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| 5/23 |
| 2007/3/22 [Recreation/Dating, Science/Biology] UID:46053 Activity:nil 76%like:46056 |
3/22 Divergent selection found in asexual reproducers OR Creatures
found that have not had sex for 100m years:
http://www.physorg.com/news93597385.html
http://www.timesonline.co.uk/tol/news/uk/science/article1539281.ece
Let the obligatory jokes about geeks and sex begin.
[ merged w/ thread originally posted below ]
\_ See yesterday's "Divergent selection found in asexual reproducers"
thread below.
\_ Ah, apologies for the repost. This title was more prurient.
\_ What does "species" mean when you're referring to
creatures which produce asexually?
\_ Reading http://en.wikipedia.org/wiki/Species it's probably
still undefined.
\_ My HS Bio AP understanding of "species" is that all members of
the species are genetically similar enough to interbred. It is
conceivable that random mutations and errors in DNA replication
in asexual reproducers could produce members that are no longer
able to reproduce w/ the members of the species from which they
descended.
\_ The problem in your understanding is the word "interbreed".
Individuals of asexual "species" do not interbreed, so you
can't define asexual "species" that way. -- !PP
\_ I see what you mean. What I was getting at is that
in order to interbreed a pair of creatures must have
similar/compatible DNA. Thus similar/compatible DNA
could be a basis to assign a creature to a partiuclar
speicies.
Random mutations and errors in DNA replication in
asexual reproducers could produce creatures that
are not genetically similar to creatures from which
they descended. Therefore, comparing the DNA of two
different asexual reproducers to see if they are
similar could be used to determine if they should be
classified as one specie or two.
I have no idea how to quantify the level of genetic
dissimilarity necessary to classify two creatures as
members of different species. As a rough estimate,
perhaps any two creatures whose DNA differed by more
than 1-2% could be considered different species [b/c
I think I remember reading somewhere that the DNA of
humans and chimps, which are different species, differ
by only 2%]. |
| 5/23 |
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| www.physorg.com/news93597385.html No problem A group of organisms that has never had sex in over 40 million years of existence has nevertheless managed to evolve into distinct species, says new research published today. The study challenges the assumption that sex is necessary for organisms to diversify and provides scientists with new insight into why species evolve in the first place. The research, published in PLoS Biology, focuses on the study of bdelloid rotifers, microscopic aquatic animals that live in watery or occasionally wet habitats including ponds, rivers, soils, and on mosses and lichens. These tiny asexual creatures multiply by producing eggs that are genetic clones of the mother - there are no males. Fossil records and molecular data show that bdelloid rotifers have been around for over 40 million years without sexually reproducing, and yet this new study has shown that they have evolved into distinct species. Using a combination of DNA sequencing and jaw measurements taken using a scanning electron microscope, the research team examined bdelloid rotifers living in different aquatic environments across the UK, Italy and other parts of the world. They found genetic and jaw-shape evidence that the rotifers had evolved into distinct species by adapting to differences in their environment. Dr Tim Barraclough from Imperial College London's Division of Biology explained: "We found evidence that different populations of these creatures have diverged into distinct species, not just because they become isolated in different places, but because of the differing selection pressures in different environments. "One remarkable example is of two species living in close proximity on the body of another animal, a water louse. One lives around its legs, the other on its chest, yet they have diverged in body size and jaw shape to occupy these distinct ecological niches. Our results show that, over millions of years, natural selection has caused divergence into distinct entities equivalent to the species found in sexual organisms." Previously, many scientists had thought that sexual reproduction was necessary for speciation because of the importance of interbreeding in explaining speciation in sexual organisms. Asexual creatures like the bdelloid rotifers were known not to be all identical, but it had been argued that the differences might arise solely through the chance build-up of random mutations that occur in the 'cloning' process when a new rotifer is born. The new study proves that these differences are not random and are the result of so-called 'divergent selection', a process well known to cause the origin of species in sexual organisms. Dr Barraclough adds: "These really are amazing creatures, whose very existence calls into question scientific understanding, because it is generally thought that asexual creatures die out quickly, but these have been around for millions of years. "Our proof that natural selection has driven their divergence into distinct species is another example of these miniscule creatures surprising scientists - and their ability to survive and adapt to change certainly raises interesting questions about our understanding of evolutionary processes." Citation: 'Independently evolving species in asexual bdelloid rotifers', PLoS Biology, Monday 19 March 2007. |
