No abstract

Bipolarity, the presence of a species in the high latitudes separated by a gap in distribution across the tropics, is a well-known pattern of global species distribution. But the question of whether bipolar species have evolved independently at the poles since the establishment of the cold-water provinces 16-8 million years ago, or if genes have been transferred across the tropics since that time, has not been addressed. Here we examine genetic variation in the small subunit ribosomal RNA gene of three bipolar planktonic foraminiferal morphospecies. We identify at least one identical genotype in all three morphospecies in both the Arctic and Antarctic subpolar provinces, indicating that trans-tropical gene flow must have occurred. Our genetic analysis also reveals that foraminiferal morphospecies can consist of a complex of genetic types. Such occurrences of genetically distinct populations within one morphospecies may affect the use of planktonic foraminifers as a palaeoceanographic proxy for climate change and necessitate a reassessment of the species concept for the group.

We have incorporated an additional 56 species of land snails and slugs in our ribosomal (r) RNA molecular phylogeny. The new taxa include representatives of several important groups. The molecular tree now includes 160 species of stylommatophoran land snails and slugs in 144 genera in 61 families. In the rDNA tree, the Stylommatophora are principally divided into an 'achatinoid' and a 'non-achatinoid' clade. Within these clades, several major land snail groups, including the Orthurethra, Elasmognatha, Limacoidea, and Helicoidea, are supported. Overall, the rDNA molecular phylogeny has remained stable following the incorporation of the additional taxa, with these additions having little impact on the major evolutionary patterns in the tree. Taxonomic coverage of the Orthurethra, Orthalicidae, Camaenidae, and Bradybaenidae is increased significantly. The camaenids and bradybaenids form a complex, and both appear to be paraphyletic. Several families of uncertain affinity, such as the Sagdidae and Thyrophorellidae, are included for the first time. The Sagdidae are shown to belong to the Helicoidea, and the Thyrophorellidae to the Achatinoidea.