scholarly journals Sex as a strategy against rapidly evolving parasites

2016 ◽  
Vol 283 (1845) ◽  
pp. 20162226 ◽  
Author(s):  
Stuart K. J. R. Auld ◽  
Shona K. Tinkler ◽  
Matthew C. Tinsley
Keyword(s):  
Daphnia Magna ◽  
Asexual Reproduction ◽  
Mate Finding ◽  
Pasteuria Ramosa ◽  
Host Sex ◽  
Gene Complexes ◽  
One Year ◽  
Sexual Offspring

Why is sex ubiquitous when asexual reproduction is much less costly? Sex disrupts coadapted gene complexes; it also causes costs associated with mate finding and the production of males who do not themselves bear offspring. Theory predicts parasites select for host sex, because genetically variable offspring can escape infection from parasites adapted to infect the previous generations. We examine this using a facultative sexual crustacean, Daphnia magna, and its sterilizing bacterial parasite, Pasteuria ramosa . We obtained sexually and asexually produced offspring from wild-caught hosts and exposed them to contemporary parasites or parasites isolated from the same population one year later. We found rapid parasite adaptation to replicate within asexual but not sexual offspring. Moreover, sexually produced offspring were twice as resistant to infection as asexuals when exposed to parasites that had coevolved alongside their parents (i.e. the year two parasite). This fulfils the requirement that the benefits of sex must be both large and rapid for sex to be favoured by selection.

scholarly journals The infection rate of Daphnia magna by Pasteuria ramosa conforms with the mass-action principle

2003 ◽  
Vol 131 (2) ◽  
pp. 957-966 ◽  
Author(s):  
R. R. REGOES ◽  
J. W. HOTTINGER ◽  
L. SYGNARSKI ◽  
D. EBERT
Keyword(s):  
Daphnia Magna ◽  
Infection Rate ◽  
Infection Process ◽  
Action Principle ◽  
Mass Action ◽  
Infection Model ◽  
Susceptibility To Infection ◽  
Pasteuria Ramosa ◽  
Simple Mass ◽  
Host Parasite

In simple epidemiological models that describe the interaction between hosts with their parasites, the infection process is commonly assumed to be governed by the law of mass action, i.e. it is assumed that the infection rate depends linearly on the densities of the host and the parasite. The mass-action assumption, however, can be problematic if certain aspects of the host–parasite interaction are very pronounced, such as spatial compartmentalization, host immunity which may protect from infection with low doses, or host heterogeneity with regard to susceptibility to infection. As deviations from a mass-action infection rate have consequences for the dynamics of the host–parasite system, it is important to test for the appropriateness of the mass-action assumption in a given host–parasite system. In this paper, we examine the relationship between the infection rate and the parasite inoculum for the water flee Daphnia magna and its bacterial parasite Pasteuria ramosa. We measured the fraction of infected hosts after exposure to 14 different doses of the parasite. We find that the observed relationship between the fraction of infected hosts and the parasite dose is largely consistent with an infection process governed by the mass-action principle. However, we have evidence for a subtle but significant deviation from a simple mass-action infection model, which can be explained either by some antagonistic effects of the parasite spores during the infection process, or by heterogeneity in the hosts' susceptibility with regard to infection.

scholarly journals Influences of clonality on plant sexual reproduction

2015 ◽  
Vol 112 (29) ◽  
pp. 8859-8866 ◽  
Author(s):  
Spencer C. H. Barrett
Keyword(s):  
Asexual Reproduction ◽  
Clonal Growth ◽  
Clonal Plants ◽  
Flowering Plants ◽  
Dioecious Species ◽  
Mate Finding ◽  
Mating Group ◽  
Sexual And Asexual Reproduction ◽  
Morph Ratios ◽  
Floral Displays