| www.timesonline.co.uk/tol/news/uk/science/article1539281.ece Sitemap From The Times March 20, 2007 Creature that has not had sex for 100m years A Bdelloid Rotifer Lewis Smith, Environment Reporter A tiny creature that has not had sex for 100 million years has overturned the theory that animals need to mate to create variety. Analysis of the jaw shapes of bdelloid rotifers, combined with genetic data, revealed that the animals have diversified under pressure of natural selection. Researchers say that their study "refutes the idea that sex is necessary for diversification into evolutionary species". The microscopic animals, less than four times the length of a human sperm, are all female, yet have evolved into different species that fill different ecological niches. Two sister species were found to be living together on the body of a water louse. One of them specialised in living around the louse's legs and the other stayed close to the chest. Genetic analysis showed that the two creatures were distinct, a fact backed up by observations that each type had differently shaped jaws. Asexual animals and plants usually die out quickly in evolutionary terms but the ability of bdelloid rotifers to diversify may explain why they have survived so long. A specimen trapped in amber has shown that the animals were living at least 40 million years ago and DNA studies have suggested they have been around for 100 million years. It had previously been recognised that asexual animals and plants can evolve through mutations into another species, but only into one species and at the cost of its original form. Bdelloid rotifers have displayed the ability to evolve into many different forms. The study of several bdelloid rotifers, published in the journal PLoS Biology, was carried out by an international team including researchers from Imperial College London, the University of Cambridge and the Royal Botanic Gardens, Kew. "These really are amazing creatures, whose very existence calls into question scientific understanding," said Tim Barraclough, of Imperial College. He added that the two species of bdelloid rotifer almost certainly arrived on the louse as one species and later evolved to take better advantage of the environment. There are many examples of asexual species of animals and plants, including some dande- lions. Asexuality is most common in invertebrates, such as aphids, but it is also found in a number of fish and frogs. Have your say I have not had sex in 21 years, and I am completely happy! All I need now is some bells to ring, but can't find any in my city! Twinkletoes, Sacramento, California Of course it's possible for diversification without sex -- it's just easier with sex. For the most part, these organisms are all clones of each other. Those with the mutation survive better than those without, and reproduce more. Aaron Traas, Maplewood, NJ, USA Thank you, Steve of Montreal, CA, you made my day. ChomFa, Jumbuk, Vic, Australia And here I thought I held the record for the longest time without sex, but these creatures beat me out by at least a million years or so. sigh Duane Rysh, Lafayette, Colorado No conversation involving evolution can take place without creationist morons injecting their illiterate ignorance into it. James Jonell, Cambridge, "refutes the idea that sex is necessary for diversification into evolutionary species" These are diversifications WITHIN a species. How does this prove anything with regard to diversification OF species. It is a large leap in logic to assume that variation within the species has anything to do with evolution into a new species. To make that leap one much BELIEVE or have FAITH that it occurs despite the evidence to the contrary. "Evolution into new species occurs because we have many species, some of which have some similar characteristics and there is no other explanation, even though we've never observed said evolution" Seems like that takes as much FAITH to believe as "creationism." AW, San Antonio, Texas Well clearly evolution is a lie and this proves that god created man.. SRM, Kolkata, India To assume that they are hundreds of millions of years old simply because they were found in amber is a farse. These scientists need to go back to grade school and study up on their scientific method. Can anybody offer real proof that one kind of animal has "evolved" from another? If it is, you can call yourselves scientists, otherwise you can stick with Quack! Joe, Somewheres, mi, If asexual reproduction is "common in invertebrates, such as aphids, but it is also found in a number of fish and frogs," how does it "call into question scientific understanding"? Uther Eisenheim, Springfield, MO Just goes to show that when a women is in complete control of her life, no one wants to sleep with her. Steve, Montreal, CA I know exactly how that creature feels. I haven't has sex in over 11 months and I've still survived. Richard Pilgrim, Mansfield, Notts Sexual reproduction is certainly not necessary for evolution via genetic mutations, see the comments above and the article. Asexual reproduction just gives a smaller range of potential differences for the genetic inheritance for the offspring. The surprising thing for me is the quote from Tim Barraclough, of Imperial College, which seems rather out-of-context, because it apparently displays a remarkable lack of scientific basis. There is really nothing