Researchers Discover Unusual Defenses of Asian Snakes
Juvenile Rhabdophis tigrinus snake from Ishima, a Japanese
island, curls in a defense posture.
Old Dominion University, Alan Savitsky
Vipers are born with a poisonous
bite they can use for defense. But what can nonpoisonous snakes
do to ward off predators? What if they could borrow a dose of
poison, perhaps by eating a toxic frog and recycling the
This might sound far-fetched, but it can happen,
according to an international team of researchers including two
Old Dominion University herpetologists. Their findings could be
good news for endangered species of amphibians, and for humans
with ailments that might be treated with heart-stimulating
compounds in the toxins.
A paper written by Deborah A.
Hutchinson, a postdoctoral research associate in the Department
of Biological Sciences, together with her mentor, Alan H.
Savitzky, professor of biological sciences, will appear this week
on the Web site of Proceedings of the National Academy of
Sciences (PNAS). Advance media alerts from the journal last week
stirred the interest of The New York Times, Science magazine,
National Geographic magazine and many other publications.
more than seven years, Hutchinson has been studying the Asian
snake Rhabdophis tigrinus and its relationship with a type of
toxic toad. In the PNAS article, she and her co-authors describe
dietary sequestration of toxins by the snakes. The process allows
the snakes to store in their neck glands some of the toxins from
the toads they have eaten.
When under attack, the snake
thrusts the back of its neck toward the would-be predator. The
snake’s dorsal skin often ruptures during a confrontation,
causing liquid to leak from the glands. The liquid irritates
mucous membranes and contains toxic steroids.
researchers made their case by testing Rhabdophis tigrinus on
several Japanese islands, one with a large population of the
toads and another with none of the toads, and compared them with
snakes from the main island of Honshu, where toads are scattered
here and there. The presence of toxins in the snakes’ neck
glands depended upon their access to the toads. Laboratory tests
with snake hatchlings confirmed the fieldwork.
without the borrowed toxins were more likely to turn and flee
from danger than to stay their ground and perform the
neck-thrusting defensive maneuver, according to the researchers.
Surprisingly, the researchers also found that some of the
mother snakes with high concentrations of the toxins in their
glands were able to pass on defensive toxins to their offspring.
This finding shows how maternal diet can bestow a survival
advantage on offspring.
Hutchinson said the research
identified six defensive compounds in Rhabdophis tigrinus that
are new natural products and may hold promise in medical
treatments for humans suffering from hypertension or related
blood pressure disorders.
Also, she said, “The
demonstration that a snake is dependent on a diet of toads for
chemical defense is highly unusual and, therefore, important to
the field of biology. (And) the fact that R. tigrinus is
dependent on toads for defense has implications for conservation
because amphibians are currently undergoing a global
Hutchinson, who earned a master’s
degree in biology in 2001 and doctorate in ecological sciences in
2006 from ODU, used the research project for her doctoral
Savitzky said the project was proposed by
Akira Mori from Kyoto University in Japan, and would not have
been possible without the chemical analyses provided by two
Cornell University faculty members, Jerrold Meinwald and Frank
Schroeder. The research team also included Gordon Burghardt, a
biologist at the University of Tennessee, and Xiaogang Wu,
another chemist at Cornell University. These individuals are
co-authors of the research paper.
Funding from the
National Science Foundation was critical in supporting the
important chemical analyses, Savitzky said. The findings may have
been released sooner, Hutchinson added, “but we spent
additional time ensuring that our unique findings would be
published in a highly respected journal.”
/ Credit: Old Dominion University