Phylogeny and biogeography of tropical carnivorous land‐snails (Pulmonata: Streptaxoidea) with particular reference to East Africa and the Indian Ocean

Abstract

Rowson, B., Tattersfield, P. & Symondson, W. O. C. (2010). Phylogeny and biogeography of tropical carnivorous land‐snails (Pulmonata: Streptaxoidea) with particular reference to East Africa and the Indian Ocean. —Zoologica Scripta, 40, 85–98. A phylogeny is presented for the speciose, near pan‐tropical, carnivorous achatinoid land‐snail superfamily Streptaxoidea inferred from DNA sequences (two nuclear and two mitochondrial regions) from 114 taxa from Africa, the Indian Ocean, Asia, South America and Europe. In all analyses, Streptaxidae are monophyletic, while the (two to six) previously recognised subfamilies are polyphyletic, as are several genus‐level taxa including the most speciose genus Gulella, necessitating major taxonomic review. The Asian Diapheridae are sister to Streptaxidae, which forms several well‐supported clades originating in a persistent basal polytomy. Divergence dating estimates, historical biogeography, and the fossil context suggest a Cretaceous origin of these families, but suggest Gondwanan vicariance predated most radiation. The basal polytomy dates to the Paleogene and may correspond to a rapid radiation in Africa. There is evidence for multiple Cenozoic dispersals followed by radiation, including at least two from Africa to South America, at least two from Africa to Asia and at least two from Africa to Madagascar, indicating Cenozoic turnover in tropical snail faunas. The endemic Seychelles and Mascarene streptaxid faunas each are composites of early Cenozoic lineages and more recent dispersals from Africa, with no direct evidence for an Asian origin as currently proposed. Peak streptaxid diversity in East Africa is explained by Neogene speciation among a large number of coexisting ancient lineages, a phenomenon most pronounced in the Eastern Arc‐Coastal Forests centre of endemism. This includes Miocene diversification in Gulella, a primarily East and South‐East African group which remains strikingly diverse even after unrelated ‘Gulella’ species are reclassified.

Revision of Dadagulella gen. nov., the “Gulella radius group" (Gastropoda: Streptaxidae) of the eastern Afrotropics, including six new species and three new subspecies

“…The available DNA sequence data suggest that Dadagulella gen. nov. is a sister lineage to the one that contains Gulella, and that the two became separated in the Cenozoic (Rowson et al 2010a). Further sequence data from additional species of Dadagulella gen. nov. and Gulella (Rowson & Herbert unpublished), including the type species of Gulella (Herbert & Rowson 2011), support the conclusion that the two lineages are separate, and that Gulella includes the type species of several nominal subgenera while Dadagulella gen. nov. does not.…”

“…Shells and anatomy of juveniles unknown. (Rowson et al 2010a;Rowson & Herbert, unpublished). The shells of Dadagulella gen. nov. do not correspond to those of any other existing streptaxid genus or subgenus.…”

“…Verdcourt (1953) described the radula of the Tanzanian Gulella usambarica (Craven, 1880) as consisting almost entirely of multicuspid teeth (formula 26-1-26); again, the cusps are nearly equal in size. Sequence data (Rowson et al 2010a) show that Dadagulella gen. nov. is only distantly related to G. usambarica. Thus a relationship between Dadagulella gen. nov. and Conogulella based on the multicuspid radula cannot be ruled out, but remains unproven since multicuspid teeth occur in distantly related lineages.…”

“…Further sequence data from additional species of Dadagulella gen. nov. and Gulella (Rowson & Herbert unpublished), including the type species of Gulella (Herbert & Rowson 2011), support the conclusion that the two lineages are separate, and that Gulella includes the type species of several nominal subgenera while Dadagulella gen. nov. does not. The two can be distinguished by the presence of an indel in the mitochondrial DNA sequence coding for COI (cytochrome oxidase I) in almost all Gulella species relative to Dadagulella gen. nov. (Rowson et al 2010a;Rowson & Herbert, unpublished). Another streptaxid species included in the "G. radius group" by van Bruggen (1969van Bruggen ( , 2000, the Kenyan G. pretiosa (Preston, 1911), has also been sequenced (Rowson et al 2010a).…”

“…The two can be distinguished by the presence of an indel in the mitochondrial DNA sequence coding for COI (cytochrome oxidase I) in almost all Gulella species relative to Dadagulella gen. nov. (Rowson et al 2010a;Rowson & Herbert, unpublished). Another streptaxid species included in the "G. radius group" by van Bruggen (1969van Bruggen ( , 2000, the Kenyan G. pretiosa (Preston, 1911), has also been sequenced (Rowson et al 2010a). It is clearly not closely related to either Dadagulella gen. nov. or Gulella itself, a finding also supported by anatomical data (Rowson unpublished).…”