Stories of frog malformations

"Whatever happened to the ‘deformed frogs’ problem?"
  
This is a question that we get all the time.

I have tried to answer it for Ask NRRI:

The ‘deformed frogs’ problem has not disappeared, even though it no longer makes the nightly news. Although the widespread occurrence of amphibian skeletal malformations has been considered an important environmental issue and researched extensively around the world, causes of these deformities in wild populations have been difficult to pinpoint.
One thing that scientists agree on is that deformities can result from multiple causes and that these causes vary from region to region. Scientists also believe that many of the causes are primarily due to, or exacerbated by, human activities. The major causes of malformations identified so far are chemical contaminants, parasites, and injuries from predators. At any given location, one or more of these factors could cause amphibian skeletal malformations as well as amphibian population declines. Additionally, the causes of malformations at one site may differ from those at another site.
Deformed frogs continue to be found across Minnesota and around the world, although rarely in huge outbreaks like that discovered in 1995 at Ney Pond in Le Sueur County, and other locations around Minnesota. Research continues to resolve uncertainties in the amphibian malformation phenomena.

Malformed metamorphic Northern leopard frog with extra digits (© NRRI/UMD)

Malformed metamorphic Northern leopard frog with missing foot (© NRRI/UMD)

 There is also a new book out by Judy Helgen (Peril in the Ponds: Deformed frogs, politics, and a biologist's quest) which documents how the research on amphibian malformations got started and her efforts to solve this 'mystery'.

 Minnesota Public Radio covered this story this morning on Morning Edition (Deformed Minnesota frogs still largely a mystery 17 years later) and will be covering it again on All Things Considered (sometime between 3 and 6:30 pm). Here's a preview from the Bob Collins News Cut today (7/17/12):

 "Minnesota made headlines around the world in 1995 when school children discovered dozens of grossly deformed frogs in a pond in south central Minnesota. Soon there were more reports of deformed frogs from around Minnesota and other states -- gruesome pictures of frogs with extra legs, or missing legs, or eyes in the wrong place. Everyone wondered if the frogs were a sign that something was wrong in the environment that could also spell trouble for humans. Seventeen years later scientists still have not completely solved the mystery of what caused frogs to develop those deformities. But we do know more about how the investigation unfolded and how the case of the deformed frogs spawned a fight within the Minnesota Pollution Control Agency about whether the agency should even look into the matter. MPR's Stephanie Hemphill will have the story."

There is also an article on frog malformations in the local section of the Duluth News Tribune (printed MPR story).

Tadpoles and Marsh Marigolds

Wood frog tadpoles in Duluth are about 10 mm long right now (about the length of my pinkie finger nail). At this size, they are hard to photograph.

To put this development into perspective, on this day in 2011 the wood frog eggs had just started to hatch.

In many wetlands and ditches, marsh marigolds are blooming,

marsh marigolds - look for them in your neighborhood wetland or roadside ditch

wood frogs are still hanging around,

(adult)

and spring peepers and chorus frogs are calling (and laying eggs).

Spring peeper (adult)

Western chorus frog eggs - starting to develop

Fairy Shrimp

 Fairy shrimp are small crustaceans that live in the same small temporary wetlands that wood frogs use for breeding. These aquatic critters are fascinating to watch as they swim around upside down with their many leaf-like or feathery legs.

I recently found large numbers of fairy shrimp swimming around developing wood frog eggs. There were hundreds of them! I had never seen this before, so I tried to capture some pictures.

15+ fairy shrimp next to wood frog egg mass

close-up of one of the fairy shrimp

To learn more about Fairy Shrimp (and vernal pools) visit The Vernal Pool Association's website (based in Massachusetts).

