November 28, 2017 at 12:47AM

Today I learned: 1) Tardigrades (water bears) aren't a species -- they're a freaking *phyla* with over a thousand known species. 2) There are a lot of models of evolution out there. Today I learned a bit about three classes of evolutionary model -- additive, multiplicative, and stickbreaking. These different model classes have to do with the effects of multiple mutations on an organism's fitness. It's relatively easy to understand what a single mutation might do to fitness -- if it's good, then fitness goes up, and if it's bad, fitness goes down, and if it doesn't affect the organism's ability to reproduce at all, fitness stays the same. But what if you have *two* mutations with a fitness effect? How do you combine the effects? Do you add their individual fitnesses together? Do you multiply them together? Do you write out a table where every pair of possible mutations has a unique fitness with no particular pattern? In additive models, as you might guess, the fitness effects of multiple mutations are added together to get the total fitness effect of the mutations. That means that a mutation has a property like "this mutation increases fitness by 2". In multiplicative models, the fitness effects of multiple mutations are multiplied together to get the total fitness effect of the mutations. That means that a mutation has a property like "this mutation doubles fitness". The two models are actually quite similar -- they're identical to within an exponential transformation, so you can always do the math in whatever model you want and then transform the results to see what happens in the other model. Moreover, as fitness effects become smaller and smaller, the additive and multiplicative models become identical. For continuous evolution with extremely fine-grained fitness differences, they're the same. I'm not sure if the same is true for the stickbreaking model -- it's a *little* bit different. In the stickbreaking model, each mutation moves you a fixed *fraction* of the distance from the current fitness to the maximum fitness, so each mutation has a property like "this mutation moves you halfway to the best possible fitness". This model has the somewhat different property that it makes fitness converge to a maximum, which may be a more realistic representation of physical constraints. What's the "best" model to use in an evolutionary simulation or analysis? That's still up for some debate. The Lenski long-term evolution experiment* has some relevant data -- as of a few years ago, there were several phenotypic traits for which fitness could be tracked as the population evolved. The majority of those fit the stickbreaking model best, but there were clear examples of additive and multiplicative processes as well. It sems that it depends very much on the mutations. * If you don't know about the Lenski experiment, I highly recommend looking it up. It's one of the most well-known and, I think, envied experiments in Biology. 3) There's too much naval cargo shipping capacity in the world right now! According to FreightHub's 2017 report on global shipping capacity (http://ift.tt/2k3h0ZR), about 10% of the world's shipping ships are sitting idle. This is not a new phenomena, and persists despite widespread ship-scrapping. Another fun fact -- there are between 2,000 and 3,000 known cargo ships in 2017.

November 25, 2017 at 12:39AM

Today I learned: 1) Two new butterfly anatomy facts! Firstly, butterfly proboscuses don't work the way I thought. I always assumed they were like needles, and that butterflies stick them into nectar-rich flowers and suck up the nectar like a straw. I was sorely mistaken. In fact, butterfly proboscuses come in two parts, left and right, that zip together. The center of this double-proboscus structure forms a canal. The tip of the proboscus isn't just an open end -- it's actually more like a sponge, with lots of layers of tiny pores. Liquid is drawn into the pores by capillary action, eventually bleeding into the central canal. In the canal, liquid forms little tiny bridges between proboscus zipper teeth, kind of like water caught between teeth of a comb. Some fancy fluid dynamics that I don't understand draws the liquid up, aided by a bit of suction generated by an inflatable air sack in the butterfly's head. Okay, second new anatomy fact -- in addition to antannae, butterflies have a pair of antenna-like fuzzy bits that rest right up against the head, next to their eyes. A bit of googling tells me that they're called "labial palps", and that they're essentially used for smelling. Some up-close observation of a butterfly suggests to me that they're also used as windshield wipers to clean their eyes. 2) So, everyone knows that Dolly the sheep was the first cloned mammal. Some know that Dolly died early, with pretty bad arthritis and some other medical problems. That's one of the reasons scientists haven't pursued mammalian cloning very much -- it looks like cloning isn't very good for mammals, for reasons nobody could really understand. Well... now it looks like Dolly was just an outlier. There were four other sheep cloned from the same cell line as Dolly, and they all lived pretty normal, healthy lives. Moreover, it seems that arthritis is super-common in that breed of sheep, and that it isn't particularly unusual for a sheep her age to get arthritis. Now, cloning isn't *totally* healthy -- clones tend to have more difficult, dangerous births, and require more care as infants, but once they're grown they seem to do just fine. Also, I didn't realize that mammalian cloning *has* in fact been used commercially to reproduce extremely valuable breeding cows and steers. This isn't quite new news, but for some reason this has hit some popular news outlets lately. For a reputable source, I'd check out The Atlantic's article on the subject: http://ift.tt/2mXE11y 3) There are some really strange-looking lobsters out there. Today I learned about one of these -- the slipper lobster. The slipper lobster looks a bit like someone painted a small Maine lobster gray and squished it from nose to tail. It's very squat, almost pug-nosed. It has no claws, just arms ending in shell plates. It also has the unfortunate double distinction of being endangered and incredibly tasty. Facts #1 and #3 are courtesy of the Denver Butterfly Pavilion, which it turns out is a zoo of all kinds of different invertebrate species. Some highlights of mine include a glassed-in honeybee hive, some really spectacular orb weaving spiders, two foot-long isopods, and, of course, the butterfly garden.

