The presence of the piston-pumping polychaete Lanice conchilega can induce short term oscillations in oxygen and nitrate availability at deeper sediment layers, affecting the functional properties of local microbial communities. Here, we investigated the effect of Lanice conchilega densities on the expression of the nosZ gene, a gene encoding for the enzymes involved in the last step (reduction of N2O) of the denitrification pathway. Sediments with “high” , “low” and no Lanice individuals were collected from the intertidal and incubated submerged (reflecting the high water tide) in the lab, to measure vertical oxygen profiles and oxygen oscillations during 35 minutes at 1.5 mm sediment depth before slicing the sediment, and extracting RNA for Illumina sequencing the nosZ gene. We found 502 unique amino acid sequences (“nosZ-UAT), only 21 of them were abundant (>1% relative abundance). nosZ-AUT based community analyses showed that high densities of Lanice significantly affected the nosZ transcript composition. In addition, higher variability was observed in the high density treatments as well. Further differences were observed between the top layer of the sediment (0-0.5 cm) and the investigated deeper layers. The difference in nosZ-AUT Shannon diversity between deeper sediment layers and the upper sediment layer increased with Lanice density. The observed differences in nosZ-AUT composition and diversity at small horizontal (m) and vertical (cm) scale can thus be attributed to differences in bio-irrigator densities. We hypothese that this due to stronger oscillations of both O2 and NO3- availability in the presence of high densities of bio-irrigators. Oscillations of O2 concentrations at a single spot in otherwise anoxic environments create microhabitats where coupled nitrification-denitrification is possible, while providing the environment with NO3- provides substrate for denitrification. As such, the presence of high densities of bio-irrigators increase the effect of already reported tide-related redox oscillations during periods of submersion.
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RBINS Staff Publications 2017
The Quercy Phosphorites are a set of Eocene-Oligocene deposits from South-West France that yielded numerous vertebrate fossils, including amphibians, mostly as isolated bones. However, in 1873, several exceptional amphibian specimens were discovered, with the external surface of the unmineralized tissues preserved, and were commonly referred as “mummies”. In the 19th century, they were described without any knowledge of their internal anatomy. Since 2012, we have started scanning these “mummies”, revealing the preserved internal soft tissues and articulated skeleton. A first specimen was attributed in 2013 to Thaumastosaurus gezei and we here present our results from the tomography of a second “mummified” anuran, previously identified as Bufo servatus. The tomography showed a preserved articulated skeleton, and its osteological characteristics are similar to the first scanned anuran “mummy”, representing different ontogenetic stages. Both are now both attributed to Thaumastosaurus servatus nov. comb. The new anatomical information is used to assess the affinities of T. servatus, which appears to belong to the Pyxicephalidae, an African anuran clade. Thaumastosaurus thus represents both the oldest occurrence of this clade in the fossil record and its first occurrence outside of Africa. Its presence in Europe highlights a faunistic exchange with Africa during the Eocene, also documented for several clade of squamates. The presence of this African herpetofauna in Europe might be linked to the warmer climate during the Eocene. However, most of this herpetofauna, including Thaumastosaurus, disappeared from the region around an extinction event (named the “Grande Coupure”) that took place around the Eocene/Oligocene transition (~34 Ma).
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RBINS Staff Publications 2021
