Sharks Hybridize Due To Climate Change

[Tim Smith]

The media has rather botched this story and as usual doesn't seem able to accurately report about evolution, but it's an interesting example of range expansions due to differences in water temperature.

Most of our sunfish and bass hybridize (most notoriously spotted bass and smallmouth). We can expect to see more and more of this over time.

http://www.southernfriedscience.com/?p=12398

[Justin Spencer]

Next thing you know a new super race of sharks will be following planes across oceans to terrorize those out to destroy them! The first step in a rise of the animals!

[Tim Smith]

Next thing you know a new super race of sharks will be following planes across oceans to terrorize those out to destroy them! The first step in a rise of the animals!

Yes, the media has done quite a bit of silliness on this story.

It's a fish.

[Wayne SW/MO]

Given the fact that the two were compared through DNA and considering that the science is new it raise questions in my mind. If they are backcrossing it may have been going on for a long while before DNA. If the water temp is the reason, due to global warming of course, wasn't there always a demarcation line somewhere? How would the movement of that line between them cause sudden hybridism? Didn't it always exists somewhere?

[Tim Smith]

Given the fact that the two were compared through DNA and considering that the science is new it raise questions in my mind. If they are backcrossing it may have been going on for a long while before DNA. If the water temp is the reason, due to global warming of course, wasn't there always a demarcation line somewhere? How would the movement of that line between them cause sudden hybridism? Didn't it always exists somewhere?

The link you're thinking about probably exists in an earlier species. Neither of these species are the same as their ancestor and they've been changing over time based on local selection pressures and genetic drift.

Apparently black bass like smallmouth and spotted and largemouth sometimes pass chunks of DNA back and forth to each other this way all the time. It could result in new bass species at some point in the future...or perhaps it already has.

[Wayne SW/MO]

The article says that the sharks looked normal but that they had genetic markers of another. The problem is that if the discovery was from a "rourine" venture, how do they know it's even a new occurrence? How do they know it's not an ongoing historical occurrence in the overlap area? How long have they been doing routine DNA in this area?

[Outside Bend]

The article says that the sharks looked normal but that they had genetic markers of another. The problem is that if the discovery was from a "rourine" venture, how do they know it's even a new occurrence? How do they know it's not an ongoing historical occurrence in the overlap area? How long have they been doing routine DNA in this area?

I'm trying hard to remember my undergraduate genetics courses, but it seems like if you have the DNA, you can determine when novel genetic material is introduced into an organism. I know they've traced human migration pathways based on the genetic material contained in individuals, and I assume it'd be possible to trace shark pedigree based on the same principles- determining whom bred with whom, and when.

It's probably a really bad explanation, and I'm not even sure it's what they did. Just bouncing ideas out there.

[Tim Smith]

I'm trying hard to remember my undergraduate genetics courses, but it seems like if you have the DNA, you can determine when novel genetic material is introduced into an organism. I know they've traced human migration pathways based on the genetic material contained in individuals, and I assume it'd be possible to trace shark pedigree based on the same principles- determining whom bred with whom, and when.

It's probably a really bad explanation, and I'm not even sure it's what they did. Just bouncing ideas out there.

What you're thinking about is, I think, a "genetic clock" that tracks the accumulation of random mutations and assuming that occurs at a constant rate over time. I'm not sure these scientists would have done this analysis in this case, but it might be good to know.

In this case there are now large numbers of hybrids where there were none (at a detectable level) there before. This occurred in conjunction with a range expansion allowed by changes in water temperature. It's probably possible that low level hybridization occurred in the past, but now it has taken hold and there's a definite intermediate form that is reproducing and constitues something "new".

It's probably worth pointing out that this kind of thing is much more likely among fish which as a group regularly produce semi-fertile hybrids among closely related species.

[Tim Smith]

...and also this quote from the southernfriedscience link might be of some use.

Some of these hybrids were “F1″, meaning that one parents was a common blacktip and one was an Australian blacktip. Others were “B+”(backcrossed), which means that one parent was a common blacktip/Australian blacktip hybrid, and the other was a “purebreed” of one of those two species. According to the study’s lead author, Dr. Jess Morgan of the University of Queensland, ”our genetic marker tells us that these hybrids are ‘at least’ F1, and that these animals are reproductively viable and can produce an F2…the hybrids may be generations past F2 but the existing genetic markers can’t distinguish how many generations past the second cross have occurred.”

Genetic evidence and morphological characters have long supported the hypothesis that Australian and common blacktips are closely related, but distinct, species. They have detectable differences in their mitochondrial DNA, length at birth, length at reproductive maturity, and number of vertebrae. According Dr. Morgan, “The two blacktip species are very closely related (termed sister species) and this is probably why their hybridization has been successful. Over time the genes of species diverge away from each other due to random mutations.”

Again, it's the large number of hybrids that have appeared that provide the evidence for something recent.

...although it's also probably worth mentioning that in sunfish, F1 hybrids can be fertile but the F2s show lower levels of effective fertility so it's not 100% sure that these hybrid sharks will persist. What they are likely to do is introduce the southern species genes into the blacktip population at large.

[Wayne SW/MO]

I'm not trying to be argumentative, I'm just trying to understand how they establish whether or not this a phenomenon.

I'm a skeptic first class in the theory of mans contribution to global warming, but not in the change itself. I do fear we're so egotistical that we believe if we're the reason it is happening we can exert some control. How much we contributed to the landslide might be questionable, but we might be better off preparing billions of creatures for the bottom. We don't seem to have much more than a feable attempt to stop the trickle of our involvement.