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Bloody-minded parasites and sex: the effects of fluctuating virulence.

ABSTRACT: Asexual lineages can grow at a faster rate than sexual lineages. Why then is sexual reproduction so widespread? Much empirical evidence supports the Red Queen hypothesis. Under this hypothesis, coevolving parasites favour sexual reproduction by adapting to infect common asexual clones and driving them down in frequency. One limitation, however, seems to challenge the generality of the Red Queen: in theoretical models, parasites must be very virulent to maintain sex. Moreover, experiments show virulence to be unstable, readily shifting in response to environmental conditions. Does variation in virulence further limit the ability of coevolving parasites to maintain sex? To address this question, we simulated temporal variation in virulence and evaluated the outcome of competition between sexual and asexual females. We found that variation in virulence did not limit the ability of coevolving parasites to maintain sex. In fact, relatively high variation in virulence promoted parasite-mediated maintenance of sex. With sufficient variation, sexual females persisted even when mean virulence fell well below the threshold virulence required to maintain sex under constant conditions. We conclude that natural variation in virulence does not limit the relevance of the Red Queen hypothesis for natural populations; on the contrary, it could expand the range of conditions over which coevolving parasites can maintain sex.

SUBMITTER: Gibson AK

PROVIDER: S-EPMC5882519 | biostudies-literature | 2018 Apr

REPOSITORIES: biostudies-literature

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Bloody-minded parasites and sex: the effects of fluctuating virulence.

Gibson Amanda K AK Stoy Kayla S KS Lively Curtis M CM

Journal of evolutionary biology 20180312 4

Asexual lineages can grow at a faster rate than sexual lineages. Why then is sexual reproduction so widespread? Much empirical evidence supports the Red Queen hypothesis. Under this hypothesis, coevolving parasites favour sexual reproduction by adapting to infect common asexual clones and driving them down in frequency. One limitation, however, seems to challenge the generality of the Red Queen: in theoretical models, parasites must be very virulent to maintain sex. Moreover, experiments show vi ...[more]

PMID: 29460507

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Project description:Malaria parasites must undergo a round of sexual reproduction in the blood meal of a mosquito vector to be transmitted between hosts. Developing a transmission-blocking intervention to prevent parasites from mating is a major goal of biomedicine, but its effectiveness could be compromised if parasites can compensate by simply adjusting their sex allocation strategies. Recently, the application of evolutionary theory for sex allocation has been supported by experiments demonstrating that malaria parasites adjust their sex ratios in response to infection genetic diversity, precisely as predicted. Theory also predicts that parasites should adjust sex allocation in response to host immunity. Whilst data are supportive, the assumptions underlying this prediction - that host immune responses have differential effects on the mating ability of males and females - have not yet been tested. Here, we combine experimental work with theoretical models in order to investigate whether the development and fertility of male and female parasites is affected by innate immune factors and develop new theory to predict how parasites' sex allocation strategies should evolve in response to the observed effects. Specifically, we demonstrate that reactive nitrogen species impair gametogenesis of males only, but reduce the fertility of both male and female gametes. In contrast, tumour necrosis factor-? does not influence gametogenesis in either sex but impairs zygote development. Therefore, our experiments demonstrate that immune factors have complex effects on each sex, ranging from reducing the ability of gametocytes to develop into gametes, to affecting the viability of offspring. We incorporate these results into theory to predict how the evolutionary trajectories of parasite sex ratio strategies are shaped by sex differences in gamete production, fertility and offspring development. We show that medical interventions targeting offspring development are more likely to be 'evolution-proof' than interventions directed at killing males or females. Given the drive to develop medical interventions that interfere with parasite mating, our data and theoretical models have important implications.

Project description:BackgroundGranulomatosis with polyangiitis (GPA) is a syndrome of refractory vasculitis involving the upper respiratory tract, lungs, kidneys, and systemic small and medium-sized arteries that affects all age groups. No pediatric case with a bloody pericardial effusion resulting in cardiac tamponade and co-existing hematochezia has been reported.Case presentationA 14-year-old boy was referred for evaluation of prolonged fever, chest pain, and intermittent hematochezia. Diagnostic imaging showed a prominent pericardial effusion. Immediately after admission, his systolic blood pressure decreased. Emergent pericardiocentesis resulted in aspiration of a massive amount of bloody pericardial fluid. This was diagnosed as cardiac tamponade because his blood pressure recovered immediately after the drainage. The patient had an elevated serine proteinase 3-anti-neutrophil cytoplasmic antibody (PR3-ANCA) level on serological examination. Head MRI showed thickening of nasal and sinusoidal mucosa and a cystic mass in the left sphenoid sinus. After ruling out malignancy based on the cytology of the effusion, chest MRI, and gallium scintigraphy, total colonoscopy showed multiple irregular-shaped aphthae from the right transverse colon to the cecum on the contralateral side of the mesenteric attachments. Biopsy specimens of aphthous lesions confirmed necrotizing granulomatous inflammation. A diagnosis of GPA was made based on these findings, and oral prednisolone (PSL) and azathioprine were started. The hematochezia disappeared rapidly, and no recurrence of pericardial effusion was seen after PSL tapering was completed. The PR3-ANCA level decreased into the normal range immediately after the initial therapy.ConclusionsPericarditis is a common cardiac complication of GPA, but there have been no reports of resultant cardiac tamponade. This is the first case of pediatric GPA with cardiac and gastrointestinal complications preceding the common symptoms such as respiratory or renal symptoms. A case of pediatric GPA with hematochezia is also extremely rare. In conclusion, serial measurement of ANCA levels is important in patients with persistent fever and bloody stool, such as in inflammatory bowel disease, to make the diagnosis of a vasculitic syndrome.

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Bloody-minded parasites and sex: the effects of fluctuating virulence.

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Bloody-minded parasites and sex: the effects of fluctuating virulence.

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