new: asexual reprodiction exists, and evolution can occur from it. Interesting, but nothing to shake the foundations of "science". JasoN McGuiness, London, I assume these creatures do not actually **live** 100 million years, and that they procreate using parthenogenesis. These can modify genetic makeup in various ways, even during the lifetime of an individual. So I am not very surprised about the results of this research. I am however baffled by the impact suggested, which is not there for me. Rob Vens, Usquert, Netherlands Natural Selection does not have to occur through sexual reproduction. When a specimen creates offspring (either sexual or asexual), errors in teh process of copying the genetic information occur: Mutations. As someone already pointed out here (Ian Kemmish), sexual reproduction only increases the chance for genetic differences (thus, with a larger number off different genetic makeups, more benficial genetic makeups will occur, and those have a higher chance to survive), but it is not necessary. If Sexual reproduction would be necessary fro evolutionary proccesses to occur, Live on earth would still be on the mono-cellular level, since they created offspring asexually. Roland Granitzki, Wuppertal, Germany How do these creatures adapt without sex? Don't animals normally adapt by surviving an event because of a certain characteristic, and then mate with another animal with the same characteristic? Starling, Lancaster, I don't know about these critturs, but lack of sex affects my demeanor. Lee Hadden, Sterling, Virginia, USA I always knew Darwinin logic was flawed! HA, those pesky sociobiologists can all talk now can't they? John Winston Price, Oldham, England "refutes the idea that sex is necessary for diversification into evolutionary species". Any claim that such an idea is widely accepted is erroneous. An organism needs merely to be able to reproduce, not necessarily sexually. This reporter neglects to explain the alleged source of this claim . Rami Samara, Croydon, UK I guess this means that I no longer hold the record... Tom M, St Louis, Misouri, USA Did Dr Barraclough really say "These really are amazing creatures, whose very existence calls into question scientific understanding"? I sincerely hope he didn't, and that he can clarify that his comments were printed out-of-context by a careless journalist. These creatures certainly do not call scientific understanding into question - they pose interesting problems and conundrums but the discoveries made enhance and further scientific understanding. Uninformed science-bashers promoting religion, creationism and other such superstitions will positively leap at ill-considered statements like this one which appear to dismiss at a stroke all of our carefully accumulated scientific knowledge. George Lennan, La Ro... |
| en.wikipedia.org/wiki/Species A species consists of individual organisms which are very similar in appearance, anatomy, physiology and genetics due to having relatively recent common ancestors. Traditionally, multiple examples of a proposed species must be studied for unifying characters before it can be regarded as a species. The commonly used names for types of animal in English and many other languages often do not correspond to species. Books and articles sometimes intentionally do not identify species fully and use the abbreviation "sp." in the plural in the place of the specific epithet, for example Canis sp. This commonly occurs in the following types of situation: * The authors are confident that some individuals belong to a particular genus but are not sure to which exact species they belong. as a short way of saying that something applies to many species within a genus, but do not wish say that it applies to all species within that genus. If scientists mean that something applies to all species wiith a genus, they use the genus name without the specific epithet. Most textbooks define a species as all the individual organisms of a natural population that generally interbreed at maturity in the wild and whose interbreeding produces fertile offspring. Various parts of this definition are there to exclude some unusual or artificial matings: * Those which occur only in captivity (when the animal's normal mating partners may not be available) or as a result of deliberate human action. tigons, apparently cannot produce offspring when mated with one of their own kind (eg a mule with a mule), but sometimes do produce offspring when mated with members of one of the parent species (eg a ligon with a lion). Usually in such hybrids the males are sterile, so one could improve the basic textbook definition by changing "... whose interbreeding produces offspring in which both sexes are normally fertile". All definitions of the word "species" assume that an organism gets all its genes from one or two parents which are very like that organism, but horizontal gene transfer makes that assumption false. evolve into one or more others after a few million years; the original type of organism and the final one are so different that one could not regard the ancestors and the descendants as members of the same species if they existed at the same time; chronospecies to describe the simplest case, where at the end of the process there is only one descendant type of organism and there are no longer any individuals of the ancestral type. But even this refinement does not work in cases where several descendant types are alive at the same time or where the ancestral