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    [–] Are there any living things that excrete/are composed of a non-biodegradable substance? tea_and_biology 14 points ago * (lasted edited 7 days ago) in askscience

    Ooh, pretty much anything with a calcium carbonate shell; so pretty much all shelled aquatic invertebrates from oysters n' mussels to teeny dinoflagellate plankton, along with coral skeletons, land snails and all reptile n' bird eggs. Despite containing carbon, calcium carbonate is considered an inorganic salt - no enzyme nor any other biological process will break it down. Not degraded by anything but erosion, it tends to stick around, slowly accumulating at the bottoms of, say, the oceans where, over time, it's hardened under pressure forming limestone.

    Likewise, silicon dioxide is another inorganic compound that forms the skeletons of sponges, the shells of odd marine plankton, and can be found within a range of plants as a form of predator defense (i.e. grass; it's thought because the silicates wear down teeth, it may discourage plenty of animals from eating it, like ourselves).

    Of additional interest, though it's perfectly biodegradable nowadays, for an awful long time the organic biopolymer lignin that makes up the cell walls of plant cells in wood and bark, couldn't be broken down. It arose during the Carboniferous period, some 300+ million years ago; without any fungi or bacteria capable of successfully biodegrading it around, dead wood simply piled up for long enough periods of time that it was able to fossilise on a large scale. A few hundred million years later and we dig it all up, as coal.

    [–] How did scientists consider the first Homo Sapiens as ''Homo Sapiens''?​ What was the distinguishable feature they had that their parents did not? tea_and_biology 33 points ago in askscience

    Biologist here! The answer to your question is that your question doesn't actually make sense, biologically speaking. There can never be such a thing as a 'first' individual of any given species - evolution simply doesn't work like that.

    One way to think about it is like trying to divide the colour spectrum into neat little compartments; in reality it doesn't work.

    Pick any part of the 'green'-ish area here and pixel-by-pixel try and draw a discrete line when 'green becomes blue'. Wherever you draw your line, the pixels directly on either side are going to be nigh on indistinguishable from one another. How then can you say all pixels on one side are 'green', and on the other 'blue'? You can't.

    Likewise it is with 'species'. Over long periods of time, a species will gradually morph into something altogether different. When you compare an individual far removed in time from an original individual (at two different 'snapshots' of time; say a Homo erectus fossil and modern man), it's obvious they're different species. Just like how a very blue pixel many, many pixels away from a very green pixel is something we can safely say is very blue. But there's isn't a nice 'here is blue, here is green' cut-off on the spectrum, just like there isn't a nice 'here is species A, here is species B' point in time when looking at evolutionary history (likewise, check out the Sorites paradox).

    In other words, this means, evolutionarily speaking, there are no such things as 'first members' of any species, and no parent will ever give birth to a member of a different species. Incidentally this is also why the age old question about chickens and chicken eggs likewise makes no sense - neither came 'first', it just don't make sense, 'innit.

    [–] If proteins in food are responsible for food allergies, which are overreactions of the immune system, why can't we genetically alter the protein structure of a certain food source, like peanut, to produce allergen-free nuts? tea_and_biology 15 points ago * (lasted edited 7 days ago) in askscience

    We can, sort of! Scientists around the world claim to have the answer to an 'allergy-free' peanut, either via conventional breeding or genetic modification (I even know a graduate student in my Plant Sciences Dept. who's been CRISPR-ing some, basically just for the lulz).

    The problem with peanuts in particular though, is that a dozen or more genes have so far been identified as producing the protein isoforms that cause an immune response, and we still don't know if that's all of them. We can - and have - removed a bunch of these, the most common, from peanut strains with some success, but we wouldn't be able to remove all of them - nutritional content, flavour and the rest aside, we don't know what removing all of these genes would do to a living plant, or whether it'd even be viable. Removing a few genes is manageable, removing every single one required to make a 'hypoallergenic' peanut possible, safe and marketable is an altogether different question.

    In which case, sure, we can (and have) produced peanut strains that some people will find they can now tolerate, but we aren't ever likely to edit a peanut so that everyone could happily nom them. There's just a bit too much involved. Whatever we would make, if anything, wouldn't really be able to be called a peanut at all.


    Sources:

    Perkins, T., Schmitt, D.A., Isleib, T.G. et al. (2006) Breeding a Hypoallergenic Peanut. Journal of Allergy and Clinical Immunology. 117 (2), S328

    Miller, D.S., Brown, M.P., Howley, P.M. & Hayball, J.D. (2016) Current and Emerging Immunoterapeutic Approaches to Treat and Prevent Peanut Allergy. Expert Review of Vaccines. 11 (12), 1471-1481

    Nice article on the topic: Spitter, J. (2016) Allergy-Free Peanuts? Not So Fast. Scientific American.

    [–] Do sunsets look like sunrises? tea_and_biology 30 points ago * (lasted edited 7 days ago) in askscience

    To some extent, apparently so - sunsets tend to be more colourful, owing to slight changes in atmospheric condition in the evening compared to the morning. The sun itself, of course, is emitting exactly the same light, and the amount of air that sunlight needs to pass through likewise remains the same. However, increased activity on the ground during the day throws more particulate matter (dust, pollution, haze etc.) into the lower atmosphere, as can the heat of day result in an increase in low atmospheric water vapour levels.

