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    DNA Testing Enough to Separate Species? Not for Yellow and Scopas Tangs

    Are you a lumper or a splitter? In ichthyology this question is becoming even more important as meristics go head to head with DNA testing. Meristics are quantifiable measure that ichthyologists use to identify fish. Some measures include dorsal spines, fins, scales, etc. There is even a meristic formula that identifies fish based on these […]

    Yellow Tang 360

    Are you a lumper or a splitter? In ichthyology this question is becoming even more important as meristics go head to head with DNA testing. Meristics are quantifiable measure that ichthyologists use to identify fish. Some measures include dorsal spines, fins, scales, etc. There is even a meristic formula that identifies fish based on these features. For example DXI, which means 11 dorsal spines as often exhibited on Amphiprion ocellaris.

    With the advent of DNA testing, the classification of species is becoming even more convoluted. In regards to hybrids, skeptics will often pipe in with… it’s just a variant until proven with DNA evidence. Keep in mind it is unlikely that DNA evidence was used to identify the suspected parents of the hybrid! The question of what really is (insert species name) is becoming a real question. Recently a study by Dirk Steinke at the Canadian Centre for DNA Barcoding lead a research team on examining the DNA of marine ornamental fish. Their findings were recently released in a study entitled  Barcoding Nemo: DNA-Based Identifications for the Ornamental Fish Trade.

    Spanning a period of three years, over 1,600 specimens were obtained via losses sustained by fish importers. In this study they were able to separate the genetics of most fish to classify them as separate species. However, the closer related two fish are… the more difficult this becomes. Such is the case with the Yellow Tang (Zebrasome flavescens) and the Scopas Tang (Zebrasoma scopas). With the DNA testing being used these two fish were indistinguishable… leaving meristics and obvious color differences to be the deciding factors.

    This is not too surprising given past reasearch, such as the fairly recent work of Bowen on the three Atlantic Centropyge species. The drastically different looking Centropyge argi, Centropyge resplendens and Centropyge aurantonotus are all indistinguishable by DNA testing.

    Is physical appearance and structure enough to differentiate species? Either way this is exciting for fish geeks. DNA testing will drastically change the way we identify and classify animals… these types of questions are just the beginning. Ask yourself this– at what point does a fish become a separate species?

    Hat tip to PFK. See more on Atlantic Centropyges:

    Bowen, BW. Shallow mtDNA coalescence in Atlantic pygmy angelfishes (genus Centropyge) indicates a recent invasion from the Indian Ocean. Hawaii Institute of Marine Biology. Journal of Heredity. Jan-Feb;97(1):1-12. Epub 2006 Jan 4.

    [cover photo : flickr : e. brian]

    2 Comments

    1. September 1, 2009 at 12:30 PM | Permalink

      “Such is the case with the Yellow Tang (Zebrasome flavescens) and the Scopas Tang (Zebrasoma scopas).”

      I assume this is answered in the paper or some other reference above my head, but I assume it’s not really that those *are* the same species, just with visually distinct features? Meaning, that these 2 “species” could interbreed, they just look different.

    2. September 2, 2009 at 4:28 PM | Permalink

      @ Richie

      To be sure, species definitions are arbitrarily assigned denominations. You can’t make clean slices between animals that are pseudo-transitional (I know, messy term, but I haven’t had my coffee yet…) forms of one another.

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