type and at least one descendant type are alive at the same time - and both of these situations are common in the evolution of life on Earth. One definition that is widely used is that a species is a group of actually or potentially interbreeding populations that are reproductively isolated from other such groups. sexual reproduction, it leaves the term undefined for a large class of organisms that reproduce asexually. Biologists frequently do not know whether two morphologically similar groups of organisms are "potentially" capable of interbreeding. Further, there is considerable variation in the degree to which hybridization may succeed under natural and experimental conditions, or even in the degree to which some organisms use sexual reproduction between individuals to breed. Consequently, several lines of thought in the definition of species exist: Typological species A group of organisms in which individuals are members of the species if they sufficiently conform to certain fixed properties. The clusters of variations or phenotypes within specimens (ie: longer and shorter tails) would differentiate the species. This method was used as a "classical" method of determining species, such as with Linnaeus early in evolutionary theory. However, we now know that different phenotypes do not always constitute different species (eg: a 4-winged Drosophila born to a 2-winged mother is not a different species). Morphological species A population or group of populations that differs morphologically from other populations. duck because they have different shaped bills and the duck has webbed feet. Species have been defined in this way since well before the beginning of recorded history. This species concept is much criticised because more recent genetic data reveal that genetically distinct populations may look very similar and, contrarily, large morphological differences sometimes exist between very closely-related populations. It does not distinguish between the theoretical possibility of interbreeding and the actual likelihood of gene flow between populations and is thus impractical in instances of allopatric (geographically isolated) populations. The results of breeding experiments done in artificial conditions may or may not reflect what would happen if the same organisms encountered each other in the wild, making it difficult to gauge whether or not the results of such experiments are meaningful in reference to natural populations. Biological / reproductive species Two organisms that are able to reproduce naturally to produce fertile offspring. Mate-recognition species A group of organisms that are known to recognize one another as potential mates. Like the isolation species concept above, it applies only to organisms that reproduce sexually. Unlike the isolation species concept, it focuses specifically on pre-mating reproductive isolation. Phylogenetic (Cladistic)/ Evolutionary / Darwinian species A group of organisms that shares an ancestor; a lineage that maintains its integrity with respect to other lineages through both time and space. At some point in the progress of such a group, members may diverge from one another: when such a divergence becomes sufficiently clear, the two populations are regarded as separate species. Subspecies as such are not recognized under this approach; either a population is a phylogenetic species or it is not taxonomically distinguishable. Ecological species A set of organisms adapted to a particular set of resources, called a niche, in the environment. According to this concept, populations form the discrete phenetic clusters that we recognize as species because the ecological and evolutionary processes controlling how resources are divided up tend to produce those clusters Genetic species based on similarity of DNA of individuals or populations. Cohesion species Most inclusive population of individuals having the potential for phenotypic cohesion through intrinsic cohesion mechanisms. This is an expansion of the mate-recognition species concept to allow for post-mating isolation mechanisms; evolutionary significant unit is a population of organisms that is considered distinct for purposes of conservation. Often referred to as a species or a wildlife species, an ESU also has several possible definitions, which coincide with definitions of species. In practice, these definitions often coincide, and the differences between them are more a matter of emphasis than of outright contradiction. Nevertheless, no species concept yet proposed is entirely objective, or can be applied in all cases without resorting to judgement. Given the complexity of life, some have argued that such an objective definition is in all likelihood impossible, and biologists should settle for the most practical definition. the difference between the BSC and the PSC can be summed up insofar as that the BSC defines a species as a consequence of manifest evolutionary history, while the PSC defines a species as a consequence of manifest evolutionary potential. Thus, a PSC species is "made" as soon as an evolutionary lineage has started to separate, while a BSC species starts to exist only when the lineage separation is complete. trinomial nomenclature) by which scientists typically refer to organisms. After thousands of years of use, the concept remains central to biology and a host of related fields, and yet also remains at times ill-defined. edit Implications of assignment of species status The naming of a particular species s... |