Quantitative relationships between oligochaete communities and phosphorus concentrations in lakes

SUMMARY.

• 1 The relative abundance of oligotrophic species in tubificid and lumbriculid communities was related to phosphorus concentration in eight lakes of Western Europe and three large lakes of North America.
• 2 Mean annual concentrations of total phosphorus, recorded in the whole lake during the 5 years preceding the sampling of worms, were averaged and this mean was used to indicate the trophic state.
• 3 Mean relative abundance (%) of oligotrophic species (OS) was negatively correlated with mean concentrations (mg m^?3) of total phosphorus (TP): OS = 80.29 – 8.35 TP^0.5r²= 0.81
• 4 Location and depth from which worms were sampled also influenced values of OS.

     

Male–female associations and female olfactory neurogenesis with pair bonding in Mus spicilegus

Mound‐building mice Mus spicilegus exhibit life‐history traits that are unique among the Mus species complex, such as the cooperative mound‐building behaviour that gives the species its common name. In this and other socially coordinated activities, such as those associated with reproduction, these mice should be able to recognize individuals (via discrimination based on kinship, population and species) to mediate their interactions. Our previous studies have provided evidence of population and species recognition in M. spicilegus. The aims of the present study were: (i) to study associations of mice during their reproductive period (in outdoor enclosures), (ii) to investigate whether there is an influence of relatedness of females in these associations, (iii) to determine whether female M. spicilegus are able to make kin vs. non‐kin discriminations, and (iv) to study certain neurobiological correlates of male–female bonds. Stable male–female associations were found in almost all the experimental groups, both those with unrelated and unfamiliar females and those with unfamiliar sisters. Kinship between females did not affect female associations in our enclosure experiment, but in our kin discrimination experiment females did distinguish between unfamiliar sisters and unfamiliar unrelated females. Shared kinship may not encourage cooperative rearing of pups but could enhance cooperation in building mounds where mice over‐winter. Male–female associations could be based on a social bond, as hypothesized from previous laboratory experiments. This was substantiated in this study by increased olfactory bulbar neurogenesis in females that preferred (in two choice tests) their sexual partner 3 weeks after their first mating. Based on these results there is clear evidence to suggest that the mating system of M. spicilegus is social monogamy. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 84 , 323–334.     

Tillering Responses to the Light Environment and to Defoliation in Populations of Perennial Ryegrass (Lolium perenneL.) Selected for Contrasting Leaf Length

Tillering responses to the light environment and to defoliationwere studied in two populations of perennial ryegrass (LoliumperenneL.) selected for contrasting leaf lengths. The objectiveof this study was to determine whether differences in tilleringresponses between populations, as a result of management practices,affected their competitive ability. Young seedlings were exposed,under controlled conditions, to defoliation, neutral shading(decreased photosynthetic photon flux), low red:far-red ratioand/or decreased blue light. Selection for longer leaves reducedthe tillering rate. After defoliation, this difference betweenshort- and long-leaved populations was magnified. Defoliationdecreased both site filling and phyllochron of the long-leavedpopulation but had no effect on the short-leaved population.Lowering the photosynthetic photon flux reduced the phyllochronin both population. Decreasing the red:far-red ratio reducedtillering rate by reducing site filling, whereas decreasingblue light had no significant effects on tillering. Tilleringresponses to photosynthetic photon flux and to red:far-red ratiowere similar in the two populations selected for contrastingleaf length. The implication of these tillering responses indefining the competitive ability of the grass plants is discussedin relation to their management.Copyright 1999 Annals of BotanyCompany Blue light, defoliation, far-red, irradiance, leaf size,Lolium perenne(L.), perennial ryegrass, photomorphogenesis, phyllochron, shading, site filling, tiller production.     

Mechanism of Host Cell Restriction in African Green Monkey Kidney Cells Abortively Infected with Human Adenovirus Type 2

Host cell restriction by GMK cells in abortive infections of adenovirus type 2 can be partially relieved by co-infection with SV40.     

Dynamics of Architectural Development of Isolated Plants of Maize (Zea mays L.), in a Non-limiting Environment: The Branching Potential of Modern Maize

The maximal architectural development of a modern maize cultivar(Zea mays L. ‘Dea’) was studied in fully isolatedand carefully irrigated plants. Under these favourable conditions,this (usually) non-tillering and non-prolific cultivar displayeda large amount of branching (down to the third order), includinglarge basal tillers and prolific ear shoots. This developmentwas analysed by combining: (1) architectural analysis, initiallydeveloped for trees; and (2) quantitative analysis of tilleringkinetics, designed for other grass species. The architecturalunit of maize included a main long axis (A1) and lateral shortshoots bearing a terminal spike (A2). The basal tillers (notedA1') resulted from a complete and sylleptic reiteration. Itskinetics were consistent with tillering models, but with a particularlylong delay in branch emergence (seven phyllochrons), comparedto other grass species. This delay is likely to enhance regulationby leaf (or root) density in stands and explains the inhibitionof branch development, as usually observed in field conditions,even at low density. Similarly, the suppression of the basalreiteration in secondary branches observed in isolated plantsprobably results from increased intra-tussock density. In isolatedplants, androgenous axes combining A1' and A2 morphologies werealso produced in intermediate positions. It is shown that theycan result from a basipetal sequence of A2 differentiation reachingbuds in the course of their A1' development. The consequencesof these unexpected results are discussed in terms of maizedevelopment and architectural analysis of grasses. Copyright1999 Annals of Botany Company Plant architecture, development, maize (Zea mays L.), tillering, branching, shoot, prolificacy, phyllochron.     

Detecting the impact of oceano-climatic changes on marine ecosystems using a multivariate index: The case of the Bay of Biscay (North Atlantic-European Ocean)

Large‐scale univariate climate indices (such as NAO) are thought to outperform local weather variables in the explanation of trends in animal numbers but are not always suitable to describe regional scale patterns. We advocate the use of a Multivariate Oceanic and Climatic index (MOCI), derived from ‘synthetic’ and independent variables from a linear combination of the total initial variables objectively obtained from Principal Component Analysis. We test the efficacy of the index using long‐term data from marine animal populations. The study area is the southern half of the Bay of Biscay (43°–47°N; western Europe). Between 1974 and 2000 we monitored cetaceans and seabirds along 131000 standardized line transects from ships. Fish abundance was derived from commercial fishery landings. We used 44 initial variables describing the oceanic and atmospheric conditions and characterizing the four annual seasons in the Bay of Biscay. The first principal component of our MOCI is called the South Biscay Climate (SBC) index. The winter NAO index was correlated to this SBC index. Inter‐annual fluctuations for most seabird, cetacean and fish populations were significant. Boreal species (e.g. gadiformes fish species, European storm petrel and Razorbill …) with affinities to cold temperate waters declined significantly over time while two (Puffin and Killer Whale) totally disappeared from the area during the study period. Meridional species with affinities to hotter waters increased in population size. Those medium‐term demographic trends may reveal a regime shift for this part of the Atlantic Ocean. Most of the specific observed trends were highly correlated to the SBC index and not to the NAO. Between 40% and 60% of temporal variations in species abundance were explained by the multivariate SBC index suggesting that the whole marine ecosystem is strongly affected by a limited number of physical parameters revealed by the multivariate SBC index. Aside the statistical error of the field measurements, the remaining variation unexplained by the physical characteristics of the environment correspond to the impact of anthropogenic activities such overfishing and oil‐spills.