Flowering plants possess an unrivaled diversity of mechanisms for achieving sexual and asexual reproduction, often simultaneously. The commonest type of asexual reproduction is clonal growth (vegetative propagation) in which parental genotypes (genets) produce vegetative modules (ramets) that are capable of independent growth, reproduction, and often dispersal. Clonal growth leads to an expansion in the size of genets and increased fitness because large floral displays increase fertility and opportunities for outcrossing. Moreover, the clonal dispersal of vegetative propagules can assist “mate finding,” particularly in aquatic plants. However, there are ecological circumstances in which functional antagonism between sexual and asexual reproductive modes can negatively affect the fitness of clonal plants. Populations of heterostylous and dioecious species have a small number of mating groups (two or three), which should occur at equal frequency in equilibrium populations. Extensive clonal growth and vegetative dispersal can disrupt the functioning of these sexual polymorphisms, resulting in biased morph ratios and populations with a single mating group, with consequences for fertility and mating. In populations in which clonal propagation predominates, mutations reducing fertility may lead to sexual dysfunction and even the loss of sex. Recent evidence suggests that somatic mutations can play a significant role in influencing fitness in clonal plants and may also help explain the occurrence of genetic diversity in sterile clonal populations. Highly polymorphic genetic markers offer outstanding opportunities for gaining novel insights into functional interactions between sexual and clonal reproduction in flowering plants.

scholarly journals How clonal are clones? A quest for loss of heterozygosity during asexual reproduction in Daphnia magna

2019 ◽  
Vol 32 (6) ◽  
pp. 619-628 ◽  
Author(s):  
Marinela Dukić ◽  
Daniel Berner ◽  
Christoph R. Haag ◽  
Dieter Ebert
Keyword(s):  
Daphnia Magna ◽  
Loss Of Heterozygosity ◽  
Asexual Reproduction

Development, life cycle, ultrastructure and phylogenetic position of Pasteuria ramosa Metchnikoff 1888: rediscovery of an obligate endoparasite of Daphnia magna Straus

1996 ◽  
Vol 351 (1348) ◽  
pp. 1689-1701 ◽  
Keyword(s):  
Life Cycle ◽  
Daphnia Magna ◽  
Egg Production ◽  
Body Cavity ◽  
The Body ◽  
Maximum Parsimony Analysis ◽  
Phylogenetic Position ◽  
Artificial Culture ◽  
Pasteuria Ramosa ◽  
Development Life Cycle

The development, life cycle, ultrastructure and phylogenetic position of an obligate, spore-forming endoparasite of Daphnia magna Straus is described. The microparasite was found in the body cavity of three Daphnia species (D. magna , D. pulex and D. longispa )collected in England and Russia during 1992-1994 and maintained in artificial culture by co-cultivation with D. magna . Transmission of the endoparasite occurred horizontally through waterborne spores released from the remains of dead infected hosts. Progeny of infected hosts were never infected, indicating that vertical transmission does not occur. Egg production by infected mothers ceased soon after infection and death ensued after 46 days ( ± 7 standard error) at 20 °C. Phase contrast light microscopy and transmission electron microscopy of the infection process showed the endoparasite to have a polymorphic life cycle beginning with the appearance of branched ‘cauliflower-like’ rosettes and ended with the development of single, oval endospores, nippled at one end and with complex internal structure. Endospore formation resembled that found in endosporeforming bacteria. Morphologically the parasite has strong resemblance to the Pasteuria ramosa that Metchnikoff isolated from D. magna and D. pulex in Ukraine and described in 1888. Identification of this parasite has been an enduring puzzle since Metchnikoff. The previously confused phylogenetic position of P. ramosa (it has been classified as bacterium, yeast and protozoa) was resolved by sequencing the 16SrDNA molecule. Fluorescent in situ hybridizations confirmed that the 16S rDNA sequence obtained from the spores within the D. magna body cavity originated from the endoparasite. Maximum likelihood and maximum parsimony analysis showed that P. ramosa belongs to the low G + C Gram positive branch of the eubacteria and resides within a clade containing Bacillus tusciae , Alicyclobacillus cycloheptanicus and A. acidocaldarius as its nearest neighbours. These results confirm suggestions that this parasite is a bacterium and refute its previous tentative placement based on its morphological complexity among the Actinomycetales.

