28 September, 2012

Euscorpius sicanus in Tunisia is natural and not recently introduced

Euscorpius sicanus from Italy. Photo: Jan Ove Rein (C)
The presence of Euscorpius (Euscorpiidae) in some areas in North Africa has been known for many years. These populations have been regarded of many as introduced by humans, but some have raised the questions if they represented isolated relict populations.

Matt Graham and co-workers have now published a DNA barcoding study of Euscorpius sicanus (C. L. Koch, 1837) from Tunisia. By comparing specimens from Tunisia with conspecifics from Malta, Sardinia and Greece, they have showed that the North African populations of this species were probably not recently introduced and instead represent an ancient and isolated natural population. Interestingly, analysis of the data suggests that the isolation between the African and European populations happened in the timeframe when scientists think that the Mediterranean basin was refilled after the "Messinan salinity crisis" (late Miocene).

We used a DNA barcoding marker (mitochondrial cox1) to investigate the controversial natural occurrence of Euscorpius sicanus (C.L. Koch) in North Africa. We tested this hypothesis by comparing a sample collected from a mountain in Tunisia to disjunct populations in Sardinia, Malta, and Greece. Using these samples, and a few additional Euscorpius spp. from southern Europe as outgroups, we reconstructed the maternal phylogeny. We then used a molecular clock to place the phylogeny in a temporal context. The Tunisian sample grouped closest to a specimen from Sardinia, with both being more distantly related to E. sicanus from Malta, which is known to be genetically similar to samples from Sicily. Molecular clock estimates suggest an ancient disjunction across the Mediterranean Sea, with the divergence between samples from Sardinia and Tunisia estimated to have occurred between the Late Miocene and late Pliocene. The divergence date (mean = 5.56 Mya) closely corresponds with the timing of a sudden refilling of the Mediterranean Sea after it had evaporated during the Messinian salinity crisis. This rapid influx of water, in conjunction with tectonic activity, could have sundered connections between Euscorpius in North Africa and what is now the island of Sardinia. These results provide yet another case in which DNA barcodes have proven useful for more than just identifying and discovering species.

Graham MR, Stoev P, Akkari N, Blagoev G, Fet V. Euscorpius sicanus (Scorpiones: Euscorpiidae) from Tunisia: DNA barcoding confirms ancient disjunctions across the Mediterranean Sea. Serket. 2012;13(1/2):16-26.

Thanks to Matt Graham for sending me their paper!

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