We have a front and a back and two legs. We walk around on our two legs. When we need to change the direction we are moving in, we first turn our body to face the new direction and then use our same two legs to keep going. It works for us.
But what about a round animal that also has an odd number of limbs? This is the question that Henry Astley, a graduate student in Tom Robert’s lab here at the Brown UniversityDepartment of Ecology and Evolutionary Biology, set out to answer. Like their relatives the starfish, brittlestars have five arms. Unlike starfish, which crawl around with the thousands of sticky tube feet that line the bottoms of their arms, brittlestars get around by moving their whole arms. They can move much more quickly than starfish, scurrying under a rock or sprinting across the ocean bottom.
Surprisingly, nobody had previously described the details of how brittlestars get around with their arms. Do all five arms play an equal part all the time, or do only some of the arms move at once? Do they have a favorite front and back, or can any arm serve as the front or back?
In his paper published this week (“Getting around when you’re round: quantitative analysis of the locomotion of the blunt-spined brittle star, Ophiocoma echinata“), Henry answers all these questions. It turns out that most of the work of getting around is only done by two arms at a time. These arms move in a rowing motion, much like a sea turtle crawling along the beach, while the other arms stay out of the way. My favorite part of the story though, is how brittlestars turn. Rather than rotate their body to face a new direction, as we do, they just chose a new front and back and row with a different pair of arms. Not only do they not have a favorite front and back, they constantly change their front and back to change direction.
Male kangaroos kick at each other. Male elephant seals gore each other with their large canine teeth. Male Giant Australian cuttlefish also undergo intense competition for females, but besides physically grabbing and biting each other, they also showcase a brilliant pattern on their skin.
Dr. Roger Hanlon who studies cephalopod camouflage at the Marine Biological Laboratory in Woods Hole, MA describes the mesmerizing “passing cloud” pattern and the purpose behind this agonistic display.
Here is a little plant that starts it’s life high up in the tree tops, where it can find more light than the dark understory of the rainforest. As it grows though, soon getting enough water becomes limiting factor, and the plant will drop a shoot to the ground.
Matt Ogburn, a graduate student in Erika Edwards’ lab at Brown University, describes this little plant, the strangler fig, and explains how it eventually grows to take over the whole host tree and strangle it to death.
This is a really nice video that was published in the Journal of Plankton Research this past February, as a part of this article about krill.
Even though krill make up a large fraction of the living mass of the ocean (and are also the food for large charismatic sea mammals), many aspects of their biology is unknown, including the way they reproduce. Recently Dr. Kawaguchi and his colleagues filmed the process happening near the sea floor, which was surprising because krill are notorious for living their lives swimming around up higher in the water, far from the floor.
The footage that the researchers collected was a bit chaotic (above, left), and so they gave it to Lisa Roberts, an animator (and CreatureCast contributor), to illustrate the process. She traced the motions of the crustaceans from the videos, and also practiced the moves with some shrimp from the market (above, right).
The original video footage from the deep sea is also really nice to watch, and can be found here, at the Journal of Plankton Research website.
This video is about the enzymes that, for me, first turned cells into little toy chests full of delightful tiny gadgets.
All of the mechanical things that our bodies do, like keeping other things out, or seeing, can be described by somewhat abstract functions. For example, ‘the skin makes a protective sheet’ or ‘the lens focuses light’. But then all of those abstract functions can be broken down again into mechanical motions of the small molecules inside the cells, complete with hinges and springs, making them seem tangible once more, at least to my mechanism-oriented mind: The outside of each skin cell is littered with little molecules that hold on to the same types of molecules on the next cell in a strong handshake, forming a tight, grime-proof layer, while lens cells pack hundreds of copies of a single type of protein up tight against each other, forming almost a crystal, and then jettison all of things in the cell that would scatter light, like DNA or mitochondria, in order to let light pass cleanly through the cell.
This story in this video is about a problem that all living things have — how long and thin DNA is, and how easy it would be to get it all tangled. Not only is there a huge amount of DNA in each cell (around two meters in each human nucleus, for example), but also every time a cell divides into two, the two strands of all of that DNA have to be untwisted from each other to be copied. Think about pulling the fibers of a length of twine apart; the wound end gets tighter and tighter and then twists up on itself, making it impossible to move forward. Thankfully there are these little enzymes, called topoisomerases, that are there to iron out the wrinkles.
In the vast ocean, without walls and far from the floor, jellyfish can become drifting islands of activity. Creatures from far and wide will congregate on them to act out the ups and downs of life and death. Jellyfish have symbiotic relationships with living things of all sizes, from fish and shrimp that feed off them or off the pieces of food left between their tentacles, to single-celled photosynthesizing organisms that take shelter inside the cytoplasm of the jellyfish’s cells.
In this video, Trisha Towanda talks about one particular jellyfish, the fried egg jelly, and some of the other creatures that hang around it. There are moon jellies that the fried egg jelly eats. These moon jellies have little parasitic crustaceans on them called amphipods, which jump to the fried egg jelly while the moon jelly is being eaten. There are also crabs that ride around on the fried egg jelly, that are parasitic in their youth, but then grow to be helpful symbionts by eating off the little amphipods. This sort of coming of age story, where a symbiont’s relationship changes over its lifespan is an unusual one. Trisha put the pieces together by staring at them for hours and days and weeks when she was in Erik Thuessen‘s lab at Evergreen State College.
Many thanks to Trisha Towanda, who is now stationed in the Seibel lab at the University of Rhode Island. This video was edited and animated by Sophia Tintori, with an original score by local pop hero Amil Byleckie. It is released under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 license. Here is the paper Trisha wrote about the story.