Does Regional Variability play a HUGE roll in evolutionary development?

[Miles]

I noticed something the other day..

All the rays with 'extended long tails' come from the Northwest part of South America..

Tiger, Flower, Reticulata, and Antenna rays all come from the same few regions..

Leopoldi, Henlei, Itaituba, and Pearl all come from the same few regions..

and many of the brown rays (Motoro, Castexi, Orb/Humerosa, etc), although found in almost all locations, are most concentrated in the western/southwestern regions..


It's also interesting conversation to think that all Motoros are different species (based on teeth, denticles, body shape, etc) but have actually evolved their patterns to best fit their ecosystem - ie: The common motoro pattern has the most benefit of all stingray patterns, so every species eventually will morph into a Motoro..

If you crossed a WILD Motoro with a Leopoldi and it produced 100% Leopoldi offspring.. wouldn't you be AMAZED? What if your 'WILD' Motoro actually shared the physical characteristics of a Leopoldi, but has morphed through hybridization and natural selection to display a Motoro type pattern (ie: pearl rays) .. crazy stuff.. Frank and a few others have been dropping 'hints' at this theory for the Synposium..



Some interesting discussion points..

Anyone else have thoughts on this sort of stuff?

 

[Miles]

I was also thinking the long tails could have something to do with how fast, how often, and what direction the rivers flow in that region, compared to other regions..

Perhaps the 'long tailed' rays use their tails to navigate through faster flowing streams in those locations, much like a Kite uses it's tail to help aid in stability.. just like I would assume a Tigrinum or Juruense uses its long streamers for the same reasons. (Also to detect prey)..

Rays with 'bladed' tails perhaps come from slower moving waters, or as the natives call them, Cochas, which are basically like tidepools and coves along large riverways.. Perhaps the bladed tails in these rays act more as a 'rudder' like a Helicopter, allowing them to navigate left to right more swiftly in slower moving water..

It's also interesting to think that most black rays come from slower moving water, where it is more likely to actually be 'blackwater'.. perhaps the black coloration is an adaptation to environment..

 

[Miles]

Heres a few interesting pix for topic of discussion..

a Leopoldi hanging out in a 'Cochas'.. slow moving water..

and an aerial view of when Black water meets White Water..

Perhaps 'sensitive' rays don't ever leave their black water areas, while 'hardy' rays like Motoros move in and out due to food restrictions, breeding, etc.. Also proves that not all South American fish and/or Stingrays come from super soft water and likely go through major pH fluctuations quite regularly.

 

[Hawkfish3.0]

That is a very interesting observation, Miles. Although in terms of evolution, this would have taken thousands of years to take place. It makes sense though. You make a strong case for this.

 

[rayman]

All the rays with 'extended long tails' come from the Northwest part of South America..

Plesiotrygon iwamae has a very large distribution, from Peru to the Baja de Marajo (Belem).

 

[Miles]

Plesiotrygon iwamae has a very large distribution, from Peru to the Baja de Marajo (Belem).

Ah I was under the impression they mainly came from Peru, Colombia, and Venezuala..

I find it interesting that the AquaLog notes a 'black tailed antenna' ray which maxes out at a much smaller size (15"?) and looks AMAZINGLY similar to a reticulated ray..



Andreas, do have any insight as to why the P. Iwamae would have the long tail, and or what kind of functionality it serves and if the river systems might play a roll in this.. ?

 

[Miles]

That is a very interesting observation, Miles. Although in terms of evolution, this would have taken thousands of years to take place. It makes sense though. You make a strong case for this.

Rather then evolution, let's say Adaptation.. Keep in mind that Stingrays, being livebearing and having a fairly short gestation period, have really 'jumped' up the evolutionary scale with their adaptation to freshwater and how their internal organs have made that adaptation as well.. and yeah.. I am thinking in terms of hundreds of thousands of years.

I just want to better understand why each Potamotrygon (and others) are the way they are and if the regionality/rivers play a big roll in their physical appearance, while at the same time they could all be distinctly different species (while still sharing the same patterns)..

 

[Gr8KarmaSF]

Nice read with some thought provoking ideas...

I especially like your theory on the Motorros ability to move back and forth from white to black water! Any ideas what the difference is in food availabiltyfor rays? Is there only specific types of food in any given type of water?

 

[rayman]

Hi Miles,

the distribution of freshwater rays, where theyr ancestor came from and how the species developed is very difficult.

There is some scientific work regarding that topic:

Brooks, D. R. 1995. Neotropical freshwater stingrays and their parasites: a tale of an ocean and a river long ago.
In: Oetinger, M. I. and G.D. Zorzi (eds.). The Biology of Freshwater Elasmobranch. Journal of Aquariculture and Aquatic Sciences 7:52-61.

Marques, F.P.L., 2000. Evolution of neotropical freshwater stingrays and their parasites: taking into account space and time.
University of Toronto (Canada), 325pp

Lovejoy, N.R., 1997. Stingrays, parasites, and neotropical biogeography: a closer look at Brooks et al.‘s hypothesis concerning the origins of neotropical freshwater rays (Potamotrygonidae).
Systematic Biology 46: 218-230.

Without the insight in these hypothesis all we do is pure speculation.

 

[rayman]

I find it interesting that the AquaLog notes a 'black tailed antenna' ray which maxes out at a much smaller size (15"?) and looks AMAZINGLY similar to a reticulated ray..

The largest "blacktailed antennas" in captivity have already a size of 14", maybe they max out at 16". And with the very long tail they look very different compared with reticulatus. But the pattern of juvenils is similar to reti.

Andreas, do have any insight as to why the P. Iwamae would have the long tail, and or what kind of functionality it serves and if the river systems might play a roll in this.. ?

Don't know exactly, but these are very active rays, often free swimming. You can compare them a bit with the eagle rays, they are free swimming and have long tails too.