Comments on: Hybrid Sharks Found off Australia

By: Great White

Great White — Wed, 04 Jan 2012 23:44:38 +0000

They hybridize because they´re smarter than a lot of people.

By: Nen

Nen — Wed, 04 Jan 2012 20:05:30 +0000

I couldn’t resist. I just read the whole report and here’s what I found out.

The study was inspired by anomolies in morphological and molecular data where there was overlap between the two speices of sharks. The hypothosis was that where that overlap occurs there could be hybrids. They tested this treating the obvious Australian sharks as one species, the obvious common sharks as another species, and the ones that had morphological/molecular elements of both as possible hybrids. They found that there is sufficient morph/mol AND life history evidence to support that, while the two species are similar (and later we find out that they had fertile offspring) they are distinctly different species. In addition, they find that the possible hybrid group also shares these kinds of similarities and are distinctly different from the parent species.
The DNA sequencing of 17 of the hybrid group sharks showed that they had one Australian and one common parent. The other 40 hybrids had DNA that showed that they were second generation hybrids, having either two hybrid parents or one hybrid and one “purebred” parent. Therefore, at least some of the first generation hybrids are fertile.
Despite the fertility the of hybrids, the Australian and the common are still thought to be different species based on all other evidence. The fertile hybrids can be thought of as genetic freaks.
In the conclusion of the paper, the authors mention that it is super unusual to see naturally occuring hybrids, super unusual and really cool to find fertile hybrids, and extrordinary to find a large population of them over a large area.

However, they never make the claim that these hybrids are a new species, but say only that further research is necessary.

If you think that’s not how evolution works, go back middle school.

By: MyTake

MyTake — Wed, 04 Jan 2012 20:04:59 +0000

BK Knightrider – “Well MYTAKE, it seems that you have a fundamental misunderstanding of the meaning of species and subspecies.” As I stated, the definition of species HISTORICALLY meant whether or not the offspring of two organisms would produce viable offspring. Consequently horses and donkeys were considered separate species, as they could produce offspring (mules) but the offspring could not themselves reproduce. This was problematic but generally followed in determining whether or not a new organism constituted a new species or was simply a variation of an existing species. My basic point is that arguing that the Australian and common black-tip shark as distinct species rather than subspecies of a more general group that can interbreed might be (no pun intended) specious.

By: Virgil H. Soule

Virgil H. Soule — Wed, 04 Jan 2012 19:03:01 +0000

Hybridisation in fishes apparently has a different meaning than in mammals. People have been breeding mules for centuries. Lion/tiger crosses produce ligers and tiglons. Crosses in the wild between Alaskan Brown Bears and Polar Bears have been reported. Mammal crosses are typically sterile. Mules are sterile as are the many cat crosses. The wild bear crosses are evidently sterile or a distinctly different species of bear would exist today in the Arctic. If a genetic cross produces no offspring, the progeny cannot be considered a separate species.

That’s not how evolution works. Evolution depends on variation within species. Not all Polar Bears are the same. Some will survive global warming and give rise to a new breed of polar bear adapted to live in a world without ice.

As for the Shark crosses, question is: are they fertile or are they just a dead end. If they are fertile, Australian and Common Black Tips are not separate species. Either that or the meaning of species is different for fishes.

By: Nen

Nen — Wed, 04 Jan 2012 18:46:29 +0000

I’m sorry (no I’m not) but one more thing…
One of the things that can initialize evolution of a species is to have a hybrid that is a genetic freak and is not sterile. There are plenty of documented occurances of fertile hybrids in the vertebrate clade, even fertile mules.

By: Nen

Nen — Wed, 04 Jan 2012 18:41:31 +0000

A VOICE OF REASON: Let’s suppose the wooly mammoth lost its hair. That was step one in adapting to end of the ice age. What was step two? Oh yeah… EXTINCTION!
Two more important thing if you’re comparing the climatic change at the end of the last ice age and the climatic change happening now is 1) the current warming is happening much faster giving species less time to adapt, and 2) this warming is not natural where the glacial/interglacial cycle IS natural.

