Comments on: Big-headed tiger snakes support long-neglected theory of genetic assimilation

By: Captain Skellett

Captain Skellett — Wed, 04 Nov 2009 02:42:59 +0000

Some Tiger Snakes were inadvertently introduced by travelling humans? How does that happen? Did they sneak a lift in a suitcase or the back of boat, or maybe hide inside someone’s clothing… a whole new meaning for the word trouser snake. Those things are big and lethal, I’m surprised anyone took it for a ride without realising. Maybe that’s just what they told customs.

By: DeLene

DeLene — Tue, 03 Nov 2009 13:14:12 +0000

I agree with the first three posters, regarding questioning what maintains the plasticity in the mainland population once canalization sets in. Also, I’m curious what mechanism(s) triggers activation of plasticity once the young snake is in the new environment with larger prey; and at what age or developmental stage the snake is simply too old to have the plasticity function kick in.

By: IanW

IanW — Mon, 02 Nov 2009 13:57:12 +0000

So are tiger snakes the result of a dehydrated toad mating with another species – such as a tiger…?!

By: wazza

wazza — Sun, 01 Nov 2009 19:17:59 +0000

Qetzal: in this case, the selective pressure was not advantage, but an individual by the name of Conrad Waddington, who was artificially selecting the double-thorax flies.
If anyone’s ever read the Science of Discworld books, they discuss this concept in their section on folk genetics, and use the example of Thalidomide babies. When two Thalidomide-affected adults have a child, the child has a greater chance of having the same defects as if they had been exposed to Thalidomide. This is not due to a mutation caused by Thalidomide, but to the natural mutations that made these people susceptible to Thalidomide’s effects in the first place coupled with the human breeding patterns which lead individuals to seek mates that share their weirdness. These mutations initially needed an environmental stressor like Thalidomide to lower the threshold, but with two parents with such genes (which are quite rare; the rate of birth defects with Thalidomide was actually fairly low, with millions of users producing less than 20000 cases of birth defects worldwide) the threshold is lowered such that natural stressors can do the same job as Thalidomide.
Though, to me, this does look like just a restatement of the good old variation->selection->speciation deal.

By: Briana

Briana — Sun, 01 Nov 2009 11:01:05 +0000

Hm… I first read about this study in a book about epigenetics. They didn’t mention Wattington’s theory at all. It also didn’t mention that there was a type of tiger snake that couldn’t change its jaw size. It is difficult for me to comprehend the idea of epigenetics because of the many theories that relate to the idea, or sound similar, but are not the same.
If the island snakes were left on the mainland for 30 years do you suppose they’d start to develop plasticity as well? You’d think it would be a two way street. Have they identified differences in genes that are more “plastic” compared to the ones that are canalized? Or is that difference outside the genes… perhaps explained by epigentic processes? Agh, so confused! It’s great.

By: Ed Yong

Ed Yong — Sun, 01 Nov 2009 00:35:26 +0000

You’re asked to review this website for Genetics class? That’s AWESOME! Can you tell me more?

By: Steffano Mottl

Steffano Mottl — Sat, 31 Oct 2009 20:13:19 +0000

“All species have a certain amount of variation built in to their developmental program, which they can exploit according to the challenges they face”.
I like how that sounds, a lot. I apologize if my scientific literature doesnt fit in here, but we are asked every week to review this website for Genetics class, and sincerely Im in love with this site.

By: Hypocee

Hypocee — Sat, 31 Oct 2009 03:21:03 +0000

Nah, no somatic mutations involved in the ether thorax thing – you’re looking at depressed Hox signals. Provided intraspecific variation in the strength of Hox secretion, breed for a drop and soon enough you don’t need the ether because the natural secretion’s fallen below the threshold. Bingo bongo.
‘Genetic assimilation’ seems like the closest thing yet to a real-world example of the Baldwin Effect, where a learned behavior gets fossilized into the genome of a population. Here’s hoping that’s next!

By: qetzal

qetzal — Fri, 30 Oct 2009 18:52:53 +0000

David,
Even if it’s more common in ether, it’s hard for me to see how that explains the observed canalization. What is the likelihood that ether just happens to promote both double-thorax as a developmental anomoly, AND mutations that cause ‘constituitive’ double-thorax?
The only way I could see that as a credible possiblity is if the apparent developmental anomoly actually results from mutations in relevant somatic cells during early development.
I guess I could stop being lazy and actually try to look at the research.

By: David Marjanović

David Marjanović — Fri, 30 Oct 2009 18:05:19 +0000

The only thing I can think of is that the double-thorax phenotype is somehow advantageous in the presence of ether.

Can’t imagine how. The question is: is that mutation more common in ether than in the wild?