delticola or no del...
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delticola or no delticola?

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Let's discuss the validity of southern black-knobbed map turtles (sawbacks) aka delta map turtles (G. n. delticola). So, in  2014 Joshua Ennen and colleagues published a paper called "Clinal variation or validation of a subspecies? A case study of the Graptemys nigrinoda complex (Testudines: Emydidae)".  This is a really good controversial topic (the G. n. delticola debate) in the map turtle world that has been going on since this subspecies was described in 1969 by Folkerts and Mount. For a least a little while, there was some rebuttals going back and forth in journals over the validity of this subspecies. This is how scientists "duke it out", they write rebuttals in a peer-reviewed journals.

  Freeman (1970) basically said that G. n delticola should not be considered a subspecies a year after it was described by Folkerts and Mount (1969). The same year that the rebuttal came out, Folkerts and Mount made their own rebuttal to the rebuttal defending their claim. It appears that Folkerts and Mount won that argument, but over the next decades many people still discussed/questioned it, especially after the subspecies concept became less popular and the term "clinal variation" started to gain steam and erase a lot of formerly recognized subspecies due to advances in DNA studies.

   Now with Ennen et al. (2014), this subspecies has been sunk again and has been removed from most peer-reviewed Common Name lists, such as SSAR and new books about turtles. Several mitochondrial DNA studies performed before the Ennen et al. (2014) study by Lamb (1994) and Stephens and Wiens (2003) did not show any difference  between the two subspecies either. However, even after Ennen's paper seemed to be accepted by the scientific community, along comes Guyer, Bailey, and Mount's Turtles of Alabama book in 2015. Long behold, they keep (resurrect) the name G. n. delticola a year after Ennen et al. sunk it. Their explanation for keeping the name alive was "we expect subspecies to exhibit the levels of gene flow coupled with distinctive morphology and coloration documented in their study." Leaving the science out of it for now, there are a few connections that should be obvious.

1.George Folkerts and Robert Mount were professors at Auburn University. Mount is a Professor Emeritus at Auburn University and wrote the Reptiles and Amphibians of Alabama, which is a great, great book.

2. Howard Freeman was from Rutgers University.

3. Josh Ennen graduated from University of Southern Mississippi State.

4. Craig Guyer is a professor at Auburn University

5. Mark Bailey went to Auburn University

My personal opinion on this is that it looks like Auburn does not want to give up the designation of G. n. delticola no matter what. I have had a hard-time giving up subspecies myself over the past few decades. I learned the names of all these and more subspecies when I was young. The reason I like subspecies, is that it tells you something about the animal immediately. If someone said I saw a G. nigrinoda nesting yesterday, I would think..that could be in any part of the Alabama river system. If they said, I saw a G. n. delticola nesting yesterday, chances are that animal is in the very southern part of Alabama, likely in the Tensaw basin. Subspecies gives you a little bit of locality information, as well as some morphological information as to how the animal looks. However, the trend, for at least a couple decades, has been to get away from naming subspecies and call variations in a species clinal variations and many get elevated to species status. There is currently only two recognized subspecies of map turtle, but there were six not too long ago.

As far as the differences between the former "northern black-knobbed map turtle and the southern black-knobbed map turtle". If you are not in the "intergrade zone" or blending zone where the two clinal variations or "subspecies" overlap, the two forms look quite different phenotypically (visually).

Here are the obvious traits simplified.

   "G. n . nigrinoda"                             

1. no plastral pattern                           

2.grayish skin color                            

3.well defined postorbital mark      

4.lower domed carapace                   

5.females smaller                             

6.Found in many counties north of the two most southern counties   

"G. n. delticola"

1. large plastral pattern

2. black skin color

3. reduced postorbital mark

4. higher domed carapace

5. females larger

6. Mobile and Baldwin counties only

*There is a large section of the Alabama and Tombigbee rivers north of Mobile and Baldwin counties where there is a blending of the two forms as you approach or depart each clinal variation or subspecies. The best term for this is intergrade zone.

What are your thoughts on this?



This topic was modified 5 years ago 5 times by graptemys2