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

Establishment of a global three-dimensional kinematic reference frame using VLBI and DORIS data

The main aim of this paper is to provide an algorithm to combine VLBI (Very Long Baseline Interferometry) and DORIS (Doppler Orbitography and Radio positioning Integrated by Satellite) data sets into the same kinematics reference frame. In a rst stage of computation the VLBI and DORIS networks are knitted together using the velocities of each station with their covariance matrices that were obtained from individual solutions. A sequential least squares adjustment was used. In a second stage of computation a method of iterative weighted similarity transformation has been elaborated. In order to x the three-dimensional kinematic reference frame (KRF), a system of constraints or datum equations based on vertical component of some quasi-stable reference stations are used. This strategy provides a datum that is robust to unstable reference points and gives less distorted displacements. This method has been applied to the VLBI and DORIS data collected during the last decades. Without survey ties available, and consequently without relative velocities between collocated VLBI and DORIS points, we forced the velocities of collocated sites to the same value and constrained their root mean squares to be equal to zero. As VLBI information is formally for some stations ten times more precise than the DORIS information, reference frame and precision of the VLBI stations were practically not aected by this computation. But precision of DORIS station velocities of the joint network is improved by almost 15% and fairly close agreement between ITRF2000 solution, NNR Nuvel-1A model predictions, and our solution has been found. The technique presented provides a method to dene KRF without any information from a geological plate motion model. It is thus possible to verify any geological model using only geodetic information itself

Global combination of astro-geodetic techniques at the normal equations level: Possible contribution to future ITRS realizations

International audienc

Contribution of multi-technique combinations at the “observation level” to the realization of ITRF2008

International audienc

Global Combination of the Terrestrial Frame and Earth Orientation Parameters at the Observation Level: Contribution to ITRF2008 realization

International audienc

Consistent Combination of the Space Geodetic Techniques for a homogeneous determination of Earth Orientation Parameters and Terrestrial Reference Frames

International audienc

GRGS combination of the Terrestrial Frame and Earth Orientation Parameters at the observation level: Contribution to the ITRF2008 realization

International audienceA new version of ITRF (ITRF2008) is planned and requests combination of the various astro-geodetic techniques over a period of several years. In the framework of the « Groupe de Recherches de Géodésie Spatiale » GRGS, we are combining normal equations derived from the processing of 4 techniques on a regular basis (GPS, VLBI, SLR and DORIS). Observations of these techniques are separately processed at different analysis centres of GRGS using the software package GINS-DYNAMO, developed and maintained by (GRGS). The strength of the method is the use of a set of identical up-to-date models and standards in unique software. In the procedure, the datum-free normal equation matrices weekly derived from the analyses of each technique are stacked to derive solutions of station coordinates, and Earth Orientation Parameters (EOP). In this presentation, the first part compares our individual results to the international corresponding official combinations, as those delivered by the IGS, IVS, ILRS and IDS using models specific to each technique. The second part demonstrates how this global combination can contribute to the new ITRF

Report of IERS components: GRGS combination centre

International Earth Rotation and Reference Systems Service (IERS) Annual Report 2006, edited by W. R. Dick and B. Richter, Verlag des Bundesamts für Kartographie und Geodäsie Frankfurt am Main 2008, p 14