DNA from extinct cattle species appears in plankton samples collected at sea near Durban
Durban — Imagine looking at plankton samples and finding DNA from a cattle species that has been extinct for 400 years.
Well, it happened to the South African Association for Marine Biological Research (Saambr) Oceanographic Research Institute (ORI) scientists.
Saambr’s Ann Kunz said the mythical aurochs, a giant wild cattle species and ancestor of modern domestic cattle, has been extinct for 400 years, with the last live aurochs recorded in Poland in 1627.
“So, imagine the surprise of scientists at ORI when DNA from an aurochs appeared in plankton samples collected at sea near Durban,” Kunz said.
She said the discovery offers a poignant glimpse into a distant past when these animals roamed wild.
But how could one explain their DNA's presence in coastal waters in 2024, Kunz asked.
Kunz said the first clue was the sighting of a cow carcass floating in coastal waters near Durban following recent storms and flooding from rivers.
The second was that modern domestic cattle (Bos taurus) had occasionally interbred with aurochs (Bos primigenius) in ancient times, leading to genetic similarities and the preservation of some inherited aurochs DNA in today’s cattle populations.
The third clue was that today’s environmental DNA sampling methods are so sensitive that they can identify any species based on tiny fragments of tissue drifting freely in the ocean. The method used to do this is called DNA metabarcoding, which links each species to a unique barcode which is made up of a specific sequence of DNA. These barcodes are all stored online on the Barcode of Life Database (BOLD; www.boldsystems.org) and GenBank, accessible to anybody.
“The explanation for the aurochs DNA in our plankton sample was therefore that it was inherited DNA in a cow that washed out to sea, where the carcass shed tiny tissue fragments that were incidentally collected in tow nets for zooplankton. Thus, while sequencing a tiny fragment of DNA from the entire genome of modern domestic cattle, genetic material inherited from the extinct aurochs was inadvertently identified,” Kunz explained.
“Though the aurochs no longer exist, traces of their DNA are present in the strangest of places.”
According to a research article, Net type, tow duration and day/night sampling effects on the composition of marine zooplankton derived from metabarcoding by Ashrenee Govender, Sandi Willows-Munro, Sohana P. Singh, Johan C. Groeneveld, DNA metabarcoding provides a rapid and accurate method to record the species composition of mixed marine zooplankton samples. It allows for high-resolution detection in biodiversity censuses, the ability to identify all life stages to the species level, including eggs, larvae and juveniles and the detection of rare species in large mixed samples. In combination with traditional quantitative and morphological analysis of samples, metabarcoding offers a comprehensive tool to characterise zooplankton community structure and biomass.
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