The sense that the self exists somewhere close to the brain or heart is an intuitive one for humans. It also seems to apply to most of the animals we regularly encounter, even when they can regrow parts of their body. When a crayfish gets into a tight spot and loses one of its claws, the part of the crayfish with the head will regrow the lost claw, but the claw won’t regrow a body and head.
For many animals, though, there is no such essential center of the organism. When a flatworm gets its tail cut off, both the tail and head will fill in the missing parts and make two whole flatworms that are clones of each other. Its body is arranged such that there isn’t a single part of the animal that can be identified as the core.
Here is a bit of footage taken by Stephanie Spielman, an undergraduate in Casey Dunn and Gary Wessel’s seminar on the evolution of multicellularity at Brown University. The clip features the flatworm Dugesia tigrina swimming around the Dunn lab. It is released under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 license. The crawfish video is from Day at the River (1928), a video from DeVry School Films, Inc., which is under public domain.
Early last year, at the Australian Antarctic Division (AAD), I saw an unusual sight: the birth of a live Antarctic krill, Euphausia superba.
The newborn appeared on a video screen that projected the view of a camera poised over a petri dish. A tremulous form emerged from its egg with its legs beating furiously!
This event began a continuing conversation with krill research leader, So Kawaguchi.
Back in my Sydney studio, I worked with So’s words and images. He explained (by email) how krill grow, and sent me diagrams by John Kirkwood to work with. I also found data sets online of how krill appendages move (Uwe Kils). Piano music was improvised by an 11 year old friend, Sophie Green.
This is the first of some animations that I am making to more fully describe this elusive and most important creature.
Krill are central to the marine life food web. Their health is endangered as a result of oceans becoming more acidic (as carbon increasingly enters the atmosphere and then dissolves into the water).
A new research project at the AAD is to record changes in normal krill development in increasingly acid water. Next month (June 2010) I return to the AAD krill nursery to find out more about this research.
I will also record So Kawaguchi describe what he has identified as a circling krill mating dance. What a fine gesture of continuity!
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.
If you are stuck to a rock it is tricky to get close enough to a partner to mate. One solution to this problem would be to release eggs or sperm into the open water, which is what many animals in this situation do. Acorn barnacles (Semibalanus balanoides), however, found a different solution. They have evolved the longest penis relative to their body size of any animal. In this video the penises of several barnacles are probing the neighborhood for mates. The penis is re-grown each mating season.
Acorn barnacles are hermaphrodites, each one has both male and female organs. The specimens in the photos below have been removed from the rock and turned upside down. Two yellow egg clusters can be easily identified (top and middle images). The testis occur as white regions along the body of the animal which is here removed from its calcareous shelter (middle image). The penis is centered in between the feeding structures (bottom image).
During the mating process, the penis of one barnacle is inserted into the body cavity of another and the sperm are released. Each barnacle can be fertilized by multiple partners, which means that a mothers offspring often have several different fathers. The developing embryos remain within the mother for several weeks before the larvae are eventually released.
Genetic paternity tests on the offspring performed by David Rand indicate that the closest neighbors are often not mates, which suggests that mating could be a selective process influenced by more than just the availability of partners. The barnacle penis shows adaptive plasticity— J. Matthew Hoch has shown that barnacles growing where waves are stronger have thicker penises. The barnacles shown here were collected by Brown graduate student Patrick Flight who, together with David Rand, uses them as models to study genome evolution. Photos and video by Stefan Siebert.
The leaves are starting to turn and the garden is getting thin as most fruits and vegetables are harvested. There are some fun surprises among the plants that remain, including this tobacco hornworm (Manduca sexta) above that was chewing on our tomatoes. It stayed in one spot, and over the course of two days more and more parasitoid wasp larvae, probably Cotesia congregata, emerged to spin their cocoons. When the mother wasp injected her eggs into the young caterpillar, she also injected a virus that had been multiplying in her ovaries. This virus continued to reproduce in its new host, castrating the caterpillar and preventing it from metamorphosing. This trick provides the the perfect feeding ground for the wasp babies.
Other organisms are also at their peak, and the woods are full of beautiful and delicious fungi. The specimen below is Laetiporus, also known as chicken of the woods because it is so common and quite eatable.
Photos by Casey Dunn. Thanks to Doug Morse, Alan Bergland, and Erika Edwards.