Daphnia magna egg piRNA cluster expression profiles change as mothers age

Background: PiRNAs prevent transposable elements wreaking havoc on the germline genome. Changes in piRNA expression over the lifetime of an individual may impact on ageing through continued suppression, or release, of transposable element expression. We identified piRNA producing clusters in the genome of Daphnia magna by a combination of bioinformatic methods, and then contrasted their expression between parthenogenetically produced eggs representing maternally-deposited germline piRNAs of young (having their 1st clutch) and old (having their 5th clutch) mothers. Results from eggs were compared to cluster expression in three generations of adults. Results: As for other arthropods, D. magna encodes long uni-directionally transcribed non-coding RNAs consisting of fragmented transposable elements which account for most piRNAs expressed. Egg tissues showed extensive differences between clutches from young mothers and those from old mothers, with 578 and 686 piRNA clusters upregulated, respectively. Most log fold-change differences for significant clusters were modest, however. When considering only highly expressed clusters, there was a bias towards 1st clutch eggs at 41 upregulated versus eight clusters in the eggs from older mothers. F0 generation differences between young and old mothers were fewer than eggs, as 179 clusters were up-regulated in young versus 170 old mothers. This dropped to 31 versus 22 piRNA clusters when comparing adults in the F1 generation, and no differences were detected in the F3 generation. Inter-generational losses of differential piRNA cluster were similar to that observed for D. magna micro-RNA expression. Conclusions: Little overlap in differentially expressed clusters was found between adults containing mixed somatic and germline (ovary) tissues and germ-line representing eggs. A cluster encompassing a Tudor domain containing gene important in the piRNA pathway was upregulated in the eggs from old mothers. We hypothesise that regulation of this gene could form part of a feedback loop that reduces piRNA pathway activity explaining the reduced number of highly-expressed clusters in eggs from old mothers

Parasitism and environmental sex determination in Daphnia

International audienceHypothesis: Daphnia exposed to cues associated with the onset of a parasite epidemic will have more males and resting eggs.Organisms: Seven clones of Daphnia magna (chosen for high levels of sexual reproduction) and the bacterial parasite Pasteuria ramosa.Methods: We explored how parasite infection (simulated by creating crowding conditions using infected hosts) might influence male and resting egg production compared with crowding conditions created using healthy hosts. We also explored the effects of putting bacterial spores in water. Conclusions: Both crowding and crowding with infected hosts led to higher numbers of males and resting eggs. Direct exposure to parasite transmission spores had no effect. Male production in response to treatment was host-clone specific, with some clones responding strongly to the presence of infected hosts, but others not responding or only responding to water crowded with healthy Daphnia. Resting-egg production in response to treatment was also host-clone specific, but differences were not affected by crowding conditions

Maternal effects on offspring consumption can stabilize fluctuating predator–prey systems

Maternal effects, where the conditions experienced by mothers affect thephenotype of their offspring, are widespread in nature and have the potentialto influence population dynamics. However, they are very rarelyincluded in models of population dynamics. Here, we investigate a recentlydiscovered maternal effect, where maternal food availability affects the feedingrate of offspring so that well-fed mothers produce fast-feeding offspring.To understand how this maternal effect influences population dynamics, weexplore novel predator–prey models where the consumption rate of predatorsis modified by changes in maternal prey availability. We address the‘paradox of enrichment’, a theoretical prediction that nutrient enrichmentdestabilizes populations, leading to cycling behaviour and an increasedrisk of extinction, which has proved difficult to confirm in the wild. Ourmodels show that enriched populations can be stabilized by maternal effectson feeding rate, thus presenting an intriguing potential explanation for thegeneral absence of ‘paradox of enrichment’ behaviour in natural populations.This stabilizing influence should also reduce a population’s risk ofextinction and vulnerability to harvesting

The separate and combined effects of MHC genotype, parasite clone, and host gender on the course of malaria in mice

