Daniel Jablonski from Comenius University in Bratislava during field research. (source: Archive of D. J. )
Spread all the way from Pakistan to Indonesia and commonly found near human settlements, the Asian black-spined toad is one of the most poisonous invasive toad in the world.
Due to its proximity to humans, it regularly, although involuntarily hitches a ride on ships and planes, eventually invading places in which it can cause great damage – so much so that Australia and several other countries have already black-listed the species, as it is considered a threat to numerous animals.
Scientists know that its genetic diversity in the region bears traces of human activity. To make matters more interesting, a new study by an international team of scientists has found that the Asian black-spined toad, also known by its scientific name Duttaphrynus melanostictus, is not a single species, but actually two. While the "true" species is found in the Indian subcontinent, the other diversified across Southeast Asia. And both have invaded places located thousands of kilometres away.
The team included researcher Daniel Jablonski from the Faculty of Natural Sciences of Comenius University Bratislava. The Slovak Spectator talked to him about the study and how it highlights the impact of globalisation.
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Jablonski has been studying Southeast Asian amphibians and reptiles, including the Asian black-spined toad, for several years now. In 2018, his research took him to Pakistan, the western-most and northern-most boundary of the toad's spread. He was looking for its subspecies, called Duttaphrynus melanostictus hazarensis, which was first described in 2001.
However, according to the researcher, the description wasn't taxonomically accurate and contained several methodological issues. For example, it wasn't clear whether morphological differences between this subspecies and other populations were actually well-defined. Moreover, the subspecies' DNA had yet to be studied.
"When I sequenced them, I found that according to its mitochondrial DNA (mtDNA) and one fragment of nuclear DNA, they belong to one of the evolutionary lineages widespread across the northern Indian subcontinent," Jablonski tells the Slovak Spectator.
mtDNA is inherited only from the mother. As it can be isolated from easily collected biological material like hair and dead skin, it is easier to obtain than nuclear DNA. Moreover, there can be up to several thousand copies of mtDNA in a cell, meaning the sheer number increases the chance of an analysis being successful. Although the method is very useful, it doesn't necessarily provide the full picture, especially for purposes of molecular taxonomy.