    Molecules and small particles in the atmosphere change the direction of light rays as they hit, causing them to scatter, and this scattering affects the colour of light that we see coming from the sky. Furthermore, warmer air has a slightly different refraction index than cooler air, which can likewise alter the direction of light, and therefore colour.

    It seems to be the case then that higher levels of vapour and particulate matter in the warmer atmosphere during sunset mean light is scattered slightly differently, and colours towards the red end of the spectrum will occupy more of the sky (during the night, particles settle and water vapour condenses - hence morning dew and a less jazzy sunrise) - all depending, of course, on what's happening on the ground during the day.

    Otherwise, I'd imagine all else being equal, sunrise and sunset are nigh on indistinguishable.

    [–] Is it possible to find a dinosaur in a very old glacier / ice? tea_and_biology 41 points ago * (lasted edited 7 days ago) in askscience

    Alas, it'd be impossible. During the Late Cretaceous period, when dinosaurs still roamed the Earth, there were no polar ice caps* - average global temperatures sat around 23°C (compared to 15°C today) and land within the Antarctic Circle (which today would be Eastern Australia, New Zealand and some, but not all, of Antarctica itself) was covered in temperate and coniferous forest, home to dinosaurs like Leaellynasaura (they had large eyes, moreso than their tropical counterparts, suggesting they remained in the polar region year-round, even through the extended periods of total darkness). So polar ice is out; but what about glaciers on high mountains?

    Well, the most glacier rich, highest mountain range currently on Earth, the Himalayas, didn't begin to form until the Indian subcontinent crashed into the Eurasian one some fifteen million years or more after the dinosaurs. Indeed, climate models suggest it was too warm on Earth, even at the highest altitudes, for any glaciers to persist through much of the Cretaceous, and certainly not through the so-called Eocene Thermal Maximum. Glaciers have a habit of moving too, so any unlikely poor lost dinosaur that might've fallen down a crevasse or something would eventually have rolled its way down and thawed into a pool of meltwater. Alas, no hope there either!

    Sorry to say, but we won't be digging up any dinosaur popsicles any time, well, ever.


    Sources:

    Benson, R.B.J., Rich, T.H., Vickers-Rich, P. & Hall, M. (2012) Theropod Fauna from Southern Australia Indicates High Polar Diversity and Climate-Driven Dinosaur Provinciality. PLoS One. 7 (5)

    Ladanta, J. & Donnadieu, Y. (2016) Palaeogeographic regulation of glacial events during the Cretaceous supergreenhouse. Nature Communications. 7, 12771

    MacLeod, K.G., Huber, B.T., Berrocoso, A.J. & Wendler, I. (2013) A stable and hot Turonian without glacial δ18O excursions is indicated by exquisitely preserved Tanzanian foraminifera. Geology. 41 (10), 1083-1086

    * Well, in truth, the debate rages on, most heavily in favour of an ice-free world, though some argue there may have been a partial ice cap at some point. Maybe.

    [–] In evolution, did forelimbs and hindlimbs (or more accurately their precursor fins, or fin-stubs) appear simultaneously as the result of a single mutation? Or did one set appear first (if so, which?) and then a subsequent mutation doubled them up? tea_and_biology 21 points ago * (lasted edited 7 days ago) in askscience

    Well, to start, there was no single mutation - at no point did a parent fish swimming about in a lagoon give birth to a mutant child ready to do the can-can. Going from fins to the fully-fledged pentadactyl limb known and loved today required hundreds, thousands of altered genes, with gradual change spanning millions of years.

    You can see it encapsulated in living species today - from yer' typical goldfish, through to sturgeon (with their elongated bodies, and typical fish fins, albeit placed where you might eventually find legs), to bichir (air-breathing denizens of swampy pools, with fleshy fore- and hindfins; terrible for free swimming, but excellent for snake-ing through thick vegetation), through to the Australian lungfish (with even fleshier fore- and pelvic fins).

    In which case, looking at the broad brush strokes of evolution, it appears at least the placement of the fore- and hindlimbs began well before significant 'limbiness' started to appear. So what of their genetics? It's complicated, very complicated, and a dash controversial. It involves a suite of genes activated during early development known as Hox genes, which are involved in deciding where along the anterior-posterior (head-tail) axis of your body stuff - head, arms, legs etc. - goes, and the genes TBX4 and TBX5 which, today, specifically regulate development of the hind- and forelimbs respectively. I won't go into all the hypotheses, but one theory involving HOX gene expression patterns suggests the HOX genes associated with modern forelimbs initially acted as 'posterior-encoding' genes, that were subsequently turned on around where forelimbs should be; meaning genetically-speaking 'limb placement' arose with hindlimbs first. However another answer involves the original pre-TBX4/5 gene being duplicated before it was localised to the forelimb, thus becoming a separate TBX4 and TBX5, which were then localised to each location. In which case, if true, one answer to your question would be that the placement of paired fins in our early fishy ancestors happened simultaneously with this duplication event.

