The ultrastructure, neuroanatomy and central projection patterns, including the intercellular connections of the statocyst hair cells of the pond snail, Lymnaea stagnalis, were studied, applying different intra- and extracellular cellular staining techniques combined with correlative light- and electron microscopy. Based on the ultrastructure different hair cells could be distinguished according to their vesicle and granule content, meanwhile the general organization of the sensory neurons was rather uniform, showing clearly separated perinuclear and “vesicular” cytoplasmic regions. Following intra- and extracellular labeling with fluorescence dyes or HRP a typical, local arborization of the hair cells was demonstrated in the cerebral ganglion neuropil, indicating a limited input-output system connected to the process of gravireception. Correlative light- and electron microscopy of HRP-labeled hair cells revealed both axo-somatic and axo-axonic output contacts of hair cell varicosities, and input on sensory axons located far from the terminal arborizations. Our findings suggest (i) a versatile ultrastructural background of hair cells corresponding possibly to processing different gravireceptive information, and (ii) the synaptic (or non-synaptic) influence of gravireception at different anatomical (terminal, axonal and cell body) levels when processed centrally. The results may also serve as a functional morphological background for previously obtained physiological and behavioral observations.
Authors:H. Hautala, T. Kuuluvainen, T.J. Hokkanen, and A. Tolvanen
We examined the composition and spatial structure of the understorey vegetation at two sites with different fire histories in a mature Pinus sylvestris L. forest in eastern Finland. The entire study area had regenerated after a fire in the early 19thcentury. Besides, a part of the area was subsequently hit by a surface fire in 1906, which divided the study area into two parts. Vegetation and environmental variables measured from the these two parts, the 1800+ burn site and the 1906 burn site, have considerably different spatial pattern. Deciduous shrubs and ground layer, consisting primarily of bryophytes, had a more distinct patch structure at the 1800+ burn site than at the 1906 burn site, while with lichens the situation was the reverse. Cover of the field layer, dominated by evergreen shrubs, was significantly higher at the 1800+ burn site than at the 1906 burn site. At both sites, the spatial pattern of plant functional types was obviously strongly regulated by the spatial influence of living trees. Gradual formation of strong clonal patch structures of V. myrtillus, V. vitis-idaea and mosses, seems to be another important process affecting the properties of the understorey vegetation. The post-fire recovery of the understorey community was slow: in the 1906 burn site, the community composition and spatial structure were still in transition after almost 90 years since the last fire.
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Widder , S. , K. Besemer , G.A. Singerb , S. Ceolae , E. Bertuzzof , C. Quinceg , W.T. Sloang , A. Rinaldof and T.J. Battin . 2014 . Fluvial network organization imprints on microbial co-occurrence networks . Proc. Nat. Acad. Sci. USA 111