Species identification of the psammophilous tenebrionid beetles Phaleria acuminata Juster, 1852 and Phaleria bimaculata (Linnaeus, 1767) from central Mediterranean beaches: geometric morphometrics and molecular insights from species to population level

Dominating global arid environments, fromdesert to coastal dunes, most Tenebrionidae are highlyspecific in their habitat preferences and display limiteddispersal potential, thus exhibiting a remarkable degree ofregional genetic and morphological differentiation. Thetenebrionid genus Phaleria is speciose and widely distributed,with P. acuminata and P. bimaculata having awide Mediterranean distribution, with numerous morphologicaldifferentiations at population level, often describedas different taxa of doubtful taxonomical significance. Inorder to investigate the variability of the central Mediterraneanpopulations of P. bimaculata and P. acuminata andto compare the results obtained with different identificationtechniques, these species were sampled on sandy beachesin Sicily (southern Italy) and on circum-Sicilian and Malteseislands. Collected samples were studied through theapplication of geometric morphometrics and the sequencingof a fragment of the mitochondrial COII gene. Geometricmorphometrics and molecular analyses gavecongruent results, allowing a sound separation of the twospecies. At the population level, the two species showeddifferent patterns. P. acuminata showed a remarkablemorphological and molecular homogeneity throughout thesampled area. Conversely, two well-characterized subcladeswere detected within P. bimaculata, and within thetwo lineages, a low-to-absent inter-populations differentiationwas observed, in spite of the physical isolation of thesampled sandy beaches and of their geographical distance.These two P. bimaculata lineages, hereby named ‘‘Tyrrheniansub-clade’’ and ‘‘Southern sub-clade,’’ might becompatible with the hypothesis of subspecific statusalready proposed for the populations from the Aeolianarchipelago (as P. bimaculata marcuzzii Aliquo`).