    But that's just one gene, in one small part of the fin-to-limb story - simply regarding one aspect fin placement. If you were to focus on the increasing 'limbiness' aspect, then it appears the forelimbs developed additional 'limbiness' before the hind at some points in time (i.e. just look at modern bichir), and then in tandem at others, and then again fore- predates hind- (check out fossil Panderichthys), and then once more in tandem (check out fossil Tiktaalik) etc. etc. etc.

    In short: it's an awful long story involving genes that are sometimes biased towards one limb (usually always the fore-) and other genes that are involved in both. Depending on when and where you want to narrow down your scope to, you can get completely different answers! The Don et al. (2013) paper below gives a very comprehensive review, if you're interested.

    In any case, your arms derive from forefins and your legs from separate pelvic fins. Both fins evolved into limbs together; but sometimes genes for different aspects of limb evolution, especially at the very early stages, arose in one or the other 'first', and sometimes one of the two pairs of fins became more 'limb-like' sooner than the other.


    Sources:

    Don, E.K., Currie, P.D., & Cole, N.J. (2013) The evolutionary history of the development of the pelvic fin/hindlimb. Journal of Anatomy. 222 (1), 114-133

    Hinchliffe, J.R. (2002) Developmental basis of limb evolution. Int J Dev Biol. 46 (7), 835-845

    Ledje, C., Kim, C.B., Ruddle, F.H. (2002) Characterization of Hox genes in the bichir, Polypterus palmas. J Exp Zool. 294 (2), 107-111

    Yano, T. & Tamura, K. (2013) The making of differences between fins and limbs. Journal of Anatomy. 222 (1), 100-113

    [–] What is the evolutionary advantage to poisonous berries? tea_and_biology 50 points ago * (lasted edited 7 days ago) in askscience

    Berries that may be poisonous to us, may not be poisonous to other animals. Indeed, that's the whole point of the poison from the plants perspective - it only wants target species to eat the berries, those who, for example, won't destroy the seeds in their digestive tracts, and therefore employs poisonous compounds to discourage non-target species. Alternatively, the plant wants animals to eat the berries only at the most opportune time - which is why, for example, mullberries and elderberries are poisonous when unripe, but edible when ripened. It doesn't want to spread the seeds until it's ready.

    Anywho, to use the go-to example, capsaicin is the chemical compound found in chilli peppers that makes them spicy. Capsaicin can bind to the tongues of humans and other mammals and cause a painful reaction, whereas birds are utterly indifferent - not coincidentally, mammal digestive systems destroy chilli seeds; whereas bird guts can happily carry them to be dropped elsewhere in a nice little bit of poop fertiliser.

    So next time you're sweating over a hot curry, or hunched over the bowl passing last night's impulse burrito, remember you're only doing this to yourself - the plants didn't want you to eat them.


    Sources:

    Cipollini, M.L. (1996) Secondary Metabolites Of Fleshy Vertebrate‐Dispersed Fruits: Adaptive Hypotheses And Implications For Seed Dispersal. The American Naturalist. 150 (3)

    Julius, D. & Jordt, S.E. (2002) Molecular basis for species-specific sensitivity to "hot" chili peppers. Cell. 108 (3), 421-430

    [–] The first domesticated foxes, 60 years in the making tea_and_biology 1 points ago in Awwducational

    Hey u/Acrobaticfrog,

    I'm afraid I've removed your submission as you didn't quite follow our required formating - you need to include a standalone fact in the title, and a verifiable source in the comments (Rules #2 and #3; a Youtube video doesn't count as a source either, I'm afraid). Feel free to take a peek at our submission guidelines in the sidebar, along with 'verified' posts in the subreddit, for a better idea of what we're looking for.

    Thanks for your time!

    T&B

    [–] Why do organisms larger than insects not go through a metamorphosis? What caused certain insect species to evolve to have a metamorphic process in their life cycle? tea_and_biology 23 points ago * (lasted edited 7 days ago) in askscience

    Why do organisms larger than insects not go through a metamorphosis?

    Many do! For example, within the vertebrates, (almost) all amphibians and a considerable number of fish go through a process of metamorphosis (i.e. tadpoles becoming frogs), all of which is controlled by thyroid hormones. But yeah, sure, they don't go through something called holometabolous metamorphosis, unlike insects. So let's ask, why do only insects go through holometabolous metamorphosis?

    Well, first of all, what does holometabolous even mean? Time for a bit of background: wee critters like bees, unlike say birds, have a problem, a problem with growth. Their exoskeleton (the outer carapace surrounding their body) is a hard barrier, which means in order to grow you need to get rid of that barrier first - hence why all arthropods, including insects, need to undergo ecdysis, or moulting, to grow. How does metamorphosis fit in? Well adult insects have wings they're not born with, and there are two ways to approach this:

    Hemimetabolous Metamorphosis: Also known as 'incomplete' metamorphosis, young individuals are born looking like teeny versions of adults, albeit without wings. To grow these wings, young nymphs simply go through successive periods of moulting, each time gradually forming their wings - until finally they do one last moult to produce an adult; a fully-winged individual that can breed. Examples here include grasshoppers, cockroaches and mayflies.

