On November 22nd, Darwin got a chance to do some of the horseback riding he loved so much. He was out roaming the range with his fellow adventurer Robert Hamond:
“Rode with Mr Hamond to the Rio St Lucia.— the distance is about 12 miles & the path lies over an undulating plain of turf.— On our return we were obliged to go some miles round to avoid one of the great beds of thistles. These are quite impassible, as they are armed with long prickles, & grow close together to the height of six feet.— Riding is the only source of enjoyment in this country.” (Nov 22)
Thistle (including the one shown below) is a common resident on the pampas. It is a relatively general name for a group of prickly asters. The thistles, which cover all parts of the plant, are an adaptation that evolved to provide a defense against grazing animals. However, by all accounts, the thistle that is found in Uruguay did not evolve on the pampas – it was imported from Europe (by the Spanish settlers). It is interesting that this introduced species had already taken over enough of the pampas for it to hamper Darwin’s travels almost 200 years ago. Clearly exotic species are not a new problem.
Artichoke Thistle (Cynara cardunculus) from CA Dept of Agriculture:
Enough about prickly bushes…back to yesterday’s story of Bufo and Lacerta….
In the same sentence as Lacerta (in his Zoological Notebook), Darwin also mentions encountering Bufo. Much like Lacerta, Bufo is a generic term – in this case for toads (at least it is Latin for toad). Specifically Bufo is a genus of toad with about 150 species.
According to the list of Amphibians found in Uruguay, there are no members of the genus Bufo. However, there are some toads listed as being part of the same family – Bufonidae, aka the “true toads”.
Amphibians of Uruguay (from status of reptiles and amphibians in Uruguay):
True toads are found around the world (other than Antarctica and Australia – not including introduced toads). Along with their lack of teeth and “warty” appearance, one feature they all have in common are glands on the back of the head that secrete toxins when the toad is stressed. One of the more common of these alkaloid toxins is even named bufotenin (a major component of bufotoxin) after its amphibian source. These toxins evolved as a way of protecting the toads from predators (like the prickles on the thistles). After all, eating toxins is generally not a good idea. Some of these toxins are hallucinogenic – such as the bufotenin secreted by the Sonoran desert toad that has been used “recreationally”. But ingesting too much (about 200-300 mg per kg) can be lethal.
Darwin did not describe the toad he observed, so I don’t know what type of toad he encountered. Based on the list above, there are a couple of possibilities from the Bufonidae family including the:
Uruguay Red-Bellied Toad (from the Amphibian Avenger)
and the D’Orbigny’s Toad (which I believe is show here in a photo from the Noah Project):
By the way – you’ll hear more about D’Orbigny soon. I like to think of him as young Darwin’s nemesis… (RJV)