A terrible beauty.
Kit Prendergast investigates a group of tiny, exquisite amphibians that are
well known for their toxic secretions, but equally notable for their
unparalleled parental care.
mall, cute and colourful, but
with toxic secretions so
incredibly deadly they are
believed to be the most poisonous
animals on earth...
Poison dart frogs comprise a group
of approximately 210 species of
frogs in the family Dendrobatidae.
New species continue to be
discovered – Ameerega shihuemoy
was described as recently as 2017.
All are native to tropical Central and
South America, where they primarily
inhabit the leaf litter of rainforests.
Typically diurnal (with Aromobates
nocturnus, the Skunk frog, being the
single known nocturnal species),
most dendrobatids are also small,
and may be less than 1.5cm in
length, with a few species capable of
reaching 6cm. This group includes
some of the most beautiful of frogs,
with various species exhibiting
ostentatious hues of gold, copper,
yellow, red, blue and black,
together with elaborate markings and
patterns. This aposematic colour-
ation advertises to would-be
predators the frogs’ toxicity if
ingested. Interestingly, a group of
dendrobatids is called an ‘army’.
The toxicity of dendrobatids derives
from potent lipid alkaloids secreted
from the skin. The most toxic of all
dendrobatid species is the Golden
Poison Frog (Phyllobates
terribilis). This species exudes the
steroidal alkaloids batrachotoxin,
homobatrachotoxin, and
batrachotoxinin A, which are
incredibly potent modulators of
voltage-gated sodium channels in
cells. The alkaloids cause the
channels to remain open, thereby
irreversibly depolarising nerve and
muscle cells, and leading to
arrhythmias, fibrillation, and
eventually cardiac failure. The
Golden Poison Frog has twenty
times the levels of toxins found in
other dendrobatids – enough to kill
at least 10 humans!
But not all dendrobatids are
poisonous; some are cryptically
coloured and non-toxic. And the
frogs themselves are not inherently
toxic, as the toxins are sequestered
from their diet. Ants, termites,
centipedes and mites (in particular
oribatid mites) are major dietary
components of poisonous dendrobat-
ids, and these in turn owe their
toxicity to plant poisons they
assimilate in their diet. Because
dendrobatid toxicity is reliant upon
diet, toxic species are rendered
harmless if fed on a different diet in
captivity. Recent studies have shown
that in at least one species, the
Strawberry Poison Frog (Oophaga
pumilio) there is some transfer of
toxicity from mother to offspring, as
the female lays unfertilised eggs
containing trace amounts of
alkaloids which are fed upon by her
tadpoles. This in turn makes the
tadpoles toxic and deters potential
predators such as dragonflies.
Rather than a single evolutionary
divergence, phylogenetic studies
have revealed that toxicity amongst
dendrobatids has evolved independ-
ently at least four times. In general,
studies have supported the link