Parasite infection induces size-dependent host dispersal: consequences for parasite persistence

Host dispersal is now recognized as a key predictor of the landscape-level persistence and expansion of parasites. However, current theories treat post-infection dispersal propensities as a fixed trait, and the plastic nature of host's responses to parasite infection has long been underappreciated. Here, we present a mark-recapture experiment in a single host-parasite system (larval parasites of the freshwater mussel Margaritifera laevis and its salmonid fish host Oncorhynchus masou masou) and provide, to our knowledge, the first empirical evidence that parasite infection induces size-dependent host dispersal in the field. In response to parasite infection, large fish become more dispersive, whereas small fish tend to stay at the home patch. The observed plasticity in dispersal is interpretable from the viewpoint of host fitness: expected benefits (release from further infection) may exceed dispersal-associated costs for individuals with high dispersal ability (i.e. large fish) but are marginal for individuals with limited dispersal ability (i.e. small fish). Indeed, our growth analysis revealed that only small fish hosts incurred dispersal costs (reduced growth). Strikingly, our simulation study revealed that this plastic dispersal response of infected hosts substantially enhanced parasite persistence and occupancy in a spatially structured system. These results suggest that dispersal plasticity in host species is critical for understanding how parasites emerge, spatially spread, and persist in nature. Our findings provide a novel starting point for building a reliable, predictive model for parasite/disease management

Transurethral resection for botryoid bladder rhabdomyosarcoma

The outcome of multimodal therapy for localized bladder rhabdomyosarcoma is quite good in terms of morbidity, and conservative surgery is generally recommended. However, in cases originating in the bladder neck, tumorectomy or partial cystectomy has adverse effects on bladder function. A 2-year-old girl underwent transurethral resection of a bladder tumor (TUR-BT), chemotherapy consisting of vincristine, actinomycin-D, and cyclophosphamide, and radiotherapy. She was in remission for 3 years when frequent urination became evident. Her bladder capacity and compliance were low; however, her urinary symptom was controlled using anticholinergic medication. Accordingly, TUR-BT could be an optional approach for bladder rhabdomyosarcoma

A delayed effect of the aquatic parasite Margaritifera laevis on the growth of the salmonid host fish Oncorhynchus masou masou

Parasitic species often have detrimental effects on host growth and survival. The larvae of the genus Margaritifera (Bivalvia), called glochidia, are specialist parasites of salmonid fishes. Previous studies have reported negligible influences of the parasite on their salmonid hosts at natural infection levels. However, those studies focused mainly on their instantaneous effects (i.e., during the parasitic period). Given the time lag between physiological and somatic responses to pathogen infections, the effect of glochidial infection may become clearer during the post-parasitic period. Here, we examined whether the effect of glochidial infections of Margaritifera laevis on its salmonid host Oncorhynchus masou masou would emerge during the post-parasitic period. We performed a controlled aquarium experiment and monitored fish growth at two time intervals (i.e., parasitic and post-parasitic periods) to test this hypothesis. Consistent with previous observations, the effects of glochidial infection were unclear in the middle of the experiment (day 50; parasitic period). However, even with a natural glochidial load (48 glochidia per fish), we found a significant reduction in growth rates of infected fish in the extended period of the experiment (day 70; post-parasitic period). Our results suggest that examining only instantaneous effects may provide misleading conclusions about mussel-host relationships

Data from: Parasite infection induces size-dependent host dispersal: consequences for parasite persistence

Host dispersal is now recognized as a key predictor of the landscape-level persistence and expansion of parasites. However, current theories treat post-infection dispersal propensities as a fixed trait, and the plastic nature of host’s responses to parasite infection has long been underappreciated. Here, we present a mark-recapture experiment in a single-host parasite system (larval parasites of the freshwater mussel Margaritifera laevis and its salmonid fish host Oncorhynchus masou masou) and provide the first empirical evidence that parasite infection induces size-dependent host dispersal in the field. In response to parasite infection, large fish become more dispersive, whereas small fish tend to stay at the home patch. The observed plasticity in dispersal is interpretable from the viewpoint of host fitness: expected benefits (release from further infection) may exceed dispersal-associated costs for individuals with high dispersal ability (i.e., large fish) but are marginal for individuals with limited dispersal ability (i.e., small fish). Indeed, our growth analysis revealed that only small fish hosts incurred dispersal costs (reduced growth). Strikingly, our simulation study revealed that this plastic dispersal response of infected hosts substantially enhanced parasite persistence and occupancy in a spatially structured system. These results suggest that dispersal plasticity in host species is critical for understanding how parasites emerge, spatially spread, and persist in nature. Our findings provide a novel starting point for building a reliable, predictive model for parasite/disease management

Hypoxia/re-oxygenation-induced, redox-dependent activation of STAT1 (signal transducer and activator of transcription 1) confers resistance to apoptotic cell death via hsp70 induction.

STAT1 (signal transducer and activator of transcription 1) is potentially involved in cell survival, as well as cell death, in different types of cells. The present study was designed to examine the effects of STAT1 on hypoxia/re-oxygenation (H/R)-induced cell death and/or survival, and the underlying mechanisms of any such effects. H/R was shown to induce apoptotic cell death of rat hepatocytes. The addition of a STAT1-specific inhibitor, fludarabine, significantly increased the fraction of apoptotic cells after H/R. Following H/R, STAT1 was activated and sequential phosphorylation of Tyr701 and Ser727 was observed, which could be inhibited by the antioxidant N-acetyl-L-cysteine. Tyrosine and serine phosphorylation of STAT1 was mediated by Janus kinase 2 and phosphoinositide 3-kinase/Akt kinase respectively in a redox-dependent manner following H/R. STAT1-induced HSP70 (heat-shock protein 70) expression and the suppression of apoptosis occurred concomitantly. In conclusion, STAT1 activation, in a redox-dependent manner, following H/R may play crucial roles in cell survival, at least partly via HSP70 induction

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The Relative Effects of Biotic and Abiotic Factors on the Recruitment of Freshwater Mussels (Margaritifera laevis)

Freshwater mussels, Unionoida, are endangered across the globe due to recruitment failure. In the present study, with general linear mixed models, we investigated the relative effects of biotic (host fish density) and abiotic (water depth, fine sediment, water temperature, and water quality) factors on the recruitment of Margaritifera laevis in 10 streams of Hokkaido, northern Japan. We additionally examined the factors regulating the density of the host fish Oncorhynchus masou masou with general linear models. The proportion of juvenile mussels had a unimodal relationship with the host density, which was the most influential factor among the others examined. The positive relationship between mussel recruitment and host density can be attributed to an increased host fish infection rate. The negative correlation between mussel recruitment and host density at high fish densities may be due to reduced larval growth on host fish that are in poor physical condition. We also found that host fish density was negatively affected by nutrient enrichment. Our results suggest that mitigating water quality degradation to recover host fish density should be prioritized to improve mussel recruitment. Although stock enhancement is effective for increasing the salmon population density, excess stocking can further disturb mussel recruitment