MEDILL REPORTS (Northwestern University, Chicago, Illinois) 22 May 08 Conservationists crusade to save an endangered Illinois salamander (Angela Nitzke)
“Where do babies come from?” is a loaded question that makes most adults squirm. Explaining reproduction is not easy, but there is only one answer...a female produces eggs that are then fertilized by male sperm, right?
But not if you are a silvery salamander surviving in a remote pond in Illinois.
The silvery salamander is a hybrid, resulting from ancient interbreeding between the Jefferson salamander and the Blue-spotted salamander, but this is just the beginning of the story.
Scientists thought they had figured out that the silvery salamander, also called a Jefferson / Blue-spotted complex salamander, was the result of ancient interbreeding of those two species until they took a closer look at the DNA and found that a third salamander was involved.
Mitochondrial DNA is genetic information passed on to offspring by the mother and scientists were surprised to find that the mitochondrial DNA of silvery salamanders matched neither of the two species they originally thought were the parents.
What they found was that a third species, the small mouth salamander, had gotten its mitochondrial DNA into one of the two parent species of this strange hybrid. Nothing about this salamander is straight forward. “I don’t know why we were surprised,” said Christopher Phillips, associate professional scientist with the Illinois Natural History Survey.
The female parent in the original hybridization event had the “wrong” mitochondrial DNA. “How that happened we are not exactly sure,” said Phillips.
The mysterious mitochondrial DNA is just icing on the cake for scientists studying the unique genetics of silvery salamanders. The real story begins with the way the blue-spotted salamander and the Jefferson salamander managed to make babies in the first place.
It is rare that two different species can mate successfully, so most offspring probably died, but they kept making mistakes by mating together and eventually something molecular happened and the offspring didn’t die, said Phillips.
The salamanders made enough repeated mistakes and a hybrid was formed, said Phillips. The chromosomes from each parent, [pieces of DNA that contain genes] were equal in number but different enough that the fertilized eggs couldn’t complete the typical reproductive process, said Phillips. Yet they managed to reproduce anyway.
Some trick, but the story of the silvery salamander does not end there. The hybrid not only must survive but be fertile. And over thousands of years, one survived that was fertile and it mated back with the Jefferson salamander. “Something really weird happened. Now you have even bigger problems,” said Phillips.
When the hybrid salamander mated with the male Jefferson salamander their offspring were triploids, with three sets of chromosomes. Somewhere along the way the female laid eggs with two sets of chromosomes rather than the normal set,” said Phillips. So now you have a female salamander contributing two sets of chromosomes [diploid], and the male it mates with contributed a third set.
Things start to get dicey when the number of chromosomes continues to add up. The triploids couldn’t keep mating with male salamanders that would add more DNA to the mix, so they evolved a way to reproduce without needing males, well almost not needing them.
And did I mention that silvery salamanders are always female? “Once all the nuts are cracked, you have all female triploids who are clonal,” said Philips. That is, they are genetically identical.
How can a salamander make babies without DNA from the males to fertilize their eggs? Scientists think the females started to reject the sperm. There is already a mechanism for this in place in amphibians – frogs, toads and salamanders. The process is similar to human reproduction, in which an egg is fertilized; of several thousand sperm for one egg only one makes it in to the egg, said Phillips.
So with silvery salamanders, “only the ones who could repel that first sperm could survive,” said Phillips. The males were not contributing any genetic material. Known as gynogenesis, only physical contact was required for the egg to start its first division and eventually become an embryo.
Because there are no male silvery salamanders, the females rely on male salamanders from related species to stimulate egg development, for example the blue spotted salamander or the Jefferson salamander.
All of this means that this goofy little animal needs male salamanders from the Ambystoma family for its continued survival. (Ambystoma is the taxonomic classification for the family of salamanders commonly referred to as "mole salamanders.” Found throughout most of North America, fully grown adults have robust bodies and limbs and short, blunt heads).
What makes these salamanders special also poses a challenge to conservationists hoping to save this family from extinction.
The silvery salamanders “need male jeffs [Jefferson salamanders] to trick into getting sperm,” said Phillips. But sometimes the silvery salamanders are found in places where there are no Jefferson salamanders, so they had to find another species of salamanders that breed at the same time. “Maybe this happened because they spread to a pond that jeffs didn’t spread to or maybe jeffs went extinct and they found themselves stuck,” said Phillips. Either way, Phillips said, there is no way this happened quickly and there were probably many silvery salamanders that went extinct when separated from male Jefferson salamanders.
Conservation of Illinois’ Salamanders:
Scientists had only been able to find silvery salamanders living at one pond in Illinois, but Phillips thinks he may have found a second population as recently as March. He has spent much of his career studying these unique animals and has even found some tetraploid salamanders, with four sets of chromosomes, the fourth set coming from male small mouth salamanders. Either there are “super strong sperm or females are losing ability to repel that sperm,” said Phillips.
