Veterinary Question ! The Ectothermic Thyroid

[Timotei]

Hi,

I have been asking myself for some time now, exactly what purpose does the thyroid serve in ectotherms ? I know it's responsible for collection of Iodine from the blood, and regulates metabolism in endotherms, but I'm struggling to imagine exactly how much it does in ectotherms, considering their body temperature (and even a lot of their energy) does not depend on its function.

Can anyone shed some light on this for me ? I would be muchly impressed and intellectually sated ^^

Oh and if you're feeling brave, could someone also explain to me exactly how ectotherms are able to get away with such a variable body temp ? Are their enzymes that different to endotherms that they can cope with the great differences..? Is the active site less likely to denature..? So many questions !!

I often ask myself why endotherms do so well - ectotherms seem to just totally dominate in way of energy conservation.

[natrix]

you tell us Tim , you're the Vet student .

[dragon lady]

aha..interesting!....hmmm
i also would like to understand more!

[Timotei]

Originally Posted by natrix

you tell us Tim , you're the Vet student .

Yes, STUDENT

[Chrisreptile]

We're sorta doing this stuff in 3+4 biology at the moment, ill try and ask my teacher tomorrow if he knows the answers.

[natrix]

Sorry for my unhelpful reply before .
Type ' Thyroid function in ectotherms' into google & there are a bunch of articles on it .
I got the drift but aren't going to be pretentious enough to try & communicate it convincingly
One of the papers suggest that it facilitates shedding amongst other functions.

[DennisS]

Go out and buy " THE BIOLOGY,HUSBANDRY AND HEALTH CARE OF REPTILES" 3 books or if you lived in Adelaide i'd lend them to you to read.

[reptilesDownUnder]

Originally Posted by Timotei

I have been asking myself for some time now, exactly what purpose does the thyroid serve in ectotherms ?

It's also involved in growth and metamorphosis (you can induce an axolotl to change to the adult form if you give it thyroxine). Were you after more specific info than that? I don't know anything more off the top of my head, but Google Scholar does. If you find out anything interesting, make sure you let us know.

Originally Posted by Timotei

Oh and if you're feeling brave, could someone also explain to me exactly how ectotherms are able to get away with such a variable body temp ?

I'm not a biochemist, but keep in mind that ectotherm enzymes still have a fairly narrow optimal temperature range (although it's still much wider than that of endotherms).

Originally Posted by Timotei

I often ask myself why endotherms do so well - ectotherms seem to just totally dominate in way of energy conservation.

That all depends on what you mean by 'do so well'. Endotherms don't do well at variable body temperatures. Endotherms don't do well in extreme environments. 99%* of all extant, described species are ectothermic. Endotherms clearly didn't do so well in the numbers game. Don't sell ectotherms short! It's all about diversity.

If you don't have a copy already, I highly recommend Reptile medicine and surgery, edited by Douglas Mader. (I just had a look in there and it's got bugger all on the thyroid gland.)


Stewart
* Note: this is a figure I plucked from the air, but I'd be surprised if it's not conservative.

[Timotei]

Wow, thanks for your detailed response reptilesDownUnder.

Originally Posted by reptilesDownUnder

It's also involved in growth and metamorphosis (you can induce an axolotl to change to the adult form if you give it thyroxine). Were you after more specific info than that? I don't know anything more off the top of my head, but Google Scholar does. If you find out anything interesting, make sure you let us know.

Yeh, I was just curious as to whether it still controls the rate of metabolism as in endotherms, considering ectotherms don't use metabolic processes to maintain their body temp the same way that endotherms do.

Originally Posted by reptilesDownUnder

That all depends on what you mean by 'do so well'. Endotherms don't do well at variable body temperatures. Endotherms don't do well in extreme environments. 99%* of all extant, described species are ectothermic. Endotherms clearly didn't do so well in the numbers game. Don't sell ectotherms short! It's all about diversity.

Yeh, by "do so well" I meant that they exist in the numbers that they do at all - their energy expenditure is so crazy.

Originally Posted by reptilesDownUnder

If you don't have a copy already, I highly recommend Reptile medicine and surgery, edited by Douglas Mader. (I just had a look in there and it's got bugger all on the thyroid gland.)

I have actually been looking at that book for a while now, but lack the funds I bought the book Herpetology by Kenneth R. Porter about a month ago, I'll have another read in there to see what it says and post some more.

Thanks again for your info

[Timotei]

Well I spoke to one of my lecturers, Endocrinologist Dr. David Miller, and he told me that its purpose was regulation of metabolism to an extent, but primarily it regulated skin growth, sloughing and metamorphosis.

So there you go !

[reptilesDownUnder]

Thanks for letting us know.

Going back to one of your original points about endotherms having really high energy expenditures... It's true that they use a lot of energy to maintain their body temp (I think I've heard somewhere in the order of half of all energy consumed is used to generate body heat, but don't quote me on that), but that obviously gives them a huge advantage over ectotherms. So while it is costly, the price is obviously well worth it.

It might be interesting to note that various degrees of endothermy have evolved on about four separate occasions:
Birds
Mammals
Brooding pythons
Leatherback turtle

That gives you an idea of how advantageous it can be.

One theory on the evolution of endothermy in mammals is that it allowed them to be active at night, and therefore avoid the mouths of hungry, diurnal reptiles. It's possible that their high and stable body temps allowed the mammals to flourish after the catastrophic event that spelled doom for most of the dinosaurs.


Stewart

[Shannon]

That is an amazing series of books! I have a copy and bought a copy for my reptile vet too - she loved them!! They're expensive but worth it.

Originally Posted by DennisS

Go out and buy " THE BIOLOGY,HUSBANDRY AND HEALTH CARE OF REPTILES" 3 books or if you lived in Adelaide i'd lend them to you to read.