    Holometabolous Metamorphosis: Known as 'complete' metamorphosis, this is the most radical, and includes a stage of 'inactivity' without feeding - yer' typical cocoon or pupa. Young are born as larvae, looking nothing like the adults, and after their final larval moult they undertake one extended transformation to form their adult body, developing their wings internally in one fell swoop, ready to bang other six-legged hotties.

    Holometabolous metamorphosis has evolved only once (all butterflies, beetles, bees etc. have a shared ancestor), within the insects, and is unique to them. But why?


    What caused certain insect species to evolve to have a metamorphic process in their life cycle?

    One word: competition. By splitting the juvenile and adult stages of life cycle into two very distinct phases, it allows the young and old versions of an insect to use different resources and therefore prevents competition between them. Caterpillars eat leaves, butterflies drink nectar. Newly hatched caterpillars aren't going to find all the nearby leaves have already been eaten by their mother. A good idea, right?

    This splitting of the life cycle furthermore drives specialisation, and opens the doors of insectkind to ecological possibilities they previously couldn't imagine - say, parasitism, for example; without having to worry about slowly developing wings or legs, you can spend lotsa' time burrowing into the untapped niche that is some poor animals body instead. Hurrah!

    Now that's the functional reason; what was the mechanistic reason. It's easy to see how you can go from direct development (ametabolous metamorphosis in non-insect hexapods like springtails, and wingless insects like silverfish; infants look exactly like wingless adults, and they simply 'moult up') to incomplete metamorphosis - you just add a pair of slowly growing wings. The jump from incomplete to complete metamorphosis however seems a bit more of a jump; though it isn't really. All hemimetabolic incomplete metamorphosing insects actually do undergo a radical transformation in body plan, albeit inside the egg. Open up a grasshopper egg and you'll find something resembling a wee grub. What has happened with holometabolous insects then is that they've undergone something called neoteny, whereby 'juvenile' characteristics are held onto for longer periods of time; in this case, keeping the larval grub-like stage beyond birth and into the early stage of their life. Butterflies simply moved their massive transformation from inside the egg, to outside - all the processes were already there, evolution just tinkered with the timing.


    TL;DR: Only some insects go through complete metamorphosis, radically transforming their bodies, and they do so to avoid competition between flying adults and flightless young. To accomplish this they moved the timing of their transformation from when it happened inside the egg, to a bit later on.

    [–] Why do some birds have forked tails? tea_and_biology 1 points ago in askscience

    Ah, whoops - edited with Google Drive link instead!

    [–] Do animals generally mate with others near their same age the way humans do? tea_and_biology 60 points ago * (lasted edited 8 days ago) in askscience

    Biologist here! Your question is so broad it's difficult to answer - considering the depth and breadth of the animal kingdom, a simple answer would be yes, no, maybe and I don't know all in one. Dolania americana mayfly adults, for example, erupt en masse from bodies of water together, their entire reproductive lifespans lasting a grand total of 5 minutes. Individuals here are mating with others who themselves were conceived within minutes of one another a year prior, and certainly entering adulthood together now.

    In contrast, humans live for many multiple decades and, depending on your age and sex, your taste for age preference in your partner can vary dramatically (in contrast to your initial question; for example, in this study, men aged 60+ prefer partners the same age or a decade or more younger than them, whilst women in their 30s preferred either same-ish age or ten or more years older).

    So there's no overarching general trend. However, we can break your question down a little bit and find intriguing answers.

    But first, let's talk about sex, baby. Almost universally across the animal kingdom, females are picky, males take whatever they can get. Why? Well, eggs are expensive, and sperm is dirt cheap. This cost differential explains a whole host of differences in form and behaviour between the sexes right across the animal kingdom (see: sexual selection). It's also a major influencing factor on mate age preference when other factors aren't in consideration (we'll get to those in a hot second!). By default, as far as males are concerned; they're easy, or at best otherwise choose younger, more productive females.

    As for the ladies, in theory, all else being equal, you'd think they should prefer to mate with older males as they have demonstrated ability to survive, and therefore their offspring should inherit a fitness advantage. However, male ageing is also associated with reduction in the quantity and quality of sperm. Turns out under experimental settings, this latter problem is more important. Drosophila fruit fly females, for example, will preferentially mate with younger males; they were observed to deliver more sperm, and females who mated with them produced more eggs and successful progeny (although they did die earlier too).

    In which case, one overgeneralisation would be to say females prefer younger males. But fruitflies don't raise their young, and they don't rely on resources provided by a mate. Sperm count alone might be good enough for them, but all else isn't equal for other female animals and other things need to be considered.

    In species where parents engage in parental care, like in all birds, preference instead is usually given by females to males experienced in raising offspring, which is age-associated, and means more of their chicks will likely survive to adulthood than with relatively inexperienced males (they readily 'cheat' with younger guys though; see extra-pair copulation).

