Host performance as a target of manipulation by parasites: a meta-analysis.

The mechanisms underlying parasite-altered host behavior and fitness remain largely unanswered. The purpose of this review is to provide a perspective that has not been fully incorporated into the debate on how parasites manipulate their hosts. We argue that performance capacity is an important target of parasitic manipulation, and we aim to integrate the study of performance with that of parasitic manipulations of host behavior and fitness. We performed a meta-analysis from the published literature of 101 measures of the effect of parasites on host performance capacity to address the following questions. (1) Do parasites exert an important effect on host performance capacity? (2) Is that effect routinely to decrease or enhance performance capacity? And, (3) what factors explain variation in the effect sizes that have been quantified? Although negligible-small effect sizes were detected in 40/101 measures, host performance capacity was overall affected by parasitic infection, with a negative direction and medium-large magnitude in 58/101 measures and an increase in performance capacity in 3/101 measures. Host age, type of host performance, the host tissue infected by the parasite, and whether the study was experimental or based on natural infections each explained a significant amount of the variation in effect size. The significance of each factor is briefly discussed in light of the potential adaptive character of host manipulations by parasites.

Effects of a muscle-infecting parasitic nematode on the locomotor performance of their fish host.

The southern flounder Paralichthys lethostigma, host to the nematode Philometroides paralichthydis that is embedded in place of the inclinator muscles of the dorsal and anal fin elements, is hypothesized to impair two aspects of locomotor performance (swimming and burying capacity). Peak swimming acceleration and both measures of burying performance did not differ between infected and uninfected fish, whereas swimming velocity of infected fish was significantly lower than that of uninfected fish. Smaller infected fish swam at significantly slower speeds than smaller uninfected fish, whereas there was no difference among larger fish. Neither the location nor the number of worms affected either swimming or burying performance. The decrease in swimming velocity observed in smaller infected fish may be sufficient in rendering them more vulnerable to predation and environmental stressors.

Deep-sea hydrothermal vent parasites: why do we not find more?

While parasitism is recognized as the most common mode of existence on the planet, and hosts from virtually all ecosystems have been studied, very little is known about the parasites found in deep-sea hydrothermal vent ecosystems and even less is known about their ecology, evolution, and effects on their hosts. The purpose of this work is to offer a comprehensive review of our state of knowledge about parasitism in the deep-sea vents and to pose and address specific questions for future studies. Because the deep-sea environment itself may influence the number and types of parasites found in the vents, non-vent (below 1000 m) and vent deep-sea data were used in a comparative analysis to account for this factor as a potential major determinant of the parasite fauna in the vents. Based upon analysis of these data, it is highly likely that the reason why so few parasites are currently known from deep-sea vents, even given the low diversity of hosts in this ecosystem, is simply that their inconspicuous nature has caused them to be overlooked by vent biologists.

Sex discriminatory effect of the acanthocephalan Acanthocephaloides propinquus on a gobiid fish Gobius bucchichii.

Most studies which aim at detecting effects of parasites on fish show that intermediate stages of parasites affect their host while adult parasites are usually less virulent in the final host. We studied the effect of the acanthocephalan Acanthocephaloides propinquus on one of its final hosts, the fish Gobius bucchichii. This study showed that the adult parasites affect host fitness. Moreover, our results showed that at the same level of infection in male and female gobiids, the female's reproductive success was negatively correlated to parasite abundance while the male's reproductive success was not. The negative effects on females includes reductions in gonado-somatic index and egg production. We hypothesized that it might be more difficult for females to compensate the cost of parasitism because of the very high cost of egg production. We discussed these results in terms of host population regulation.

Recombinant human interleukin-1-mediated killing of Schistosoma mansoni primary sporocysts in Biomphalaria glabrata.

Previous work has indicated that injection of recombinant-human interleukin (rhIL)-1beta in Schistosoma mansoni-infected M-line Biomphalaria glabrata resulted in a significant reduction in the number of cercariae shed. The purpose of the present work was to determine if primary sporocysts were killed following rhIL-1beta injection in susceptible snails and, if so, to determine if killing was the direct result of hemocyte activity. Counting of primary sporocysts indicated a 50% reduction in the number surviving at 3 days PE in snails from 2 susceptible strains following injection. Histological analysis indicated that killing occurred with little-to-no observable hemocyte/parasite contact, whereas short-term culture of primary sporocysts with cell-free plasma (hemolymph) from injected snails rapidly initiated killing in vitro. Because levels of a snail IL-1-like molecule (SnaIL-1) drop significantly following schistosome exposure in M-line snails, because resistant snails maintain higher SnaIL-1 levels following infection, and because rhIL-1beta upregulates hemocyte cytotoxic mechanisms, these data support the contention that SnaIL-1 plays a role in determining resistance in B. glabrata. These data also indicate that schistosome death may be separated from parasite encapsulation by hemocytes and that an as yet unidentified humoral killing mechanism/factor may exist in B. glabrata. Lastly, these data further support the hypothesis that cytokine-like molecules are important, functionally conserved immunodefense mediators in both vertebrates and invertebrates.

