Wikipedia:Reference desk/Archives/Science/2017 December 4

= December 4 =

Color and pattern convergence across unrelated species
Today I saw a Hermit Thrush and was struck by how much it looked like a Spotted Sandpiper, with its brown back and white spotted belly. The birds are not closely related and they live in different habitats, so why are their patterns so similar? I have also observed that some tropical fish have patterns similar to warblers. Why would a bird and fish have the same face pattern? Is it just a coincidence, or does the resemblance have to do with some pigmentation process shared across all vertebrates? 169.228.159.244 (talk) 05:12, 4 December 2017 (UTC)
 * See Convergent evolution. ←Baseball Bugs What's up, Doc? carrots→ 06:01, 4 December 2017 (UTC)
 * That's not really much of an answer -- one lives in coniferous forest, the other near fresh water. They both do nest on the ground, which presumably has something to do with it (they should blend in with a nest from a distance, which puts limits on the dorsal plumage).  But overall, I would be lying if I tried to say if the similarity was coincidence or adaptive or if so then as an adaptation to what. Wnt (talk) 15:37, 4 December 2017 (UTC)
 * It's a good partial answer: mottling is good at obscuring a figure both for many types of viewers and against many backgrounds. Consider that many fish and birds both benefit from light undersides and dark top sides, and for the same reason, even though their habitats are very different.
 * But there's another angle too: lots of animal patterns are created by reaction diffusion systems, as described by The_Chemical_Basis_of_Morphogenesis (well ok he was guessing, but later work has confirmed this is the case in many specific examples). So there is also likely an aspect of a shared basis of pattern formation, shared even by birds and fish. Pattern_formation is sparse, but Animal_coloration has plenty of good reading, links, and refs. SemanticMantis (talk) 18:21, 4 December 2017 (UTC)
 * And to clarify: I think the two birds in the fist example are well explained by a combination of convergent evolution, general effectiveness of mottling, and similar mechanistic basis of coat patterns. For the fish and the bird, I don't think an appeal to convergent evolution is very apt. In that case, sexual selection is likely a strong force influencing the showy pattern on the bird and fish. There may be some mechanisms of pigmentation and patterning shared between the bird and fish that makes these sorts of patterns more likely to occur, but that is just a conceptual possibility, not a claim I would make. There is a lot of research about what pigment/pattern features are common to all vertebrates, as well as the genetic basis of such. See here   for a selection of scholarly overviews. These are behind academic paywalls, I can provide copies to anyone who is interested. The first paper linked is especially relevant, using both a bird and a fish as model species in the study of pattern formation. SemanticMantis (talk) 19:12, 4 December 2017 (UTC)
 * This is a great answer, and I don't want to disparage it in the least. But ... I abandoned starting down a similar road in my own because I couldn't see how to get to numbers and say coincidence or not.  There is no shortage of beautiful birds with spectacular plumage that can't be confused for anything else.  Yet most birds look, well, kind of plain, at least for birds.  If there's a mechanism that enforces plainness, then does a near match in appearance result from a random walk within a narrow set of rules that some species diverged from during evolution, or does it mean that it is a convergent set of adaptations?  I'm not sure there is a difference between those two things... Wnt (talk) 23:34, 4 December 2017 (UTC)
 * In my circles, people get touchy about whether or not a given trait can/should be considered "adaptive", especially in the narrow sense of providing a clear fitness advantage. In that light, your two options are indeed rather different, as the one case is "this is the way it has worked, and it doesn't hinder", whereas the other is "offspring with this trait have more reproductive success than those without". My WP:OR is that truly neutral traits are vanishingly rare, much like pulling zero at random out of the (-1,1) interval has probability zero. SemanticMantis (talk) 17:13, 5 December 2017 (UTC)


 * As for birds, note that brown coloration with speckling is very widespread, and may even be a symplesiomorphy or 'common primitive trait' of the birds, especially given that it is found in many chicks (consider the speckles of ducklings, so the pattern may also be an example of neoteny. In other words, this is an old pattern still found in the young of many species, as well as even ratites like the Hooded Tinamou (right) which are more closely related to the Ostrich (speckled chick (left) than to thrushes or snipes.


 * A similar phenomenon occurs in mammals, with the brown/black -- tan/red -- white tricolor agouti pattern found in many dogs (collies, beagles, German shepherds), calico-cats, horses, and guinea pigs with a dominant color highlighted, often on the head and limbs with patches of the other colors.


 * All of this points to the common genetic pathways alluded to above. We should also explicitly mention counter shading, as I dont' think it's been linked to above. μηδείς (talk) 18:12, 5 December 2017 (UTC)


 * Another relevant article, not yet linked: Piebald (and related links in 'See also' section). 2606:A000:4C0C:E200:7851:71F8:C463:FC20 (talk) 23:54, 5 December 2017 (UTC)


 * Thank you all, interesting links! The camo explanation makes sense for why the thrush and sandpiper look similar. 169.228.150.149 (talk) 23:57, 5 December 2017 (UTC)

What's this arachnoid?


