No, scientist know for a fact that freshwater rays evolved from saltwater rays... They just don't know how!!
On the Origins of Freshwater Amazonian Stingrays
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No, scientist know for a fact that freshwater rays evolved from saltwater rays... They just don't know how!!
Pretty sure that freshwater rays have a highly reduced if not absent rectal gland and do not retain urea the way that marine sharks and rays do (why they STINK so terribly when they die!).
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http://www.biolbull.org/content/154/3/508.abstract
Looks like they have a rectal gland that is vestigial.
Looks like they have a rectal gland that is vestigial.
The Amazonian stingrays are a favorite of mine. Their patterns vary greatly, even within individual species. A Motoro ray from one area of the Amazon can have a background color and pattern that is strikingly different. This is due to genetic drift. It's the same reason that we find equatorial human populations with a darker skin tone than in temperate regions. It's an evolutionary advantage. The same can be said of Motoro rays with varying patterns. While they are still the same species, they have adapted to their environment. The coloration of the markings as well as the background color is a direct product of the coloration of their environment. Their color pattern allows for better camouflage within the region of the Amazon in which they live.
Even more interesting is how stingrays came to live in the Amazon. There are two competing hypotheses. The first of these is freshwater invasion, which occurs when marine species venture into fresh water, probably because there is an abundance of food at the mouth of a river. An individual that is more tolerant of freshwater is more likely to survive and reproduce because they have more options available to them for food sources. Eventually, over a great period of time, the marine population becomes more tolerant of fresh water (euryhaline) and can spend a greater amount of time, if not all of their time, in fresh water. In the latter case, the species may revert to intolerance of differing salinity and become stenohaline, just as freshwater Amazonian stingrays happen to be.
The second hypothesis is the entrapment of marine rays by the uplift of the Andes mountains. As time passed bodies of water on the western coast of South America slowly became cut off from the ocean. This rise reversed the flow of the Amazon river (it used to travel east to west). As the saltwater flowed out of the bodies of water in which the rays were trapped, freshwater flowed in through run-off. This occurred at a pace that was slow enough (over many generations) to allow the marine rays to adapt to their changing environment.
Either circumstance presents us with an amazing answer to a bewildering question. Such is the beauty of life.
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A few things about your post. First, genetic drift is genetic variation which occurs in the absence of selection. This is however not the case for the variation of humans with respect to skin color. There is an obvious advantage of lighter skin color as you move away from equatorial regions and begin to cover your skin with clothing. UV light is needed to convert vitamin K into vitamin D which is necessary for calcification of bones. If most of your skin is covered by clothing and you have dark pigment on the exposed areas not letting in the small amount of necessary UV to do the conversion, your bones become weaker and you are selected against. The variation in coloration of rays could be due to selection or due to genetic drift, there is really no compelling evidence either way as of yet. Generally these rays are vastly understudied as a group.
I appreciate the post, but what is your motivation here? You are correct that there are two valid scientific hypotheses, but what you do not mention is that it is very likely that both are functionally correct. Keep in mind that the straits of Panama had not yet formed until about a million years ago. Therefore the founding population of rays was likely an ancestor of the ray species which exist both in the carribean as well as the eastern tropical pacific system.
Again, what is your motivation for this post? Are you trying to spark a true scientific debate with people who are not qualified to discuss this? Or are you trying to get acknowledgement of you superb intelligence on the topic? Fact of the matter is this is a topic that can not be discussed without backgrounds well above what most of us here have. That is not to say that there are many people here who know substantially more about rays then those caring for them at public aquariums around the world. We just aren't people qualified to have this type of debate.
To answer another question on this thread. Evidence shows that cartilagenous fish (sharks, rays, skates, ratfish) as a group evolved in the marine environment and few have been able to reinvade fresh water habitats. The evidence shows that bony fish however seem to have evolved in fresh water habitats and then secondarily reinvaded marine habitats.
Don't get me wrong, I love this type of debate when appropriate. But this type of post usually means someone is fishing for a compliment. If you need someone to tell you how smart you are then your really not that smart. Smart people don't need others to tell them how smart they are, they know already.
Even more interesting is how stingrays came to live in the Amazon. There are two competing hypotheses. The first of these is freshwater invasion, which occurs when marine species venture into fresh water, probably because there is an abundance of food at the mouth of a river. An individual that is more tolerant of freshwater is more likely to survive and reproduce because they have more options available to them for food sources. Eventually, over a great period of time, the marine population becomes more tolerant of fresh water (euryhaline) and can spend a greater amount of time, if not all of their time, in fresh water. In the latter case, the species may revert to intolerance of differing salinity and become stenohaline, just as freshwater Amazonian stingrays happen to be.
The second hypothesis is the entrapment of marine rays by the uplift of the Andes mountains. As time passed bodies of water on the western coast of South America slowly became cut off from the ocean. This rise reversed the flow of the Amazon river (it used to travel east to west). As the saltwater flowed out of the bodies of water in which the rays were trapped, freshwater flowed in through run-off. This occurred at a pace that was slow enough (over many generations) to allow the marine rays to adapt to their changing environment.
Either circumstance presents us with an amazing answer to a bewildering question. Such is the beauty of life.
View attachment 751559[/QUOTE]
A few things about your post. First, genetic drift is genetic variation which occurs in the absence of selection. This is however not the case for the variation of humans with respect to skin color. There is an obvious advantage of lighter skin color as you move away from equatorial regions and begin to cover your skin with clothing. UV light is needed to convert vitamin K into vitamin D which is necessary for calcification of bones. If most of your skin is covered by clothing and you have dark pigment on the exposed areas not letting in the small amount of necessary UV to do the conversion, your bones become weaker and you are selected against. The variation in coloration of rays could be due to selection or due to genetic drift, there is really no compelling evidence either way as of yet. Generally these rays are vastly understudied as a group.