    Likewise in species where mate choice is tied with resource dependence - say, in elephant seals competing for the best spots on the beach, or in lions or social baboons defending and maintaining productive territories. In these situations, females with motivation to seek the best resources for themselves and their young tend towards older males who're at the top of their game; who've so far claimed victory over both environmental pressure to survive (they can find food) and intraspecific competition to maintain their high status, hold territory and see off rivals (not only can they find food, but they can secure it long-term). Of course, eventually a male gets too old and another will replace 'im, so there's some rought cut-off point. In any case, it's being able to provide is what matters most. Perhaps this explains to some extent generalised female mate choice in us humans - 'aint nothing like a golddigger, 'ight? Security is important, or something.

    Anywho, that's a lot of words, and only the briefest of skims across the surface of the diverse and complicated world of mate age-associated preference choice. We haven't even got into things like courtship displays, secondary sexual characteristics, or any other indicator of age-associated fitness either. Yikes!

    In short: Animal mate age preference can depend on a lot. Like, really, a lot. Generally though, males are easy with anyone and anything, females are understandably more discerning. If a female is looking for mates who can demonstrably raise young and provide for her, she'll tend to go for either same-ish age or older, the most capable guys. If she doesn't care though, it's the young bucks and their big bags o' sperm who get the business.


    Sources:

    Rezeai, A., Krishna, M.S. & Santhosh, H.T. (2015) Male Age Affects Female Mate Preference, Quantity of Accessory Gland Proteins, and Sperm Traits and Female Fitness in D. melanogaster. Zoolog Sci 32 (1), 16-24

    Jouventin, P., Leugette, B. & Dobson, F.S. (1999) Age-related mate choice in the wandering albatross. Animal Behav. 57 (5), 1099-1106

    Schwarz, S. & Hassenbrauck, M. (2012) Sex and age differences in mate-selection preferences. Hum Nat. 23 (4), 447-466

    [–] ELI5: Why are there no snails in the zoo, even though they are animals? tea_and_biology 5 points ago * (lasted edited 8 days ago) in explainlikeimfive

    There are plenty of snails in zoos. I guess it depends on which zoos you go to.

    For example, the entire global population of 11 species of Partula land snails from French Polynesia exist solely in zoos, after the international zoo community rescued them from extinction. Peeps living on Tahiti accidentally released giant african snails which were eating crops. In order to combat this, they brought in carnivorous wolfsnails to eat the invaders. As with all these things, the wolfsnails instead turned to the local shelly bois for dinner and 48 species went extinct.

    Anywho, check out the Partula Programme Consortium, run out of ZSL London Zoo, that globally coordinates and manages their captive breeding programme. They're currently releasing a bunch of them back into the wild, now that the breeding programme has been so successful!

    Likewise with Partula, giant african land snails (which are often kept as pets), apple snails and a whole loada' marine snails are also pretty common in zoo exhibits too.

    ELI5: Zoos have lots of snails, and have even saved a bunch from being wiped out completely. You just gotta' go to the good ones and keep your eyes peeled!

    [–] Why are smaller animals more resistant to ionising radiation? tea_and_biology 62 points ago in askscience

    Hmm, it's tempting to think the presence of a chitinous exoskeleton might have some influence too. Alas, I've failed to find any evidence to support the claim. If anything, according to this sourced from here, marine invertebrate chitin shells readily degrade under exposure to ionising radiation; though a contradictory claim by this material science paper seems to suggest the material itself is quite resistant (in either case, structural resistance doesn't mean it blocks its passage, or anything). I'm a bit out of my depth on this, so haven't really a clue, sorry!

    [–] How do caterpillars maintain basic bodily functions as they transform to butterflies within the chrysalis? tea_and_biology 435 points ago * (lasted edited 8 days ago) in askscience

    When a caterpillar forms a chrysalis to metamorphose, despite common misconception, a suite of enzymes doesn't literally digest the body down to a rich fluid to reform anew from scratch. Only some of their organs do that; the rest remain largely intact and simply undergo radical remodelling via cells undergoing programmed death to be replaced by other rapidly dividing cells. A chrysalis is not quite just a bag of protein goop.

    With this in mind, how does a caterpillar survive? Let's break it down:

    Oxygen: A developing chrysalis clearly needs some sort of gas exchange taking place to keep breathin'. All insects breathe through teeny pores that line their bodies called spiracles, which lead into long tendril-like tubes that penetrate deep into the body, carrying oxygen. Thankfully, during metamorphosis, this respiratory system remains intact (even through a bit of renovation), allowing the developing butterfly to continue breathing throughout.

    Nutrients: Unable to forage for food, a stationary chrysalis is at risk of running out of energy - after all, it uses a considerable sum to forge a new body. However, before enclosing itself in a hard outer shell, the caterpillar spends almost all waking moments gorging itself, storing up an enormous amount of energy as body fat. During metamorphosis, it's this stored fat that's broken down into the requisite resources needed to survive; a chrysalis can lose over half its weight during the entire process, as this fat is broken down.

    Waste: As with the spiracles that provide oxygen and remove carbon dioxide, a series of malpighian tubules remove excretory waste - albeit in this case not outside the chrysalis. They're likewise retained through much of metamorphosis and release concentrated nitrogenous waste into an isolated subsection along where the caterpillars intestines once hung about. When the butterfly emerges, it releases all of this, well, poop and bits of old caterpillar carcass as a red fluid out the abdomen, known as meconium. Finally released of this debris of its past experience, it can stretch its wings and fly away.


