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Species classification

Discussion in 'Advanced Tortoise Topics' started by Anyfoot, Dec 27, 2017.

  1. Anyfoot

    Anyfoot Well-Known Member

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    What does it take for a species of tortoise to be classified as a separate species on its own? How's it all work?

    For example the Redfoot(Chelonoidis carbonaria) and the yellowfoot( Chelonoidis denticulata) are classed as separate species. Yeah obviously there are color, morph and even social differences but this could also be evolution. If so at what point do they qualify as separate species, or is there some sort of internal diagnosis differential that has to be met to qualify as it's own species.
  2. Tom

    Tom The Dog Trainer 5 Year Member

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    @Will can explain this better than I can, and better than most.
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  3. Will

    Will Well-Known Member 5 Year Member

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    There are a few somewhat competing explanations of 'species'. Keep in mind the concept sorta does not take into account speciation and evolutionary process. Species for the most part is a balance sheet of what "IS" right now. Give or take a few hundred decades.

    The Traditional concept as taught in High School biology in the 1970's suggest that like things will look alike but not reproduce with each other. Those like things are organized into ever higher categories until you reach animal/vegetable dichotomy for organism with nucleated (DNA in an inner membrane) cells (Eukaryotas), versus living things with out nucleated (no inner membrane and DNA in a circle like configuration) Prokaryotic.

    That's the super big picture from some 50 years ago. Species were the smallest unit of animals that were distinct and thought to be reproductive isolated.

    In the more traditional way of morphology as the basis bones were/are used alot as they are thought to be inelastic, highly resistant to change. Color and hair etc. being much more elastic as a comparison. In this way alot worked out. Several species of giraffe were not confused with other hoof stock type animals, that long neck being made of bone and distinct. So what drove the process that resulted in the different kinds of giraffe?

    They were all one giraffe at some point in time derived from some other 'not giraffe' animal. Maybe the original giraffe got separated by a new river, or something. Over time, the two groups grew apart and had no chance to keep the entire population homogeneous. They become both geographically and reproductively isolated. One species is now two. In this case maybe the river dries up and they mix again, but now the mating recognition system has changed too, and they just don't like each other in that intimate way.

    This is fuzzy, the morphology alone as an explanation. Along comes phylogenetics and now the trend is to sort out species based on genes. You can actually tell to some extent how long the two giraffes have been separate. In each cell are mitochondria (with their own DNA) and they differentiate at a different rate that the nucleated DNA. Some science magic (my excuse of an explanation) can indicate how long they have been separated.

    Ever more genes are found that indicate these are not like those, but that geographic isolation is still important, so understanding the historic range over all time helps better understand which group is "these" and which group is "those".

    One of the extremes in thought is that each individual represent at that moment in time, their own species until they successfully reproduce. Then they are in a group of individuals that breed together.

    Cattle egrets offer a within out lifetime chance to see specie-ation that may happen. They were all more or less in Africa, and now they are on every continent less Antarctica. Big storms and human intervention have done this. Over time they may specialize in each habitat they live in to the extent that they don't know each other as cattle egrets anymore.

    Another cool real time observation is with fruit flies in Hawaii. A contiguous forest supports one species of fruit fly. Volcano erupts and they forest is fragmented. Each fragment in an observable few years fruit flies no longer breed with each together as they are geographically isolated over enough generations.

    Reproductive isolation comes in a few forms. Parts don't fit each other anymore, and that can be gross anatomy or fine anatomy, penis versus semen.
    They don't know how to talk to each other anymore if that includes some sort of ritual (head bobs, tail wagging), or smell (estrus), or could even be how food is accessed when a certain food time no longer occurs in-sink with population "a" to population "b".

    Over time the differences ad up to the point where they are completely incompatible.

    Then there are all kinds of mutation effects and molecular changes as well. Such that the sperm and the egg don't get along.
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  4. Anyfoot

    Anyfoot Well-Known Member

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    Thanks @Will. That was detailed and I think I understood. Need to read again when kids are in bed.

    Does this mean sub-species are in a closer time period than different species?
    For example Galapagos tortoise. I believe there are 15 sub species. In another 10 million yrs these 15 sub species may very well evolve into 15 completely different species.
  5. Markw84

    Markw84 Well-Known Member 5 Year Member

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    A definitive list of all chelonian species was just published current as of July 2017. It lists 356 species (with an additional 122 subspecies). In just 2014, the listing before had 335 species and 118 subspecies. SO this is indeed a moving target. Just this month a new paper now is proposing another species - splitting a new species from the razorback musk turtle. That published paper is a solid indication of what it takes to get a new species recognized. If it is widely accepted through peer review, it may be then accepted as an "official" new species. This is done by the IUCN (International Union for Conservation of Nature) who has the SSC (Species survival Commission). Under that operates the TTWG (Turtle Taxonomy Working Group)

    The paper looked at various indicators mostly mentioned by @Will above. To accept a new species they will normally be looking at genetic differences, morphological differences, (look and structure of the animal itself), physiological differences (the way the organism functions chemically and metabolically), geographical separation factors, and behavioral differences. Enough of these factors must be established as statistically distinct over a large enough sampling to warrant a new species distinction.

