“Sooooo squishy!” George exclaimed as he cupped a grapefruit-sized salamander egg mass in both his hands.
His chuckles caused the jello-like cluster of eggs to shake, which in turn made him laugh even more. “How can a yellow spotted salamander lay all these eggs?” he asked.
“Well,” I replied, “remember, back on Salamander Night I mentioned that we would come back to the frog pond and see the most amazing things? One thing I’m always amazed at is how large the egg masses are, even though I know it’s because the jelly envelopes swell up with water. The eggs aren’t nearly that big when the salamander deposits them. The size of the egg mass tends to make you think there are more eggs in there than there really are. I’d guess there are maybe less than a hundred eggs in this one.
“Another amazing thing is how many egg masses are in the vernal pool. There are more than half a dozen right here at our feet and a lot more up there where we saw the salamander dance back in March.”
“Look.” George pointed across the water. “There are a bunch more egg masses over on that side!”
“These are wood frog eggs,” I said as I waded over and scooped up a wood frog egg mass. “See how their eggs kind of run through my fingers? They are not enclosed in the stiff jelly like salamander eggs are.
“The eggs of the wood frogs and salamanders look slightly different, but the amazing things I’ll show you happen to both kinds. You can’t really see what I’m thinking of right now, but I can show you if we take an egg mass home and keep it in my aquarium. Here, I’ll scoop up some pond water in this bucket and you can put in the salamander eggs.”
After George plopped the eggs into the bucket, he exclaimed, “Hey, there are a whole lot of tiny dots swimming around in the bucket!”
“Sure enough,” I said. “Those are ostracods. Some people call them seed shrimp. Ostracods look like tiny clams. They have two little shells they can open up slightly to stick their legs out and swim or walk around. Let’s go over to that log that sticks out over the water, and you’ll be able to watch the ostracods in the shadow of the log while I fetch my microaquarium from my backpack.”
After I had retrieved the microaquarium (it’s about the size of a business card—just a bit thicker) and placed in it a few dropperfuls of pond water containing ostracods, I told George, “Here, take a close look at the ostracods with my hand lens (10x loupe). I could see he was enthralled, so I continued, “Once we are back home, we can put the microaquarium under my microscope.”
“Speaking of an aquarium, did you know, when I was your age, I had a big aquarium on the buffet in our dining room? I would bring things home from the frog pond to keep in it.
“That gives me an idea! Let’s add a wood frog egg mass to our bucket and also some of the leaves and muck from the bottom of the frog pond. We’ll take this home for my aquarium, and then we’ll have a little vernal pool right on the porch.”
Back home, I said to George, “Fish the salamander egg mass out of the bucket and rinse it off. Then you can put it into the aquarium with some clear water while I get my camera and set it up for a time lapse. That way I can show you one of those amazing things I’ve been talking about.
After the setup was ready, I told George, “OK. Now that the camera is set up, I’ll have it take a picture every few seconds for the next half hour. After that, we can play it back in about thirty seconds, and you’ll be able to see that those embryos are spinning around and around.”
When we watched the time lapse, George said, “Oh, WOW! That’s amazing! It looks like a whole bunch of miniature clocks all spinning around all in different directions! Why are they spinning like that?”
“Well,” I said, “there are several things going on here. First thing to understand is that the still water of the vernal pool is a low-oxygen environment, and all those rotting leaves contribute to the low oxygen. Additionally, the egg mass’s jelly envelope slows down the oxygen’s diffusion from the water into the egg mass, especially for the eggs that are deep inside the egg mass. At this stage of development, the embryos need more oxygen even though they haven’t developed muscle movement yet.
The Creator provided a “fix” for this “problem.” For a certain period of time, the embryos are covered in cilia. These tiny ‘hairs’ beat in a wave-like motion which spins the embryos slowly around inside their eggs. This stirs things up like a slow-motion mixer. The mixing helps move oxygen throughout the egg mass.
“Oh,” said George, “like a slow-motion mixer.”
“Yep,” I said, “The next time you come. I’ll show you one of the most amazing things I have ever seen!”
“Grandpa, the salamander eggs turned GREEN! Are they ok?”
“Yes!” I said. “Look closely at them with a magnifying glass. What do you see?”
As George peered through the glass, he stated, “The baby salamanders are looking out at me with yellow eyes, and they have two feathery things sticking out on each side of their head.”
“Those are gills,” I said. “Look closely again at an egg. Can you see there are several faint lines circling the center green part of the egg?”
“Yes, I can see them!”
“Those lines are different layers of the egg. See how the green color is only in the center of the egg? Now look the salamander larva right in the eye. Can you see something in the black center of its eye?”
“Ummmm, yeah, tiny green circles?”
“Yes! Those green dots are algal cells. They are algae growing inside the egg with the salamander larva. The green color of the egg comes from all of those algal cells.”
“How did they get there, and what are they doing there?” wondered George.
“The algae are apparently inside the adult salamanders and are transferred to the egg from the start. At the right time during the embryo’s development, there’s this algal bloom. The algae provides extra oxygen for the embryo during daylight hours and likely uses up the embryo’s wastes. That symbiotic algal bloom inside an egg has to be one of the most amazing things I have ever seen! It’s like each salamander larva has its own little incubator.”