Comparative phylogeography of parasitic Laelaps mites contribute new insights into the specialist-generalist variation hypothesis (SGVH)

BACKGROUND: The specialist-generalist variation hypothesis (SGVH) in parasites suggests that, due to patchiness in habitat (host availability), specialist species will show more subdivided population structure when compared to generalist species. In addition, since specialist species are more prone to local stochastic extinction events with their hosts, they will show lower levels of intraspecific genetic diversity when compared to more generalist. RESULTS: To test the wider applicability of the SGVH we compared 337 cytochrome oxidase I mitochondrial DNA and 268 nuclear tropomyosin DNA sequenced fragments derived from two co-distributed Laelaps mite species and compared the data to 294 COI mtDNA sequences derived from the respective hosts Rhabdomys dilectus, R. bechuanae, Mastomys coucha and M. natalensis. In support of the SGVH, the generalist L. muricola was characterized by a high mtDNA haplotypic diversity of 0.97 (±0.00) and a low level of population differentiation (mtDNA Fst= 0.56, p < 0.05; nuDNA Fst = 0.33, P < 0.05) while the specialist L. giganteus was overall characterized by a lower haplotypic diversity of 0.77 (±0.03) and comparatively higher levels of population differentiation (mtDNA Fst = 0.87, P < 0.05; nuDNA Fst = 0.48, P < 0.05). When the two specialist L. giganteus lineages, which occur on two different Rhabdomys species, are respectively compared to the generalist parasite, L. muricola, the SGVH is not fully supported. One of the specialist L. giganteus species occurring on R. dilectus shows similar low levels of population differentiation (mtDNA Fst= 0.53, P < 0. 05; nuDNA Fst= 0.12, P < 0.05) than that found for the generalist L. muricola. This finding can be correlated to differences in host dispersal: R. bechuanae populations are characterized by a differentiated mtDNA Fst of 0.79 (P < 0.05) while R. dilectus populations are less structured with a mtDNA Fst= 0.18 (P < 0.05). CONCLUSION: These findings suggest that in ectoparasites, host specificity and the vagility of the host are both important drivers for parasite dispersal. It is proposed that the SGHV hypothesis should also incorporate reference to host dispersal since in our case only the specialist species who occur on less mobile hosts showed more subdivided population structure when compared to generalist species

The culture history of Madagascar

Madagascar's culture is a unique fusion of elements drawn from the western, northern, and eastern shores of the Indian Ocean, and its past has fascinated many scholars, yet systematic archaeological research is relatively recent on the island. The oldest traces of visitors are from the first century AD. Coastal settlements, with clear evidence of ties to the western Indian Ocean trading network, were established in several places over the next millennium. Important environmental changes of both plant and animal communities are documented over this period, including the extinctions of almost all large animal species. Urban life in Madagascar began with the establishment of the entrepôt of Mahilaka on the northwest coast of the island in the twelfth century. At about the same time, communities with ties to the trade network were established around the island's coasts. From the fourteenth to the sixteenth century, social hierarchies developed in several regions of the island. During the succeeding two centuries, Madagascar saw the development of state polities.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45256/1/10963_2004_Article_BF00997802.pd

Adaptation of Ψ-MOSFET technique for ultra thin SOI

International audienc

Collisional erosion during accretion and Earth's non-chondritic Sm/Nd ratio

Superchondritic Sm/Nd (Samarium/Neodymium) ratio has been evidenced in Earth's mantle rocks [1]. This observation is at odds with the canonical view of planetary accretion from chondritic building blocks, leading to chondritic ratios of lithophile (i.e. rock loving elements) and refractory elements in the silicate Earth. Here we evaluate the influence of collisional erosion during accretion on the budget of lithophile and refractory elements such as Sm and Nd. During the late stages of planetary accretion, planets grow by colliding with other embryos and a remnant planetesimals population. It has been suggested that the superchondritic Sm/Nd could have been produced by collisional striping of the Earth's early crust during its accretion. We quantitatively constrain the amount of eroded mass during the late-stage growth of Earth analogs using a combination of analytical modeling [2] and N-body numerical simulations [3]. Our model takes into account the distribution of impactors and their evolving compositions during accretion. The effect of changing accretion scenarios is also studied (e.g. with or without a Grand-Tack). The final Sm/Nd ratio of the bulk silicate Earth is determined under 3 sets of assumptions: (1) The mantle and crust fully reequilibrate after each impact; (2) The accreted material merges with the crust only and the mantle does not reequilibrate with the crust (3) an intermediate case that depends on the size of the impactors. We show that planetesimal impacts play a dominant role in determining Earth's Sm/Nd ratio due to the efficiency of crustal erosion. This work has implications for understanding Earth's accretion history. [1] Boyet and Carlson, 2005. Science 309, 576-581 [2] Svetsov, 2011. Icarus 214, 316-326 [3] Raymond, O'Brien, Morbidelli, Kaib, 2009. Icarus 203, 644-66

Crustal Stripping and Chemical Evolution of the Proto-Earth During Accretion

Quantification of the influence of collisional erosion during accretion on the budget of lithophile and refractory elements such as Sm and Nd

Crustal Stripping and Chemical Evolution of the Proto-Earth During Accretion

International audienceQuantification of the influence of collisional erosion during accretion on the budget of lithophile and refractory elements such as Sm and Nd

Quantitative estimates of impact induced crustal erosion during accretion and its influence on the Sm/Nd ratio of the Earth

International audienceDynamical scenarios of terrestrial planets formation involve strong perturbations of the inner part of the solar system by the giant-planets, leading to enhanced impact velocities and subsequent collisional erosion. We quantitatively estimate the effect of collisional erosion on the resulting composition of Earth, and estimate how it may provide information on the dynamical context of its formation. The composition of the Bulk Silicate Earth (BSE, Earth's primitive mantle) for refractory and lithophile elements (RLE) should be strictly chondritic as these elements are not affected by volatile loss nor by core formation. However, an excess in 142 Nd compared to the 144 Nd has been emphasized in terrestrial samples compared to most measurements in chondrites

Electrical characterization of ultra-thin SOI films : comparison of the pseudo–MOSFET and Hg–FET techniques

International audienc

The effect of collisional erosion on the composition of Earth-analog planets in Grand Tack models: Implications for the formation of the Earth

International audienceImpact-induced erosion of the Earth's early crust during accretion of terrestrial bodies can significantly modify the primordial chemical composition of the Bulk Silicate Earth (BSE, that is, the composition of the crust added to the present-day mantle). In particular, it can be particularly efficient in altering the abundances of elements having a strong affinity for silicate melts (i.e. incompatible elements) as the early differentiated crust was preferentially enriched in those. Here, we further develop an erosion model (EROD) to quantify the effects of collisional erosion on the final composition of the BSE. Results are compared to the present-day BSE composition models and constraints on Earth's accretion processes are provided. The evolution of the BSE chemical composition resulting from crustal stripping is computed for entire accretion histories of about 50 Earth analogs in the context of the Grand Tack model. The chosen chemical elements span a wide range of incompatibility degrees. We find that a maximum loss of 40wt% can be expected for the most incompatible lithophile elements such as Rb, Th or U in the BSE when the crust is formed from low partial melting rates. Accordingly, depending on both the exact nature of the crust-forming processes during accretion and the accretion history itself, Refractory Lithophile Elements (RLE) may not be in chondritic relative proportions in the BSE. In that case, current BSE estimates may need to be corrected as a function of the geochemical incompatibility of these elements. Alternatively, if RLE are indeed in chondritic relative proportions in the BSE, accretion scenarios that are efficient in affecting the BSE chemical composition should be questioned