Researchers study eastern hellbender salamanders parental habits
Although eastern hellbender salamanders are known by many unflattering nicknames — mud puppy, snot otter, grampus, and Allegheny alligator — about 70 percent of adult male hellbenders should more accurately be known as doting fathers.
Unlike most wildlife species, male hellbenders provide exclusive care for their young for an extended period of seven months. A male eastern hellbender with his eggs in an underwater nest box. Photo courtesy Cathy Jachowski.
William Hopkins, professor of wildlife in the College of Natural Resources and Environment, is the principal investigator on a new grant from the National Science Foundation (NSF) for $738,817 to study parental care in the eastern hellbender salamander.
This two-foot long salamander, found in cold, rocky, fast-moving rivers and streams in the Appalachian region, is one of the largest and most fascinating amphibians in the world.
These giant salamanders were once common in streams across the eastern United States, but have experienced drastic population declines in the past 30 years due to habitat loss caused by erosion and pollution and are increasingly threatened by climate change.
"Hellbenders are a fascinating and misunderstood species surrounded by folklore and misinformation. Their recent rapid population declines are a cause for conservation concern," said Hopkins, director of the Global Change Center, an arm of the Fralin Life Science Institute.
The hellbender requires well-oxygenated, clean streams and rivers; they are especially sensitive to environmental changes and pollution because they breathe by absorbing oxygen through their skin. Small changes in water quality affect them much more quickly than local fish and other wildlife, making the hellbender an important indicator for local habitat conditions.
One commonality among most declining hellbender populations is indirect evidence that their reproduction may be disrupted. "Because Virginia harbors some of the hellbenders' healthiest remaining populations as well as declining populations, our work represents one of the last opportunities to reveal the role that reproductive physiological ecology plays in the viability of hellbender populations," said Hopkins.
The research team spans three colleges and brings together diverse expertise to tackle these important questions. Co-principal investigators on the grant are Richard Helm, associate professor of biochemistry in the College of Agriculture and Life Sciences, and Joel McGlothlin, associate professor of biological sciences in the College of Science.
The interdisciplinary team's research will advance the understanding of how environmental conditions and hormonal processes interact to influence reproduction in the eastern hellbender.
"Hellbenders may soon be an endangered species, so the broader impacts of this work have the potential to be huge. Learning more about their reproductive behavior may help to reverse some of the declines we see in so many populations," said McGlothlin, an affiliated faculty member of the Global Change Center.
Male hellbenders exhibit extraordinary parental care under normal conditions. In the fall, hellbenders start breeding. The female hellbender lays the eggs and the male fertilizes them externally. The male then runs the female off and provides 100 percent of the parental care. The male will stay with the nest until the following spring and defend the eggs against predators. The male hellbender also waves his tail over the eggs to keep them well-oxygenated until they hatch.
Many animals provide care for their young, which is critical for early development, but disruption of this relationship can lead to neglect, abandonment, and the death of offspring. Researchers have found that about 30 percent of the time, eastern hellbenders switch from being protective, doting fathers to the extreme of eating their own young, also known as filial cannibalism.
More than 100 different species of animals will eat their own young, but the underlying mechanism that causes this drastic switch in behavior is unknown in most species. The investigators hope to unravel this mystery with the research funded by this grant. Changes in the environment, hormonal imbalance, and energy deficits are among the viable hypotheses as to why this may be happening.
"Cannibalism of offspring has long fascinated scientists, but little is known about the environmental factors that provoke this behavior or the physiological changes that underlie the decision to care for or eat one's young. From an evolutionary standpoint, this behavior has long baffled scientists," said Hopkins.
Answering these questions will provide insights into how and why adults terminate parental care in a broad range of species.
Hellbenders are a great model organism for studying this behavior because the researchers have developed techniques in the field where they can study hellbenders under natural conditions. Their study will employ underwater nest boxes in streams across a variety of hellbender habitats to determine what hormones trigger this switch in behaviors and what environmental factors influence cannibalism. Hellbenders are large, so researchers can take blood samples repeatedly over a span of time.
Researchers from Hopkins' lab will take blood samples from the hellbenders as well as egg samples and work with McGlothlin's lab to rule out the hypothesis that male hellbenders eat their eggs when they think that another male has fertilized some of them. Students working in McGlothin's lab will use DNA paternity testing to test for this possibility.
"Although we suspect that this type of extra-pair paternity is rare, not much is known about the hellbender breeding system, so we might be surprised," said McGlothlin.
Helm's research team will analyze blood samples from the hellbenders with mass spectroscopy and targeted assays to test if hormonal and environmental changes are an underlying cause of filial cannibalism.
Mass spectroscopy is an analytical technique that ionizes samples of a chemical species and sorts the ions based on their mass-to-charge ratio. Helm's team will be able to identify the differences in hormones, metabolites, and proteins from hellbenders exhibiting different behaviors.
"This will allow us to associate the chemical features in blood serum with hellbenders before, during, and after the mating season. We can then link the features to behavior, potentially segregating caretakers from cannibals," said Helm.
Helm's team will also be able to analyze chemical differences in hellbenders found in environments favorable to hellbender growth and development, and environments that are not, allowing them to help tease out the answers to some of the questions about how physiology and the environment affect hellbender parental care.
Not only will this research advance knowledge of parental care, but the team's study will also employ high school science teachers in an integrated outreach effort to conserve the hellbender species.
"Southwest Virginia is home to a number of underserved groups, including rural Appalachian communities that face a number of socioeconomic and educational access challenges. These same communities live in one the most biodiverse regions in North America, though few citizens recognize the global significance of the ecosystems that surround them," said Hopkins.
Hellbenders are well-established in the folklore of Appalachia, providing a platform to access rural communities in Southwest Virginia about science and environmental issues. Hopkins' research team will take advantage of the charismatic nature of the eastern hellbender to reach local and global audiences.