According to a new study reported in the journal Evolutionary Biology, bottlenose dolphins (Tursiops truncatus) only colonized the Mediterranean after the last Ice Age, approximately 18,000 years ago.
A group of bottlenose dolphins.
The study is the most detailed ever conducted into the genetic structure of the bottlenose dolphin population in the Mediterranean to date.
Its authors, including Dr Andre Moura of the University of Lincoln, UK, collected tissue samples from 194 adult bottlenose dolphins from the five Mediterranean basins, namely the Tyrrhenian, Ionian, Adriatic, Aegean and Levantine seas.
Their aim was to investigate the population structure and historical processes that may be responsible for the geographic distribution of the species in that area.
No other study has compared the fine scale genetic structure within the Mediterranean, with the well described genetic structure in the North Atlantic.
The Mediterranean basin in particular is a global biodiversity hotspot and several marine species exhibit complex population structure patterns over relatively short geographic distances.
It is therefore a particularly interesting region for scientists to investigate the drivers of population structure in marine organisms.
“As a consequence of the bottlenose dolphin only colonizing the Mediterranean after the last glacial maximum or Ice Age (about 18,000 years ago), population structure in the Mediterranean mainly arises from the different colonization routes the various early colonizers took, and the genetic varieties they carried,” said Dr Moura, who is the senior author on the study.
“Similar to the North Atlantic, two ecological types are likely to exist, one occupying deep ‘pelagic’ – or away from the coast – waters, and another occupying ‘coastal’ shallow water areas.”
“By comparing our results with genetic data from previous studies on Atlantic bottlenose, we concluded that bottlenose dolphin in the North Atlantic, Mediterranean and North Sea are likely to represent a single metapopulation.”
This is a particular type of population structure, when a single population is subdivided into regional subgroups that exchange individuals at varying rates.
“These results have important implications for the understanding and conservation of Mediterranean biodiversity,” Dr Moura said.
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Stefania Gaspari et al. Drivers of Population Structure of the Bottlenose Dolphin (Tursiops truncatus) in the Eastern Mediterranean Sea. Evolutionary Biology, published online February 17, 2015; doi: 10.1007/s11692-015-9309-8
