Getting there and around: Host range oscillations during colonization of the Canary Islands by the parasitic nematode Spauligodon.

Episodes of expansion and isolation in geographic range over space and time, during which parasites have the opportunity to expand their host range, are linked to the development of host-parasite mosaic assemblages and parasite diversification. In this study, we investigated whether island colonization events lead to host range oscillations in a taxon of host-specific parasitic nematodes of the genus Spauligodon in the Canary Islands. We further investigated whether range oscillations also resulted in shifts in host breadth (i.e., specialization), as expected for parasites on islands. Parasite phylogeny and divergence time estimates were inferred from molecular data with Bayesian methods. Host divergence times were set as calibration priors after a priori evaluation with a global-fit method of which individual host-parasite associations likely represent cospeciation links. Parasite colonization history was reconstructed, followed by an estimation of oscillation events and specificity level. The results indicate the presence of four Spauligodon clades in the Canary Islands, which originated from at least three different colonization events. We found evidence of host range oscillations to truly novel hosts, which in one case led to higher diversification. Contemporary host-parasite associations show strong host specificity, suggesting that changes in host breadth were limited to the shift period. Lineages with more frequent and wider taxonomic host range oscillations prior to the initial colonization event showed wider range oscillations during colonization and diversification within the archipelago. Our results suggest that a lineage's evolutionary past may be the best indicator of a parasite's potential for future range expansions.

The dynamics of macroparasite host-self-infection: a study of the patterns and processes of pinworm (Oxyuridae) aggregation.

OBJECTIVES: Among parasites, Taylor's power law identifies a tight relationship in aggregation of macroparasite infection intensity with few exceptions; notably, the nematode family Oxyuridae tends to have higher than expected aggregation. Oxyuridae infect a wide range of mammalian hosts and have a unique reproductive strategy that involves conventional horizontal transmission, as well as re-infection of an already infected host. We asked the question, do the unique aspects of pinworm life-history explain an exception to the widely observed patterns of aggregation of parasite populations? METHODS: We empirically examined the differences among Oxyuridae (genus: Syphacia) compared with other helminth (genus: Heligmosomoides) parasite aggregations in 2 rodent hosts with similar ecology: the yellow-necked mouse (Apodemus flavicollis) from Trento, Italy and the white-footed mouse (Peromyscus leucopus) from Pennsylvania, USA. To investigate the effects of pinworm life-history characteristics on generating aggregation, we present a stochastic model that explores aggregation under a range of host-self-infection, parasite death, and transmission scenarios. RESULTS: Oxyuridae parasites had consistently greater aggregation compared to other nematodes regardless of host or parasite species identity, and pinworm aggregation exceeded the range of macroparasite aggregation described previously. CONCLUSIONS: Our simulations demonstrate that host-self-infection, on its own, is sufficient to generate aggregation values greater than the predicted values.

Syphacia obvelata modifies mitogen-activated protein kinases and nitric oxide synthases expression in murine bone marrow cells.

Syphacia obvelata is a rodent nematode parasite with high prevalence in laboratory mice. In our previous work we have demonstrated that this gut-dwelling helminth induces significant hematopoietic changes, characterized by increased myelopoiesis and erythropoiesis in infected animals, and accompanied with altered reactivity of bone marrow hematopoietic progenitors to interleukin (IL)-17. In this study we extended these investigations by demonstrating that naturally acquired S. obvelata infection induces significant alterations in murine bone marrow cells manifested at the molecular level. Namely, S. obvelata infection induced sustained phosphorylation of the members of three major groups of distinctly regulated mitogen-activated protein kinases (MAPKs), the p38, the c-Jun amino-terminal kinase (JNK) and the extracellular signal-regulated kinase (ERK), as well as enhanced expression of mRNA for the inducible nitric oxide synthase (iNOS) in the bone marrow cells of infected animals. Furthermore, the infection interfered with the IL-17-mediated effects in bone marrow cells, since in normal mice IL-17 significantly enhanced phosphorylation of p38 MAPK and upregulated the expression of iNOS and the constitutive, endothelial (e)NOS mRNA, while in S. obvelata-infected animals IL-17 did not influence the MAPKs activation, but markedly down-regulated the expression of both NOS isoforms. The data obtained demonstrating that S. obvelata is able to manipulate signal transduction pathways in the hosts' bone marrow cells, pointed to the multiple layers of immunomodulatory ability of this pinworm parasite and highlighted the importance of working under pinworm-free conditions when using experimental murine models for immunohematopoietic investigations.

Evaluation of coinfection with pinworms (Aspiculuris tetraptera, Dentostomella translucida, and Syphacia obvelata) in gerbils and mice.

Mongolian gerbils (Meriones unguiculatus) naturally infected with the nematode Dentostomella translucida and mice (Mus musculus) that were either pinworm-free or harboring either or both Aspiculuris tetraptera and Syphacia abvelata were crossinfected experimentally with these nematode species. Gerbils were susceptible to infections by S. obvelata and A. tetraptera from mice, whereas mice were resistant to infection by D. translucida from gerbils. The data presented are the first regarding coinfections with these three pinworms in gerbils.

The effect of Toxoplasma gondii and other parasites on activity levels in wild and hybrid Rattus norvegicus.

Using both correlational and experimental evidence, the relationship between parasite load and host activity was assessed in brown rats, Rattus norvegicus. Two hypotheses were tested--(1) that parasites with indirect life-cycles, involving transmission between a prey and its predator, will alter the activity of the intermediate host so as to increase its susceptibility to predation by the definitive host and (2) that activity levels in parasitized rats would be increased rather than decreased. Four groups of rats (n = 140) were examined. One group (n = 50) were wild brown rats trapped from 3 UK farmsteads, with naturally occurring parasites. The others were purpose-bred wild/laboratory hybrid rats with experimentally induced parasitic infections of either (n = 15) adult-acquired or (n = 15) congenitally-acquired Toxoplasma gondii (an indirect life-cycle parasite), or (n = 15) Syphacia muris (a direct life-cycle parasite). Uninfected hybrid rats ( n = 45), matched for sex, age and weight, served as controls. Rats were housed individually in outdoor cages, and their activities were recorded on video-tapes for 6 non-consecutive 10 h nights. Exercise wheels were also available for the hybrid rats. Out of 6 parasite species detected in the wild rats, T. gondii was the only one which required predation by a definitive host to complete its life-cycle, and was also the only parasite to be associated with higher activity levels in infected than uninfected rats. Hybrid rats infected with T. gondii were also more active than those uninfected, whereas there were no differences in activity levels between S. muris infected and uninfected rats. This study shows that the indirect life-cycle parasite T. gondii can influence the activity of its intermediate host the rat. I suggest that this may facilitate its transmission to the cat definitive host.