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N A T U R A L  H I S T O R Y  R E S E A R C H  R E P O R T S

IGUANA  •  VOLUME 14, NUMBER 2  •  JUNE 2007 131NATURAL HISTORY RESEARCH REPORTS

Asian Snake Stores Toad Toxins
The Asian snake Rhabdophis tigrinus pos-
sesses specialized defensive glands on its
neck that contain steroidal toxins known
as bufadienolides. HUTCHISON ET AL.
(2007. Proceedings of the National
Academy of Sciences of the United States of
America 104:2265–2270) hypothesized
that R. tigrinus does not synthesize these
defensive steroids, but instead sequesters
the toxins from toads it consumes as
prey. To test this hypothesis, the authors
conducted chemical analyses on the glan-
dular fluid from snakes collected in toad-
free and toad-present localities and per-
formed feeding experiments in which
hatchling R. tigrinus were reared on con-
trolled diets that either included or
lacked toads. They demonstrated that the
cardiotonic steroids in the nuchal glands
of R. tigrinus are obtained from dietary
toads. Hatchling snakes had bufadieno-
lides in their nuchal glands only if they
were fed toads or were born to a dam
with high concentrations of these com-
pounds. Because geographic patterns in
the availability of toxic prey are reflected
in the chemical composition of the glan-
dular fluid, snakes in toad-free regions
are left undefended by steroidal toxins.
The ability to sequester dietary toxins

underlies geographic variation in
antipredatory behavior in this species.

Male Scents Signal a 
Better Immune System

Despite the importance of chemorecep-
tion in sexual selection of lizards, few
studies have examined the composition
of chemical signals, and whether and
how chemicals provide honest informa-
tion is unknown. Chemical signals might

be honest if they indicated a trade-off
between sexual advertisement and the
immune system. LÓPEZ AND MARTÍN

(2005. Biology Letters 1:404–406)
showed that proportions of cholesta-5,7-
dien-3-ol in femoral secretions of male
Iberian Wall Lizards (Podarcis hispanica)
were related to their T-cell-mediated
immune response. Thus, only males with
a good immune system may allocate
higher amounts of this chemical to sig-
naling. Furthermore, females selected
scents of males with higher proportions
of cholesta-5,7-dien-3-ol and lower pro-
portions of cholesterol. Thus, females
might base their mate choice on the
males’ quality as indicated by the compo-
sition of their chemical signals.

Lizards “Shout” in Noisy Habitats
Many acoustically communicating ani-
mals compensate for background noise
by using acoustic properties that enhance
the transmission of vocalizations in noisy
habitats. ORD ET AL. (2007. Proceedings
of the Royal Society B: Biological Sciences
274:1057–1062) showed that visual
noise from windblown vegetation has an
equally important influence on the pro-
duction of dynamic visual displays. They
found that two species of Puerto Rican
lizards, Anolis cristatellus and A. gund-
lachi, increase the speed of body move-
ments used in territorial signaling to
improve communication in visually
“noisy” environments of rapidly moving

Hatchling Asian Grass Snakes (Rhabdophis tigrinus) have toxins in specialized defensive glands
only if they consume toads or were born to a dam with high concentrations of poisonous com-
pounds.

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Female Iberian Wall Lizards (Podarcis hispanica) might base their mate choice on male “quality”
as indicated by the composition of their chemical signals.

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vegetation. Together with previous work
on acoustic communication, these data
show that animals with very different
sensory ecologies can face similar envi-
ronmental constraints and adopt remark-
ably similar strategies to overcome those
constraints.

Natural History of 
St. Vincent Dwarf Geckos

STEINBERG ET AL. (2007. Journal of
Herpetology 41:326–332) documented
population densities, microhabitat prefer-
ences, desiccation rates, and diets of
Sphaerodactylus vincenti on St. Vincent,
West Indies. The authors predicted and
observed high densities (to 5,625/ha) in
moist, shaded leaf-litter. Such microhabi-
tats provide refuges, access to prey, and

protection against water loss, as S. vincenti
is vulnerable to high desiccation rates.
They found significant differences in mass-
specific water-loss rates and body mass
between conspecific populations at differ-
ing elevations, with larger geckos less resist-
ant to water loss living in more mesic envi-
ronments at higher elevations. Stomach
content analysis suggests that S. vincenti is
a dietary generalist that feeds on a variety
of small arthropods primarily by day.

132 IGUANA  •  VOLUME 14, NUMBER 2  •  JUNE 2007 NATURAL HISTORY RESEARCH REPORTS

Virgin births 
at the London Zoo

Four Komodo Dragons (Varanus komod-
oensis) hatched at the London Zoo were
the result of parthenogenesis, the devel-
opment of an egg without fertilization by
a sperm. A clutch of dragon eggs laid in
August 2005 fascinated reptile keepers.
The female had arrived in London on
loan from Thoiry Zoo in France in early
2005, and the clutch of eggs was laid
more than two years after she had last
lived with Thoiry’s male. Initially, keep-
ers suspected sperm storage, but Curator
of Herpetology, Richard Gibson, wasn’t
entirely convinced and resolved to inves-
tigate further.

Genetic fingerprinting techniques at
Liverpool University confirmed that the
four dragons were actually the result of
parthenogenesis. The female later mated
with the London Zoo’s male and subse-
quently laid a second clutch of eggs from
which a single, “normal” dragon hatched,
demonstrating that Komodo Dragons

can switch reproductive strategies
depending on the availability of a mate.

Richard Gibson said: “I am delighted
that the mysterious parentage of our
Komodo Dragon babies has been solved,
and that we have discovered something
new to science at the same time. Knowing
that the world’s largest lizard can repro-
duce like this suggests that many other
reptiles may also do this more often than
we thought, and may lead to changes in
the way we manage this and other species
in breeding programs. This discovery also
raises important questions about the nat-
ural history of dragons in the wild, and

will therefore help to safeguard the future
of the species.”

Zoological Society of London
21 December 2006

Homing Behavior in Baby Snakes
We all know that children behave like
their parents in many ways, especially as
they grow older (even though many chil-
dren deny it!) — and most of us suspect
that the similarity is partly due to learn-
ing, and not just genetics.

Researchers from the University of
Sydney have discovered that baby snakes
also behave like their parents, and prob-
ably for similar reasons as in humans. For
more than a decade, Drs. Greg Brown
and Rick Shine have been studying the
ecology of small non-venomous
Keelback Snakes (Tropidonophis mairii)
on the floodplain of the Adelaide River,
on the outskirts of Kakadu National Park
in the Northern Territory.

N E W S B R I E F S

Puerto Rican Crested Anoles (Anolis cristatel-
lus) increase the speed of body movements
used in territorial signaling to improve com-
munication in visually “noisy” environments.

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Four Komodo Dragons (Varanus komodoen-
sis) hatched at the London Zoo were the
result of parthenogenesis, the development of
an egg without fertilization by a sperm.

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Populations of larger St. Vincent Dwarf Geckos (Sphaerodactylus vincenti) living in more mesic
environments at higher elevations are less resistant to water loss.

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