The radiation of alopiine clausiliids in the Sicilian Channel (Central Mediterranean): phylogeny, patterns of morphological diversification and implications for taxonomy and conservation of Muticaria and Lampedusa

Abstract

The phylogeny, biogeography and taxonomy of the alopiine clausiliids of the Sicilian Channel, belonging to the genera Lampedusa and Muticaria, were investigated using morphological (shell characters and anatomy of the reproductive system) and genetic (sequencing of a fragment of the mitochondrial large ribosomal subunit 16S rRNA, and the nuclear internal transcriber spacer 1, ITS-1 rRNA) data. Classically, the genus Lampedusa includes three species: L. imitatrix and L. melitensis occurring in circumscribed localities in western Malta and on the islet of Filfla, and L. lopadusae on Lampedusa and Lampione. The genus Muticaria includes two species in southeastern Sicily (M. siracusana and M. neuteboomi) and one in the Maltese islands (M. macrostoma), which is usually subdivided into four entities based on shell characters (macrostoma on Gozo, Comino, Cominotto and central-eastern Malta; mamotica in southeastern Gozo; oscitans on Gozo and central-western Malta; scalaris in northwestern Malta). These have sometimes been considered as subspecies and sometimes as mere morphs.\n\nThe Lampedusa of Lampedusa and Lampione form a well distinct clade from those of the Maltese Islands. The population of Lampione islet is a genetically distinct geographic form that deserves formal taxonomic recognition (as L. nodulosa or L. l. nodulosa). The Lampedusa of Malta are morphologically distinct evolutionary lineages with high levels of genetic divergence and are confirmed as distinct species (L. imitatrix and L. melitensis).\n\nThe Muticaria constitute a clearly different monophyletic clade divided into three geographical lineages corresponding to the Sicilian, Maltese and Gozitan populations. The Sicilian Muticaria form two morphologically and genetically distinguishable subclades that may either be considered subspecies of a polytypic species, or two distinct species. The relationships of Maltese and Gozitan Muticaria are complex. Two of the three Maltese morphotypes resulted monophyletic (oscitans and scalaris) while the other was separated in two lineages (macrostoma); however this picture may be biased as only few samples of macrostoma were available to study. The Gozitan morphotypes (macrostoma, mamotica and oscitans) where resolved as polyphyletic but with clear molecular evidence of mixing in some cases, indicating possible relatively recent differentiation of the Gozitan Muticaria or repetitive secondary contacts between different morphotypes. Definitive taxonomic conclusions from these results are premature. Maltese Muticaria could be subdivided into three taxa according to morphological and molecular data (M. macrostoma or M. m. macrostoma, M. oscitans or M. m. oscitans and M. scalaris or M. m scalaris). Gozitan Muticaria could be considered a distinct polytypic species (for which the oldest available name is Muticaria mamotica) subdivided into subspecies showing a morphological range from macrostoma-like to mamotica-like and oscitans like.\n\nOnly the two Maltese species of Lampedusa are legally protected (by the European Unions Habitats Directive and Maltese national legislation). The present study has shown that the alopiine clausiliids of the Sicilian Channel constitute a number of genetically and/or morphologically distinct populations that represent important pools of genetic diversity, with, in some cases, a very circumscribed distribution. As such, these populations deserve legal protection and management. It is argued that without formal taxonomic designation, it would be difficult to extend international legal protection to some of the more threatened of these populations.