EVERYONE ELSE WHO HAS SOMETHING IRRATIONAL TO SAY ABOUT THIS STORY: How do you know whether or not these two sharks are the same species?!?! Huh? Have you spent years studying them? Do you even know how new taxonomy happens between scientists? Well here’s how: The experts (Like this Dr. Morgan is an expert on black tipped sharks and YOU are NOT) study their species carefully making morpological assessments, DNA assessments, or whatever other information they need or can get until they are satisfied that they can make a call. They don’t set out to find new species when they are reviewing taxa, nor do they try keep them together or to do anything. They just try to find the truth. THEN they write up a formal report of their findings, submit it for peer review, publish it (or not if it failed peer review), and then the rest of the experts in that field decide if they are going to adopt the new taxonomy.

Have any of you commenters been involved in the taxonomic study of black-tipped sharks!!! NO?!?! I didn’t think so!

The process for naming new species, like if these hybrids prove to be a new species (THEY HAVE NOT MADE ANY CLAIMS IN THIS STORY THAT THE HYBRIDS ARE A NEW SPECIES), is very similar, so I will refrain from explaining it to you. All I’ll say is that the evolutionary/shark biologists in this story don’t need to have “species” defined for them. I’m pretty sure you don’t become lead researcher of a shark biology project without knowing a thing or two about SHARK BIOLOGY!

By: B-K KnightRider

B-K KnightRider — Wed, 04 Jan 2012 18:30:33 +0000

Now, in all fairness to MYTAKE, misunderstanding the species/subspecies problem is understandable considering how different experts have proposed about two dozen different ways to define/identify new species. Another example of how two different species can hybridize comes from lions and tigers. Some offspring of lions and tigers, which can only interbreed in captivity, are furtile.

By: B-K KnightRider

B-K KnightRider — Wed, 04 Jan 2012 18:21:57 +0000

Well MYTAKE, it seems that you have a fundamental misunderstanding of the meaning of species and subspecies. Each subspecies within a species group is still a genetically distinct organism. Species is still the lowest or basal rank within taxonomy. The term subspecies simply means there is more than one similar but distinct organism within a species group. The fact that two different subspecies can interbreed does not mean they are different species. For example, the cayote, wolf, and dog can all interbreed even thought they are simultaneously genetically distinct species and subspecies. Considering how the experts define the taxonomy of species according very strict standards of the International Code of Zoological Nomenclature and the International Code of Botanical Nomenclature I am perectly willing to accept the word of the experts when they say two genetically distinct species are two species. Whether or not they are also subspecies is irrelevant to the reality of their nature as genetically distinct organisms. The organisms within one specieis group will still not be able to breed with organsims of a different species group.

By: B-K KnightRider

B-K KnightRider — Wed, 04 Jan 2012 17:45:05 +0000

A VOICE OF REASON: “Don’t forget, the wooly mammoth adapted to the end of the ice age by losing their hair. What a sham “global warming” is.” – - – NO, they did not. The Mammoths (Mamuthus) simply went extinct. Mammoths, African elephants (Loxodanta) and Asian elephants (Elephas) are at least three different species that evolved from a common ancestor, Primelephus. The African elephant (which might be two or three subspecies) branched off FIRST, as in the African elephant evolved BEFORE the mammoth. Mammoths branched off from Primelephus second. Then, for about two million years Primelephus, Mamuthus, and Loxodonta were alive on the planet at the same time. Mammoths even coexisted in Africa with the African elephant for a while. The Asian elephant (Elephas) was the last branch to evolve from Primelephas and they did not coexist with mammoths even when both species were alive at the same time. It is quite easy to find information about the evolution of elephants online.

By: MyTake

MyTake — Wed, 04 Jan 2012 17:39:49 +0000

B-K Knightrider – “What part of “distinct species” that was confirmed through ‘DNA analysis’ did you not understand?” Historically “species” was the only level of taxonomic classification that was defined by objective criteria, namely the ability or inability of organisms to produce viable offspring. Anything classification above species was defined by perceived (subjective) morphological similarities and anything below it was variously termed subspecies, variety, breed, race or the like. Assuming that their descendants produce hybrids that can reproduce calling the Australian black-tip and common black-tip “distinct species” as opposed to different black-tip subspecies in this case seems completely arbitrary, as their mating behavior was constrained by environmental rather than genetic factors.