Water lilies and scarabs: faithful partners for 100 million years?

Night-flowering water lilies (Nymphaeaceae) in South America are pollinated by Cyclocephala scarab beetles (Scarabaeidae: Cyclocephalini) in a specialized relationship involving synchronized flowering movements, strong floral scent, food tissues, and heat-producing flowers. We report that a similar and closely related association exists in West Africa between Nymphaea lotus L. and Ruteloryctes morio Fabricius (Cyclocephalini). This finding strongly supports a late Early Cretaceous origin of a symbiosis between the night-flowering water lilies and pollinating Cyclocephalini beetles. We believe that this is the first unambiguous evidence of a plant-pollinator relationship of this age.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80 , 539–543.     

Contribution from Stolons and Roots to Estimates of the Total Amount of N2Fixed by White Clover (Trifolium repensL.)

Growth and N-accumulation rates in leaves, stolons and rootsof individual white clover plants were studied in three experimentsusing two methods. In a growth chamber experiment, the relativedifferences between tissues were found to be almost constantfor a wide range of clover plant sizes. The stolon dry matter(DM) production was 56% and the root DM production 40% of theDM production in leaves. The N yield of stolons was 30% whileN yield in roots was 34% of N yield in leaves. The effect ofN application on these relations was investigated in a glasshouseexperiment. Application of N reduced the root:shoot N ratiofrom 0.50 to 0.28, whereas the stolon+root:leaf N ratio (i.e.for abovevs.below cutting-height tissues) was only reduced from0.97 to 0.80. In a field trial with two contrasting N regimes,growth and N accumulation were measured on individual cloverplants. Dinitrogen fixation was estimated by¹⁵N isotope dilutionbased on analysis of leaves-only or by including stolons. Usingleaves-only did not affect the calculation of percentage ofclover N derived from N₂fixation (% Ndfa) since the¹⁵N enrichmentwas found to be uniform in all parts of the clover. A correctionfactor of 1.7 to account for N in below cutting-height tissueis suggested when N₂fixation in white clover is estimated byharvesting the leaves only.Copyright 1997 Annals of Botany Company Leaves; N accumulation; N₂fixation; ¹⁵N isotope dilution; pastures; roots; root/shoot ratio; stolons; Trifolium repensL.; white clover     

A revised ammonite zonation of the Boreal Oxfordian and its application in northeast Greenland

A revised ammonite zonation for use in the Middle–Upper Oxfordian of the Boreal province is put forward. The zonation is used to date late Jurassic sediments in the Wollaston Forland area of northeast Greenland. The sediments broadly comprise basinal mudstones and shallow marine and shoreline sandstones, which were deposited in westerly tilted fault blocks during three transgressive pulses. On the peneplaned surfaces of wide tilted fault blocks a thick sequence of tidally and fluvially influenced marine sandstones of Middle Jurassic age was deposited. In the Upper Jurassic deposition initially took place in the centre of the basin where 80 m of shoreface sandstones accumulated (Jakobsstigen Member). In the second pulse the upthrown margin of the next fault block to the west was transgressed and deposition of basinal mudstones (Bernbjerg Formation) commenced in the basin centre on the main part of the dip-slope of the eastern block. Finally the crestal areas of the block on Kuhn Ø were inundated in Kimmeridgian times, and then subsided rapidly.     

Life history, growth and production of Mysis relicta in the large, fiord-type Lake Mjøsa, Norway

SUMMARY.

• 1 Biomass, production and life history of Mysis relicta were studied in the large Lake Mjøsa during the years 1976–80. Biomass fluctuations were large, but biomass averaged about 1 g wet wt m^?2 or 200 ind. m^?2. Cumulative net production during summer ranged from 1.6 to 2.1 g wet wt m^?2. Mean population P/B-ratio was close to 2.
• 2 Neither production or biomass of Mysis were correlated with the biomass of phytoplankton or the main Zooplankton prey species (Daphnia and Bosmina), suggesting a predominant ‘top down’ control of Mysis in this lake.
• 3 The life cycle was well synchronized with development of food items, but predation pressure also affected life-history patterns. The proportion of juveniles apparently increased in years with strong fish predation pressure, producing a predominantly 1-year life-cycle pattern the following year.
• 4 Mysis had a predominant 2-year life history, but a traction of the population may reproduce after 1 or 3 years. Reproduction occurred exclusively during winter. Even in such a large and stable system, where Mysis has coexisted with its main food items and predators for 8–10 000 years, a flexible life history is maintained and is probably an important buffer against year-to-year fluctuations in food and predator abundance.

     

Comparison of iron,manganese, and phosphorus retention in freshwater littoral sediment with growth of Littorella uniflora and benthic microalgae

Sediment columns from an oligotrophic lake were percolatedwith artificial porewater in two 46-day experiments toexamine the effects of Littorella uniflora and benthicmicroalgae on retention of phosphorus (P) by either iron(Fe) or manganese (Mn). Cumulative retention of P, Fe, andMn was 2–5 times higher in sediment with L. uniflora thanin sediment with microalgae, because of higher P uptake andmore efficient Fe and Mn oxidation by L. uniflora than bymicroalgae. Thus 34% and 21%of added P was retained in L. uniflora inhabited sediments asmetal-oxide bound P compared to 11% and2% in microalgae inhabited sediments, inexperiments supplied with Fe and Mn, respectively. Theatomic ratio of Fe/P precipitation was about 1 and forMn/P precipitation it was about 5. These ratios indicateprecipitation of Fe(III)-phosphate (strengite) and metastableMn(IV)-compounds containing phosphate and hydroxide ions invariable amounts. In addition to metal-oxide P precipitation,increased P retention in the vegetated sediment was also causedby the presence of humic acid compounds, which accountedfor about 26% of total retained P.     

Population genetic structure of a rare high-elevation black fly, Metacnephia coloradensis, occupying Colorado lake outlet streams

1. Using a portion of the mitochondrial cytochrome oxidase I gene, we evaluated the population genetic structure of a geographically rare black fly (Metacnephia coloradensis) that is a habitat specialist in outlet streams of large, productive, alpine lakes in Colorado, U.S.A. Given its rarity and life history traits that restrict dispersal, we hypothesised that genetic structure would show a signature of allopatric fragmentation associated with climatic warming since Pleistocene glaciations. 2. We tested for genetic isolation by distance (IBD) and applied nested clade analysis (NCA) to ask whether current genetic structure is primarily a consequence of historic fragmentation or if there is evidence of ongoing gene flow. 3. Only four populations were located despite a thorough search of potential sites, and they demonstrated a significant degree of genetic structure (F_ST = 0.17). However, there was some evidence of IBD in a plot of genetic versus geographic distance, and NCA further supported IBD and restricted ongoing gene flow in clades at all nested levels. Compared with a more widespread alpine black fly (Prosimulium neomacropyga) in the same region, M. coloradensis demonstrated significantly less population genetic structure. 4. Although these results counterintuitively implicate limited ongoing gene flow driving current population structure, significant IBD may be a signature of historic gene flow, especially if migration–drift equilibrium has not yet been reached since a late‐Pleistocene fragmentation event. Extraordinarily dense local populations probably allowed M. coloradensis to maintain large effective population sizes and minimise genetic drift rates. 5. Despite large local populations, M. coloradensis is vulnerable to continued rapid environmental change because of its limited geographic distribution and high habitat specificity.