Mixed Breed Sharks??

[archman]

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.

The bulk of reared animal hybridization work (on wild animals) is rather tame. Usually it's little more than placing related species in close proximity to one another, or skewing the sex ratios between them. A lot of this work isn't even designed to promote hybridization, it just *happens*. A lot of the tropical bird and freshwater aquarium trade works this way.

But since the animals are closely monitored in a closed environment, it is possible for us to track individual offspring to parents. Excepting charismatic megafauna, this ability is generally unavailable to biologists that work in the field. Since a lot of hybrid forms take more to one parent than another in appearance and behavior, the vast majority of them go unreported. That's one of the new prevailing theories, anyway.

*****
Robb, I have hunted all over the place for any reports of hybrid sharks. I have not only found NOTHING, there's virtually no theoretical discussion of it either. Of course, compared to many other fish lines, our knowledge of shark life history stinks for all but a few species. I don't think it's anything that is being seriously looked at. But don't feel too bad, inter-species breeding isn't looked at for the overwhelming majority of other animal species, either.

 

[SeanQ]

I remember learning all this stuff. The approach our instructor took was to outline the various pre- and post- zygotic barriers to producing viable offspring.

Archman: Would that be an oviparous shark egg?

 

[archman]

I remember learning all this stuff. The approach our instructor took was to outline the various pre- and post- zygotic barriers to producing viable offspring.

Archman: Would that be an amniotic egg?

I avoid vertebrate embryology like the plague, sorry. I probably know less than you do.

But not knowing those details, I would say that the biggest barrier for interspecies-breeding in sharks would have to do with their copulation method.

 

[SeanQ]

Amniotic was a typo, I changed it above. Not sure what I was thinking.

The prezygotic barriers would be things like temporal, behavioral and mechanical isolation. For example some organisms mate in spring and don't naturally mate with an similar organism that reproduces during the fall. A 30m blue whale can't naturally mate with a 6m minke whale; this is a mechanical isolation.

A post zygotic barrier is something that prevents a hybrid offspring from being successful, such as sterility.

Those can be applied to organisms other than vertibrates. Different coloured flowers that attract different insects is an example of mechanical isolation.


As for the egg comment, that was related to the fact that shark species have different methods of reproduction. Some are oviparous and lay the eggs externally, some are ovoviviparous and retain the eggs, while others are viviparous and have live births.

 

[liberato]

What? You don't know about hinnies, the freakishly weird "fertile" mules?

Thanks! That was an oddly interesting read. I now know what a hinnie is (note that it's not necessarily fertile as your sentence implies). And I also now know jackasses are only half of all the asses out there. I feel enlightened!

 

[archman]

Oh, how strange. To me, anything making use of the word "zygote" would confine itself to embryology. Ecologists like me and Bill use different terminology.

I was assuming that a "pre-zygote barrier" would be strictly something in-copula, like a sperm/egg incompatibility. This happens in many insect groups.

Likewise, "post-zygote barrier" would be something that prohibits embryonic development to reach full term. Killer genes would be one example, albeit an extreme one.

 

[archman]

I now know what a hinnie is (note that it's not necessarily fertile as your sentence implies).

Well... why do you think I put "fertile" in quotes?

 

[robbcayman]

The bulk of reared animal hybridization work (on wild animals) is rather tame. Usually it's little more than placing related species in close proximity to one another, or skewing the sex ratios between them. A lot of this work isn't even designed to promote hybridization, it just *happens*. A lot of the tropical bird and freshwater aquarium trade works this way.

But since the animals are closely monitored in a closed environment, it is possible for us to track individual offspring to parents. Excepting charismatic megafauna, this ability is generally unavailable to biologists that work in the field. Since a lot of hybrid forms take more to one parent than another in appearance and behavior, the vast majority of them go unreported. That's one of the new prevailing theories, anyway.

*****
Robb, I have hunted all over the place for any reports of hybrid sharks. I have not only found NOTHING, there's virtually no theoretical discussion of it either. Of course, compared to many other fish lines, our knowledge of shark life history stinks for all but a few species. I don't think it's anything that is being seriously looked at. But don't feel too bad, inter-species breeding isn't looked at for the overwhelming majority of other animal species, either.

I wish we had more info on sharks, but that's how it goes. Thanks for the response!!!!

 

[drbill]

Oh, how strange. To me, anything making use of the word "zygote" would confine itself to embryology. Ecologists like me and Bill use different terminology.

Of course when I went to college (way back in the Dark Ages, a period of time one isn't supposed to remember if they were truly there!), we did use the terms pre- and post-zygotic RIM's.

If I were to have to actually teach biology today, I'd have to relearn a lot of what I "learned" back then. I think of the astronomy class I taught in the early 1970's. Many of the "facts" we "taught" (forced our students to memorize) would need revision! Glad that my focus is on a different form of education where I don't need to get too technical.

Off to dive again today.

 

[Rick Murchison]

HHhhaarrr! I love it. The "species" arguments haven't really changed a whit since I was in college in the 60's, and they were old then.
The one constant I came away with is that there's always an exception
Rick