Effect of local spatial plant distribution and conspecific density on bumble bee foraging behaviour

1. Size variations in pollinator populations may modify competitive interactions among foragers. Competition among pollinators has been shown to lead to one of two contrasting behaviours: either specialisation to the most profitable plant species or generalisation to several species. When foraging, pollinators are also confronted with heterogeneity in the spatial distribution of plant resources. Because variations in both the forager density and plant spatial distribution can affect pollinator behaviour, focus was on the interactive effect of these two factors. 2. Bumble bee (Bombus terrestris L.) individuals were trained on a focal species (Lotus corniculatus L.) and experimentally tested whether variations in the forager density (two or six bumble bees foraging together), plant community spatial distribution (two plant species: L. corniculatus and Medicago sativa, which were either patchily or randomly distributed), and their interaction modified bumble bee foraging behaviour. 3. It was shown that when confronted with a high forager density, bumble bees focused their visits towards the most familiar species, especially when foraging under a random plant distribution. These modifications affected the fruiting of the focal plant species, with a significantly lower reproductive success under low density/patchy conditions. 4. This study demonstrates that the foraging decisions of bumble bees are influenced by variations in both the conspecific density and plant spatial distribution. Given the increasing impact of human activities on plant‐pollinator communities, this raises the question of the potential implications of these results for plant communities in natural conditions when confronted with variations in the pollinator density and spatial distribution of plants.     

Localisation of the Vacuolar Proton Pump (V-H+-ATPase) and Carbonic Anhydrase II in the Human Eccrine Sweat Gland

The localisation of the vacuolar proton pump (V-H+ -ATPase) and the enzyme carbonic anhydrase II (CAII) was investigated in the human eccrine sweat gland employing standard immunohistochemical techniques after antigen retrieval using microwave heat treatment and high pressure. The high-pressure antigen retrieval unmasked the presence of V-H+ -ATPase in the clear cells of the secretory coil, with a distribution similar to that previously observed for CAII. However, the dark cells were unreactive to both antibodies. In addition, heat and high-pressure antigen retrieval demonstrated the presence of CAII in the apical zone of luminal cells of the reabsorptive duct, a location not previously reported. The localisation of V-H+ -ATPase and CAII in the secretory coil clear cells suggests that the formation of HCO3- and H+ by carbonic anhydrase II and the transport of H+ by V-H+ -ATPase may play an role in sweat fluid secretion. Their presence at the apex of the duct cells indicates involvement in ductal ion reabsorption.     

There is No Somatic Meiosis in Embryogenic Leaves of Cichorium

Several papers dealing with carrot cell cultures describe meiosis-likedivisions and haploid cells prior to somatic embryogenesis.We have studied the first division in embryogenic mesophyllcells of a diploidCichorium intybus L. and of a tetraploid hybridC.intybus L.xC. endivia L. which undergo direct somatic embryogenesisfrom single cells when leaf fragments are placed in a liquidagitated inductive medium (modified MS with 1x10^-7M NAA and2.5x10^-6M 2-iP), in darkness, at 35°C. MicrosporogenesisinC. intybus provided aspects of meiosis for comparison. Inleaves incubated in inductive conditions, DAPI staining of nucleishowed normal mitosis on days 3–6; about 0.6% cells inprophase had undergone spontaneous endoreduplication leadingto a tetraploid somatic embryo. Immunocytochemistry of tubulinrevealed the constant presence of a preprophase band, as ina normal mitosis. The first pluricellular somatic embryos becamevisible on day 5 of culture. Flow cytometric determination ofnuclear DNA on days 4, 5 and 6 did not show any peak correspondingto the 1C DNA level for the diploid plant or to the 2C DNA levelfor the tetraploid. Instead there was a weak but constant peakat the 4C and 8C levels. We conclude that inCichorium leaves,the first division of somatic embryogenesis is a normal mitosis,with a small shift to endoreduplication. In our opinion, somaticmeiosis is not a prerequisite during direct somatic embryogenesis. Cichorium ; chicory; somatic embryogenesis; cell division; flow cytometry; tubulin     

Sexual and Asexual Development of Cryptosporidium parvum in Five Oocyst– or Sporozoite-Infected Human Enterocytic Cell Lines

ABSTRACT. The human enterocytic cell lines Caco-2, HT29, HCT8 and the Caco-2 clones TC7 and PF11 were studied for their ability to support Cryptosporidium parvum development. Following the addition in cultures of either oocysts or excysted sporozoites, immunofluorescent and transmission electron microscopy revealed the presence of all stages of the parasite life cycle by both procedures, and no difference in the ration of infected cells was found among cell lines. More oocysts were seen in cell monolayers infected with oocysts than with sporozoites (p < 0.0001). The number of meronts observed was the same after either oocysts or sporozoites inoculation. Data suggest that the two methods yield a same cell infection rate.