Parasitism and decreased response to sex pheromones in malePeriplaneta americana (Dictyoptera: Blattidae)

Parasites are known to alter the behavior of their hosts, but little is known about their effects on responses to sexual stimuli. Periplaneta americanainfected with the acanthocephalan Moniliformis moniliformiswere compared to uninfected animals in their behavioral and electroantennogram responses to a synthetic P. americanapheromone component, periplanone-B, and a pheromone mimic, bornyl acetate. In a t-maze there was no significant difference between infected animals' responses to periplanone-B and a random binomial distribution; the responses of uninfected animals were significantly nonrandom. The electroan-tennogram responses of infected and uninfected animals to bornyl acetate or periplanone-B did not differ significantly, however, indicating that the alteration probably does not occur at the peripheral level but at a central nervous system level.     

The immune response of a Cyprinid fish to infections of the acanthocephalan Pomphorhynchus laevis

1972. The immune response of a Cyprinid fish to infections of the acanthocephalan, Pomphorhynchus laevis. International Journal for Parasitology 2: 459–469. Chub (Leuciscus cephalus) were found to produce precipitating antibody in response to natural and experimental infections of an acanthocephalean Pomphorhynchus laevis, although no apparent manifestation of resistance was evident The parasites matured only in the chub although they occurred in five other species of naturally infected fish. Furthermore, this was the only fish species which responded, at least by humoral antibody formation to the parasite. Preliminary experiments indicated that the helminth antigen was an excretory or secretory product and was probably produced only by mature adult worms. The antibody was detected in both the serum and intestinal mucus of the chub. The presence of antibody in the mucus of fish might suggest the presence of a secretory antibody system although the precipitins appeared to have similar chemical characteristics to IgM-type antibody.     

Acanthocephalan parasites in sea otters: Why we need to look beyond associated mortality…

The acanthocephalan parasite, Corynosoma enhydri, uses sea otters (Enhydra lutris) as definitive host. Despite high prevalence and abundance in southern sea otters (E. l. nereis), sublethal impacts of infection on otter health are unknown. Parasites are an integral part of ecosystem structure and functioning. Many affect host behavior, reproduction, predation, or prey preference. Parasites can suppress host immune response, facilitate secondary bacterial, viral, or parasitic infections, and influence concurrent microbial infection. Acanthocephalan infections can have significant effects on host metabolism, digestion, nutrient absorption, and energetics. Because high metabolic expenditures and resource limitations are known to affect southern sea otter populations, even subtle effects of infection could negatively impact individual health and population recovery. In this review we summarize reports of host–parasite-environmental interactions for helminth infections and discuss how these same attributes could manifest in southern sea otters and coastal food web dynamics. Based on these data, investigation of potential sublethal impacts of C. enhydri is warranted. We recommend expanding understanding of the significance of parasites in marine ecosystems beyond associated mortality. Future investigation into the ecological implications of sublethal effects are essential to fully grasp parasite impacts on host populations, and predict potential additive effects with climate change in ecosystem functioning.     

Variation and covariation in infectivity,virulence and immunodepression in the host–parasite association Gammarus pulex–Pomphorhynchus laevis

Parasites often manipulate host immunity for their own benefit, either by exacerbating or suppressing the immune response and this may directly affect the expression of parasite virulence. However, genetic variation in immunodepression, which is a prerequisite to its evolution, and the relationship between immunodepression and virulence, have rarely been studied. Here, we investigated the variation among sibships of the acanthocephalan parasite, Pomphorhynchus laevis, in infecting and in immunodepressing its amphipod host, Gammarus pulex. We also assessed the covariation between infectivity, parasite-induced immune depression and host mortality (parasite virulence). We found that infectivity, the intensity of immunodepression and virulence were variable among parasite sibships. Infectivity and the level of immunodepression were not correlated across parasite sibships. Whereas infectivity was unrelated to host mortality, we found that gammarids that were exposed to the parasite sibships that immunodepressed their hosts the most survived better. This positive covariation between host survival and immunodepression suggests that gammarids exposed to the less immunodepressive parasites could suffer from damage imposed by a higher activity of the phenoloxidase.     

The Parasite Moniliformis moniliformis Alters the Escape Response of its Cockroach Host Periplaneta americana

The immature stages of some parasites live in prey animals (intermediate hosts) and only reach reproductive maturity when they are eaten by final host predators. Some of these parasites alter intermediate host behavior in ways that increase the likelihood of predation (parasite transmission). Using the acanthocephalan (Moniliformis moniliformis) in the cockroach (Periplaneta americana), we show that infected cockroaches experienced a decrease in wind-evoked escape responses, a predator avoidance behavior, that consisted of fewer escape responses, longer latency and higher threshold for escape behavior. We found no correlates of the impairment of the escape behavior in the abdominal portion of the escape neuronal circuitry. This study demonstrates a parasite-induced alteration of a behavior dedicated to predator avoidance.     

An acanthocephalan parasite mediates intraguild predation between invasive and native freshwater amphipods (Crustacea)

1. The balance of predation between closely related invasive and native species can be an important determinant of the success or failure of biological invasions. In Irish freshwaters, the introduced amphipod Gammarus pulex has replaced the native G. duebeni celticus, possibly through differential mutual intraguild predation (IGP). Theoretically, parasitism could mediate such predation and hence the invasion outcome. However, this idea remains poorly studied. 2. In a field survey, we show that the acanthocephalan parasite Echinorynchus truttae is present in more G. pulex populations than G. d. celticus populations. In addition, within parasitised populations, E. truttae is more prevalent in the invader than in the native. 3. We show for the first time that an acanthocephalan parasite mediates predation between its intermediate macroinvertebrate hosts. In a field experiment, E. truttae parasitism of the invader lowered IGP upon the unparasitised native. In laboratory experiments, parasitism of G. pulex significantly reduced their predatory impact on recently moulted female G. d. celticus. Parasitism also appeared to cause reduction in predatory behaviour, such as attacks per contact on precopula guarded female natives. 4. We conclude that higher parasite prevalence in invaders as compared with natives, by mediation of interspecific interactions, could promote species coexistence, or at least slow species replacements, in this particular biological invasion.