The Euscorpius tergestinus (C.L. Koch, 1837) complex in Italy: Biometrics of sympatric hidden species (Scorpiones: Euscorpiidae)

This work stems from the results of a recent phylogenetic investigation on the Euscorpius carpathicus species complex from the Italian peninsula (Salomone et al. 2004. Phylogenetic relationships between the sibling species Euscorpius tergestinus and E. sicanus (Scorpiones, Euscorpiidae) as inferred from mitochondrial and nuclear sequence data. In: Proceedings of the16th Congress of Arachnology, August 2-7, 2004, Ghent University, Belgium, 268pp.; Salomone et al. in prep.). Molecular investigation produced interesting and unexpected findings on the scorpion Euscorpius tergestinus (C.L. Koch, 1837). Both nuclear and mitochondrial sequence data provided evidence of substantial genetic differentiation in specimens identified as Euscorpius tergestinus according to recent taxonomical changes (Fet and Soleglad 2002. Morphology analysis supports presence of more than one species in the “Euscorpius carpathicus” complex (Scorpiones: Euscorpiidae). Euscorpius 3, 51pp.). These specimens clearly belong to two well-differentiated evolutionary lineages. Molecular results highlighted the need for a new morphological investigation. The present study undertook the morphological analysis of specimens belonging to both genotypes with the aim of identifying morphological characteristics able to discriminate between the two taxa. The analysis of trichobothria patterns, morphometric ratios, granulation patterns and the observation of the pectinal sensilla confirm the difficulty in distinguishing these two genotypes and the high polymorphism of the subgenus Euscorpius Thorell, 1876. The length of pedipalp segments and dorsal patellar spurs (DPS), as well as femur leg granulation, are the main diagnostic characters; other ratios together with body color also help to distinguish the different genotypes. This study confirms the presence in Italy of two different cryptic species belonging to the “Euscorpius tergestinus” complex. Euscorpius tergestinus is a reddish, slender euscorpiid with a large dorsal patellar spine (DPS). A darker and generally squat phenotype with a short DPS, which corresponds to Euscorpius carpathicus concinnus sensu Caporiacco (1950), is elevated to the species level: Euscorpius concinnus (C.L. Koch, 1837). These two species are sympatric in several Italian regions, and their distribution pattern is possibly determined by intraguild predaction interaction.