    More and more genetics, and importantly phylogenetics, is becoming an important and weighted factor in defining species. In particular the use of mitochondrial DNA. You see this used in genealogical tests. mtDNA differs from nuclear DNA in that it is only passed on maternally - so no mixing of DNA sequences occurs as with nuclear DNA that gets 1/2 from the male and 1/2 from female. So it is extremely useful in determining the lineage of an animal and identifying the species it is related to. However, since it is also slow mutating, other considerations must be used to differentiate between many closely related species. So morphological, physiological, geographic and behavioral differences then come into consideration.

    Bottom line - it is not exact and often debated. What is "different enough" is subjective.
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  6. Anyfoot

    Anyfoot Well-Known Member

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  7. Markw84

    Markw84 Well-Known Member 5 Year Member

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    Yes, that is the current listing of all species. That is a great reference. All the turtle and tortoise species currently recognized along with range map and picture of each one. The PDF is free. You can also order a hardcover book of it.
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  8. Will

    Will Well-Known Member 5 Year Member

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    There are what are called lumpers (typically not recognizing subspecies or to some extent different species) and then splitters who will find subspecies under every bush. Padloppers in RSA are a good example. Northern speckled padloppers were consider subspecies from southern speckled padloppers because they looked so different. Someone did a genetic look-see and found they were genetically not very distinguished from each other at all. It would seem the color difference is based on the granite they hide in, so the geographic line between the two 'subspecies' is very nearly also a line between two types of granite. Subspecies is very fuzzy.

    As it's people who are making these rules up, to say subspecies are nearer in time to each other would be a simplification, but not wrong.
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  9. Alaskamike

    Alaskamike Well-Known Member

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    I find this information so interesting. Glad we have some scientists on this site to clarify difficult issues. Always been intrigued with evolutionary biology & the emergence of distinct species.

    Within the turtle/ tortoise realm, it is interesting that Leopards & Sulcata can breed. This indicates to me that their common ancestors were very recent ( in evolutionary terms ) yet they look very different.

    I wonder how many other different tortoises can successfully cross breed. Only heard of the
    “ Leprocatas” but are there others ? And if so , would the offspring be infertile like a mule ?

    Was also taught in school ( eons ago ) that species were differentiated by not being able to breed. Apparently now it’s more subtle than that.
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  10. Anyfoot

    Anyfoot Well-Known Member

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    It's a very interesting subject. One I'm going to have to sit down and study when time allows. I'm a bit busy at the moment. I'm going to get the book version of the 2017 Chelonian species so I can read it in bed each night and start from there.
    Although I personally am not interested in x breeding any species I've often wondered where the line is drawn for 2 species not being sexually compatible. More so, Is there a line.

    I think I've seen on here:-
    radiated x redfoot
    Yellowfoot x redfoot
    Redfoot x sulcata
    Leopard x sulcata.
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  11. Will

    Will Well-Known Member 5 Year Member

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    I found in a paper published somewhere, and cited here on TFO somewhere, that there is indeed a place of mutual gross territory for sulcata and leopards where they do not breed based on morphology inspection. The 'artificial opportunity' provided in captivity does not indicate too much.

    Reproductive compatibility is an odd thing. Sometimes what might be thought of as hornyness runs the individual past the 'handshake' and to proceed with mating. Much like when females mate other females or males, and males other males and females. Only one of those actually works. I would suggest that this is what happens with the the "tortoise Frankenstein breeders" get results. Each and every A$$ hat one of them. They are often attractive to look at but ugly to think about.
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  12. Markw84

    Markw84 Well-Known Member 5 Year Member

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    It is true the common standard for describing a different species is the ability to produce fertile offspring. But that has been generally expanded into the understanding of the "likelihood" of breeding. Factors such as geographic separation, mating ritual differences that developed, "attractiveness" of the prospective mate (coloration, head striping, pheromone attraction) etc, etc. have all now become considerations.

    Since in order for an organism to reproduce, the chromosomes must be of the same number and sequence to match up and provide the genetic map that creates a successful embryo and animal. As populations experience mutations to the chromosome (which is relatively common) those subtle mutations can exist in a population. This mutation would cause a mismatch in the gene/chromosome alignment and It becomes hard for the member that has that mutation to produce fertile offspring sometimes. But in those cases, it that individual mates with another member of the population that is also now carrying that mutation, there is again high fertility and the offspring will carry on that mutation. If that is occurring in an isolated population, this trait could eventually become the dominate and more successful breeders and we have a new species emerging.

    So, now there are considerations of this that are not simply genetic, but also geographic isolation that makes mating impossible in nature. Or new behavioral mating rituals that makes mating not occur in nature any more. Those animals can still carry compatible chromosomes, yet do not breed in nature. Scientists may agree there is now enough of a total NATURAL breeding barrier to establish a new species. However, in captivity, if introduced 'artificially' they can breed successfully. In most cases there has been enough of a mutation in the order of chromosome alignment where fertility is greatly reduced, but it can happen. The resulting offspring would normally be infertile as they are genetically not compatible to another possible mate they could come in contact with. HOWEVER - if they happen to be introduced to another animal that has a similar genetic arrangement (similar mutation) they could, on rare instances, then produce a viable offspring. So we can have the very rare mule produce a viable offspring.
  13. Anyfoot

    Anyfoot Well-Known Member

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    Boom. That's me entertained for s while :D
    image.jpg
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