> On Nov 6, 3:30 pm, Mujin wrote:
>> Lorentz
yahoo.com> wrote
[snip]
>> One thing that has interested me lately is the fact that TTX is
>> highly concentrated in the ovaries, but not in the testes.
>> Apparently the idea that TTX levels are higher during the fugu
>> spawning season hasn't been supported by experiment - in fact the
>> opposite has been found to be true in a couple of Takifugu species:
>>
>> Yu & Yu "Are puffer fish more toxic in their spawning seasons?"
>> Marine Biology 140(5):1432-1793, May
>>
2002http://www.springerlink.com/content/mnatxrbyywtldcbp/
>>
>> This seems to follow: if spawning season triggered higher TTX
>> retention, then surely one would expect the testes - which are only
>> produced for spawning - to have a high level of toxin;
> Maybe because the milt doesn't stay around long enough to be eaten by
> predators, it diffuses too fast. Therefore, there is no advantage to
> having poisoned sperm. Eggs now get eaten, and they stick to each
> other. Therefore, a small predator who eats an egg might just die
> before eating the sisters. In other words, kin selection applies to
> the eggs, not the sperm, in this case.
I agree that it makes sense that the fugu wouldn't have evolved to
specifically concentrate TTX in the milt; protecting the milt doesn't make
any sense since it's effectively disposable. However, remember that testes
and ovaries are homologous structures, and so we ought to see some
accumulation in *both* if there was actually preferential accumulation
going on.
Also, it's interesting to note that Lagocephalus species (as opposed to
Takifugu species which I focussed on in my original cites) seem to have
*more* toxic testes than ovaries:
http://www.blackwell-synergy.com/doi/abs/10.1111/j.0919-9268.2003.00749.x
If kin selection was responsible for the high concentration of toxin in
Takifugu ovaries, I would expect to find the pattern of high ovary
concentration and low testis concentration in all species. This appears
not to be the case, so I think an alternative explanation is necessary.
>>
>>> Or maybe the liver just
>>> happens to collect the toxin for disposal, like it does many
>>> toxins.
>>
>> Exactly. But what about the ovaries? I'm stumped on that one.
>>
>
> Well, it makes a little more sense to me since the eggs are
> poisoned. Again, kin selection for the eggs.
It would be interesting to know what the TTX concentrations in Lagocephalus
milt is.
> The liver still seems incidental to me. The liver collects toxin
> to protect the pufferfish from the toxin. There is no extra protection
> from predators by a poisoned liver.
In retrospect, I think I have an alternative explanation, esp considering
the problem of the Lagocephalus species.
The gonads are one of the organs routinely assayed when testing for the
accumulation of environmental toxins. No doubt the high rates of blood
flow and the high concentration of endocrine receptors in the gonad tissues
contribute to accumulation. Takifugu testes don't actually develop until
the spawning season, so there isn't much time for incidental accumulation
of tetrodotoxin to occur. The ovaries are active developing eggs for a
much longer portion of the year, however.
I think an incidental accumulation makes more sense in this context.
--
Bon nou mujin sei gan dan