BACKGROUND: The link between host MHC (major histocompatibility complex) genotype and malaria is largely based on correlative data with little or no experimental control of potential confounding factors. We used an experimental mouse model to test for main effects of MHC-haplotypes, MHC heterozygosity, and MHC × parasite clone interactions. We experimentally infected MHC-congenic mice (F2 segregants, homo- and heterozygotes, males and females) with one of two clones of Plasmodium chabaudi and recorded disease progression. RESULTS: We found that MHC haplotype and parasite clone each have a significant influence on the course of the disease, but there was no significant host genotype by parasite genotype interaction. We found no evidence for overdominance nor any other sort of heterozygote advantage or disadvantage. CONCLUSION: When tested under experimental conditions, variation in the MHC can significantly influence the course of malaria. However, MHC heterozygote advantage through overdominance or dominance of resistance cannot be assumed in the case of single-strain infections. Future studies might focus on the interaction between MHC heterozygosity and multiple-clone infections

DNA methylation differs extensively between strains of the same geographical origin and changes with age in Daphnia magna

Background Patterns of methylation influence lifespan, but methylation and lifespan may also depend on diet, or differ between genotypes. Prior to this study, interactions between diet and genotype have not been explored together to determine their influence on methylation. The invertebrate Daphnia magna is an excellent choice for testing the epigenetic response to the environment: parthenogenetic offspring are identical to their siblings (making for powerful genetic comparisons), they are relatively short lived and have well-characterised inter-strain life-history trait differences. We performed a survival analysis in response to caloric restriction and then undertook a 47-replicate experiment testing the DNA methylation response to ageing and caloric restriction of two strains of D. magna. Results Methylated cytosines (CpGs) were most prevalent in exons two to five of gene bodies. One strain exhibited a significantly increased lifespan in response to caloric restriction, but there was no effect of food-level CpG methylation status. Inter-strain differences dominated the methylation experiment with over 15,000 differently methylated CpGs. One gene, Me31b, was hypermethylated extensively in one strain and is a key regulator of embryonic expression. Sixty-one CpGs were differentially methylated between young and old individuals, including multiple CpGs within the histone H3 gene, which were hypermethylated in old individuals. Across all age-related CpGs, we identified a set that are highly correlated with chronological age. Conclusions Methylated cytosines are concentrated in early exons of gene sequences indicative of a directed, non-random, process despite the low overall DNA methylation percentage in this species. We identify no effect of caloric restriction on DNA methylation, contrary to our previous results, and established impacts of caloric restriction on phenotype and gene expression. We propose our approach here is more robust in invertebrates given genome-wide CpG distributions. For both strain and ageing, a single gene emerges as differentially methylated that for each factor could have widespread phenotypic effects. Our data showed the potential for an epigenetic clock at a subset of age positions, which is exciting but requires confirmation

Pathogen dynamics across the diversity of ageing

Reproduction, mortality, and immune function often change with age but do not invariably deteriorate. Across the tree of life, there is extensive variation in age-specific performance and changes to key life-history traits. These changes occur on a spectrum from classic senescence, where performance declines with age, to juvenescence, where performance improves with age. Reproduction, mortality, and immune function are also important factors influencing the spread of infectious disease, yet there exists no comprehensive investigation into how the aging spectrum of these traits impacts epidemics. We used a model laboratory infection system to compile an aging profile of a single organism, including traits directly linked to pathogen susceptibility and those that should indirectly alter pathogen transmission by influencing demography. We then developed generalizable epidemiological models demonstrating that different patterns of aging produce dramatically different transmission landscapes: in many cases, aging can reduce the probability of epidemics, but it can also promote severity. This work provides context and tools for use across taxa by empiricists, demographers, and epidemiologists, advancing our ability to accurately predict factors contributing to epidemics or the potential repercussions of senescence manipulation

Successfully resisting a pathogen is rarely costly in Daphnia magna

<p>Abstract</p> <p>Background</p> <p>A central hypothesis in the evolutionary ecology of parasitism is that trade-offs exist between resistance to parasites and other fitness components such as fecundity, growth, survival, and predator avoidance, or resistance to other parasites. These trade-offs are called costs of resistance. These costs fall into two broad categories: constitutive costs of resistance, which arise from a negative genetic covariance between immunity and other fitness-related traits, and inducible costs of resistance, which are the physiological costs incurred by hosts when mounting an immune response. We sought to study inducible costs in depth using the crustacean <it>Daphnia magna </it>and its bacterial parasite <it>Pasteuria ramosa</it>.</p> <p>Results</p> <p>We designed specific experiments to study the costs induced by exposure to this parasite, and we re-analysed previously published data in an effort to determine the generality of such costs. However, despite the variety of genetic backgrounds of both hosts and parasites, and the different exposure protocols and environmental conditions used in these experiment, this work showed that costs of exposure can only rarely be detected in the <it>D. magna-P. ramosa </it>system.</p> <p>Conclusions</p> <p>We discuss possible reasons for this lack of detectable costs, including scenarios where costs of resistance to parasites might not play a major role in the co-evolution of hosts and parasites.</p

