Testing, testing, 1,2,3… First blog post – I’d like to take the time to rehash some super cool stuff I learned at the 12th Annual UNC Neuroscience Symposium.
When I think of sensory receptors, I think of eyes, nose, ears, tongues – the obvious ones. However, I was recently exposed to the myriad of different receptors that organisms use, and I was introduced to the term “umwelt”. Umwelt refers to an organism’s perceptual world, and the umwelt of different species can vary quite a bit. While electric charges in general aren’t detectable by terrestrial organisms (i.e. electric currents can’t easily travel through air), lots of aquatic animals can sense small changes in electricity in the environment and can get information out of those changes. These animals use electroreceptors on the skin that send signals to the brain when they sense electricity. Additionally, lots of long distance (and not so long distance) travelers – birds, sea turtles, bacteria - can get information from the earths magnetic field.
The receptors that are used to sense magnetic fields are still a bit of a mystery, but one possible mechanism is through the use of magnetite, an iron-based molecule (the same one that is found in your compass needle). Magnetite is essentially a little magnet inside an animal’s body. It is thought to work by attaching to other sensory cells and pulling or pushing on them as it moves with the earth’s magnetic field.
An animal’s umwelt typically reflects aspects of its environment. Fish that live in caves have super poor vision but great touch receptors, while fish that in shallow streams have great vision. This general finding, that evolution of animal’s sensory abilities reflects its physical and social environment, helps explain why a word like umwelt is needed. Sensory perceptions are variable across different species.
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| Oh Cool! a magnetotactic bacterium. That chain in the middle is magnetite (photo: nature.com) |
The receptors that are used to sense magnetic fields are still a bit of a mystery, but one possible mechanism is through the use of magnetite, an iron-based molecule (the same one that is found in your compass needle). Magnetite is essentially a little magnet inside an animal’s body. It is thought to work by attaching to other sensory cells and pulling or pushing on them as it moves with the earth’s magnetic field.
An animal’s umwelt typically reflects aspects of its environment. Fish that live in caves have super poor vision but great touch receptors, while fish that in shallow streams have great vision. This general finding, that evolution of animal’s sensory abilities reflects its physical and social environment, helps explain why a word like umwelt is needed. Sensory perceptions are variable across different species.
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| Blind cave fish (notice the loss of pigment as well) (photo: nature manchester) |
Well, for the most part they are. There are some types of sensory receptors that are common across lots of organisms. These kinds of receptors reflect the similar evolutionary history and similar environmental conditions from invertebrates to vertebrates. One such receptor was discussed by Cori Bargmann from Rockefeller University, in her talk on nematode social behavior. Sometimes nematodes clump together, this typically happens when they are in poor environments that are low in oxygen. Bargmann's lab has found the nematode oxygen receptor cells. In most nematodes, they rapidly detect changes in oxygen levels. However, there are some types of nematodes that don’t clump together in low oxygen environments. Why are these nematodes different from the others? These nematodes have been living in laboratories for the past 50 years. In lab conditions, oxygen levels are about 10X higher than in the wild. These nematodes have lost their sensitivity to oxygen levels as they have evolved in this super cushy oxygen environment.
What do humans have in common with nematodes? Well, one thing is that we are also sensitive to oxygen levels. Another thing is that we can also adapt to different levels of oxygen. Andean and Tibetan human populations have evolved in lower oxygen levels, and are more efficient at utilizing oxygen compared to most human populations. So, while our umwelt may differ dramatically from other species, evolutionary processes continue to shape them, just like the nematode.
