Monday, April 8, 2013

Amphibian Eggs

Southern leopard frog eggs- note individual coating
Our first foray for morels on a rare sunny warm day was too early in the season, but like any foray into the woods, it had its own treasures.  In this case, we found eggs in several ponds where we hadn't seen them before.  One small 10 foot wide pond is only 10 years old and is way up in the woods 250 feet higher than the valley floor.  It collects water from the ridge top and we found the Southern leopard frog eggs above.  How they made it up here to start families remains a mystery to me.

We are new to amphibian eggs this year and sought the guidance from our more knowledgeable friends.*  If you too are new to this, here are some of the lessons learned.  The first one is to differentiate between frog and salamander eggs.  Frog eggs have a coating of jelly around each individual egg which can be seen in the picture below.  A mass of frog eggs may contain 500-2000 eggs.

Leopard frog egg mass in water- compare to maple leaf
Different frogs and toads may lay their eggs in identifiable clusters as seen at this USGS site.  Toads lay their eggs in long strings.  Newts wrap their eggs individually in leaves.
American toad eggs
The southern leopard frog eggs shown in the picture at the top of the page have black and white coloration.  As they mature, they lose the white color and the tail of the tadpoles start to develop as seen below.  Soon they will emerge and begin the arduous trip toward frogdom.  Only a few will survive to adulthood and eventual parenthood.  The rest will provide food for other creatures around the small pond.  It is probably best that way as there is no way this little pond could support 1,000 frogs. 
Leopard frog eggs- some showing early tails
Spotted salamander eggs have a thick layer of jelly covering the whole mass of eggs.  Typically there will be less than 100 eggs in the glob.  As you can see from the picture of the pond, the egg cluster appears as a single smooth blob with the eggs hard to define under water, compared to the individual frog eggs clustered in the pond picture above.

Spotted salamander eggs in water.
Spotted salamander eggs, were not unexpected as they breed in February.  Their typical home is in vernal pools (ephemeral or temporary) in hardwood forests, exactly where we found them.  They tend to live in leaf litter or burrows in the forest but make a mass migration to ponds when the spring rains hit.

Spotted salamander eggs- note all the eggs in one jelly coating
The thick clear jelly coating around the eggs protects them from drying out but inhibits oxygen absorption. This is especially important when the pond dries up, as happens to ephemeral ponds which are critical for many amphibians.  A pond that disappears every year means that no fish or even bull frogs live there, a critical source of predators.  Temporary wet pools (ephemeral) means more babies survive.

Imagine being an egg in the middle of the mass, far away from the edges where the dissolved oxygen in the water exists.  Spotted salamanders have an interesting and unique symbiotic relationship with a single celled green alga, Oophila amblystomatis.  The algae takes up carbon dioxide and nitrogen waste products from the eggs and photosynthesizes oxygen.  The eggs acquire the needed oxygen, continuing to develop into larvae while producing more carbon dioxide and the cycle continues.  The New Scientist article calls this The First Solar-powered Vertebrate.  The relationship has been known before but now there is proof that the algal cells exist inside the cells of the salamanders themselves.  The algae is thought to be contained in the salamander germ cells and thus transmitted to each new generation.

MDC has a spotted salamander video but don't expect a lot of action as this one was rather bored with the whole process.  Perhaps it had already bred and now was just waiting for next year, knowing that spotted salamanders have been known to live up to 32 years.  A lot more pictures and information is available at fcps.edu/islandcreekes. **

* Thanks to Rhonda Rimer (MDC) for identifying the eggs and Jeff Brigler (MDC State Herpetologist) for confirming the ID.  Also thanks to Brian Edmonds for the information on the green algae association.

** fcps.edu/islandcreekes/ecology/organism_menu is one of my favorite resources on ecology.  In addition to great photographs of many species of plants and animals, it has a comprehensive listing of Relationships in Nature, listing prey, predators, shelter and other ecological associations.  You will find its links scattered throughout the Resources link on the right.

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