Intra-Genomic Ribosomal RNA Polymorphism and Morphological Variation in Elphidium macellum Suggests Inter-Specific Hybridization in Foraminifera

Elphidium macellum is a benthic foraminifer commonly found in the Patagonian fjords. To test whether its highly variable morphotypes are ecophenotypes or different genotypes, we analysed 70 sequences of the SSU rRNA gene from 25 specimens. Unexpectedly, we identified 11 distinct ribotypes, with up to 5 ribotypes co-occurring within the same specimen. The ribotypes differ by varying blocks of sequence located at the end of stem-loop motifs in the three expansion segments specific to foraminifera. These changes, distinct from typical SNPs and indels, directly affect the structure of the expansion segments. Their mosaic distribution suggests that ribotypes originated by recombination of two or more clusters of ribosomal genes. We propose that this expansion segment polymorphism (ESP) could originate from hybridization of morphologically different populations of Patagonian Elphidium. We speculate that the complex geological history of Patagonia enhanced divergence of coastal foraminiferal species and contributed to increasing genetic and morphological variation

Initial core descriptions. Deep Sea Drilling Project, Leg 95, August 17-September 26, 1983, New Jersey Transect.

Contains written and graphic descriptions of two continuous core drilled sites on the middle slope and upper rise of the New Jersey Transect. Five distinct lithologic units are documented at Site 612. The lowermost unit V is of Campanian age. In unit IV calcareous nannofossil groups are well represented and indicate an age of early and middle Maestrichtian. Both units II and III contain bathyal microfossil assemblages. The abundance of siliceous microfossils is especially notable in unit II. Unit I is too thin to be easily separated into subunits. For Site 613 three distinct lithologic units are documented, the lowermost unit III comprising of early Eocene nannofossils. Both calcareous and siliceous microfossils are abundant and well preserved in unit II. Unit I is composed of a complex sequence of interbedded, greenish gray mud or calcareous mud, glauconitic or pyritic silty sand and sandy mud. The section was not continuously cored.-after Author

Initial reports of the Deep Sea Drilling Project, Leg 95, St. John's, Newfoundland, to Ft. Lauderdale, Florida, 1983 (DSDP).

Leg 95 took place on the continental slope and upper rise of the New Jersey transect and drilling investigated the Cenozoic and Upper Cretaceous sections. The 31 papers (abstracted separately) are on palaeontological, sedimentological, geophysical, geochemical, and regional geological aspects. Emphasis is on the stratigraphic framework and depositional history of this passive margin.-M.A.Bas