Pollination by flies, bees, and beetles of Nuphar ozarkana and N. advena (Nymphaeaceae)

Nuphar comprises 13 species of aquatic perennials distributed in the temperate Northern Hemisphere. The European species N. lutea and N. pumila in Norway, the Netherlands, and Germany are pollinated by bees and flies, including apparent Nuphar specialists. This contrasts with reports of predominant beetle pollination in American N. advena and N. polysepala. We studied pollination in N. ozarkana in Missouri and N. advena in Texas to assess whether (1) there is evidence of pollinator shifts associated with floral-morphological differences between Old World and New World species as hypothesized by Padgett, Les, and Crow (American Journal of Botany 86: 1316–1324. 1999) and (2) whether beetle pollination characterizes American species of Nuphar. Ninety-seven and 67% of flower visits in the two species were by sweat bees, especially Lasioglossum (Evylaeus) nelumbonis. Syrphid fly species visiting both species were Paragus sp., Chalcosyrphus metallicus, and Toxomerus geminatus. The long-horned leaf beetle Donacia piscatrix was common on leaves and stems of N. ozarkana but rarely visited flowers. Fifteen percent of visits to N. advena flowers were by D. piscatrix and D. texana. The beetles’ role as pollinators was investigated experimentally by placing floating mesh cages that excluded flies and bees over N. advena buds about to open and adding beetles. Beetles visited 40% of the flowers in cages, and flowers that received visits had 69% seed set, likely due to beetle-mediated geitonogamy of 1st-d flowers. Experimentally outcrossed 1st-d flowers had 62% seed set, and open-pollinated flowers 76%; 2nd-d selfed or outcrossed flowers had low seed sets (9 and 12%, respectively). Flowers are strongly protogynous and do not self spontaneously. Flowers shielded from pollinators set no seeds. A comparison of pollinator spectra in the two Old World and three New World Nuphar species studied so far suggests that the relative contribution of flies, bees, and beetles to pollen transfer in any one population depends more on these insects’ relative abundances (and in the case of Donacia, presence) and alternative food sources than on stamen length differences between Old World and New World pond-lilies

Earliest Phases of Star Formation - Physical and Chemical Properties of Prestellar Cores

With the goal of constraining the initial physical and chemical conditions of low-mass star formation, the thermal dust emission of a sample of prestellar cores has been observed with the Herschel Space Observatory. From these observations, the most accurate maps of the dust temperature and density structures in prestellar cores existing today have been derived using a ray-tracing technique. Based on this new information on the physical conditions in the prestellar cores I model the chemical evolution of the associated gas. Comparison of the models to molecular line observations reveals that CO freezes out strongly in the core centers and that even the high density tracer N2H+ is affected by depletion. I derive a chemical age of the gas in all cores on the order of 10^5 yr which is comparable to the free-fall time of the cores. Furthermore, I calculate the thermal equilibrium distributions of the prestellar cores between the two methods confirming the reliability of the ray-tracing technique. It is also shown that the agreement is good for a large range of dust models. Finally, I present ammonia observations of three prestellar cores and use them as a gas temperature probe. Comparison of gas and dust temperatures shows that both agree in the inner parts of two cores traced by ammonia while the gas is slightly warmer than the dust in the third object; maybe due to a reduced collisional coupling between gas and dust because of coagulation of the dust grains

Electron beam driven alkali metal atom source for loading a magneto-optical trap in a cryogenic environment

We present a versatile and compact electron beam driven source for alkali metal atoms, which can be implemented in cryostats. With a heat load of less than 10mW, the heat dissipation normalized to the atoms loaded into the magneto-optical Trap (MOT), is about a factor 1000 smaller than for a typical alkali metal dispenser. The measured linear scaling of the MOT loading rate with electron current observed in the experiments, indicates that electron stimulated desorption is the corresponding mechanism to release the atoms.Comment: 5 pages, 3 figure