Studying the Secrets of Salamander Sisterhood
Nobody said life was fair. Some manage to slip through life scot-free, while others are left to do all the work. Ask any mother. It's even true farther down the food chain.
When brown four-toed salamanders lay their eggs and skip out, shirking their maternal duties, another female steps in to hatch the abandoned eggs and protect the mossy nest.
Biology professors Reid Harris and Ivor Knight are trying to discover why this obliging second female bothers. Clearly, there's no emotional tie among salamanders. Why, the professors wonder, would she risk her health, her reproductive potential and that of her descendants by expending her energy on others' offspring?
At least on the surface, the professors say, such behavior contradicts evolutionary theory, which says that organisms behave in ways most likely to strengthen, not weaken, their chances of survival. Either Darwin was wrong or, more likely, Knight and Harris reason, there's got to be a Darwinian explanation for this apparent martyrdom.
They suspect that the obliging salamander makes this sacrifice because she is genetically related to the females who left their eggs behind - perhaps a sister, aunt or cousin. For Harris and Knight, the quest to confirm their suspicion is a major research project in evolutionary behavior financed with a $215,000 grant from the National Science Foundation over the next three years.
If they are right, and the salamanders are related, this brooding female does have a stake - a genetic one - in the survival of her nest's offspring. "Relatedness would explain their altruistic behavior in light of evolutionary theory," Harris says.
While nesting, the brooding female doesn't forage or eat or enjoy the same advantages as the females who lay eggs and leave, Knight explains. "There is a cost. Over generations, that translates to less healthy salamanders with lower reproductive output, which could lead to the extinction of her genes."
But if the eggs the brooding females protect are related, he says, there is compensation.
"At least part of her genes are going on to the next generation," Knight says. "I share half of my genes with my sister and a fourth of my genes with my nieces and nephews, and so on with my cousins, etc. So as a female salamander who remains in the nest, I am protecting my gene pool."
Research into this curious communal nesting behavior may offer clues into the behavior of other amphibians as well as other animal species and could provide clues about their future survival. The project marks a collaboration between molecular biology and evolutionary ecology, the JMU professors' specialties.
Evolutionary ecologist Harris and his students wade along the banks of two ponds in the George Washington National Forest to collect salamanders and larvae, while molecular biologist Knight and his students study the salamanders' DNA characteristics with the use of sophisticated equipment including an automated DNA sequencer.
|Harris acknowledges his is the grubbier side of the research. He and students trudge through mud and muck to reach the study area, a fenced-in habitat that provides the perfect place to study the intimate secrets of salamander nesting behavior. Daily they check their salamander traps, which are nothing more than empty No. 10 vegetable cans from Gibbons Hall. Both professors say the project gives them and their students a rare chance to study the intricate web of pond life.
Back in the lab, the trick is to identify who's who among the salamanders. They are distinguishable by the spot pattern on their bellies, which is as unique to a four-toed salamander as a fingerprint is to a human. Harris takes pictures with a digital camera, records the information and shares it with Knight.
"The spots are their signatures," Knight says. And, on the lighter side of research, Harris adds, "We give them names based on the spots' design, such as 'the Holy Cross.'"
From there, Knight identifies the salamanders' relatedness using the same highly publicized DNA profiling technology used to determine paternity and identify biological evidence at crime scenes.
"I apply it in a completely different organism," Knight says. "We use the same sets of techniques. I take a bit of tissue from the salamanders and then extract the DNA out of the tissue."
The professors then set their charges loose in cattle water tanks at the University Farm. They keep track of them by matching the salamanders' DNA profiles with their signature spots and assigned names.
"Once Ivor and his students figure out who's who among the salamanders, we can set up populations in the tank, and change or adjust the genetic composition of the population, to find out if there is more shared nesting when the relatedness is high, or less shared nesting when relatedness is low," Harris says.
Knight and Harris are conducting the only known joint nesting behavior study among amphibians. "And among amphibians," Harris adds, "this joint nesting behavior is unique."
One of his former undergraduate honor students, Tomalei Vess, now in Duke University's doctoral zoology program, established earlier that salamanders, even as larvae, can recognize their kin. Harris hypothesizes the recognition is based on smell.
"The evidence from the larvae stage is valuable because if they recognize each other as larvae, they may as adults," Knight says. Salamander larvae have been found to swim over to siblings, leaving nonrelatives alone. "Somehow they know," Knight says.
Step by step the professors and their students have been building on their past studies to establish a scientific basis for brown four-toed salamanders' behavior. Vess has already established kin recognition. "And we documented the salamanders' nesting behavior for several years," Knight says. "Now we want to know whether they are related."
The answer will tell the professors and the field of evolutionary science how communal nesting makes sense in terms of evolution, Harris says.
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