Last month a study was published in the Journal of Biogeography by an international group of scientists led by the University of Bologna, indicating that great whites have been occupying the Mediterranean Sea since the Pliocene Epoch around 3.2 million years ago.
Starting from the analysis of specimen exhibits and ancient trophies on display in museums, the researchers sequenced the DNA of Mediterranean white sharks. Their approach combined genetics and mathematical models which proved to be effective in tracing back their peculiar evolutionary history.
Mediterranean white sharks have received little attention by researchers due to the decline in their population over the last century, making it difficult for scientists to locate and sample them. However a publication in 2010 by Gubili et al. which used samples from fin-clips of white sharks caught near Turkey in 2008 and another in Tunisia in 2006 as well a historical fin sample from the 1980’s from Sicily. Found after sequencing the mitochondrial control region of these white sharks, that there was little genetic variation between these sharks and those from Indo-Pacific lineages, but a strong separation from the geographically closer Atlantic/Western Indian Ocean sharks.
The 2010 study suggested that the estimated divergence time of Mediterranean and Pacific sharks was around 450,000 years ago. Hypothesising that dramatic and dynamic Pleistocene climate change could in part explain the migration and potential navigational errors of white sharks around South Africa being pushed northward and ultimately resulting in the existence of Mediterranean white sharks. With the possibility of a later migratory event following MED/Indo-Pacific divergence, which again could be invoked by the same climatic trigger occurring repeatedly in the late Pleistocene.
However this latest study has expanded the data set and as a result the researchers were able to estimate that the white shark population in the Mediterranean started to evolve differently from other cognate populations around 3.2 million years ago. They suggest that white sharks originating from the Pacific Ocean, travelled across the Atlantic through the Central American waterway, before the Isthmus of Panama was formed, and they eventually reached the Mediterranean Sea. 3.5 million years ago.
Both studies agree that as the genetic variance between individual Mediterranean sharks is so low and the population number so small, they are at a considerably increased risk of extinction.