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Wpływ doświadczalnych pożarów na zespoły mezofauny (Collembola i Acarina) dwóch typów łąk

100%

Olejniczka I. , Russel S. , Prędecka A.

2011

tom 9

nr 3

85-96

The impact of experimental fires in grasslands on soil mesofauna was studied in the field experiment. Study was carried out on two kinds of meadows: on mineral (meadow I) andorganic soils (meadow II), near Warsaw (52010’N; 20050’E). In November 2007 sampling plots, 1 m2 in size were chosen at random and burnt. Soil samples were taken just after fire and in April, July and November, 2008 to the depth of 10 cm from unburned places (control), at the border of fire and in burnt plots. The soil mesofauna was extracted from soil samples in the Tullgren apparatus. There were not found any effects of experimental fires on mesofauna densities. However, slightly increase of mesofauna abundance was s observed in burned plots 12 months after experimental fires on the meadow I and decrease on the meadow II. Just after fire, in burned plots, only euedaphic species of Collembola were present among mites communities dominated Oribatida, with thick cuticule.

Predetermination of cytokinesis and transition from holoblastic to partial superficial cleavage in early embryonic development of Tetrodontophora bielanensis (Collembola)

88%

Klag J. , Krzysztofowicz A. , Jura C. , Kisiel E.

nr 3-4

137-142

In the T. bielanensis embryo, only karyokinesis occurs during the first cleavage division, and a two-nuclear syncytial embryo forms. Then, two cytoplasmic concentrations in the form of elongated rolls perpendicular to each other develop below the periplasm at the animal pole of the egg. The second cleavage division is also associated with karyokineses only. After the embryo reaches the four-nuclear stage, cytokineses occur at its animal pole, and two cleavage furrows perpendicular to each other develop in the periplasm above the cytoplasmic concentrations. The cell membranes forming within the furrows do not invade the cytoplasmic concentrations, but their growing tips push them into the egg interior, where they merge and form the central cytoplasmic concentration. The developing cell membranes do not invade the central cytoplasm; they band and grow above its surface. Four pyramidal blastomeres form as a result of this. The eight-blastomere embryo forms through both karyokinesis and cytokinesis, but the growing cell membranes now band below the previous ones and cut off anucleate parts of the mother blastomeres, which fuse with the central cytoplasm. Thus, during this phase of development the transition from holoblastic to partial superficial cleavage is initiated. Morphological analysis suggests that the formation of the first two cytokineses is predetermined by and depends on factors connected with the animal pole periplasm. It also suggests that the central cytoplasm constitutes the morphological field, inducing the transition from holoblastic to partial superficial cleavage.