Wicked Big Puddles: What an Odd Spring

The strange spring and how it impacting vernal pools and amphibians is noticed in other parts of the country: Wicked Big Puddles: What an Odd Spring

FROM WICKED BIG PUDDLES: Dry pool in Stoneham, MA, 26 March, 2012

Wood frogs still calling

Wood frog adults and eggs appear to have survived the freezing temperatures last week. This frog species is well adapted to cold (it is the only amphibian in Alaska) and has started calling again after a break during the cold weather over the last week or so.

On Friday afternoon last week there were many frogs calling in Duluth parks and backyards. In a pond in Hartley Park, the wood frogs were making a huge racket (along with one spring peeper).

Wood Frog eggs in Hartley Park (about 2 weeks old)

Some wood frogs laid eggs 2 weeks ago, and many of these eggs are developing well. The small black embryos are elongated with visible heads and tails. In some locations they have started to emerge from the gelatinous envelopes of the eggs, but are not yet free-swimming. In the egg masses that I have been following, there are also many that are not developing due to the cold temperatures or other causes.

Developing wood frog embryos (black) in egg masses turned green from symbiotic algae (notice the dead eggs, which have almost entirely white centers)

 

 

How are frogs impacted by the early spring?

The early spring could benefit or harm the frogs. We have several frog species that start calling (and breeding) as soon as the ice-melts in wetlands and small ponds.

The earliest breeder of these is the wood frog (Rana sylvatica), which sounds like quark-quark. This species emerges from hibernation as soon as the small wetlands they breed in have open water. Wood frogs can benefit from the early spring by breeding earlier, which gives their tadpoles longer time to grow over spring and summer. Bigger tadpoles turn into bigger froglets, which increases their likelihood of survival through the fall and following winter.

Adult wood frog

HOWEVER, early springs are often associated with low snow pack, which means that these small, usually temporary, ponds start the season with much lower water levels than in a typical spring. As these ponds are generally fed by snowmelt and precipitation (no, or little, connection to groundwater), the water levels at wood frog breeding time are directly tied to snowmelt, and maintaining adequate water levels for tadpoles to develop depends on spring and early summer rains. If the ponds dry up in June (even for just a few days), before the tadpoles metamorphose into frogs, the entire generation of frogs from the pond is lost.

Another impact of the early spring is the possibility of extended calling for wood frogs (who usually just call for a few days to a week) which could greatly exhaust the males as they wait for females to arrive in the ponds to lay eggs. Male frogs arrive in ponds first and beginning calling individually or in groups. Females arrive later, select a mate (based on factors we don't fully understand) and lay eggs. In an early spring, male wood frogs can start calling WEEKS before the eggs are laid - especially if the weather shifts between warm and cold several times a week. Frog calling is very energetically demanding activity, and male wood frogs complete breeding before foraging for food on the forest floor. If the warm spring weather starts and stops (as it has this year), the male wood frogs could get really worn out and deplete their energy reserves while calling on and off for multiple weeks while they wait for the weather to be consistently warm enough for the females to arrive and be ready to lay eggs.

(as posted on Ask NRRI)

Wood frog eggs - April 6, 2012

Reports of frog calls have been coming in for 2 weeks. First reports were on Friday March 23, 2012 from Hartley Park - the earliest date since I've been keeping track. Most likely these were all wood frogs.

Last week, frogs started and stopped calling a few times. Now I can say it is spring because the wood frogs have started laying eggs! I found my first wood frog eggs this afternoon, amidst a full chorus of calling wood frogs.
 

Example of wood frog eggs (freshly laid)

Lots of egg masses in one pond, but only a few in another - I expect egg laying will continue over the next few days.

Wood frogs are explosive breeders, meaning that they lay all their eggs during the same short stretch of days (usually in one central location per pond).


I will continue to follow the development of eggs and tadpoles in these and other ponds through the spring and summer.

Early Spring in Duluth!

Reports of wood frogs calling are coming in weeks earlier than last year.

All you need to do to see the early spring is look out the window and remember what it looked like last year.

Wood frog breeding habitat - April 2011

In case you need more than your own eyes:

Scenes from an Early Spring - MPR report from last week