With the possible exception of the ubiquitous rocket frog (Allobates insperatus) by far the most common thing I find on the trails in Ecuador is this species. Despite their abundance, they are a species I rarely get tired of seeing because each individual you come across is unique. Some can be really well camouflaged, looking just like dead leaves, so spotting those makes you feel like a pro; but mostly I spot them by movement. One thing they do share in common, though, is a big depressing frown across their face – almost as if they’re my spirit animal.
The crested forest toad (Rhinella margaritifera) is a widespread species in the Amazon. They reach about 8cm in length and come in a huge range of colours – brown, black, gold, red, even blue! If that wasn’t enough variation, the cranial crests that give the species their name can be different too. Most pronounced in the females, they range from horizontally flat out the side of their head to almost vertical and in a range of sizes, you’d be hard pressed to find two that look alike.
The species is actually in what’s known as a species complex. That’s a scientific euphemism for nobody really knows what is going on and there’s not enough time/resources/people who care to work it out. This was realised in 2007 when some researchers did the first work looking into the genetic variation and geographic structuring of the species. Their results suggested at least 11 species in the complex, though current estimates say 17 species are in the R. margaritiferacomplex, with more still undescribed.
Geographic barriers often lead to the formation of new species. If a big river or mountain range splits up a population of toads, it’s unlikely they’ll be able to meet and reproduce ever again. You’d think, then, that the Andes would obviously be a formidable barrier and that toads either side would be different species, but up until 2015 this wasn’t the case – taxonomically anyway. Either these toads doubled up on leg day and could hop over mountains, or something was amiss. Some researchers decided that they’d try and solve at least some of the puzzle by taking the DNA from toads on the East and West of the Andes and using this to analyse the phylogeny of the species, almost like a family tree.
The researchers in the work above put the toads on the West of the Andes into the Rhinella alata species while those in the Amazon on the East remained as R. margaritifera. From a brief search of the literature, it still seems that this species is in a complex. If anyone reading wants a quick way of naming a new species, studying this lot is probably a strong bet.
Quick facts:
• Extremely abundant throughout the Amazon in South America.
• Has a wide range of variation in colour and size/shape of the cranial crests.
• Remains in a species complex with many cryptic species still to be defined.
Further reading:
• Dos Santos, S. P., Ibáñez, R., & Ron, S. R. (2015). Systematics of the Rhinella margaritifera complex (Anura, Bufonidae) from western Ecuador and Panama with insights in the biogeography of Rhinella alata. ZooKeys, (501), 109.
• Focal paper of the tale. They took samples from populations of toads in the Amazon on the East, Choco on the West and from SE Panama too and used mitochondrial and nuclear DNA to establish phylogenetic relatedness. Along with morphological evidence they had enough to reassign the western and Panamanian populations to Rhinella alata.
• Fouquet, A., Vences, M., Salducci, M. D., Meyer, A., Marty, C., Blanc, M., & Gilles, A. (2007). Revealing cryptic diversity using molecular phylogenetics and phylogeography in frogs of the Scinax ruber and Rhinella margaritifera species groups. Molecular phylogenetics and Evolution, 43(2), 567-582.
• The first study to look into the phylogenetic and phylogeographic distribution of the crested forest toad. Using similar methods as the study above, they sampled mostly from French Guiana and looked into the phylogeny of both R. margaritifera and Scinax ruber another neotropical amphibian.
Tales of Scales 