Rapid change in parasite infection traits over the course of an epidemic in a wild host-parasite population

By combining a field study with controlled laboratory experimentation, we examined how infection traits of the sterilizing bacterium, Pasteuria ramosa, changed over the course of a growing season in a natural population of its crustacean host Daphnia magna. The number of parasite transmission spores per infected host increased ten-fold over the course of the season, concomitant with a decline in the density of infected hosts. Plausible explanations for this variation include changes in environmental conditions, changes in host quality, or that parasite migration or natural selection caused a genetic change in the parasite population. We sought to distinguish some of these possibilities in a laboratory experiment. Thus, we preserved field-collected parasite spores throughout the season, and later exposed a set of hosts to a fixed dose of these spores under controlled laboratory conditions. Parasites collected late in the season were more infectious and grew more rapidly than parasites collected early in the season. This result is compatible with the hypothesis that the observed increase in infectivity in the field was due to genetic change, i.e. evolution in the P. ramosa population

Family Matters: Immigrant Women’s Activism in Ontario and British Columbia, 1960s -1980s

This article uses oral history interviews to explore the ways in which different attitudes towards family and motherhood could create major tensions between mainstream feminists and immigrant women’s activists in Ontario and British Columbia between the 1960s and the 1980s.&nbsp; Immigrant women’s belief in the value of the family did not prevent immigrant women from going out to work to help support their families or accessing daycare and women’s shelters, hard fought benefits of the women’s movement.&nbsp; However, these women demanded access to job training, English language classes, childcare, and women’s shelters on their own terms, in ways that minimized the racism they faced, respected religious and cultural values, and respected the fact that the heterosexual family remained an important resource for the majority of immigrant women.&nbsp; Immigrant women activists were less likely to accept a purely gender-based analysis than mainstream feminists. They often sought to work with men in their own communities, even in dealing with violence against women. And issues of violence and of reproductive rights often could not be understood only within the boundaries of Canada. For immigrant women violence against women was often analyzed in relation to political violence in their homelands, while demands for fully realized reproductive rights drew on experiences of coercion both in Canada and transnationally.Cet article s’appuie sur des entrevues d’histoire orale pour explorer les façons dont différentes attitudes à l’égard de la famille et de la maternité pouvaient créer des tensions considérables entre les féministes traditionnelles et les femmes immigrantes activistes en Ontario et en Colombie-Britannique entre les années&nbsp;1960 et 1980. L’attachement des femmes immigrantes aux valeurs familiales ne les a pas empêchées d’aller travailler pour aider à nourrir leur famille et de se prévaloir des garderies et des refuges pour femmes battues, avantages gagnés de haute lutte par le mouvement féministe. Toutefois, ces femmes ont exigé d’avoir accès à la formation professionnelle, aux cours d’anglais, aux garderies et aux refuges pour femmes battues à leur façon, de manière à minimiser le racisme qu’elles rencontraient, à honorer leurs valeurs religieuses et culturelles et à respecter le fait que la famille hétérosexuelle restait une ressource importante pour la majorité des immigrantes. Les immigrantes militantes étaient moins susceptibles d’accepter une analyse purement sexospécifique que les féministes traditionnelles. Elles cherchaient souvent à travailler avec les hommes dans leur propre communauté, même dans le domaine de la violence contre les femmes. Et les questions de violence et de droits génésiques ne peuvent souvent pas être comprises uniquement à l’intérieur des frontières du Canada. Pour les femmes immigrantes, la violence à l’égard des femmes était souvent analysée en liaison avec la violence politique dans leur pays d’origine, tandis que leurs exigences en faveur de la pleine réalisation de leurs droits génésiques s’appuyaient sur des expériences de coercition tant au Canada que dans d’autres pays