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Université de Fribourg

The impact of infection on host competition and its relationship to parasite persistence in a Daphnia microparasite system

Refardt, Dominik ; Ebert, Dieter

In: Evolutionary Ecology, 2012, vol. 26, no. 1, p. 95-107

Evolutionary studies often estimate fitness components with the aim to make predictions about the outcome of selection. Depending on the system and the question, different fitness components are used, but their usefulness for predicting the outcome of selection is rarely tested. Here we estimate host fitness components in different ways with the aim to test how well they agree with each other...

Université de Fribourg

Population genetics of duplicated alternatively spliced exons of the Dscam gene in Daphnia and Drosophila

Brites, Daniela ; Encinas-Viso, Francisco ; Ebert, Dieter ; Pasquier, Louis Du ; Haag, Christoph R.

In: PLoS ONE, 2011, vol. 6, no. 12, p. e27947

In insects and crustaceans, the Down syndrome cell adhesion molecule (Dscam) occurs in many different isoforms. These are produced by mutually exclusive alternative splicing of dozens of tandem duplicated exons coding for parts or whole immunoglobulin (Ig) domains of the Dscam protein. This diversity plays a role in the development of the nervous system and also in the immune system. Structural...

Université de Fribourg

Converging seasonal prevalence dynamics in experimental epidemics

Lass, Sandra ; Hottinger, Jürgen W. ; Fabbro, Thomas ; Ebert, Dieter

In: BMC Ecology, 2011, vol. 11, p. 14

Background Regular seasonal changes in prevalence of infectious diseases are often observed in nature, but the mechanisms are rarely understood. Empirical tests aiming at a better understanding of seasonal prevalence patterns are not feasible for most diseases and thus are widely lacking. Here, we set out to study experimentally the seasonal prevalence in an aquatic host-parasite system. The...

Université de Fribourg

Benefits of host genetic diversity for resistance to infection depend on parasite diversity

Ganz, Holly H. ; Ebert, Dieter

In: Ecology, 2010, vol. 91, no. 5, p. 1263–1268

Host populations with high genetic diversity are predicted to have lower levels of infection prevalence. This theory assumes that host genetic diversity results in variation in susceptibility and that parasites exhibit variation in infectivity. Empirical studies on the effects of host heterogeneity typically neglect the role of parasite diversity. We conducted three laboratory experiments...

Université de Fribourg

Experimental evolution of field populations of Daphnia magna in response to parasite treatment

Zbinden, Marc ; Haag, Christoph R. ; Ebert, Dieter

In: Journal of Evolutionary Biology, 2008///doi:10.1111/j.1420-9101.2008.01541.x

Although there is little doubt that hosts evolve to reduce parasite damage, little is known about the evolutionary time scale on which host populations may adapt under natural conditions. Here we study the effects of selection by the microsporidian parasite Octosporea bayeri on populations of Daphnia magna. In a field study, we infected replicated populations of D. magna with the parasite,...

Université de Fribourg

Parasites promote host gene flow in a metapopulation

Altermatt, Florian ; Hottinger, Jürgen W. ; Ebert, Dieter

In: Evolutionary Ecology, 2007, vol. 21, no. 4, p. 561-575

Local adaptation is a powerful mechanism to maintain genetic diversity in subdivided populations. It counteracts the homogenizing effect of gene flow because immigrants have an inferior fitness in the new habitat. This picture may be reversed in host populations where parasites influence the success of immigrating hosts. Here we report two experiments testing whether parasite abundance and...

Université de Fribourg

A selective advantage to immigrant genes in a Daphnia metapopulation

Ebert, Dieter ; Haag, Christoph ; Kirkpatrick, Mark ; Riek, Myriam ; Hottinger, Jürgen W. ; Pajunen, V. Ilmari

In: Science 295(5554): 485 - 488, 2002, 2002, vol. 295, no. 5554, p. 485-488

Immigrants to habitats occupied by conspecific organisms are usually expected to be competitively inferior, because residents may be locally adapted. If residents are inbred, however, mating between immigrants and residents results in offspring that may enjoy a fitness advantage from hybrid vigor. We demonstrate this effect experimentally in a natural Daphnia metapopulation in which...

Université de Fribourg

Quantitative PCR to detect, discriminate and quantify intracellular parasites in their host: an example from three microsporidians in Daphnia

Refardt, Dominik ; Ebert, Dieter

In: Parasitology, 2006, vol. 133, p. 11–18

Reliable detection, discrimination and quantification of parasites are important for host-parasite studies and diagnostics. Microsporidial infections are problematic in this respect. Their discrimination and quantification using light microscopy is difficult because spores are the only light microscopically visible form of the parasite and they offer few distinct characters. We developed a...

Université de Fribourg

Apparent seasonality of parasite dynamics: analysis of cyclic prevalence patterns

Lass, Sandra ; Ebert, Dieter

In: Proceedings of the Royal Society B: Biological Sciences, 2006, vol. 243, no. 1583, p. 199-206

Seasonal disease dynamics are common in nature, but their causes are often unknown. Our case study provides insight into the cyclic prevalence pattern of the horizontally and vertically transmitted microsporidium Octosporea bayeri in its Daphnia magna host. Data from several populations over a four year period revealed a regular prevalence increase during summer and a decrease over...

Université de Fribourg

Empirical support for optimal virulence in a castrating parasite

Jensen, Knut Helge ; Little, Tom ; Skorping, Arne ; Ebert, Dieter

In: Plos Biology, 2006, vol. 4, no. 7, p. e197

The trade-off hypothesis for the evolution of virulence predicts that parasite transmission stage production and host exploitation are balanced such that lifetime transmission success (LTS) is maximised. However, the experimental evidence for this prediction is weak, mainly because LTS, which indicates parasite fitness, has been difficult to measure. For castrating parasites, this simple model...