A potential explanation for the disjunct distributions of Western Mediterranean scorpions in the genus Euscorpius

 

The genus Euscorpius Thorell, 1876 (Euscorpiidae) is widespread and have a high diversity in the Western Mediterranean, including several islands with endemic species. An interesting case is Euscorpius oglasae Caporiacco, 1950 from the island of Montecristo. Based on morphological analysis it has been regarded as closely related to the species Euscorpius balearicus Caporiacco, 1950 in the Balearic islands. But how is this possible as the distance between these islands is very large? 

Javier Blasco-Aróstegui and co-workers have recently published molecular study where they try to explain the disjunct distributions of Western Mediterranean scorpions in the genus Euscorpius. The study confirms the previous conclusion that the two above mentioned species are indeed closely related, and it offers an explanation of how the initial diversification of E. oglasae happened in the Paleogene time period.

Abstract:
Aim: Small wood-scorpions (Euscorpius Thorell, 1876) are widespread across the Mediterranean forests, mountains, coastlines, and islands of Europe. Their ancient origins make them an excellent model system for reconstructing the complex biogeographical history of the western Palaearctic. The present study focused on the islands of the western Mediterranean, which are geologically dynamic and harbour many endemic and relictual taxa, and on the relationships among Euscorpius species inhabiting Montecristo and the Balearic Islands, in particular. Two hypotheses were tested: (1) long-distance dispersal from the Balearic Islands after Montecristo emerged following the HT/LP plutonic intrusion (8.4–7.2 Ma), and (2) a multi-phase scenario beginning with vicariance from the Balearic, Calabrian, Corsican, Sardinian and Sicilian (Ba-Ca- Co- Sa- Si) microplate fragmentation, followed by dispersal to Montecristo during the Messinian Salinity Crisis (5.97–5.33 Ma) or later Pliocene–Pleistocene sea-level regressions (3.6–0.2 Ma).
Location: Western Mediterranean islands of France, Spain, and Italy, including the Balearic Islands, Corsica, Sardinia, and the Tuscan Archipelago.
Time Periods: Eocene, Oligocene, Neogene, and Quaternary.
Taxon: Scorpiones: Euscorpiidae: Euscorpius Thorell, 1876: Euscorpius balearicus Caporiacco, 1950; Euscorpius canestrinii (Fanzago, 1872); Euscorpius concinnus (C.L. Koch, 1837); Euscorpius oglasae Caporiacco, 1950; Euscorpius sicanus (C.L. Koch, 1837).
Methods: Multi-locus phylogenies were inferred from 2815 base-pairs of concatenated DNA sequence of the nuclear region comprising 18S rDNA (partial) and the Internal Transcribed Spacer II, and mitochondrial 12S rDNA, 16S rDNA, and Cytochrome c Oxidase Subunit I loci using Maximum Likelihood, and divergence times estimated in a Bayesian framework with conservative fossil calibration constraints. Ancestral areas and biogeographical transitions were reconstructed using parametric models complemented by Principal Coordinates Analysis and Isolation-by- Distance tests to assess spatial genetic structure.
Results: Molecular clock dating and biogeographical analyses suggest initial diversification of E. oglasae occurred after break-up of the Ba-Ca- Co- Sa- Si microplate during the Oligocene (25.9 Ma), which transferred the lineage to the Corsica-Sardinia block. A likely passive dispersal event (i.e., transient lands, orogenies) towards Montecristo only occurred after its emergence (8.4–7.2 Ma), probably during the Messinian Salinity Crisis (5.97–5.33 Ma).

Reference:
Blasco-Aróstegui J, Isaia M, Barba-Montoya J, Tolve M, Roppo M, Prendini L. Ancient Divergence, Recent Island: Microplate Fragmentation and Dispersal Explain Disjunct Distributions of Western Mediterranean Scorpions. Journal of Biogeography. 2026;53(9). [Subscription required for full text]