scholarly journals Genetic variation in the cellular response of Daphnia magna (Crustacea: Cladocera) to its bacterial parasite

2010 ◽  
Vol 277 (1698) ◽  
pp. 3291-3297 ◽  
Author(s):  
Stuart K. J. R. Auld ◽  
Jennifer A. Scholefield ◽  
Tom J. Little
Keyword(s):  
Genetic Variation ◽  
Daphnia Magna ◽  
Cellular Response ◽  
Cell Types ◽  
Parasite Fitness ◽  
Pasteuria Ramosa ◽  
Cellular Immune ◽  
Genetically Determined ◽  
Host Parasite ◽  
Parasite Exposure

Linking measures of immune function with infection, and ultimately, host and parasite fitness is a major goal in the field of ecological immunology. In this study, we tested for the presence and timing of a cellular immune response in the crustacean Daphnia magna following exposure to its sterilizing endoparasite Pasteuria ramosa . We found that D. magna possesses two cell types circulating in the haemolymph: a spherical one, which we call a granulocyte and an irregular-shaped amoeboid cell first described by Metchnikoff over 125 years ago. Daphnia magna mounts a strong cellular response (of the amoeboid cells) just a few hours after parasite exposure. We further tested for, and found, considerable genetic variation for the magnitude of this cellular response. These data fostered a heuristic model of resistance in this naturally coevolving host–parasite interaction. Specifically, the strongest cellular responses were found in the most susceptible hosts, indicating resistance is not always borne from a response that destroys invading parasites, but rather stems from mechanisms that prevent their initial entry. Thus, D. magna may have a two-stage defence—a genetically determined barrier to parasite establishment and a cellular response once establishment has begun.

scholarly journals Daphnia magna shows reduced infection upon secondary exposure to a pathogen

2012 ◽  
Vol 8 (6) ◽  
pp. 972-975 ◽  
Author(s):  
Seanna J. McTaggart ◽  
Philip J. Wilson ◽  
Tom J. Little
Keyword(s):  
Daphnia Magna ◽  
Natural Host ◽  
Important Predictor ◽  
Secondary Exposure ◽  
Pasteuria Ramosa ◽  
Host Pathogen ◽  
Vertebrate Hosts ◽  
Protection Against Infection ◽  
Pathogen Exposure

Previous pathogen exposure is an important predictor of the probability of becoming infected. This is deeply understood for vertebrate hosts, and increasingly so for invertebrate hosts. Here, we test if an initial pathogen exposure changes the infection outcome to a secondary pathogen exposure in the natural host–pathogen system Daphnia magna and Pasteuria ramosa . Hosts were initially exposed to an infective pathogen strain, a non-infective pathogen strain or a control. The same hosts underwent a second exposure, this time to an infective pathogen strain, either immediately after the initial encounter or 48 h later. We observed that an initial encounter with a pathogen always conferred protection against infection compared with controls.

scholarly journals Phenoloxidase but not lytic activity reflects resistance against Pasteuria ramosa in Daphnia magna

2010 ◽  
Vol 7 (1) ◽  
pp. 156-159 ◽  
Author(s):  
Kevin Pauwels ◽  
Luc De Meester ◽  
Ellen Decaestecker ◽  
Robby Stoks
Keyword(s):  
Daphnia Magna ◽  
Lytic Activity ◽  
Ecological Immunology ◽  
Host System ◽  
Pasteuria Ramosa ◽  
Natural Range ◽  
Baseline Levels ◽  
Spore Load

The field of ecological immunology strongly relies on indicators of immunocompetence. Two major indicators in invertebrates, the activity of phenoloxidase (PO) and lytic activity have recently been questioned in studies showing that, across a natural range of baseline levels, these indicators did not predict resistance against a manipulated challenge with natural parasites. We confirmed this finding by showing that baseline levels of PO and lytic activity in the host Daphnia magna were not related to spore load of the parasite Pasteuria ramosa . Yet, PO levels in infected hosts did predict spore load, indicating PO activity can be useful as an indicator of immunocompetence in this model parasite–host system.

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