One thing is clear, the more researchers learn, the more complex the story becomes. And there is a lot more to learn about these nutty little creatures. “There are not a lot of vertebrates out there who do this, a few fish and a few lizards, so this is a really sexy system,” said Phillips
But salamanders are facing habitat loss and are extremely sensitive to environmental changes. The Jefferson salamander is a threatened species in Illinois, which means that it is likely to become endangered in Illinois in the foreseeable future. The silvery salamander is already listed as endangered in Illinois, which means is in danger of extinction as a breeding species.
The silvery salamanders’ unique evolutionary lineage is the source of some conflict over whether it should be considered a distinct species and given a Latin species name. This controversy means that some states do not list the silvery salamanders among their threatened or endangered species, which could complicate conservation efforts.
The unique reproductive biology of silvery salamanders makes management activities a little more complicated, said Phillips. “Aside from the environmental conditions these salamanders need this other salamander,” said Phillips.
“Amphibians aren’t all that different than us, but one striking difference is that they don’t have any protective covering on their skin like skin or scales,” said Stephen Mullin, associate professor of biological sciences at Eastern Illinois University, who jokingly refers to amphibians as “naked vertebrates.”
The Jefferson salamander is long and thin, about four to eight inches in length, and varies in color from dark brown, to slate-gray, and can have blue colored flecks on its body, tail and legs. The secretive salamanders live in moist woodlands near breeding ponds, and spend much of their time underground, under rotting logs or rocks, or in leaf litter.
Silvery salamanders are virtually identical to Jefferson salamanders and can only be differentiated by looking at the chromosomes or blood cells.
Monitoring amphibian populations is important because they are indicators of environmental quality. They are susceptible to changes in climate and geochemistry long before it really affects our lives, said Mullin. He noted that amphibians are referred to as “canaries in the environmental coal mine.”
The threats to amphibian populations are not limited to environmental factors, they are also faced with habitat loss.
The Illinois landscape has changed dramatically in the last 200 years and much of it has been developed. Illinois has lost over 90 percent of its original wetlands and close to 100 percent of its original prairie. The silvery salamander and Jefferson salamander are two of the 424 species that are listed as threatened or endangered. Over the past 30 years, populations of many wildlife species have faced serious decline.
To confront these declines, the Wildlife Preservation Fund has funded research that will improve conservation efforts by identifying the distribution and habitat of Jefferson Salamanders,
The fund is a grant program managed by the Illinois DNR is funded by tax payers who donate money when filling out their state tax form. “There is a core group of taxpayers with an interest in helping with this work,” said Glen Kruse, head of the Division of Natural Heritage in the Illinois DNR.
Using grant money from the Wildlife Preservation Fund, Mullin and members of his lab captured salamanders that lived near one of the two Illinois ponds over the course of two years and recorded their sex and size. Before releasing them back into the wild, they were marked for future identification. Data were kept on the number of salamander eggs, how many hatched and then the number of juvenile salamanders to develop a population model.
When it is time for the silvery salamander to lay her eggs, she attaches the small egg masses to twigs in underwater breeding ponds. In spring, salamanders hatch from the eggs that the mother laid in the pond during the winter. The young at this stage is called a larva, and it has gills which enable it to live in the water. The next stage in the baby salamander’s life is metamorphosis, when it loses its gills and develops lungs that enable it to breathe air. As the pool dries, the salamander moves onto dry land.
So far 2008 has been quite a wet year with nearly two times as much rain than we would normally receive by this time of the year, said Mullin. If the precipitation continues there will probably be enough water to support metamorphosis,” said Mullin.
This has not been the case in previous years. His lab found that the pond dried down faster than it would normally take for these animals to complete larval development in 2004 and 2005. In 2005, it dried too quickly for any of the larvae to survive, he said
Mullin’s lab made suggestions to the Illinois DNR for maximizing the effectiveness of conservation efforts by focusing on enhancing the survival of the salamander larvae, for example by bulldozing ponds in mid winter before the salamanders lay their eggs. The bulldozers can scrape out deeper basins, so the ponds will hold water for longer periods of time, he said.
What on the surface may seem like just a simple slimy salamander turns out to be a complex combination of evolutionary genetics and reproductive biology, where even basic concepts like species name, fertilization and sex, don’t fall into the traditional categories used to explain the biology of other animals. Similarly perplexing is the best way to protect them. Christopher Phillips seem convinced that conservation efforts are worth it.
“They are part of our natural heritage and that is reason enough. You should do everything you can to keep them [salamanders] here,” said Phillips. Salamanders are not like bald eagles in terms of aesthetics, said Phillips, “Salamanders don’t knock you on the head.”
Some people visiting the Middle Fork Nature Preserve “think it is pretty cool” to know that a salamander, found only in one (or perhaps two) pond in Illinois, is around, said Phillips.
Conservationists crusade to save an endangered salamander