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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

Host starvation decreases parasite load and mean host size in experimental populations

Pulkkinen, Katja ; Ebert, Dieter

In: Ecology, 2004, vol. 85, p. 823-833

While host stress in vertebrate populations has often been linked to outbreaks of epidemics, which are attributed to the immuno-compromise of the stressed hosts, no predictions have been made about the response of invertebrate host populations to stressful conditions. Experiments conducted on individual invertebrate hosts, however, suggest that starved hosts may be a poor resource for...

Université de Fribourg

An operating cost of learning in Drosophila melanogaster

Mery, Frederic ; Kawecki, Tadeusz J.

In: Animal Behaviour, 2004, vol. 68, p. 589-598

Although the fitness benefits of learning are well understood, we know little about its costs; yet both are essential to understand the evolution of animal learning. We tested the hypothesis that learning has an operating cost, such that an animal repeatedly forced to use its learning ability would show a reduction in some fitness component(s), relative to an animal of the same genotype that does...

Université de Fribourg

Evidence for epistasis: reply to Trouve et al.

Ebert, Dieter ; Salathé, P. ; Kawecki, Tadeusz J.

In: Journal of Evolutionary Biology, 2004, vol. 17, p. 1402-1404

Salathé and Ebert (2003, J. Evol. Biol. 16: 976-985) have shown that the mean logarithmic fitness of Daphnia magna clones declined faster than linearly with increasing inbreeding coefficient F. They interpreted this result as evidence for synergistic epistasis. Trouve et al. (2004, J. Evol. Biol., doi: 10.1111/j.1420-9101.2004.00755.x) suggested that hybrid vigour could be an alternative...

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, no. 4, 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, no. 4, 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

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...