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Tadpole development rates

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chubsta View Drop Down
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    Posted: 12 May 2013 at 2:21pm
After a bumper egg-laying season, well i say season but due to poor weather before and after it only lasted a couple of nights, my pond is now teeming with frog tadpoles. I am very interested in the pond and it was clear that the eggs all pretty much hatched out around the same time, but when i look in the pond today there are tadpoles of hugely differing sizes. Some look like it wont be long before they start getting legs, others are tiny things that dont look long out of the egg even though they must be similar ages.

I am basically wondering why this should be? Is the rate of development tied into the parents ie genetic so some will develop slower than others, or even just be smaller tadpoles/smaller frogs, or is it more to do with environment - amount of food available, over crowding etc - or the benefits of having a constant stream of tadpoles maturing and leaving the pond rather than a mad dash for it all at the same time that predators could take advantage of?
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Caleb View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Caleb Quote  Post ReplyReply Direct Link To This Post Posted: 13 May 2013 at 10:39am
There's some evidence that large tadpoles can secrete substances that inhibit the growth of smaller tadpoles, especially when overcrowded. This means that once tadpoles have a small size advantage, they can race ahead of smaller ones. 

I brought some spawn indoors to raise this year, and the vast majority of the tadpoles are roughly the same size, with the odd one or two that have stayed pretty small. 

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Noodles View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Noodles Quote  Post ReplyReply Direct Link To This Post Posted: 21 May 2013 at 10:46am
My tadpoles (or my son's, more correctly) have all remained the same size too. However, they do get rigorously fed. Perhaps the growth inhibitor deposited in the faeces plays a more important role in nature, where food competition is more an issue. Perhaps higher levels are generated in the gut during food shortages/overcrowding?
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Caleb View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Caleb Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 2013 at 2:21pm
As I understand it, the general rule is that small tadpoles are more susceptible to the inbiting substance/organism, and large tadpoles are more likely to emit it.

So if the tadpoles all grow at the same rate, none will be inhibited by the others- but if there's a wide variation in growth rate, the smaller ones will never be able to catch up.

I guess there are lots of possible reasons why some tadpoles wouldn't grow so fast in the first place...
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