Subject: [Tweeters] Hooded Mergansers and Rough Skinned Newts
Date: Oct 7 14:25:39 2008
From: Julie Smith - smith at plu.edu


Hi,

Dennis is right it is due to geographic variation in selection.
It is a fascinating tale of coevolution. Newt toxicity levels and snake
resistance levels are closely matched geographically due to reciprocal
selection. Populations of garter snakes outside the range of newts have
have low levels of TTX (tetrodotoxin) resistance.
TTX is a powerful neuritoxin it blocks the sidium channels in nerve and
muscle tissue. The blocked channela are unable to transmit action
potentials an dthe tissues are paralyzed. The predator ingesting the
newt usually dies of respiratory failure. Newt populations on Texada
Island in BC lack TTX and those on the Olympic peninsula also have low
levels and snakes have low levels of resistance. You also get areas
where there has been strong reciprocal selection and newts have evolded
high levels of toxin and snakes high levels of resistane. There is one
such coevolutionary hotspot near San Francisco. In other areas
reciprocal selection is not strong. These areas are coevolutionary
coldspots.

They do not know what suite of selection pressures favors coevolutionary
escalation in some areas but not others. One idea is that it may be due
to the presence or absence of predators that prey on the snakes. The
ability to be resistant to the toxin comes at a cost. They have a very
reduced sprint speed making them susceptible to their own predators.
They hypothesize that escalation of very high levels of TTX in newts and
TTX resistance in snakes may occur only in areas in which the predators
of the snakes are uncommon and the alternative food for the snakes is
limited. They may have figured out this piece of the puzzle I have not
been keeping up on it.

Best,

Julie

Dennis Paulson wrote:
> Hi, Don and Sandi.
>
> I looked in my old notes from when I taught vertebrate zoology, and I
> had juvenile Pied-billed Grebe and Mallard listed as birds that had died
> after eating Rough-skinned Newts. I can't recall where I got the Mallard
> info, but the grebe is a specimen in the Slater Museum collection that
> was found dead shortly after the observer saw it eat a newt. It was an
> albino, one of the reasons the observer was sure it was the same bird.
>
> Some populations of Common Garter Snakes are immune to the newts'
> toxins, but populations of the same species in areas where the newts
> don't occur are not. Newt toxicity, on the other hand, definitely varies
> from population to population, so I suppose it is possible that the
> Orcas Island ones aren't among the most poisonous. Are garter snakes
> common at this pond? Natural selection, with differential predator
> pressure in different areas, could easily lead to differences in
> toxicity in different populations. That's probably why rattlesnakes are
> less dangerous in Washington than in Arizona.
>
> So there are three possible alternatives. 1) Your newts aren't toxic. 2)
> The mergansers get rid of most of the skin toxins by their actions. 3)
> Hooded Mergansers, at least these birds, are immune to tetrodotoxin. A
> lot of data would have to be gathered to distinguish among these
> hypotheses. It's amazing how many observations in nature lead to more
> questions than answers!
>
> Dennis
>
> On Oct 7, 2008, at 12:03 PM, tweeters-request at mailman2.u.washington.edu
> <mailto:tweeters-request at mailman2.u.washington.edu> wrote:
>
>> Date: Mon, 6 Oct 2008 18:59:41 -0700
>>
>> From: Don McVay <dmcvay at cmc.net <mailto:dmcvay at cmc.net>>
>>
>> Subject: [Tweeters] Hooded Mergansers and Rough Skinned Newts
>>
>> To: Tweeters <tweeters at u.washington.edu
>> <mailto:tweeters at u.washington.edu>>
>>
>> Message-ID: <E1A14850-307E-4650-9204-BD1708E2DC21 at cmc.net
>> <mailto:E1A14850-307E-4650-9204-BD1708E2DC21 at cmc.net>>
>>
>> Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes
>>
>>
>> Hi Tweets,
>>
>>
>> On Orcas Island in a small fresh water pond near Deer Harbor Saturday
>>
>> afternoon we made another observation of a Hooded Merganser eating a
>>
>> Rough Skinned Newt (Taricha granulosa). We posted this behavior on
>>
>> Tweeters for the first time in the Spring of 2003.
>>
>>
>> The Merganser was a juvenile accompanied by an adult female. The
>>
>> behavior of the Merganser was similar to other observations of this
>>
>> feeding behavior. The Merganser manipulated the Newt with its beak,
>>
>> methodically rolling and passing the Newt between the mandibles and
>>
>> then rapidly swishing the newt in the water. It did this for several
>>
>> minutes before swallowing the newt. Both Mergansers were observed
>>
>> about an hour later resting among the cattails with no apparent ill
>>
>> effects.
>>
>>
>> The toxicity of this newt is well documented. Several years ago an
>>
>> Oregon college student died, when on a dare, he swallowed a rough-
>>
>> skinned newt. The tetrodotoxin or TTX is a dangerous neurotoxin to
>>
>> mammals and is similar to that found in puffer fish and the blue-
>>
>> ringed octopus. The toxin in one newt has been estimated to be
>>
>> sufficient to kill several humans.
>>
>> See: http://www.calacademy.org/calwild/sum98/eye.htm
>>
>>
>> Once again this behavior raises several questions from the previous
>>
>> post:
>>
>>
>> 1. Are rough skinned newts a common dietary regime of the HOME?
>>
>> Apparently they are since we have observed this feeding behavior of
>>
>> Hoodies on several occasions.
>>
>> 2. Do other diving ducks feed on rough-skinned newts?
>>
>> 3. Was the rolling in a serrated beak and washing of the newt a
>>
>> behavior of the HOME to remove the toxin from the newts surficial
>>
>> poison glands?
>>
>> 4. Are HOME and other birds immune to tetrodotoxin? Some reptiles
>>
>> have been observed eating Rough Skinned Newts. (Garter Snakes)
>>
>> 6. Is there a geographic difference in Newt toxicity?
>>
>> 5. How do they do that?
>>
>>
>> Don and Sandi McVay
>>
>> Queen Anne & Deer Harbor
>>
>> dmcvay at cmc.net <mailto:dmcvay at cmc.net>
>>
>
> -----
> Dennis Paulson
> 1724 NE 98 St.
> Seattle, WA 98115
> 206-528-1382
> dennispaulson at comcast.net <mailto:dennispaulson at comcast.net>
>
>
>
>
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--
Julie Smith, Ph.D.
Assistant Professor
Department of Biology
Pacific Lutheran University
Tacoma, WA 98447
253-535-7307
smith at plu.edu