Issue 1, January 2004
For the Love of Frogs: Featuring Dr. Tyrone Hayes
Jean Lee, Features Editor
Integrative biology, University of California, Berkeley, 2002
red eyed tree frog is most striking in its coloration. Source:
Hayes is an associate professor of integrative biology at the University
and he is crazy about frogs. There are literally hundreds of “froggy”
paraphernalia adorning his laboratory, peeping out from behind his
books, stuck to the refrigerator, and staring goggle-eyed at each
student visiting his office hours.
Hayes grew up in South Carolina, and as a child he loved to explore
swamps. He fondly remembers his favorite book, a gift given to him
by his grandmother, What is a Frog? In one of his very
animated presentations on his current research, Hayes told his endocrinology
students, “I was fascinated by how one cell could turn into
a tadpole, and further turn into a frog … a completely different
organism! One is aquatic and is able to swim and has gills, while
the other has four legs, hops around, and breathes with lungs on
turns out that Hayes’s passion for these unique organisms
is well founded. Frogs have proven to be important in deciphering
endocrine function and alteration; the hormones found in frogs are
the same as found in mammals, including humans.
As an endocrinologist, Hayes investigates the hormone-dependent
features of frogs and the potential implications frog population
development, coloration, and behavior has on both conservation and
human health. In a study of African Hyperolius frogs from
Ethiopia and Uganda, also known as reed frogs, Hayes and his team
examined highly varied color polymorphisms and how they may be affected
by hormonal changes in or to the frogs. The study was presented
in National Geographic magazine as well as scientific journals.
the African clawed frog, for example, colorations are due to testosterone
and estrogen levels,” Hayes explained to his Berkeley students
as he showed them what appeared to be two completely distinct species.
The two “different” species were in fact one and the
example is when you inject a tadpole with thiourea and disable its
proper levels of thyroid hormone: The tadpole becomes an abnormally
giant tadpole and not a frog.” Frog skin, laryngeal sacs,
size, shape, sexual development, and behavior can all be altered
by chemicals. The drastic effects that hormonal injections or blockages
have on the frogs’ morphologies have led to Hayes’s
use of this exciting “frog bioassay.” By studying the
effects of hormones and other chemical compounds on frogs, humans
can determine the extent to which water sources or lands are contaminated
in a cost-effective and efficient manner.
normal and healthy gecko frog. Source: AllAboutFrogs.org
Hayes has chosen to focus on environmental pollutants that produce
changes in frog endocrine functions. He has traveled all over the
world studying frogs and other amphibians. When asked, he recalls
with a smile, “I’ve been to Congo, Uganda, Ethiopia
… well, pretty much all of East Africa. I’ve been all
over Europe and Asia. I’ve even been to Turkmenistan, which
is North of Iran. I went to a conference there because that’s
where you find both Central Asian animals and Central European animals,
and a unique mixture of living organisms of the two regions.”
Hayes is zeroing in on the use of atrazine, a weed-killer that has
been used for more than 40 years in the United States on monocot
crops. More than 150 million pounds of atrazine are used each year.
“I formulate a lab model, use that for comparative studies,
then move on to field studies and field simulations, and bring all
this back to the lab,” he explains to his lecture students.
“Atrazine is an endocrine-disruptive herbicide … it
has effects on frog gonadal growth, laryngeal growth, and developmental
growth in terms of metamorphosis.” Hayes strongly asserts,
“This is relevant to us. There is a direct link to human biology.”
What affects our amphibious friends can also affect us.
very low levels of toxins in the environment (both in the lab and
in the field) have proven to irreparably damage frog systems. Hayes
tells his stunned students during a slide presentation of mutated
frog tissues, “I mean, atrazine is bad but there are a number
of chemicals in use. Just one low dose turns this species into a
hermaphrodite. A mixture is worse (such as in runoff from nearby
crop field into the lake where the frogs live). There are other
bad effects too.”
frogs can become hermaphrodites (animals with both testicular and
ovarian tissue), but even the degree of hermaphroditism goes from
bad to worse. According to slides taken from the Hayes lab at Berkeley,
some of the male frogs can reach a state where their testicular
tissue is literally exploding with eggs. The list of anomalies in
these little animals due to chemicals that humans disperse is quite
mechanism of hermaphroditism is one of active feminization and demasculinization;
atrazine turns on the enzyme aromatase, which turns the hormone
testosterone to estrogen. Atrazine inhibits laryngeal growth in
male frogs as well. While the EPA standard for atrazine levels in
water is three parts per billion (ppb), the Hayes lab found that
even 0.1 ppb causes abnormalities in frogs.
deformed frog with an additional back right leg, found in
Minnesota in 1996. Source: Minnesota Pollution Control
low doses sometimes result in more severe effects than high levels.
This is analogous to hormonal changes causing reproductive changes
in a woman’s body. Low dosages of estrogens induce egg development
and uterine lining growth (i.e., prepare for pregnancy),
but high dosages do none of these things and in fact are used in
birth control pills. Likewise in male frogs, low dosages of atrazine
induce abnormal egg development in the testes, while high doses
amazingly, many frogs don’t die,” continues Hayes. “They
adapt and find ways to avoid the toxicants and pollutants in their
environment. They develop differently, act differently, and reproduce
and recover at different rates.
“Also, I’m not only interested in just one chemical.
There is no single chemical anywhere! I want to know what mixtures
of chemicals do, and how they affect multiple species.”
Hayes laboratory typically employs 10 undergraduates, who have written
research papers for Nature and other distinguished publications.
This links to Hayes’s distinct teaching philosophy toward
his students: “You should know all that I know.” He
is quite happy to say to his lecture students, “I don’t
know the answer to your question. But you know what? No one knows
right now! I can even go next door to my fellow professors who are
working on this stuff right now and find out, but they still might
not know! That’s what makes it so exciting!”
endocrinology curriculum for his class constantly changes based
on current research, and his exams emphasize a fresh approach using
foundation knowledge. In his words, “I want to understand
what your limit of knowledge is and push it to the limit. I want
you to know how to figure out things in a new context.” For
example, after teaching his class about the major hormones that
are involved in osmoregulation, Hayes asks, “So me and my
daughter are in the desert and she’s thirsty. I give her lots
of water. Why doesn’t my daughter explode?”
research will continue to examine the morphological, behavioral,
and developmental changes that frogs undergo due to chemicals and
mixtures of chemicals. His frog assay allows for a definitive and
inexpensive method to determine the level of pollutants that surround
human populations, especially in countries that cannot afford lots
of high-tech research and analyses on their water and farmlands.
hopes to formulate a simple model of amphibians that will allow
him and others to generalize information to populations and eventually
to ecosystems. His research and instruction are truly integrative;
they encompass the fields of embryology, endocrinology, ecology,
genetics, behavioral science, evolution, public health, and conservation
biology, just to name a few. His passionate pursuit for knowledge,
as well as his youthful character, makes for a person who is both
a mentor and a friend.
of Young Investigators. 2004. Volume Ten.
Copyright © 2004 by Jean Lee and JYI. All rights reserved.