    Sources:

    Connor, W.E., Wang, Y., Green, M. & Lin, D.S. (2006) Effects of diet and metamorphosis upon the sterol composition of the butterfly Morpho peleides. J Lipid Res. 47 (7),1444-8

    Conti, B., Berti, F., Mercati, D. et al. (2010) The ultrastructure of malpighian tubules and the chemical composition of the cocoon of Aeolothrips intermedius Bagnall (Thysanoptera). J Morphol. 271 (2), 244-254 (research gate here)

    Lowe, T., Garwood, R.J. Simonsen, T.J. et al. (2013) Metamorphosis revealed: time-lapse three-dimensional imaging inside a living chrysalis. J R Soc Interface. 10 (84)

    [–] Do animal species abandon their orphaned youth? tea_and_biology 6 points ago * (lasted edited 8 days ago) in askscience

    What do animals species do with their orphaned youth?

    More often than not, the infants simply die. Sad times.

    However, adoption is nonetheless a widespread phenomenon in the animal kingdom! Take, for example, the elephant seal. Bustling about on crowded seasonal breeding beaches, pummelled by rough storms and rougher seas, between a quarter and a third of all seal pups become separated from their mothers at least once - many permanently. What's remarkable though, is that most of these orphans become adopted by other females. But why?

    Turns out most foster mothers are those who had already lost their own pups. Having perma-misplaced their own child, one hypothesis suggests that taking another under the wing allows for continued nursing, which may help induce ovulation and increase the likelihood of a successful birth to another pup next season. Likewise, given the intensity of the behavioural and physiological processes going on inside mothers following birth, the instinctual motivation may simply be so strong that mothers misdirect attention onto other pups to fulfil that need.

    Furthermore, orphans may also provide younger, less experienced females yet to give birth, essentially 'practice', providing plenty of experience points to level up their motherhood skills come the time when they have infants of their own.

    In short, at least for elephant seals, it seems like the parents just get something out of it.

    Plenty of other animals, notably group-living beasties like social primates and colony breeding birds, also exhibit high degrees of adoption and foster care. In the case of colonially nesting birds, it's often actually in the interest of the infant to seek out new parents, as it increases the period of time they're under parental care - allowing them access to more food, helping them outcompete their peers (called 'nest switching'). It's very common, with around 40% of all broods, in the case of nesting storks, containing adopted chicks. You'd think parents would wise up to this and turn gatecrashers away, but it's thought the cost of getting this wrong - by having some behaviour that rejects chicks, including their own by mistake - is evolutionarily too great, so it persists.


    Sources:

    Riedman, M/L/ & Le Boeuf, B.J. (1982) Mother-pup separation and adoption in northern elephant seals. Behavioural Ecology and Sociobiology. 11 (3), 203-215

    Redondo, T., Tortosa, F.S. & deReyna, L.A. (1995) Nest switching and alloparental care in colonial white storks. Animal Behaviour. 49 (4), 1097-1110

    [–] Why do some birds have forked tails? tea_and_biology 3 points ago * (lasted edited 8 days ago) in askscience

    Ooh, you might want to check out this paper here if you'd like more details; it's very comprehensive! Was attempting to write-up a summary, but found I couldn't really do it much justice. In short, forked tails are all about reducing aerodynamic cost (in terms of drag-to-lift ratio) when you start increasing your tail length, but there's a lot more to it than that - in any case, the mechanistic engineering-ey explanation aside, as /u/Matty1977 pointed out, they ultimately help with aerial agility.

    [–] Why are smaller animals more resistant to ionising radiation? tea_and_biology 1414 points ago * (lasted edited 8 days ago) in askscience

    As far as I'm aware, we still don't quite know.

    Compared to humans, we've known for some time that insects are generally more resistant to ionizing radiation, and multiple hypotheses have been proposed to explain this radioresistance.

    For a long time it was thought that because actively dividing cells are those most sensitive to radiation, insects would succumb less as, unlike humans with our leagues of constantly dividing cells, insects undergo discontinuous periods of growth (only with every moult). But this whole organism approach to radioresistance was tricky to interpret, as the physiology between us and, say, invertebrates is very different.

    At a cellular level however, experiments on cells controlling for proliferative rate have revealed that insect cells are de facto more radioresistant than human cells, leading us to believe division rate actually might only have a little to do with it. When you blast human and insect cells with ionising radiation, the DNA within the insect cells itself undergoes much less damage, and what damage is present is more effectively repaired. Likewise, those same insect cells experience lower oxidative stress as a consequence of radiation exposure (radiation triggers the production of rather harmful reactive oxygen species that, amongst other things, trigger cells to commit apoptotic suicide).

    So yup, it appears the suite of repair enzymes insects utilise are simply better at dealing with DNA damage, explaining why insects have greater radioresistance. As for the evolutionary reason why they're more efficient, we're still not quite sure.


