The pygmy sperm whale also lives in the Mediterranean, a species that was thought to be absent in our sea. A research group led byUniversity of Milan-Bicoccaas part of the Life CONCEPTU MARIS project coordinated by ISPRA, demonstrated the existence of the species in our sea thanks to environmental DNA. But sightings could be difficult.
What is environmental DNA and why is it a research tool
As ARPA Friuli Venezia-Giulia explains, e-DNA, which stands for ‘environmental DNA‘ (‘environmental DNA’), is the set of DNA molecules present in environmental matrices such as water, sediment and air. In fact, everyone leaves traces: all organisms, in practice. they shed DNA into the environment in the form of mucus, feces, skin cells and gametes.
e-DNA can be used as a research tool as it is possible to compare DNA sequences to each other, in order to find the most similar one to determine which species the organism under study belongs to.
In general – this has been known for some time – the closer the species are evolutionarily, the more similar these sequences are. But modern DNA sequencing techniques are able to detect even very small differences in single nucleotides and it is therefore almost always possible to associate a sequence with the relevant species.
How the discovery happened
Precisely in this way the researchers discovered that the pygmy sperm whale also lives in the Mediterranean: in particular, the research was conducted in three steps:
- Collection –> The researchers took seawater samples from commercial ferries underway: in total, 12 liters of water were collected for each of 393 sampling points spread across the central-western Mediterranean.
- Filtration –> The water was immediately filtered on board the ships by passing it through special membranes with tiny pores: this step is essential to capture all the suspended biological material containing DNA fragments.
- Analysis –> In the laboratory, DNA was extracted from the filters; subsequently, using advanced sequencing techniques, thousands of DNA sequences were obtained from each sample, then compared with vast reference databases to identify which species they belong to.
What scientists discovered
The genetic attribution was unequivocal: scientists found the DNA of De Blainville’s cogia (scientific name Kogia breviceps), also called pygmy sperm whale, in 10 samples attributable to at least 5 distinct occurrence events, distributed between the Tyrrhenian Sea and the Strait of Gibraltar. This shows that the species also lives in our sea.
The pygmy sperm whale is very difficult to observe, as it is notoriously very elusive on the surface: this characteristic has always prevented its identification. However, in the same areas and at the same time periods where the DNA of K. brevicepsobservers on board ferries had reported a disproportionately high number of sightings of “unidentified small cetaceans.” It is thought that they were indeed pygmy sperm whales, but that, given their rarity on the surface, no one had ever been able to recognize them.
Environmental DNA allowed us to “see” a species that had always remained hidden, demonstrating that there is still so much to discover even in the seas that we thought we knew thoroughly – explains Elena Valsecchi, who led the research – This study not only adds a new, fascinating marine mammal to the list of Mediterranean fauna, but also underlines the power of these tools to reveal the hidden biodiversity of our oceans. Looking at the sea with these “molecular eyes” will be fundamental to guide future conservation strategies and to also protect life forms that we do not yet know
Not only that: the research also highlighted a vast geographical and temporal distribution of the detections, together with the presence of different genetic profiles (haplotypes): for this reason the scientists believe that they are not faced with single individuals coming from the Atlantic, but a stable and rooted population of De Blainville’s type in the Mediterranean.
Among other things, what was found is a unique mitochondrial haplotype, different from those of Atlantic specimens close to Gibraltar (while it is more similar, albeit different, from those found in Scotland or the Canary Islands), which could indicate the existence of a subpopulation that remained isolated for a long time, with a long evolutionary history within the basin.
The discovery is not just a scientific curiosity: in fact, it justifies the request to officially include De Blainville’s cogia (Kogia breviceps) in the international protection lists for the Mediterranean, such as the ACCOBAMS agreement, to guarantee its protection.
The work was published on Mammal Review.
Sources: University of Milan-Bicocca / Mammal Review / Life CONCEPTU MARIS / Life CONCEPTU MARIS/Youtube / Life CONCEPTU MARIS/Facebook
