Affiner les résultats


Université de Fribourg

A test of the coevolution theory of autumn colours: colour preference of Rhopalosiphum padi on Prunus padus

Archetti, Marco ; Leather, Simon R.

In: Oikos, 2005, vol. 110(2), p. 339

According to the coevolution theory of autumn colours, the bright colours of trees evolved as a warning signal towards parasites colonizing the plant in autumn. We monitored colonization of the aphid Rhopalosiphum padi on individual tress of Prunus padus in autumn and observed a strong preference of aphids for trees with green leaves. This is the first direct observation of a key...

Université de Fribourg

Glomerular Maps without Cellular Redundancy at Successive Levels of the Drosophila Larval Olfactory CircuitGlomerular Maps without Cellular Redundancy at Successive Levels of the Drosophila Larval Olfactory Circuit

Ramaekers, Ariane ; Magnenat, Edwige ; Marin, Elizabeth C. ; Gendre, Nanaë ; Jefferis, Gregory S.X.E. ; Luo, Liqun ; Stocker, Reinhard F.

In: Current Biology, 2005, vol. 15(11), p. 982

Background: Drosophila larvae possess only 21 odorant-receptor neurons (ORNs), whereas adults have 1,300. Does this suggest that the larval olfactory system is built according to a different design than its adult counterpart, or is it just a miniature version thereof? Results: By genetically labeling single neurons with FLP-out and MARCM techniques, we...

Université de Fribourg

Hatching with the enemy: Daphnia diapausing eggs hatch in the presence of fish kairomones

Lass, Sandra ; Vos, Matthijs ; Wolinska, Justyna ; Spaak, Piet

In: Chemoecology, 2005, vol. 15(1), p. 7

Infochemicals are known to play a key role in mediating predator-prey interactions, both in aquatic and terrestrial communities. However, state-dependent variation may exist in how effectively individuals can use this information, depending on genotype, life stage and experience. For our study, we used the predator-prey model system fish-waterflea Daphnia magna Straus (Cladocera,...

Université de Fribourg

Variable success of biological control of Lythrum salicaria in British Columbia

Denoth, Madlen ; Myers, Judith H.

In: Biological Control, 2005, vol. 32, p. 269

Purple loosestrife, Lythrum salicaria, has invaded North American wetlands over the last 200 years. A biological control project was started in British Columbia, Canada, in 1993 with the introduction of Galerucella calmariensis, a leaf- feeding beetle of European origin. To evaluate the success of the biological control project in the Lower Mainland of British Columbia, we...

Université de Fribourg

Winter weather affects asp viper Vipera aspis population dynamics through susceptible juveniles

Altwegg, Res ; Dummermuth, Stefan ; Anholt, Bradley R. ; Flatt, Thomas

In: Oikos, 2005, vol. 110 (1), p. 55

Detailed studies on mammals and birds have shown that the effects of climate variation on population dynamics often depend on population composition, because weather affects different subsets of a population differently. It is presently unknown whether this is also true for ectothermic animals such as reptiles. Here we show such an interaction between weather and demography for an ectothermic...

Université de Fribourg

Stabilizing factors interact in promoting host–parasite coexistence

Flatt, Thomas ; Scheuring, István

In: Journal of Theoretical Biology, 2004, vol. 228(2), p. 241

Understanding the mechanisms that promote coexistence among species is a fundamental problem in evolutionary ecology. Such mechanisms include environmental noise, spatial population structure, density dependence, and genetic variation. In natural populations such factors may exert combined effects on coexistence. Thus, to disentangle the contribution of several factors to coexistence, their...

Université de Fribourg

Assessing natural variation in genes affecting Drosophila lifespan

Flatt, Thomas

In: Mechanisms of Ageing and Development, 2004, vol. 125(3), p. 155

Université de Fribourg

Altitudinal differences in flower traits and reproductive allocation

Fabbro, Thomas ; Körner, Christian

In: Flora - Morphology, Distribution, Functional Ecology of Plants, 2004, vol. 99(1), p. 70

We tested whether alpine plants increase their effort to attract pollinators to compensate for assumed pollinator scarcity at high altitude. A three times larger fraction of the shoot was allocated to flowers in alpine plants (30 species, 2700m asl) compared to lowland plants (20 species, 600m asl), while leaf mass fraction did not differ between the altitudes. At high elevation, a three times...

Université de Fribourg

Accumulation of deleterious mutations in hybridogenetic organisms

Archetti, Marco

In: Journal of Theoretical Biology, 2005, vol. 234(2), p. 151

Université de Fribourg

Two non-destructive neutron inspection techniques : prompt gamma-ray activation analysis and cold neutron tomography

Baechler, Sébastien ; Dousse, Jean-Claude (Dir.) ; Jolie, Jan (Codir.)

Thèse de doctorat : Université de Fribourg, 2002 ; no 1381.

Deux techniques d’inspection non-destructives utilisant des faisceaux de neutrons froids ont été développées à la source de neutrons SINQ de l’Institut Paul Scherrer : (1) l’analyse par activation neutronique prompte (PGAA) et (2) la tomographie neutronique. L’analyse par PGA (Prompt Gamma-ray Activation) est une méthode nucléaire qui permet de déterminer la concentration...