Venomous amphibians
1 AREN’T FROGS POISONOUS, NOT VENOMOUS?
People frequently mix up ‘venom’ and ‘poison’ – including JK Rowling, in her Harry Potter books. Strictly speaking, venom is injected into prey or an enemy by fangs or stings; a poisonous animal is harmful only if it is touched or eaten. For example, many snakes are venomous, with just a handful of unusual poisonous species (Q&A, May 2020). By contrast, in amphibians, poison is common but venom almost unheard of.
2 SO THERE ARE AMPHIBIANS THAT USE VENOM?
In 2015, researchers in Brazil reported their somewhat painful discovery of the first known venomous frog. During a field trip, Carlos Jared was hurt while handling a Greening’s frog, which, it later transpired, has small venom spines around its head. Similar spines were then seen in a second Brazilian species, the Bruno’s casqueheaded frog ( pictured). Because these frogs can inject an attacker, they are truly venomous amphibians.
3 BUT DO ANY HAVE A VENOMOUS BITE?
It turns out that they do. Five years after describing the frogs’ extraordinary spiny defence, Jared and his colleagues are back with another stunning discovery from Brazil. This time it involves the world’s first known amphibians with a venom-laden bite: caecilians. The team examined four species of the burrowing, legless amphibians and found venom glands inside their mouths, located near the teeth. These could be for defence but also to help them swallow prey.
Evolution is often considered a slow process. Charles Darwin took for granted that change was gradual and trudged along, like the Galápagos tortoises that partly inspired his theory. But in reality, there is no one rate, no steadily ticking clock as species alter over millennia. It can happen more quickly than you may suppose.
Evolutionary change depends on random mutations in an organism’s DNA. These tend to occur at a steady rate, but some have bigger effects than others. Change also takes place in response to selective pressures on populations – a sudden environmental change can lead to a rapid proliferation of a rare characteristic, which then goes on to become the norm. The classic example is peppered moths, which became darker during the Industrial Revolution, since it offered better camouflage on soot-stained trees. As humans exert increasing pressures on the natural world, we may see more examples of fast evolution.
Bet you looked twice! It takes a moment or two to fathom this astonishing underwater image, a 2020 runner-up in the GDT European Wildlife Photographer of the Year competition. Taken at night off the coast of Luzon in the Philippines, Magnus Lundgren’s picture shows an octopus hitching a ride on a jellyfish. Female brown paper nautiluses, unusual octopuses also known as argonauts after the heroes in Greek mythology, are well known for surfing on the bells of jellyfish, perhaps using their host for defence or to help trap food.