Schistosoma mansoni: interleukin-1 increases phagocytosis and superoxide production by hemocytes and decreases output of cercariae in schistosome-susceptible Biomphalaria glabrata.

Decreases in the number of Schistosoma mansoni cercariae released from susceptible M-line Biomphalaria glabrata were detected following injection with the recombinant human cytokine, interleukin-1. No differences in either the time post-exposure at which shedding began or the percentage of snails shedding cercariae were detected between interleukin-1 injected, heat-inactivated interleukin-1 injected, or sham injected controls. However, sham injected and heat-inactivated interleukin-1 injected snails maintained significantly higher (approximately three-fold) levels of cercarial production compared to interleukin-1 injected snails over 8 weeks of cercarial shedding. Injection of interleukin-1 into schistosome-susceptible (M-line) and resistant (13-16-R1) strains of B. glabrata increased hemocyte phagocytosis of target particles and phagocytosis stimulated O2- production in both snail strains at 24 hr postexposure to the parasite. Resistant 13-16-R1 snails maintained, on average, 2.4 times the number of O2- producing phagocytic cells than did M-line susceptible snails, indicating that the incomplete abrogation of cercarial shedding in M-line snails may be due to an inadequate number of activated circulating effector cells in these snails. These data strongly support the contention that the evolutionarily conserved cytokine, interleukin-1, or a molecule in snail plasma with interleukin-1-like immunospecificity, biological activity, and function plays a significant role in the maintenance of susceptibility or resistance to S. mansoni infection in B. glabrata. Finally, these data also supply evidence for the evolutionary conservation of the function and role of interleukin-1, O2-, and antioxidant defense mechanisms in this host-parasite relationship.

Extraembryonic membranes of the endoparasitic wasp Cotesia congregata: presence of a separate amnion and serosa.

Little information is available describing the development of endoparasitic Hymenoptera prior to hatching of the first instar larva. The present study reveals that in Cotesia congregata, and likely other braconid wasp parasites, the serosa and amnion comprise separate layers encasing the developing first instar larva. Examination of newly hatched first instar parasites in the hemocoel of Manduca sexta confirmed that the larvae were ensheathed in the remnants of an "amnion" at hatching, with patches of nucleated cells seen adhering in thin sheets to the larva. The amnion is delaminated from a cellular serosal membrane that lies directly beneath the chorion, which subsequently gives rise to teratocytes. Scanning electron micrographs indicate that remnants of the amnion remained associated with the larvae for a longer period posthatch than did the teratocytes, which rapidly dispersed into the host hemolymph. The presence of an amnion-like layer in braconid endoparasitic wasps may prove to be significant with respect to our understanding of host-parasite immunological interactions occurring during the initiation of the relationship of the parasites with their host.

[Preliminary observations of two microsporidian hyperparasites of Acanthocephala in marine and lagoon fishes]. / Premières observations sur deux microsporidies hyperparasites d'acanthocéphales de poissons marins et lagunaires.

Microsporidium acanthocephali n. sp. and Microsporidium propinqui n. sp. are two microsporidian species hyperparasitic in the tegumentary syncytium of salt-water fishes. Their ultrastructural study shows that both species have diplocaryotic meronts and spores, anisofilar polar filaments; meronts and some sporogonic stages of M. acanthocephali are surrounded by a parasitic vacuole. Spores of both parasites are oviform; those of M. acanthocephali are gigantic, 12-14 micron long and 6-7 micron broad, those of M. propinqui are only 3-4 micron X 1.25-1.50 micron. A poor knowledge of some sporogonic aspects prevents us from all precise generic assigning of these two parasites which may coexist in the same Helminth.

[Hosts of Acanthocephala. II--Definitive hosts. 1. Fishes]. / Les hôtes des acanthocéphales. II--Les hôtes définitifs. 1. Poissons.

From an attentive study of the largest number of available publications, we tried to establish the list of fish species harbouring fully mature Acanthocephala, i.e. females with completely developed eggs. This character is the sole on which we are allowed to assure that this fish is truly a definitive host for the parasite. This very preliminary work shows that acanthocephalan specificity for the definitive host is narrower than it was generally said. If few so called "primitive" Acanthocephala are indeed parasitic in "primitive" fishes, in the majority of cases the main factor for infestation is related to the trophic behaviour of the definitive host and do not depends on its phylogenic position.