Genetic diversity and demographic instability in Riftia pachyptila tubeworms from eastern Pacific hydrothermal vents

<p>Abstract</p> <p>Background</p> <p>Deep-sea hydrothermal vent animals occupy patchy and ephemeral habitats supported by chemosynthetic primary production. Volcanic and tectonic activities controlling the turnover of these habitats contribute to demographic instability that erodes genetic variation within and among colonies of these animals. We examined DNA sequences from one mitochondrial and three nuclear gene loci to assess genetic diversity in the siboglinid tubeworm, <it>Riftia pachyptila</it>, a widely distributed constituent of vents along the East Pacific Rise and Galápagos Rift.</p> <p>Results</p> <p>Genetic differentiation (<it>F</it>_<it>ST</it>) among populations increased with geographical distances, as expected under a linear stepping-stone model of dispersal. Low levels of DNA sequence diversity occurred at all four loci, allowing us to exclude the hypothesis that an idiosyncratic selective sweep eliminated mitochondrial diversity alone. Total gene diversity declined with tectonic spreading rates. The southernmost populations, which are subjected to superfast spreading rates and high probabilities of extinction, are relatively homogenous genetically.</p> <p>Conclusions</p> <p>Compared to other vent species, DNA sequence diversity is extremely low in <it>R. pachyptila</it>. Though its dispersal abilities appear to be effective, the low diversity, particularly in southern hemisphere populations, is consistent with frequent local extinction and (re)colonization events.</p

Letters to Nature: Hydrothermal activity along the southwest Indian Ridge

Twenty years after the discovery of sea-floor hot springs, vast stretches of the global mid-ocean-ridge system remain unexplored for hydrothermal venting. The southwest Indian ridge is a particularly intriguing region, as it is both the slowest-spreading of the main ridges1 and the sole modern migration pathway between the diverse vent fauna of the Atlantic and Pacific oceans2. A recent model postulates that a linear relation exists between vent frequency and spreading rate3 and predicts vent fields to be scarcest along the slowest-spreading ridge sections, thus impeding migration and enhancing faunal diversity2. Here, however, we report evidence of hydrothermal plumes at six locations within two 200-km-long sections of the southwest Indian ridge indicating a higher frequency of venting than expected. These results suggest that fluxes of heat and chemicals from slow-spreading ridges may be greater than previously thought and that faunal migration along the southwest Indian ridge may serve as an important corridor for gene-flow between Pacific and Atlantic hydrothermal fields

Statistical methodologies to pool across multiple intervention studies

Combining and analyzing data from heterogeneous randomized controlled trials of complex multiple-component intervention studies, or discussing them in a systematic review, is not straightforward. The present article describes certain issues to be considered when combining data across studies, based on discussions in an NIH-sponsored workshop on pooling issues across studies in consortia (see Belle et al. in Psychol Aging, 18(3):396–405, 2003). Several statistical methodologies are described and their advantages and limitations are explored. Whether weighting the different studies data differently, or via employing random effects, one must recognize that different pooling methodologies may yield different results. Pooling can be used for comprehensive exploratory analyses of data from RCTs and should not be viewed as replacing the standard analysis plan for each study. Pooling may help to identify intervention components that may be more effective especially for subsets of participants with certain behavioral characteristics. Pooling, when supported by statistical tests, can allow exploratory investigation of potential hypotheses and for the design of future interventions

The relationship of deep seismicity to the thermal structure of the subducted lithosphere

RECENT experimental work on silicate olivine polymorphs 1 has confirmed earlier observations of mechanical failure in analogous compounds 2,3 as a result of phase transformations when nonhydrostatic stresses were applied to a metastable phase. This 'transformational faulting' 4 mechanism is considered to be a leading candidate 5, among others involving olivine transformation 6,7, for the cause of deep earthquakes. Evidence consistent with this mechanism comes from the observation 2-4 that, worldwide, earthquakes become more numerous with increasing depth after a seismicity minimum at about 350 km depth 8. This depth lies within the range anticipated for mineralogical transformations in the subducted lithosphere 9. But individual subduction zones differ in their thermal structures, so if transformational faulting indeed contributes to deep seismicity, this should be reflected in the location of the seismicity minimum for each zone. The depth at which the minimum occurs should depend on temperature in the same way as do the polymorphic transformations of olivine, and should always lie deeper than the depth at which the equilibrium transformation takes place. Here we test these predictions for eight subduction zones worldwide. We find that, with one exception (the North Japan zone), the depth of the seismicity minimum decreases linearly with increasing thermal age of the slab (a measure of its temperature profile). These results support the proposal that deep earthquakes are a consequence of phase transformations in olivine