Sorry for the quality but you can still see its very thin legs. Sagittarian Milky Way (talk) 12:39, 4 December 2017 (UTC)
 * Hard to tell because the picture is fuzzy, but it could be a pholcus phalangioides (cellar spider), which are common worldwide and have long legs similar to your picture. -- Jayron 32 13:21, 4 December 2017 (UTC)
 * It does look like that, probably is. Almost certainly a member of the Pholcidae. SemanticMantis (talk) 18:14, 4 December 2017 (UTC)
 * Thanks both. I'd seen this distinctive but ugly spider body plan (are there any pretty ones?) more than once and wondered what it was. Sagittarian Milky Way (talk) 18:37, 4 December 2017 (UTC)
 * Beauty is in the eye of the beholder. -- Jayron 32 18:47, 4 December 2017 (UTC)
 * There are many lovely spiders. E.g. the peacock spider has many fans, even among non-spider-lovers. Spiders often pop up over at /r/awwnverts, Reddit's clearinghouse for photos of cute invertebrates. SemanticMantis (talk) 19:22, 4 December 2017 (UTC)
 * Spiders make me want to put shoe in hand. The peacock's.. a mixture of pretty and repulsive. Now insects I generally don't mind as long as they stay pets, not pests. Sagittarian Milky Way (talk) 19:43, 4 December 2017 (UTC)

Modifying magnetic pendulum circuit for larger pendulum swings
I want to make a pendulum swing back and forth using the power from a battery. I bought a solar-powered dancing flower thing and disassembled it to get this stuff which generates a regular magnetic pulse. The problem is that the swings are quite small. To get larger swings do I need a stronger magnetic pulse or just one with longer timing? Also, what is that coil called (so I can search AliExpress for a bigger one if needed)? Thanks.


 * It doesn't generate a regular pulse, it senses the pendulum approaching and then generates the pulse in response. The timing is from the mechanical behaviour of the pendulum $$2 \pi \sqrt {l / g}$$. A bit more complicated for a flower linkage, and some of them do generate timed pulses.
 * If you increase the current through the coil, you can increase the power and the possible mass of the pendulum, or the extent of the swing. You can do this with a single transistor amplifier, but (IMHE) those flowers are so tiny and their coils wound with such thin wire that this itself is difficult.
 * I'd suggest starting again from scratch. It's a simple circuit, it's not hard to make. There should be circuits for it on the web. You can wind the coil yourself quite easily. Some of these sold as kits use a PCB board with a flat coil etched onto them. Those are (again IMHE) too weak, as they have too few turns. Andy Dingley (talk) 15:00, 4 December 2017 (UTC)
 * http://www.trainelectronics.com/Pendulum/article.htm Andy Dingley (talk) 15:03, 4 December 2017 (UTC)

Winding
Why does being winded or blunt trauma to the stomach often result in nausea straight after? I don’t mean shock which may set in later if severe enough. I mean nausea which is often immediate and goes away quickly. Is it just to do with the muscles in that area going into spasm? 82.132.216.104 (talk) 20:40, 4 December 2017 (UTC)


 * Our article Celiac plexus gives a brief explanation.  D b f i r s   21:49, 4 December 2017 (UTC)


 * This article from the BBC gives some additional information, as does this first aid website . For a more scholarly reference, see this  journal article that discusses what happens when people "have the wind knocked out of them" SemanticMantis (talk) 17:09, 5 December 2017 (UTC)

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The following is off topic, and has been swept under the hat. μηδείς (talk) 02:44, 5 December 2017 (UTC)


 * Which is a good thing to keep in mind, in case anyone should ask for it. --Trovatore (talk) 22:56, 4 December 2017 (UTC)
 * Don't fool around with others' edits. You can't even spell "medical". ←Baseball Bugs What's up, Doc? carrots→ 23:00, 4 December 2017 (UTC)
 * That seems to have been Sluzzelin's typo, but I do seem to have messed up the hatting somehow. It wouldn't have been necessary if you hadn't dumped unusual HTML into the page.  I'll see if I can fix the hatting. --Trovatore (talk) 23:10, 4 December 2017 (UTC)
 * Take your complaint to whoever wrote the disclaimer originally. ←Baseball Bugs What's up, Doc? carrots→ 23:14, 4 December 2017 (UTC)
 * Yes, Trovatore, the typo/slip was mine entirely, corrected 3 minutes later (before anyone else had posted). Whatever typos linger on, may have been originated by me, but I did not post them. ---Sluzzelin talk  23:28, 4 December 2017 (UTC)
 * Fair enough. I made my edit based on your earlier version, I guess.  I moved the comment out of the center so I could respond to it.  There was an edit conflict, which I examined and resolved in favor of my text, which propagated your original version. --Trovatore (talk) 23:30, 4 December 2017 (UTC)
 * Alright, well I corrected the propagated typo now. ---Sluzzelin talk  23:31, 4 December 2017 (UTC)