Studies on Nipponnemertes Friedrich (Nemertini, Hoplonemertini). II. Taxonomy of Nipponnemertes pulcher (Johnston) and Some Other Species

The synonymity of some Amphiporus species is discussed. Amphiporus falklandicus Wheeler, 1934, A. pusillus Punnett, 1903, Nipponnemertes bergendali (Gering, 1912), N. danae (Friedrich, 1957) and Wheeler's specimens of A. gerlachei Burger, 1904 and A. lecointei Burger, 1904 are found to be synonymous with N. pulcher , while A. mesosorus Verrill, 1892, A. arcticus Punnett, 1901 and A. thompsoni Punnett, 1901 are separated from the discussion of synonymity with this species. A summary of the knowledge of the geographical distribution of N. pulcher is given. The species A. africanus Wheeler, 1940, A. magnus Punnett, 1903, A. marioni Hubrecht, 1887, A. schollaerti Wheeler, 1934 and A. scoresbyi Wheeler, 1934 are transferred to the genus Nipponnemertes Friedrich, 1968.     

Different forms of phototropic response induced by microbeam irradiation of discrete regions of an organ

Abstract Continuous unilateral microbeam (1 mm) irradiation of coleoptiles of Avena saliva L. produces growth responses in non-irradiated regions of the organ. Irradiation of the apex is followed by differential growth which commences in the apical zone, but then moves in a basipetal direction and results in positive curvature. Irradiation of the base also results in differential growth which commences at the apex and moves basipetally. However, the growth differential in this case results in negative curvature. The results of basal irradiation suggest the likely occurrence of acropetal transmission of the phototropic signal. The rate of movement of this signal is faster than the documented rate of auxin transport.     

Organotypic Culture of Human Skin to Study Melanocyte Migration

An ex vivo model system was developed to investigate melanocyte migration. Within this model system, melanocytes migrate among other epidermal cells in the epibolic outgrowth of skin explants. This process is initiated by loss of contact inhibition of epidermal cells at the rim of the explants and by locally produced chemotactic factors. Punch biopsies provided explants of reproducible diameter. Optimal culture conditions include medium consisting of Dulbecco's Minimal Essential Medium containing 10% inactivated normal human serum and placement of explants epidermal side up at the air-liquid interphase. Within 7 days, epidermal cells completely surround the explant. Approximately 3 days after the onset of keratinocyte migration, melanocytes distribute themselves within the newly formed epidermis. Throughout the 7-day culture period, melanocytes and keratinocytes show maintenance of subcellular morphology, and the dermo-epidermal junction remains intact. Melanocyte migration was quantified using immunoperoxidase staining in combination with light microscopy and computer-aided image analysis. Preliminary results using the model system to compare migration in control and nonlesional vitiligo skin indicate that no inherent migration defect is responsible for impaired repigmentation of vitiligo lesions. The organotypic culture model system allows for investigations on melanocytes within their environment of autologous epidermal and dermal components, closely resembling in vivo circumstances in human skin.     

Pelagic and benthic net production of dissolved inorganic carbon in an unproductive subarctic lake

1. Both the pelagic and benthic net dissolved inorganic carbon (DIC) productions were measured in situ on four occasions from June to September 2004, in the unproductive Lake Diktar-Erik in subarctic Sweden. The stable isotopic signal ( δ ¹³C) of respired organic material was estimated from hypolimnion water data and data from a laboratory incubation using epilimnion water.
2. Both pelagic and benthic habitats were net heterotrophic during the study period, with a total net DIC production of 416 mg C m⁻² day⁻¹, of which the pelagic habitat contributed approximately 85%. The net DIC production decreased with depth both in the pelagic water and in the sediments, and most of the net DIC production occurred in the upper water column.
3. Temporal variations in both pelagic and benthic DIC production were small, although we observed a significant decrease in pelagic net DIC production after the autumn turnover. Water temperature was the single most important factor explaining temporal and vertical variations in pelagic DIC production. No single factor explained more than 10% of the benthic net DIC production, which probably was regulated by several interacting factors.
4. Pelagic DIC production, and thus most of the whole-lake net production of DIC, was mainly due to the respiration of allochthonous organic carbon. Stable isotope data inferred that nearly 100% of accumulated DIC in the hypolimnion water had an allochthonous carbon source. Similarly, in the laboratory incubation using epilimnion water, c. 85% of accumulated DIC was indicated to have an allochthonous organic carbon source.     

Diel interactions between prey behaviour and feeding in an invasive fish, the round goby, in a North American river

1. We studied the diet of the invasive round goby (Neogobius melanostomus) on a diel basis in the Flint River, a warmwater stream in Michigan, U.S.A. Diet and available prey samples were collected seven times over a 24 h period in four consecutive months. The section of river studied lacked zebra mussels (Dreissena polymorpha), the primary prey of adult round gobies elsewhere in the Great Lakes region. 2. Diet changed on a diel basis with hydropsychid caddisfly and chironomid larvae predominating during the day, chironomid pupae dominating in the evening and heptageniid mayflies dominating at night. Simultaneous study of macroinvertebrate drift suggested that caddisfly and chironomid larvae were most likely picked from submerged rocks, chironomid pupae were most likely taken during their emergent ascent and mayflies were either captured from the drift or picked from rocks. 3. The Flint River lacks a diverse darter (Family: Percidae) and sculpin (Family: Cottidae) fauna and it appears that the round goby has occupied a generalised darter/sculpin niche. Our results indicate that round gobies have the potential to invade successfully riverine systems, particularly those lacking a diverse benthic fish assemblage.