DNA goggles

Nhu Nguyen xerantheum@gmail.com
Thu, 31 Jan 2013 23:09:07 PST
On Thu, Jan 31, 2013 at 9:22 PM, Leo A. Martin <leo@possi.org> wrote:

> So, if I threw you a box of 500 plants that morphologists said belonged to
> a number of
> different species and genera, and you chopped them up without looking at
> them to see
> their morphology, and isolated their DNA, you would be able to segregate
> them into the
> correct species and genera as determined by the morphologists?

Yep. Based on current technology (and all the resources at my disposal), I
can tell you how many individual plants there are, how many populations,
how many genera, families, order...etc. I can even tell if a plant is a
hybrid, what diseases it has, what and how many taxa of microbes live on or
within it, what beneficial fungi it is associated with. I can tell you what
it's chromosome counts are, how many functional genes it has, how the
chromosomes rearranged themselves over time, how the genes rearranged
themselves over time. Then I can infer each plant's evolutionary path and
make an educated guess as to how old the species is and more and more. And
all of this is only possible because of the many years of work botanists,
ecologists, microbiologists, and evolutionary biologists have spent
gathering knowledge. We compare what we know today to what was known

The point is especially important if you follow this example. If an alien
species invaded earth and you gave me a piece of it's skin and ask me to
sequence it's DNA and tell you want alien species it is, there is no way I
could tell you because it has never been found before. I would only label
the DNA "alien species 1". However, an alien taxonomist describes it and
gave it a name, then sequence it's DNA and deposit it in a database, then I
can match up my DNA to his, and voila, I have an identification! My point
here is that taxonomists do the base work, then others can use what they
have found. Then with DNA sometimes we discover that what the taxonomists
found isn't quite correct, so we go back and fix it. That has been the
reason for the many changes of late.

So in which cases are DNA especially useful? I will give you a few
examples. 1) You have two type specimens that carry two different names,
when you sequence them, you find out that they're pretty much the same
thing. Therefore you choose the older name as the correct name, according
to the Rule of Priorities. 2) You have a group of plants with many names
that are so difficult to tell apart from morphology so you sequence them
and find that the reason they're hard to tell apart is because they're very
similar to each other. So you decide to make them one species to make
everyone's life easier. 3) You have a group of plants with various names,
so morphologically plastic that you don't know where to make your split (in
the case of our Massonia friends), using DNA may give you a clue into where
to draw your line. It may not give you that, but it's better than going in
circles with morphology.

Botany is an old field and sequencing DNA to tell species is a relatively
new thing. But in other fields that do not have morphologically rich
characters like plants, DNA sequencing is essential and those in that field
are much more accepting. Can you imagine trying to distinguish differences
between the thousands of described bacteria species based on their three
overall shape? All you have to work with is rod, sphere, or spiral.

Dylan said it all. Despite what the public opinions are, those who study
plants by using DNA do not see morphology and DNA as conflicting, but
rather to complement each other. For those of us who delimit species using
DNA, we often go back and try to find morphological differences that can
separate out those species. The idea is that we still need to be able to
recognize the species in the field or back in the lab with a microscope.
That's why species descriptions still exist in every code of nomenclature.
The immense power of putting the correct species name on DNA allows someone
who is not an expert to quickly and correctly identify their specimens.
Instead of taking 20 years to become an expert at a genus, someone who is
trained to sequence DNA in one week can identify all of the plants. Of
course, it initially took the expert to put the correct name on the
sequence. So that is a major reason to continue training taxonomists.


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