Gyrostomella, P.Hesse, 1911

Neiber, Marco T., Korábek, Ondřej, Glaubrecht, Matthias & Hausdorf, Bernhard, 2022, A misinterpreted disjunction: the phylogenetic relationships of the North African land snail Gyrostomella (Gastropoda: Stylommatophora: Helicidae), Zoological Journal of the Linnean Society 194 (4), pp. 1236-1251 : 1245

BIOGEOGRAPHY OF GYROSTOMELLA

The classification of Gyrostomella as a subgenus of Levantina from the Middle East by Hesse (1909a, b, 1911, 1918) suggested that Gyrostomella originated by a westward long-distance dispersal event of Levantina over almost 2000 km along the North African coast or that Gyrostomella is relictual of a formerly much wider range of Levantina ( Fig. 2 ). More specifically, Neubert (1998) proposed that Gyrostomella and the Arabian Laevihelix (now considered a synonym of Levantina in the wide sense) are descendants of a southern branch of Levantina , which invaded Arabia and Northern Africa in the Miocene. With regard to the Arabian group, which is represented in our phylogeny by L. symensi Neubert, 1998 , this scenario is compatible with our dated phylogeny ( Fig. 4 ). However, our phylogenetic analyses strongly indicate that Gyrostomella is not related to the Eastern Mediterranean Levantina , but to the Maghrebian radiation of Helicinae , more specifically to Maurohelix from the Atlas Mountains ( Figs 3 , 4 ). Thus, the occurrence of Gyrostomella in the Nefusa Mountains in Libya could have originated from an eastward long-distance dispersal over about 800 km from the Atlas Mountains ( Fig. 2 ). Alternatively, the disjunct distribution of Gyrostomella in Libya and Algeria could be a relict of a formerly wider range of the lineage, which became fragmented as a consequence of aridification processes and the spread of the Saharan desert during the late Miocene or early Pliocene ( Zhang et al., 2014). Along with Eremina , which reaches the southern parts of Israel in the Middle East and dispersed also along the East African coast southwards to Cape Guardafui in Somalia and the western part of the Arabian Peninsula ( Verdcourt, 1960; Neubert, 1998), it represents an eastern outpost of the Maghrebian radiation of Helicinae .

In Tripolitania, the Western and Eastern Mediterranean elements overlap, but Western Mediterranean land snail taxa dominate. Besides Gyrostomella , further Western Mediterranean land snail taxa represented in Tripolitania are Ferussacia carnea (Risso, 1826) , Sphincterochila candidissima (Draparnaud, 1801) , Xerosecta Monterosato, 1892 and Ganula Gittenberger, 1970 , whereas Xerocrassa Monterosato, 1892 , Xeromunda Monterosato, 1892 and Helix pronuba Westerlund & Blanc, 1879 are Eastern Mediterranean taxa ( Sturany, 1909; Alzona, 1940; Neubert, 2014). In contrast, Eastern Mediterranean taxa predominate in the Cyrenaica region adjoining to the east.

Figures

Figure 2. Approximate ranges of Gyrostomella s.s., Maurohelix and Levantina. The question mark indicates the possible extension of the range of Maurohelix to eastern Morocco (see Holyoak et al., 2020). Note: map made with Natural Earth (free vector and raster map data https://www.naturalearthdata.com).

Figure 3. Bayesian 50% majority-rule consensus tree based on the combined analysis of partial sequences of the mitochondrial COI and 16 S rRNA genes, as well as a part of the nuclear ribosomal RNA cluster covering parts of the 5.8 S rRNA gene, the complete ITS2 and a part of the 28 S rRNA gene. Values at the branches represent Bayesian posterior probabilities (left) and maximum likelihood bootstrap values (right). For information on vouchers, see Supporting Information, Table S2.

Figure 4. Dated 50% clade credibility tree with median node heights based on the combined analysis of partial sequences of the mitochondrial COI and 16 S rRNA genes, as well as a part of the nuclear ribosomal RNA cluster covering parts of the 5.8 S rRNA gene, the complete ITS2 and a part of the 28 S rRNA gene. Values at the nodes represent node ages in Ma. Bars represent 95% highest posterior density intervals and coloured squares at the nodes and the tips of the tree represent (estimated) ranges from the dispersal–extinction–cladogenesis (DEC) model. The arrows indicate the nodes where the DEC model and the DEC model allowing for founder-event speciation (+J) differed with regard to the estimated ancestral range. The node used for calibration is indicated by an asterisk. Insert map: delimitation of geographical areas considered in the biogeographic analyses: (1) Western Mediterranean region of Europe (incl. western Europe, northern Europe and parts of Central Europe), (2) western North Africa (incl. Cape Verde Islands), (3) Canary Islands and Madeira Archipelago (Macaronesian Archipelagos) and (4) Eastern Mediterranean region (incl. the Middle East, parts of eastern Central Europe and eastern Europe, the Caucasus region and adjacent areas).