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The neural substrate subserving magnetic orientation is largely unknown in vertebrates and unstudied in mammals. We combined a behavioral test for magnetic compass orientation in mole rats and immunocytochemical visualization of the transcription factor c-Fos as a marker of neuronal activity. We found that the superior colliculus of the Zambian mole rat (Cryptomys anselli) contains neurons that are responsive to magnetic stimuli. These neurons are directionally selective and organized within a discrete sublayer. Our results constitute evidence for the involvement of a specific mammalian brain structure in magnetoreception.

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Background and aims: Plant‐derived, ester‐bound substituted fatty acids have been used for decades as biomarkers to identify input of plant materials in sediments and soils. However, the long‐term decomposition patterns of these biomarker compounds under natural conditions are not well understood, although this is a basic prerequisite for quantitative biomarker applications. Methods: For this study, we analyzed the decomposition patterns of root‐ and needle‐specific compounds of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) in a litterbag study conducted over 3 years. Samples were analyzed by methanolic KOH extraction with previous removal of free extractable lipids. Results: The concentrations of most detectable compounds had decreased after three years of incubation. The observed changes of concentrations followed a non‐linear path and cannot be explained by microbial uptake and metabolism alone. Other factors controlling the breakdown of ester‐bound lipids, like lipid oxidation must play a role. Between similar plant parts and different plant parts of the same species, the observed degradation patterns were heterogeneous. The estimated ratio of remaining root and needle biomass that may arise with the choice of a particular biomarker varies in this study between 0.6 and 40 times after three years. Conclusion: This range of variation does not allow reliable conclusions about the contribution of roots and needles to decomposed organic matter based on biomarkers ratios.

Root-specific and leaf-specific biomarkers have been used for decades to identify the origin of organic materials in soils and sediments. However, quantitative approaches require appropriate knowledge about the fate of these indicator molecules during degradation. To clarify this issue, we performed a 1-year incubation experiment with fine root and leaf material of six temperate tree species: European ash (Fraxinus excelsior), European beech (Fagus sylvatica), Oak spec. (Quercus spec.), Linden spec. (Tilia spec.), Norway spruce (Picea abies) and Scots pine (Pinus sylvatica). Only one molecule, x,16-dihydroxy hexadecanoic acid (x,16-C16), could be validated as a general leaf-specific biomarker for the set of all species. For roots, no general root biomarker was found. Ester-bound tricosanol (C23-OH) could be validated for five out of six species; 20-hydroxy eicosanoic acid (ωC20) could be validated for four out of six species, leaving Norway spruce without a suitable root biomarker. The results of this study suggest that the validity of leaf- and root-derived ester-bound lipids as biomarkers is highly species dependent and does not always coincide with previous findings. Concentrations of root- and leaf-derived ester-bound lipids did not stay constant within 1 year of degradation and changed without a linear trend. The change of concentrations seems to be highly species dependent. This might be due to a different structure and arrangement of the individual monomers in cutin and suberin per species, and, therefore, a different accessibility of bond cleaving enzymes. The usefulness of root and leaf biomarkers is context dependent. Our results suggest that general assumptions about litter input to forest soils solely based on biomarker analysis have to be considered carefully.

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