    Sources:

    Cheng, I.C, Lee, H.J. & Wang, T.C. (2009) Multiple factors conferring high radioresistance in insect Sf9 cells. Mutagenesis 24 (3), 259-369

    Bianchi, N.O., Lopez-Larraza, D.M. & Dellarco, V.L. (1991) DNA damage and repair induced by bleomycin in mammalian and insect cells. Environ Mol Mutagen. 17, 63-68 (research gate here)

    [–] What is an organism? tea_and_biology 1 points ago * (lasted edited 9 days ago) in AskScienceDiscussion

    Maybe I’m misunderstanding these concepts and oversimplifying things, if so let me know!

    Hmm, no; on the contrary, to skip ahead a bit, I think we're travelling down the rabbit hole into the deep and troubling philosophical field of ontology. Ultimately, we're attempting to mentally order aspects of the natural world into neat discrete categories for our own ease of use, when in fact our complex reality is not bound by the constraints applied upon it by the human mind. To take defining life, for example, really, the hard distinction between 'living' versus 'non-living' things is one we have invented; our universe contains a perfect gradient of entities across a spectrum where on one end you have a rock and on the other a human being, and then plenty else along additional axes. It's just quite convenient for us that a lot of stuff from the middle of that spectrum no longer exists for us to scratch our heads over, leaving us gaps that make it a little easier for us to draw our lines.

    As it is with life in general, it is with trying to grapple with definitions of life forms and multicellularity.

    Through our evolutionary history, there's an unbroken chain of living entities going from a colony of multiple individuals something like modern choanoflagellates - where each and every cell, yeah sure, could be considered its own 'individual organism' - to today, where every cell in a multicellular entity like ourselves is comparatively hyperspecialised and certainly anything but an individual organism. At no point along that chain, some line between parent and offspring, was there a 'this thing is made up of several organisms' and 'this is just one organism' distinction made. It was just a fuzzy gradualisation, just like the Sorites Paradox. In which case, the question is kinda' ultimately unanswerable, as it's a paradox, set by the limits of our language and requirement to classify.

    Day to day though, it's just easier and more practical to go by a bunch of 'good enough' definitions - like in my original and subsequent post. It's all illusion, really, but then we ought not to think too hard about it!

    Tl;DR: if you really want to dive into the depths and find answers, there aren't any. Not really. We're monkeys trying to define boundaries on an boundless world. So, err, use whatever you think is best for whatever situation, or something?

    [–] Does a high metabolism increase risk of cancer? tea_and_biology 3 points ago in askscience

    Well, the mechanistic theory seems sound, and applicable not only to cancer, but a wide range of age-associated diseases such as diabetes and neurodegenerative diseases, at least in experimental models. In terms of cancer itself, we know from well-established lab studies that calorie restriction (CR), without malnutrition, is broadly effective in preventing cancer in both rodents and primates. As far as I'm aware, we remain a little unsure with regards to human prognosis - I mean, thorough long-term studies take an awful long time to undertake (and smaller scale studies, say on the effect of CR on cancer therapy outcomes, are tricky; chronically starving a cohort cancer patients isn't exactly, err, desirable - to say the least!).

    Saying that, from what we can gather from CR studies on humans so far; undertaking CR certainly reduces levels of many of the nasty things, like oxidative stress markers (oxygen free radicals are by-product molecules of respiration that cause DNA damage and associated ageing), in your system that are highly associated with cancer risk.

    The jury is still out, but my personal verdict is 'it probably might help quite a lot'. At least, until additional evidence proves me wrong!


    Sources:

    Longo, V.D. & Fontana, L. (2011) Calorie restriction and cancer prevention: metabolic and molecular mechanisms. Trends Pharmacol Sci. 31 (2), 89-98

    O'Flanagan, C.H., Smith, L.A., McDonell, S.B. & Hursting, S.D. (2017) When less may be more: calorie restriction and response to cancer therapy. BMC Med. 15 (106)

    [–] Does a high metabolism increase risk of cancer? tea_and_biology 3 points ago * (lasted edited 9 days ago) in askscience

    Ah, not quite - both breast and prostate cancers are carcinoma and adenocarcinomas respectively, which means they're likewise 'vanilla' epithelial (lining of the milk ducts, typically) and glandular epithelial cell (prostate gland lining cells) based.

    Additionally, in both cases, the tissues undergo periods of rapid proliferative growth during puberty, which is one reason (along with genetic inheritance in the case of breast, and plenty others) why both tend to be amongst the carcinomas whose proportional incidence relative to other cancers is disproportionately skewed towards a lower age (particularly so with breast cancer; highest proportional incidence is for those aged 25 - 45, and almost half at 44% of all cancers diagnosed in that age group). In other words, if you're going to get any carcinoma at a younger age, it's more likely to be one of those two, than, say, colorectal or stomach - rapid tissue growth and otherwise generally continuously replicating cells is somewhat of a double-whammy.

    For the same puberty-associated reason, this is why bone cancers tend to affect young people, particularly teenagers, the most. Growth spurts and more metabolic activity means more division means increased risk of cancer. Post-puberty, incidence of those sorts of sarcomas (cancer originating from otherwise slow-diving cells) drops off dramatically.