November 14, 2017 at 04:21AM

Today I Learned: 1) Mammals were dominant as large land animals *before* the dinosaurs. Well, not really -- but our non-dinosaurian ancestors were. Mammals are part of a group called the synapsids, which began as lizard-like creatures with a slightly weird skull. These were the biggest, baddest, I *think* most common large animals (amniotes, technically) during the Permian Period, and "reigned supreme" for some 46 million years. The Permian-Triassic extinction hit the synapsids really hard, as is typical for large-bodied groups in a mass extinction, and their extinctions left ecological niches open for large animals that the dinosaurs filled nicely. Only three clades of Synapsids survived; of these, one died out later in the Triassic, one survived as a large herbivore alongside the dinosaurs, and one shrank really quickly down to rat size and began specializing in insect predation. The last group, known as eucynodonts, would eventually survive the late Cretaceous extinction event and eventually give rise to modern mammals. There's something of an open question about why dinosaurs (properly, the immediate ancestors of the dinosaurs) were able to take over from the Synapsids. One theory is that the post-Permian world was relatively arid, and dinosaurs had better adaptations for low-water environments (uric acid excretion being a key example). This theory is rather controversial, though -- after all, there are some mammals today that have adapted extremely well to arid environments, so why wouldn't the old Synapsids? 2) Another mammal fact -- there's a theory called the Nocturnal Bottleneck that says that many of the common features of mammals *are* common features of mammals because our last common ancestor was nocturnal, and was for quite some time. Evey mammal that isn't nocturnal had to evolve that way from the nocturnal ancestor. The major categories of evidence for the nocturnal bottleneck are: mammals, as a whole, have highly developed hearing and smell, but not great vision (especially in color); mammals have fur, tissues specialized in rapid heating, and extremely active mitochondria, which would help stay warm at night; mammals don't have particularly good UV protection; and burrowing behavior appears to be a basal mammalian trait. 3) Here's a nice evolution number to know -- it takes about 10 million years for a dormant mammalian gene to become completely unrecoverable by random disabling mutations.

November 09, 2017 at 12:38AM

Today I learned: 1) Cats and dogs don't drink the same way. Dogs use the undersides of their tongues as upside-down spoons, lapping into the water and cupping the tip of the tongue downward to catch water. Cats, in contrast, do *not* cup their tongues to catch water. Instead, they use the tip of their tongues to "grab" the top of the water, the flick their tongues up to pull a column of water toward the mouth. Inertia brings the column up until gravity breaks it. Also, cats have some water-trapping physiology in the mouth so that they don't have to swallow with every flick of the tongue. I quote: "Inside the mouth, cavities between the palate’s rugae and the tongue act as a nonreturn device and trap liquid until it is ingested every 3 to 17 cycles (15)." Details on cat tongue biomechanis here: http://ift.tt/2mGEHU5 2) Fans don't really "push" air the same way I imagined. That is, wind coming off a moving fan blade isn't just pushed straight off the blade -- it's actually a continuous ribbon-like vortex of air, curled kind of like a twinkie, with net forward momentum.... Look, it's kind of hard to describe, but you can see it here, along with some cat-lapping and other things-in-slow-motion: https://www.youtube.com/watch?v=gspK_Bi0aoQ 3) Human eyes can detect, at minimum, somewhere between 1 and 10 photons. See the section "Photon Counting in Vision" from http://ift.tt/2ylo6LN.