Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Biological diversity and Taxonomy

  1. Nov 17, 2004 #1

    iansmith

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    For bacterial species, it is hypothesised that only 1% of the species have been identified. Fewer species have been isolated are culturable. Most bacterial species are not culturable. Also you to include all other unicellular organism which includes, archea, some species of fungi, and protozoan. Also, it is hypothesized that virtually all insects have an bacterial endosymbionts.

    The living is more unicellular than multicellular.
     
  2. jcsd
  3. Nov 19, 2004 #2

    Phobos

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    ryokan - I'll see if I can find some more statistics for you. For now, a quick Google search says there are about 900,000 species of insects (http://www.encyclopedia.com/html/section/insect_InsectSpecies.asp) and there are believed to be around 3,000,000 species of bacteria (http://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/m0007824.html).

    Bacterial populations certainly outnumber everything else! (e.g., there can be as many as 2.5 billion bacteria in one gram of fertile soil...http://www.encyclopedia.com/html/b1/bacteria.asp)

    You may be interested to read Stephen Jay Gould's book "Full House" on this subject.
     
  4. Nov 20, 2004 #3
    Phobos, thank you for your interesting links. But my doubts remain.
    First, in one of your links I read: "Only 4,000 species of bacteria are known (1998), although bacteriologists believe that around 3 million species may actually exist" . That is a great numerical difference (three magnitude orders)
    On the other hand, it is difficult to make a comparison because different concepts are being used for bacteria and metazoans.

    Bacterial systematics has not yet reached a consensus for defining the species (Annual Review of Microbiology 2002;56:457-487)

    I believe that a phylogenetic approach is being used in bacteria. Following a report in the International Journal of Systematic Bacteriology 1987;37:463-464 a bacterial species is defined as a group of strains (including the type strain) sharing 70% or greater DNA-DNA relatedness with 5 degrees C or less difference of melting temperature (Delta Tm).

    Sex has an important role in the definition of species in insects.
    It is possible that, whereas an unified concept of species don't be in use, we cannot stablish if insect's diversity is greater than bacterial variety.
     
  5. Nov 20, 2004 #4

    iansmith

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    As I said before, only a small percentage of the bacteria are cultivable and those are usually the one that are associated with disease in farms animals and human. One of the lab in my old department was looking at the bacterial community of artic soil based on 16 rRNA. They more often identify archea and bacteria that have not been characterized. The a small portion of the bacterial community was identified.

    alot of the study on unculturable bacteria is based on DNA isolated from the environment and Winogradsky colums and its derivative.

    Have you read the paper?

    Just out of the abstract

    http://www.ncbi.nlm.nih.gov/entrez/...ve&db=pubmed&dopt=Abstract&list_uids=12142474

    So the author is suggesting that bacterial diversity is greater than that of the multicellular world.

    http://proquest.umi.com.ezproxy.lib...&VName=PQD&TS=1100979044&clientId=15814&aid=1

    That is an old report and does hold true most of the time nowadays. This concept of species is starting to lose grip on classification because new techniques and test are being developped and the scientific community is aging and new blood is coming in.

    The problem here might that the role of sex might not be of concept to identify a species. Arthropoda as a group probably one of the greatest diversity in the animal kingdom. I also agree that it is hard to compare diversity when you are not using the same concept of classification. However, the microbial world has colononized every possible niche on earths which includes arthropoda digestive system. It is hypotheised that every arthropoda digestive system have at least a unique bacterial, archeal or protozan specie. Some of which have been sequenced.
     
  6. Nov 20, 2004 #5
    What would be a good, universal, definition of species ? I don't know if there is already such definition.
    If DNA or RNA homologies are an essential component of definition, it would be possible that one insect species, for example, were also rather a genus. And, could we talk on species with reference to cells in a multicellular organism? Of course, in this case, genotype is the same, but gene expression differ. Furthermore, there are changes in genotype by somatic mutations in cancer. Make it sense talk about species of cancerous cells?
     
  7. Nov 22, 2004 #6

    iansmith

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    As far as I know, there no universal definition for a species but alot of reoganization are being done. Highly conserved genes and morphology are being used to classified insect species. I personnaly think that genetic and morphology is the way to go. Sexual behavior is sometimes missleading. If you used genetic, then you use the same level for bacteria. Although, some bacterial species have been seperated for medical purpose. The best example is Shigella and E. coli. They are both the same species but cause distinctive clinical symptomes. I personally think it's silly.

    Different gene expression in bacteria only results in different strain name or group rather than a new species. For cancer, the highly conserved genotype is unchange, it is only the genes regulating cell division that usually mutates and are usually not used in systematics. You can also tell the site of origin of the cancer. There is classification for cancer based on the site of origin but it is not a new specie.
     
  8. Nov 23, 2004 #7
    With quantitative or qualitative criteria?
    What would be important: % of homology in genomes or rather homology in selected regions?
    But sometimes changes in cancerous cells are enough important to be seen at cytological level (structural and numeric chromosomal aberrations).
    Site of origin is only one characteristic in one cancer. Histological differentiation grade is also important and clinically, as you know, criteria as TNM are very useful to make the prognosis in a lot of cancers. Now, the differentiation in expression patterns by means of microarrays is a promising way to make a best prognosis and election of therapy.
    In some form, we can talk from different species of cancer, even for a common anatomic origin, although in this case, the concept species be unrelated to the traditional concept.
     
  9. Nov 25, 2004 #8

    iansmith

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    We were having a discussion in other thread about complexity, which I split and merge with this one, and started to discuss diversity.

    We are trying to answer these questions

    I do we measure biological diversity? What should we used to measure biological diversity?

    I do we classify species and I do we group them?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Biological diversity and Taxonomy
  1. Taxonomy question (Replies: 1)

  2. Shell Taxonomy info? (Replies: 1)

  3. Genetic Diversity (Replies: 3)

Loading...