I appreciate the post, but what is your motivation here? You are correct that there are two valid scientific hypotheses, but what you do not mention is that it is very likely that both are functionally correct. Keep in mind that the straits of Panama had not yet formed until about a million years ago. Therefore the founding population of rays was likely an ancestor of the ray species which exist both in the carribean as well as the eastern tropical pacific system.
Again, what is your motivation for this post? Are you trying to spark a true scientific debate with people who are not qualified to discuss this? Or are you trying to get acknowledgement of you superb intelligence on the topic? Fact of the matter is this is a topic that can not be discussed without backgrounds well above what most of us here have. That is not to say that there are many people here who know substantially more about rays then those caring for them at public aquariums around the world. We just aren't people qualified to have this type of debate.
To answer another question on this thread. Evidence shows that cartilagenous fish (sharks, rays, skates, ratfish) as a group evolved in the marine environment and few have been able to reinvade fresh water habitats. The evidence shows that bony fish however seem to have evolved in fresh water habitats and then secondarily reinvaded marine habitats.
Don't get me wrong, I love this type of debate when appropriate. But this type of post usually means someone is fishing for a compliment. If you need someone to tell you how smart you are then your really not that smart. Smart people don't need others to tell them how smart they are, they know already.
Fact of the matter is this is a topic that can not be discussed without backgrounds well above what most of us here have. That is not to say that there are many people here who know substantially more about rays then those caring for them at public aquariums around the world. We just aren't people qualified to have this type of debate.
ok, so how Do we invite the qualified poeple into this ?
ok, so how Do we invite the qualified poeple into this ?
The problem is that many of them may not want to speak with us about this. There is a part of that world that really looks down on our world. I can say this because I am in both. I have been a hobbyist now for over 20 years, however I have worked at two major aquariums, and have both a BS and MS in Zoology. I will be returning to the world of academia in the fall to pursue a PhD in Zoology.
The scientific community as a whole sees us as seperate from them. unfortunately the pet trade is seen by most as completely negative, however most of us know that a great many advancements in the successful husbandry and reproduction of many species occurs first at the hobbyist level. Why? It is because we are passionate about the animals we keep and we want to do the best for them. Not to mention it is to our advantage finacially speaking to successfully reproduce these high end species. It is after all one of the few ways to make some money in this hobby. Not that we will do anything but reinvest it into the hobby anways, but at least we can get new tanks without our wives asking us what the latest charge on the credit card is all about.
Most of the hard science has been done so far in Brazil. The leading researchers at this time seem to be Karin H. Fehlauer-Ale and D.Timothy J. Littlewood who both work at Center for Marine Biology at the University of São Paulo. I will contact them to see if they are interested in joining our group and imparting some of their knowledge, but I wouldn't get my hopes up if I were you.
The scientific community as a whole sees us as seperate from them. unfortunately the pet trade is seen by most as completely negative, however most of us know that a great many advancements in the successful husbandry and reproduction of many species occurs first at the hobbyist level. Why? It is because we are passionate about the animals we keep and we want to do the best for them. Not to mention it is to our advantage finacially speaking to successfully reproduce these high end species. It is after all one of the few ways to make some money in this hobby. Not that we will do anything but reinvest it into the hobby anways, but at least we can get new tanks without our wives asking us what the latest charge on the credit card is all about.
Most of the hard science has been done so far in Brazil. The leading researchers at this time seem to be Karin H. Fehlauer-Ale and D.Timothy J. Littlewood who both work at Center for Marine Biology at the University of São Paulo. I will contact them to see if they are interested in joining our group and imparting some of their knowledge, but I wouldn't get my hopes up if I were you.
I can only speak for myself. I would welcome any knowledge they could or would share with the forum.
Good read
If rays have taken so many years to evolve the the least we should do is provide them with some kind of substrate without substrate who knows what they would have evolved into in the wild
They may have just climbed out of the water and lived on the land who knows
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If rays have taken so many years to evolve the the least we should do is provide them with some kind of substrate without substrate who knows what they would have evolved into in the wild
They may have just climbed out of the water and lived on the land who knows
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Substrate or no substrate is always a debate. The basic idea here is do you try to mimic the environment or do you create the most ideal situation for the organism to survive? As a trained zoologist I will tell you that mimicing the environment directly might not be the best way to keep the animal. Lets say that fish lives in murky water tanned brown with decay or plant material like many organisms we keep from the amazon. If we put them in sediment rich water like that the chance of the system crashing because of the decomposition of this plant matter is high, thereby killing our fish. In the wild there is so much water than it doesn't affect them, the polluntants are spread out.
Fact of the matter is that not having substrate gives them less of a chance of abrasions on their soft ventral surface, and doesn't allow waste to be trapped in the tank as easily. Conversly, they don't display the searching behaviors for food. This lack of stimulation in such an intelligent group may cause stress and lead to poor health over time. It is all a balancing act. We each have our own ways and just as we are all differnt, so are our rays. One ray may thrive in one set of conditions while others stress and die.
Never think that what we do is create natural environments. Far from it. We create as ideal of conditions as possible to keep our animals alive and healthy.
Fact of the matter is that not having substrate gives them less of a chance of abrasions on their soft ventral surface, and doesn't allow waste to be trapped in the tank as easily. Conversly, they don't display the searching behaviors for food. This lack of stimulation in such an intelligent group may cause stress and lead to poor health over time. It is all a balancing act. We each have our own ways and just as we are all differnt, so are our rays. One ray may thrive in one set of conditions while others stress and die.
Never think that what we do is create natural environments. Far from it. We create as ideal of conditions as possible to keep our animals alive and healthy.
