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Université de Fribourg

A new structural element containing glycine-rich proteins and rhamnogalacturonan I in the protoxylem of seed plants

Ryser, Ulrich ; Schorderet, Martine ; Guyot, Romain ; Keller, Beat

In: Journal of Cell Science, 2004, vol. 117, p. 1179-1190

The water pipes of elongating plant organs are the result of programmed cell death and are formed by the walls of dead and empty protoxylem elements. These protoxylem elements are passively elongated many times by the surrounding tissue before they are replaced and collapse. Well-known adaptations for this unique task include the characteristic secondary wall thickenings, forming rings and...

Université de Fribourg

Haunted by the past: evidence for dormant stage banks of microparasites and epibionts of Daphnia

Decaestecker, Ellen ; Lefever, Christophe ; De Meester, Luc ; Ebert, Dieter

In: Limnology and Oceanography, 2004, vol. 49, p. 1355-1364

Microparasites and epibionts have important implications for the ecology and evolution of their zooplankton host populations. Many parasites and epibionts produce resistant spores that infect new hosts upon intake. We explored the hypothesis that these spores build up dormant stage banks that remain infective for several years (decades). In laboratory experiments, we exposed Daphnia magna to...

Université de Fribourg

Within-host dynamics of a microsporidium with horizontal and vertical transmission: Octosporea bayeri in Daphnia magna

Vizoso, Dita B. ; Ebert, Dieter

In: Parasitology, 2004, vol. 128, p. 31-38

The fresh-water crustacean Daphnia magna may acquire an infection with the microsporidium Octosporea bayeri either by ingesting spores from the water (horizontally), or directly from its mother (vertically). Due to differences in the time and mechanisms of transmission, horizontal and vertical infections may lead to differences in the growth of the parasite within the host. This may influence...

Université de Fribourg

Parasite-mediated selection in experimental metapopulations of Daphnia magna

Haag, Christoph R. ; Ebert, Dieter

In: Proceedings of the Royal Society of London: Biological Sciences, 2004, vol. 271, p. 2149-2155

In metapopulations, only a fraction of all local host populations may be infected with a given parasite species, and limited dispersal of parasites suggests that colonization of host populations by parasites may involve only a small number of parasite strains. Using hosts and parasites obtained from a natural metapopulation, we studied the evolutionary consequences of invasion by single strains...

Université de Fribourg

Variation in phenoloxidase activity and its relation to parasite resistance within and between populations of Daphnia magna

Mucklow, Patrick T. ; Vizoso, Dita B. ; Jensen, Knut Helge ; Refardt, Dominik ; Ebert, Dieter

In: Proceedings of the Royal Society of London: Biological Sciences, 2004, vol. 271, p. 1175-1183

Estimates of phenoloxidase (PO) activity have been suggested as a useful indicator of immunocompetence in arthropods, with the idea that high PO activity would indicate high immunocompetence against parasites and pathogens. Here, we test for variation in PO activity among clones of the planktonic crustacean Daphnia magna and its covariation with susceptibility to infections from four different...

Université de Fribourg

A new hypothesis to explain geographic parthenogenesis

Haag, Christoph R. ; Ebert, Dieter

In: Annales Zoologici Fennici, 2004, vol. 41, p. 539-544

In many plants and animal species, asexuals are more common in marginal habitats such as high latitudes or altitudes than their closely related sexual counterparts. Here we propose a new hypothesis to explain this pattern called "geographic parthenogenesis". In marginal habitats, populations may often exist as metapopulations with high degrees of subdivision and local extinction and...

Université de Fribourg

The effect of learning on experimental evolution of resource preference in Drosophila melanogaster

Kawecki, Tadeusz J. ; Mery, Frederic

In: Evolution, 2004, vol. 58, p. 757-767

Learning is thought to be adaptive in variable environments, whereas constant, predictable environments are supposed to favor unconditional, genetically fixed responses. A dichotomous view of behavior as either learned or innate ignores a potential evolutionary interaction between the learned and innate components of a behavioral response. We addressed this interaction in the context of...

Université de Fribourg

Conceptual issues in local adaptation

Kawecki, Tadeusz J. ; Ebert, Dieter

In: Ecology Letters, 2004, vol. 7, p. 1225-1241

Studies of local adaptation provide important insights into the power of natural selection relative to gene flow and other evolutionary forces. They are a paradigm for testing evolutionary hypotheses about traits favoured by particular environmental factors. This paper is an attempt to summarize the conceptual framework for local adaptation studies. We first review theoretical work relevant for...

Université de Fribourg

Evolution in invasive plants: implications for biological control

Müller-Schärer, Heinz ; Schaffner, Urs ; Steinger, Thomas

In: Trends in Ecology and Evolution, 2004, vol. 19, p. 417-422

Evidence is increasing that invasive plants can undergo rapid adaptive evolution during the process of range expansion. Here, we argue that evolutionary change during invasions will also affect plant–antagonist inter-actions and, thus, will have important implications for biological control programmes targeted at invasive plants. We explore how altered selection in the new range might influence...

Université de Fribourg

The dynamic localization and novel functions of the Ipl1/Aurora protein kinase

Buvelot, Stéphanie ; Conzelmann, Andreas (Dir.)

Thèse de doctorat : Université de Fribourg : 2003 ; no 1400.

La ségrégation exacte des chromosomes est un événement indispensable pour une division cellulaire fidèle. Des anormalités dans la ségrégation des chromosomes résultent en une instabilité génomique et une aneuploïdie et sont corrélées avec le cancer. Le laboratoire étudie la ségrégation des chromosomes chez la levure de bière Saccharomyces cerevisiae. Étant donné que ce...