund, and homothorax, play central roles in the limb development of other insect species. When the authors disrupted the function of these genes in beetle larvae, the animals grew abnormally short horns and limbs.  Their experiment indicates their dual functions in beetles: an ancestral function for making legs, and the more recently evolved functions in making horns.  You therefore might think of these genes simply as tools for making something that sticks out, be it a limb or horn.

Genetic co-option is not limited to beetles, but by studying creatures like these we can develop a more general picture of how body structure evolves. These studies have made it clear that, just as your brain doesn’t have a neuron that is specific to your grandma, there aren’t new genes that are specific to each new structure.

The photo above, by Alex Wild, is of two Onthophagus taurus males.

Glowing worms in Bermuda

posted by Stefan Siebert / on August 19th, 2009 / in Annelids

Odontosyllis phosphorea

Reproduction is a complex business, and often requires that the partners meet. Polychaete worms belonging to Odontosyllis have developed a highly elaborate mating behavior that includes bioluminescent signals. During a recent stopover on the Bermuda islands, on a sailing trip across the Atlantic, I was able to witness the fascinating mating dance of Odontosyllis enopla. The species normally spends its life in shallow water on rocky or sandy bottoms. Once a month, 2-5 days after full moon and around 55 min after the astronomical sunset, the animals start ascending to the sea surface. Here the circling female tries to attract a male by emitting green light and the repeated release of green glowing clouds. The male signals its presence via bioluminescent flashes. In the course of this dance – which may last from 10 to 30 min – the animals spawn and the sea turns black again as they go dark. Remarkably, the worms undergo severe modifications of their body and behavior when switching from the bottom dwelling mode of living to the free floating form. In the case of the males this means, amongst other things, a considerable enlargement of the eyes. After spawning the worms return to the bottom and can potentially swarm again. The photo above, by Greg Rouse, is of the Californian species Odontosyllis phosphorea in its benthic phase. Data from Dimitri Deheyna and Michael Latz suggest the involvement of a photoprotein in the bioluminiscence of this species.

kahikai

posted by Casey Dunn / on August 16th, 2009 / in Jellies, Science & Art

scypho

Eric Roettinger and Mattias Ormestad have launched kahikai.org to showcase some of their beautiful animal photographs. Both are postdocs in Mark Martindale’s lab at the University of Hawaii, where I also spent a couple years. In addition to presenting their photos, kahikai (which means “one ocean” in Hawaiian) will be serving as a repository for primary developmental biology data, such as in situ hybridization images. Eric also curates a set of photos he has taken of other subjects at livingonabeach.org.

CreatureCast – Squid Iridescence

posted by Casey Dunn / on August 12th, 2009 / in molluscs, Podcast, Science & Art

We are pleased to present Episode 1 of CreatureCast, by Sophia Tintori. In this first video, Alison Sweeney talks about work that has been done in the Morse lab on Squid iridescence. Audio production and animations are by Sophia, who normally studies siphonophores in the Dunn lab. Music by  Lucky Dragons (here, and slowed down versions of this and this) and Sophia on the musical saw.

Creative Commons License
This video is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.

(Episode 1 was replaced with a new slightly different cut on August 18, 2009. It is now higher resolution and includes a couple different musical tracks.)

Erwin Keustermans

posted by Casey Dunn / on July 26th, 2009 / in Science & Art

Erwin Keustermans wrote me a couple years ago with some questions about symmetry in animals, and how it relates to his beautiful illustrations. Since then I’ve regularly checked in on his work, and visitors to the lab often admire his postcards.

erwin

His illustrations remind me of the science I work on in a couple different ways. There is the tie-in to modular growth in colonial animals, like siphonophores. There is also the abstract likeness to graphs of gene similarity used to cluster genes in phylogenomic analyses.

Siphonophore video

posted by Casey Dunn / on July 26th, 2009 / in Jellies, Siphonophores

These siphonophore clips were put together from a series of dives by remotely operated underwater vehicles at the Monterey Bay Aquarium Research Institute, with thanks to Steve Haddock. For more information on siphonophores, a group of deep-sea colonial animals, see siphonophores.org. I originally made the segment for the home page of the journal Current Biology when they published a Quick Guide on siphonophores.

This video shows three different species of siphonophore, filmed at depths of hundreds of meters off the coast of California. The first is Apolemia, which can reach more than 40 meters in length (yes, meters), making it one of the longest animals in the world. It is sitting motionless in the water with its tentacles retracted. The second is Erenna, which uses glowing lures to attract prey. The third is Chuniphyes moserae, a fast-swimming calycophoran siphonophore.