    Sources:

    Bodicoat, D.H., Schoemaker, M.J., Jones, M.E. et al. (2014) Timing of pubertal stages and breast cancer risk: the Breakthrough Generations Study. Breast Cancer Res. 16 (1)

    Bonilla, C., Lewis, S.J., Martin, R.M. et al. (2016) Pubertal development and prostate cancer risk: Mendelian randomization study in a population-based cohort. BMC Medicine. 14 (66)

    [–] What is an organism? tea_and_biology 1 points ago in AskScienceDiscussion

    Ah, I should have clarified to more detail.

    So gametes and somatic cells actually are organisms?

    Nope. Although individual cells extracted from a multicellular organism may be able to be cultured in vitro and, well, remain 'alive', they cannot do so independently - they require human intervention to obtain all the required resources and to remove waste. A unicellular organism like a bacterium, on the other hand, can handle these functions on its own - finding or synthesising the resources it needs, and is capable of reproducing on its own.

    The key difference here is being self-sustaining. Organisms, or life forms, are those things that are able to feed themselves, deal with their own waste, respond to stimuli, reproduce etc. etc. (see these seven traits that traditionally define 'life'). Any given gamete or somatic cell from an organism cannot do so, and therefore isn't considered a life form, or organism, in its own right.

    [–] What is an organism? tea_and_biology 1 points ago in AskScienceDiscussion

    "Organism" is synonymous with "life form". All individual living things are organisms, and all organisms are living things.

    True, if you wanna' rope viruses into the mix, it gets a little fuzzy - they exist on the boundary between living and non-living things. Some peeps like to include them under the label 'organism', others don't - it's all a bit subjective, really, and pretty much open to interpretation. Just semantics 'innit.

    Viruses aside, the phrase "non-organism life forms" is a just like saying "non-organism organisms" and doesn't really make all that much sense.

    [–] Does a high metabolism increase risk of cancer? tea_and_biology 11 points ago in askscience

    Biologist here; this actually happens to be the very topic of my research!

    In short; amongst other reasons, yes. Indeed, if you take a look across multiple species - say, all mammals - you'll notice that going from wee mice to bloaty whales, mass-specific basal metabolic rate (the amount of energy you burn for every gram of tissue, say) decreases; as do cancer incidence rates (graph here; blue is specific metabolism, red; cancer).

    Large mammals like whales and elephants have many orders of magnitude more cells than us (and have considerable lifespans), so you'd think they'd be riddled with tumours, succumbing to cancer quite readily - I mean, they have so many cells that could mutate, and an awful long time for them to do it, at first glance it's bound to happen sometime. Yet the opposite is true. This is known as Peto's Paradox, and to resolve this paradox we must somehow explain why large mammals are resistant to cancer.

    There are several co-compatible answers to this. One of them is to do with their genetics (specific genes need to be broken to cause cancer; larger mammals often have many duplicates of these genes, so even if a few are knocked out, they still retain working copies and remain cancer free), another is to do with their metabolism.

    I won't go into too much detail as the work is still under review for publication (and it's a bit maths-ey, blergh), but by building comprehensive computational models of mammalian tissue and by tweaking the dials that relate to metabolically-linked phenomenon (say, how often cells divide, the rate of production of damaging oxygen radicals etc. etc.), we can fairly accurately simulate and predict lifetime risk of cancer incidence* as a function of metabolism - and it lines up quite nicely with observed rates of cancer from mammalian veterinary reports. In a more ELI5 manner; by trying to give virtual whales lotsa' virtual cancer, we can see their metabolism is too slow for much cancer to really get going; which matches what we see in actual animals.

    So yup, it seems the hypothesis that metabolism has a major influence on cancer risk seems valid, and can be quantitatively modelled - larger animals have slower metabolisms relative to smaller ones, and this helps reduce their cancer risk. I'd be happy to elaborate on the cellular-level mechanistic explanation for why (as you mention, cell division is one reason amongst many), but for a good review see Dang (2012) linked below!

    TL;DR: Yup! Small animals with high metabolisms are almost walking tumours; big animals with super slow metabolisms are practically cancer free. Congrats, whales?!


    Sources:

    Abegglen, L.M. Caulin, A.F., Chan, A. et al. (2015) Potential Mechanisms for Cancer Resistance in Elephants and Comparative Cellular Response to DNA Damage in Humans. JAMA. 314 (17), 1850-1860

    Caulin, A.F. & Maley, C.C. (2011) Peto's Paradox: Evolution's Prescription for Cancer Prevention. Trends Ecol Evol. 26 (4), 175-182

    Dang, C.V. (2012) Links between metabolism and cancer. Genes Dev. 26 (9), 877-890


    * The black line here is observed cancer incidence rate across mammals, the individual blue dots are predicted incidence rates based on metabolic data for 600-odd mammal species, and the red line is the generalised linear model for that data - it basically shows that this simulation is very good at predicting cancer rates for almost all mammals taking into account metabolism alone, except for the very extremes (where the red line shoots up at the end) - and it's in the very largest and very smallest of mammals that we're find all the genetic trickery, like duplicated cancer genes, that's making up for what their metabolism alone can't explain.

    [–] Scientific Journal Help? tea_and_biology 7 points ago * (lasted edited 9 days ago) in zoology

    Have a PDF copy; uploaded to Google Drive here. Download while you can; will remove in a bit!