Phylogeography of the tropical planktonic foraminifera lineage globigerinella reveals isolation inconsistent with passive dispersal by ocean currents

Morphologically defined species of marine plankton often harbor a considerable level of cryptic diversity. Since many morphospecies show cosmopolitan distribution, an understanding of biogeographic and evolutionary processes at the level of genetic diversity requires global sampling. We use a database of 387 single-specimen sequences of the SSU rDNA of the planktonic foraminifera Globigerinella as a model to assess the biogeographic and phylogenetic distributions of cryptic diversity in marine microplankton on a global scale. Our data confirm the existence of multiple, well isolated genetic lineages. An analysis of their abundance and distribution indicates that our sampling is likely to approximate the actual total diversity. Unexpectedly, we observe an uneven allocation of cryptic diversity among the phylogenetic lineages. We show that this pattern is neither an artifact of sampling intensity nor a function of lineage age. Instead, we argue that it reflects an ongoing speciation process in one of the three major lineages. Surprisingly, four of the six genetic types in the hyperdiverse lineage are biogeographically restricted to the Indopacific. Their mutual co-occurrence and their hierarchical phylogenetic structure provide no evidence for an origin through sudden habitat fragmentation and their limitation to the Indopacific challenges the view of a global gene flow within the warm-water provinces. This phenomenon shows that passive dispersal is not sufficient to describe the distribution of plankton diversity. Rather, these organisms show differentiated distribution patterns shaped by species interactions and reflecting phylogenetic contingency with unique histories of diversification rates.

Vertical niche partitioning between cryptic sibling species of a cosmopolitan marine planktonic protist

A large portion of the surface-ocean biomass is represented by microscopic unicellular plankton. These organisms are functionally and morphologically diverse, but it remains unclear how their diversity is generated. Species of marine microplankton are widely distributed because of passive transport and lack of barriers in the ocean. How does speciation occur in a system with a seemingly unlimited dispersal potential? Recent studies using planktonic foraminifera as a model showed that even among the cryptic genetic diversity within morphological species, many genetic types are cosmopolitan, lending limited support for speciation by geographical isolation. Here we show that the current two-dimensional view on the biogeography and potential speciation mechanisms in the microplankton may be misleading. By depth-stratified sampling, we present evidence that sibling genetic types in a cosmopolitan species of marine microplankton, the planktonic foraminifer Hastigerina pelagica, are consistently separated by depth throughout their global range. Such strong separation between genetically closely related and morphologically inseparable genetic types indicates that niche partitioning in marine heterotrophic microplankton can be maintained in the vertical dimension on a global scale. These observations indicate that speciation along depth (depth-parapatric speciation) can occur in vertically structured microplankton populations, facilitating diversification without the need for spatial isolation.

Pyothorax-associated lymphoma: development of Epstein-Barr virus-associated lymphoma within the inflammatory cavity

Pyothorax-associated lymphoma (PAL) is a B cell lymphoma that develops in Japanese patients with tuberculosis-associated chronic pyothorax (TaCP). Epstein-Barr virus (EBV) has been shown to be causally related to PAL. To clarify the developmental process of PAL, the systemic and local presence of EBV, and serum profile of anti-EBV antibodies was investigated in TaCP. EBV genome was found in peripheral blood mononuclear cells by PCR in a 10(-4)-10(-5) amount of Raji cell-DNA in three of four patients with TaCP, but was also identified in patients with pyothorax caused by other diseases (2/2) or without pulmonary diseases (2/6). EBER1 in situ hybridization and EBNA2 immunocytochemistry revealed clusters of EBV-carrying cells in the cavity content (3/18) but not at the pyothorax wall; EBV(+) histological lymphoma cells were found in two cases and EBV(+) mononuclear cells were found in one case. A simultaneous increase in serum titers of anti-EBV viral capsid antigen IgG and IgA antibodies was observed in TaCP (4/16). These results suggest that a local factor, an inflammatory cavity, has a pivotal role in the development of PAL, which might be reflected in the serum titers of anti-EBV antibodies in patients with TaCP.