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Tadpole Postscript

Thursday, December 15, 2011


On October 7, 2011, as I was pruning my huge gardenia tree with the braided trunk for its annual trip inside, something jumped, and it wasn't a tree cricket. It was one of my tadpoles, all growed up.
Well, sort of. She was still minuscule. But man, she looked like a tree frog now. (basing this guess on the fact that females have pale throats while male throats tend to be darker). Hello, sweetheart!


Charmed beyond all measure to see a successful frog fledgling, I set about making portraits.


She climbed with that special reptilian flow that tree frogs are so good at.


I think this is my favorite shot, those long fingers, that wise face...



I reflected on how a pailful of tadpoles had enriched our lives all summer long, what a miracle, what a gift they'd been.
From watching them hatch to seeing them learn to recognize me and anticipate feeding time, watching them grow limbs and leave their watery world for the air and leaves and sun, they'd opened up a new world to us.



But as things go when one messes with nature, not everything went so swimmingly. For the only frogs that actually metamorphosed were the older tadpoles we'd saved from the driveway. The eggs I'd scooped out of the fishpond had hatched, eaten, swum, grown, and then simply stopped growing. By late November, they still hadn't metamorphosed into frogs. Why? What could be going on?

Perhaps a clue can be found in the fact that about 20 of the older tadpoles also failed to metamorphose. They didn't even sprout legs.  None of the group raised from eggs sprouted legs at all. Oh, they'd had time--the eggs were laid July 10, and gray tree frogs take about two months to mature. 


Delving into the literature, I found that several things can retard development in tadpoles. Removing the thyroid keeps them from becoming frogs. Well, that wasn't it. I hadn't touched their thyroids.  Starvation can cause retardation. With my fish food supplements, that was unlikely to be the problem. Crowding can also cause retarded growth. Hmm. These tadpoles, it seemed to me, had ample elbow room and a greater water volume than in most of our roadside puddles. But they never grew elbows.

Thinking about it (and I did, for weeks!) I concluded that perhaps the answer to the riddle could be revealed by turning it upside down. What speeds development in tadpoles? Shallow water and higher temperatures, that's what. When a tadpole in a natural pool feels the water heating up because the pool is drying, that can cause accelerated development, a race to metamorphose and be able to gulp oxygen before the watery habitat is no more. 

Perhaps my tadpoles never felt that pressure, never felt the need to metamorphose. As the summer wore on and turned to fall, the sun stopped striking their pools; on the north side, they were now in the shadow of the house. The water, which had been very warm in July and August, stayed deep, and more importantly, it cooled. And the tadpoles simply stopped growing. 

I wondered what had happened in the pond to the eggs I'd left (I'd taken half and left half to hatch there). I suspected that they'd become fish food as soon as they hatched, being tiny and wormlike. I never saw a tadpole there. 

And now, what to do with the remaining tads? We'd already had a couple of hard freezes, and their pools had become covered with ice. Amazingly, they were still alive under there, still moving feebly. When the weather warmed back up they were their lively selves again. I decided to put them in the pond where they'd started out in the first place, to see if perhaps they could survive the winter in a dormant state and take up the business of metamorphosis next spring. It was an imperfect solution, but I didn't see any other alternatives. I couldn't throw them in the Amazon tank indoors, because there were all kinds of nasty things in those pools that would probably kill my home-bred tetras. 

Neither could I simply tip the tadpools into the pond. Over the course of the summer, tiny snails had proliferated, and there were doubtless flukes and leeches, too--all of which can mess up fish. No, I'd have to dip-net the tads into clean water and then transfer them with a net. Which I did, on November 20. 

When I emptied the large tadpole pool, the bottom was covered in leeches! Yicccch!


Yep, that's a leech on my thumb, its tiny head searching for a victim. I was very glad I'd followed my instincts not to tip the water into the pond. 

For all I know, that's full of leeches, too...just about bound to be. But I didn't want to introduce anything new.


I netted all the taddies and put them through a couple of rainwater rinses. There were about 50 remaining, about 20 of those older and larger, from the driveway batch, and the rest from the July egg mass in the fish pond.



I poured the water through the net, which is the only way to catch tadpoles. Much less stressful for them than chasing them around.


Wriggling life, about to be given their second snowball's chance. I hope it works. It probably won't, but...

Into the pond they went, swimming tentatively out into the vast spaces. I felt OK about putting them in with the fish now that they were bigger--American toad tadpoles seem to do fine once they reach this size; the fish no longer seem to regard them as prey.


