Dietary specialisation in turn is
linked to heightened aerobic
capacity, probably because ants have
relatively poor nutritional value, so
the frogs have adapted by becoming
active predators, with large home
ranges.
It is not known when humans first
learnt of the deadly nature of
dendrobatids, but Amerindian
hunters have been using the poison
of three species of frogs (notably
P. terribilis) to coat the tips of their
blow darts and arrows for
centuries. Using dendrobatid
poison for hunting is by no
means a benign activity for
the frogs themselves;
P. aurotaenia and P. bicolor
are impaled on sticks or
spears, and may be heated as
well, which supposedly
maximises the amount of
toxic secretions. According to
an account published in 1978, the
method in which the local tribespeo-
ple obtain poison from P. terribilis is
completely inhumane. The hapless
frog is imprisoned in a hollow cane,
and when the poison is required, they
‘pass a pointed piece of wood down
his throat, and out at one of his legs’,
causing the frog to become agitated
and secrete toxins. Although the
poisonous secretion can remain
potent for a year, the indigenous
people apparently have nothing to
fear from consuming game felled
with poison darts or arrows, possibly
because the toxins are denatured by
cooking.
There has been much research into
the medical potential of dendrobatid
poisons. Epibatidine, a compound
isolated from the Ecuadorian
dendrobatid Epipedobates tricolor, is
a powerful painkiller, 200 times
more potent than morphine.
However, further work is required
before it hits the market, as the
therapeutic dose is very close to the
fatal dose! There is additional
potential for drugs to assist smokers
and drug users to quit their habits.
The dendrobatid frogs have escaped
predation by evolving toxicity and
advertising it. However, evolution is
often a constant arms race, and the
colubrid Erythrolamprus
epinephelus is able to predate upon
P. terribilis due to an acquired
immunity to its toxins.
Although most available information
about dendrobatids focusses on their
unsavoury attributes, they are also
highly unusual for being the only
large family of frogs in which all
species perform some aspects of
parental care. In fact, this is
obligatory, because dendrobatids lay
their eggs on land, on moist
substrates on the forest floor. Unlike
some other terrestrial-laying frogs, in
which the larvae undergo metamor-
phosis in the egg and emerge as
froglets, dendrobatid eggs hatch into
tadpoles which require an aquatic
habitat. The parents may guard the
eggs and gather moisture to prevent
them from dessicating; once the eggs
hatch, they will ‘piggyback’ the
larvae to aquatic nurseries, located in
epiphytic plants such as bromeliads.
In these little pools, the tadpoles are
not subject to dessication, are at
lower risk of predation, and can feed
on microbes, aquatic plants and
invertebrates.
Often the male is responsible for
moving the tadpoles, which adhere
to him thanks to the mucus coating
his body. In some instances, the male
will attend several clutches of eggs,
and may carry the tadpoles on his
back for up to nine days. In species
where the male is mostly responsible
for parental care, the traditional sex
roles are reversed, and the female
will often guard the male against
rivals. For example, in Dendrobates
tinctorius and D. auratus, it is the
male that both attends the eggs and
transports the tadpoles to water. In
these species, the females are highly
territorial and aggressive towards
other females, and compete for
access to males. Unlike most other
male frogs, which have loud,
complex calls to attract females, in
these species the males are not
capable of long-distance calls, and
instead produce only weak vocalisa-
tions when in the presence of a
female.
Females of some species take
parental investment to the extreme,
sacrificing eggs for the good of their
tadpoles; many species in the genera
Oophaga and Ranitomeya supple-
ment the diet of their offspring by
returning regularly to the nurseries
and depositing unfertilised
eggs into the water. In the
Oophaga pumilio clade
(O. pumilio, O. speciosus,
O. histrionicus, and
O. lehmanni) oophagy is
necessary, as the larvae
have reduced denticle rows,
making them incapable of
predating upon other food
sources. Each larva will
receive between 20-40 unfertilised
eggs during its development.
In the genus Ranitomeya both
parents work to ensure the best
chance of survival for their off-
spring. These species are phytotelm
specialists, only breeding in
Heliconia, Dieffenbachia, and
Xanthosoma plants. The eggs are
laid in pairs among the bracts of the
plant, and once the eggs hatch, the
father then transports the tadpoles.
The mum feeds the tadpoles with
unfertilised eggs, with the dad
accompanying her to help her locate
the various plant nurseries where
their tadpoles reside.
The investment of a male in his off-
spring can take on a rather darker
side. The male Allobates femoralis
both attends the eggs and transports
the tadpoles to nurseries (often
outside the male’s territory; he may
distribute the clutch in several
locations as a bet-hedging strategy).
In this species, males are highly
territorial and exhibit strong fidelity
to their territory throughout the
breeding season. Their prominent