Genotypic variability in subarctic Atlantic planktic foraminifera

Specimens of the planktic foraminiferal morphospecies, Globigerina bulloide s, Turborotalita quinqueloba, Neogloboquadrina pachyderma (dextral) and Glo bigerinita uvula, were collected along a subarctic Atlantic transect. Parti al sequences of the small subunit (SSU) ribosomal (r) RNA gene were obtaine d and a distance-based foraminiferal phylogeny constructed. The low latitud e morphospecies, Globigerina falconensis, was included to improve within cl uster resolution. G. bulloides, G. falconensis and T. quinqueloba cluster t ogether as a distinct group within the molecular phylogeny. The diversification of these three morphospecies from their common ancestor is clearly later than the main planktic spinose radiation, consistent with current interpretations of the fossil record. G. bulloides and G. falconen sis are highly divergent from one another, supporting palaeontological and biological evidence that they are separate species. N. pachyderma (dextral) clusters with Neogloboquadrina dutertrei within the benthic and non-spinos e planktic region of the tree. G. uvula also clusters within the benthic an d non-spinose planktic region of the tree, adjacent to Globigerinita glutin ata, a member of the same genus, though resolution is too low to provide ev idence of a sister-taxon relationship. The Globigerina bulloides and Turborotalita quinqueloba morphospecies compr ise a complex of distinct SSU rDNA genetic types. These fall into two group s, representing high and low latitude genotypes. Along the subarctic transe ct, G. bulloides and T. quinqueloba were each represented by two distinct g enotypes. Neogloboquadrina pachyderma (dextral) and Globigerinita uvula wer e each represented by a single genotype. Genotypes of a morphospecies exhibit distinctive and different distribution patterns. In the case of Globigerina bulloides, the genotype distribution is suggestive of differing adaptation. However, the Turborotalita quinquelo ba genotype distribution was complicated by their co-existence in the same water column throughout the eastern sector. Further investigation will be r equired to determine whether they occupy a different niche within the water column. Although only T. quinqueloba Type Ha was found in the western regi on, sampling density was low and inconclusive. The Neogloboquadrina pachyde rma (dextral) genotype was found across the entire transect. Further invest igation of genotype distribution and genotype/habitat relationships could p rovide new high-resolution proxies for past oceanographic/climate reconstru ctions. (C) 2001 Elsevier Science B.V. All rights reserved.