Maybe we'll see you next spring. Hope so.


More lessons learned, more curiosity fueled. You can think you're doing wild things a favor by helping them out, but as often as not you're just messing them up. It seems to me, mulling this over, that tadpoles were meant to grow up in shallow, hot, barren-looking mud puddles, not the Club Med for Frogs I'd so lovingly and lavishly created. They're meant to grow up without fish to prey on them, and that dictates a most ephemeral watery habitat--a puddle. Perhaps I'd doomed them by giving them everything I thought they could need. Maybe something in the food I gave them retarded their growth--I don't know...but I fed the older tadpoles, too, and most of them made it to frogdom. 

I was humbled by some photos I found online of gray tree frog eggs hatching and maturing in a large plastic plant pot saucer full of rainwater. The frog had laid its eggs there and in that almost impossibly sterile environment they'd grown and thrived. Go figure. 

There's so much more that I don't know than I know.

That's what keeps me going.

14 comments:

I think you have done as well as you can do for the little tadpoles. Are there any statistics on frog development and hatching? I would think that many tadpoles never change into frogs. Maybe its natures way? They will be fine in the pond for the winter.

Bullfrog tads take a while to grow, no? Like a couple years? Hopefully these arrested ones will use the "extra" time to grow especially fat!

; )

My backyard pond provided much to wonder at... I miss it. Any experience with raising or rescuing dragonfly larvae? I spent many summer afternoons playing at "helping" them...

I really enjoyed this series--so interesting. And so true about how once you sort of answer one question in biology, it opens up a whole new series of questions. Your comment about flukes and leaches made me think about other parasites and how they are probably a much bigger force in natural selection than the predators we focus on because we can watch them in action. Even spiders suffer multiple forms of parasites, from mites to nematodes! If you haven't yet, check out Carl Zimmer's "Parasite Rex"--you'll never see the world in the same light again.

Julie - you may not be too far off on the thyroid hypothesis. In order to make the necessary hormones they (and we) need iodine. I'm not sure how much there is in rainwater.

Gray treefrogs develop just fine in large fishless ponds at The Wilds, so I'm not sure that the size of the pond or puddle is so critical. Also, the larger the tadpoles are at metamorphosis the better they do; you probably ended up giving them a good head start. Yes they CAN metamorphose quickly in a drying puddle, but that doesn't mean a good long-term prognosis.

I've been lurking on your blog for about a month, and I just realized your last name is Zickefoose, not Zicklefoose. Insert giggle here. xD

-Motaki

Thanks for sharing your tadpole rearing experience. I tried raising Pacific chorus frogs this year. Only one successfully metamorphosed from 16 eggs that hatched the last week of May. I'm hoping they'll continue development in the spring.

I just love your curiosity. What a lovely post of your musings. Keep up the wonderful work, the world is a better place with you in it.

This series of posts has been more-than-a-'tad' delightful!! In fact, I've been r-r-ribbeted to it :-)
(...sorry)

Hi Julie:

Juvenile froglets and toadlets can't be sexed based on the color of their throats. That doesn't change until they become sexually mature.

Not sure why the other tadpoles haven't matured, but I wouldn't give up hope on them yet. Nor should you place the blame on yourself for them not maturing.

I know from personal experience that treefrogs, toads and a variety of North American tadpoles can survive freezing, so don't worry about that either.

Take it easy on yourself!

The things I learn from you... I love it!

We had something similar happen once with tadpoles rescued from a once rain filled ditch that was drying up. It seemed to me hhat they stayed tadpoles longer than they should have, swimming like little fish in their aquarium on the back porch. Then, we went on vacation for a week and it didn't rain while we were gone so the water in the tank evaporated to just a few inches left. Suddenly development speeded up. Now I know why! Seems like those of us who tended to be helicopter parents could learn a lesson from this tale. Too much care and protection results in weak offspring.

I am so happy to have found your blog and this series of posts. You've made me think about stuff I've honestly never considered--how tadpoles' mouths must change, and how they can transition from eating just algae to digesting gnats and, later, larger insects. Thank you for doing this and for sharing it online.

(I also love the red bat in one of your layout photos.)

I had forgotten how much fun it was to read your blog and have been wandering around in here with your tadpole stories...and I can learn so much here.

Love love love these tadpole-to-froggy posts!

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