Mixed Breed Sharks??

[DA Aquamaster]

I've known criminal defense and civil lawyers to crossbreed. The offspring seems normal. Does that count?

See...and all you skeptics said sharks couldn't interbreed with each other.

 

[Cacia]

oh... the wolpin pic! pretty amazing, huh? ...I am a wealth of information.

 

[robbcayman]

I should have known better LOL!!!!

 

[drbill]

Using the most generally accepted definition of a species, it would not be possible for two different species to mate and produce viable offspring. This is why a true species is a species... it is reproductively fixed.

Dog breeds are not different species. They are all still dogs. They can interbreed.

Male and female humans are considered to be of the same species. They can interbreed. Likewise human races. They are still of the same species and can biologically reproduce (and if God meant it any other way, wouldn't She have created different species of "humans" instead of just different races?).

 

[MoonWrasse]

Using the most generally accepted definition of a species, it would not be possible for two different species to mate and produce viable offspring. This is why a true species is a species... it is reproductively fixed.

Dog breeds are not different species. They are all still dogs. They can interbreed.

Male and female humans are considered to be of the same species. They can interbreed. Likewise human races. They are still of the same species and can biologically reproduce (and if God meant it any other way, wouldn't She have created different species of "humans" instead of just different races?).

I thought she did, but we humans hunted down and ate all those hairy neanderthals

 

[archman]

Using the most generally accepted definition of a species, it would not be possible for two different species to mate and produce viable offspring. This is why a true species is a species... it is reproductively fixed.

This is the vertebrate biologists' definition for a species, Bill. It doesn't really hold water for plants, fungi, microbes, and even a heap of inverts. It doesn't work very well for vertebrates, either. The "interbreeding barrier" is currently taught in college as the "classical defining parameter", and is immediately amended by other parameters (biogeography, behavior, growth media).

Here are a few viable vertebrate hybrid lines that aren't under the wikipedia definition.

Caribbean hamlets (argued as one species or several closely allied ones)
Hybrid Lepomids
-green/bluegill cross (mostly hatchery gown; low reproductive success)
-green/redear

Channel/blue catfish (so-called "CxB" hybrids, mostly hatchery reared)
Striped Bass Hybrid (usually sterile, but not always)
Genus Xiphophorus (most species interbreed)
Family Cichlidae (extensive interbreeding)

Cheloniid sea turtles (at least four species interbreed with one another)
-possibly oldest vertebrate lineage known to interbreed

Jackals & Wolves

Corn & King snakes

Members of the Bos genus (cows)

A gazillion bird species

 

[drbill]

Agree that the species definition doesn't work for a lot of taxa, but generally is good for vertebrates including sharks. My ex-GF was a native plant horticulturist and I was certainly aware of how mixed up those plants are in terms of our human definitions!!

However I think we need to look at the examples you mention and consider whether the categories we have placed them in are truly accurate or not. Many of our species placements are still quite subjective, even with molecular genetics in play. Perhaps we should look at whether hamlets truly are separate species, or somewhat distinct forms in which reproductive isolating mechanisms are not yet "perfected." Likewise with the other species groups you mention.

 

[archman]

Taxonomic delineators are, of course, not concrete. For some reason the species-level ranking seems to be put on a pedestal all it's own, but it's little more refined than any other ranking. The Linnaean system was never meant to accomodate subspecies, breeds, strains, and all that junk. The microbiologists complain endlessly.

I don't know current you keep up with contemporary systematics Bill, but there's quite a furor between traditional taxonomists, cladisticians, and those weasel geneticists. There is one movement that wishes to abolish the Linnaean system altogether, and replace everything with bar codes. There's another that wishes to nix discrete taxonomic rankings altogether (at all levels), and use percent similarity indices to rate everything. That of course, requires every student to have a computer model or cladogram in front of them whenever they want to see how critters relate to one another.

Ecologically, the criteria that currently determine a species' distinctness is multi-disciplinary in approach. Reproductive singularity was always a crap shoot, as this cannot be determined for a great many organisms. It's just not seeing if an organism's gametes are genetically compatible with another's, but if the two critters ever find themselves in behavioral and environmental situations where such combinations can be attempted.

In most known cases of fertile animal hybrids, the two species don't "want" to mate with each other. This is why there's a huge skewing towards known hybrid species in groups that are raised by hobbyists, pet breeders, zookeepers, and hatchery biologists. They provide the unusual conditions that enable genetically compatible but also genetically distinct populations to hybridize.

In the case of the Fungi, interbreeding is low on the totem pole as a species delineator. Dissimilar hyphae conjoin for a (relative) nothing, and sexual reproduction often takes second fiddle. Ergo, they don't breed.

If anything, the concept of "species" is becoming increasingly less valuable in systematics work. This pleases the cladisticians immensely. They can go suck on an egg.

 

[drbill]

Not very current on systematics, Archman, because my focus is largely ecological. It's easier to know what a species eats and what eats it than to understand their reproduction (although I love filming it). Too much subject interpretation in the taxonomic realm.

If the two species don't want to mate in the wild, it seems to me there are RIM's (reproductive isolating mechanisms) already in place. The fact that they can mate in a forced situation says little if a behavioral or ecological RIM is in place that prevents them from doing so in the wild.

It's been my position that genetic compatibility in reproduction is not the real issue. I've always seen it as a broader, multi-disciplinary assessment. If two "species" won't mate in the wild unless forced to, it seems to me they have decided they want to be separate species! Doesn't really matter what we humans think!

 

[robbcayman]

Taxonomic delineators are, of course, not concrete. For some reason the species-level ranking seems to be put on a pedestal all it's own, but it's little more refined than any other ranking. The Linnaean system was never meant to accomodate subspecies, breeds, strains, and all that junk. The microbiologists complain endlessly.

I don't know current you keep up with contemporary systematics Bill, but there's quite a furor between traditional taxonomists, cladisticians, and those weasel geneticists. There is one movement that wishes to abolish the Linnaean system altogether, and replace everything with bar codes. There's another that wishes to nix discrete taxonomic rankings altogether (at all levels), and use percent similarity indices to rate everything. That of course, requires every student to have a computer model or cladogram in front of them whenever they want to see how critters relate to one another.

Ecologically, the criteria that currently determine a species' distinctness is multi-disciplinary in approach. Reproductive singularity was always a crap shoot, as this cannot be determined for a great many organisms. It's just not seeing if an organism's gametes are genetically compatible with another's, but if the two critters ever find themselves in behavioral and environmental situations where such combinations can be attempted.

In most known cases of fertile animal hybrids, the two species don't "want" to mate with each other. This is why there's a huge skewing towards known hybrid species in groups that are raised by hobbyists, pet breeders, zookeepers, and hatchery biologists. They provide the unusual conditions that enable genetically compatible but also genetically distinct populations to hybridize.

In the case of the Fungi, interbreeding is low on the totem pole as a species delineator. Dissimilar hyphae conjoin for a (relative) nothing, and sexual reproduction often takes second fiddle. Ergo, they don't breed.

If anything, the concept of "species" is becoming increasingly less valuable in systematics work. This pleases the cladisticians immensely. They can go suck on an egg.

Are you a biology teacher??? You lost me with all sorts of jargon, maybe this is double speak So in short, different shark species can't mate because genetically it's impossible??? Would it be plausible to assume that tiger sharks and bull sharks try to make but it doesn't work?? Thanks