Academic literature on the topic 'Maritrema novaezealandensis'

SUMMARYInteractions among different parasite species within hosts can be important factors shaping the evolution of parasite and host populations. Within snail hosts, antagonistic interactions among trematode species, such as competition and predation, can influence parasite abundance and diversity. In the present study we examined the strength of antagonistic interactions between 2 marine trematodes (Maritrema novaezealandensis and Philophthalmus sp.) in naturally infected Zeacumantus subcarinatus snails. We found approximately the same number of snails harbouring both species as would be expected by chance given the prevalence of each. However, snails infected with only M. novaezealandensis and snails with M. novaezealandensis and Philophthalmus sp. co-occurring were smaller than snails harbouring only Philophthalmus sp. In addition, the number of Philophthalmus sp. rediae was not affected by the presence of M. novaezealandensis sporocysts and the within-host clonal diversity of M. novaezealandensis was not influenced by the presence of Philophthalmus sp. Our results suggest that antagonistic interactions may not be a major force influencing the evolution of these trematodes and that characteristics such as host size and parasite infection longevity are shaping their abundance and population dynamics.

SUMMARYFactors constraining host specificity are poorly understood. Intraspecific variation in host preferences in generalist parasites may reveal which factors affect patterns of host use, and thus the evolution of specialization. Here, laboratory experiments examined genetic variation in host preferences and the effect of a refugium against infection on host use. Firstly, 6 cercarial clones of the trematode Maritrema novaezealandensis (ranging widely in heterozygosities) were exposed simultaneously to 2 alternative hosts, the amphipods Heterophoxus stephenseni and Paracalliope novizealandiae, to assess host preferences and fitness correlations with parasite heterozygosity. All clones showed a distinct preference for H. stephenseni, though the extent of this preference varied among clones. No clear association was found between heterozygosity and either parasite infection success or preference for a particular host. Secondly, cercariae were exposed to the same 2 amphipods in both the presence and absence of sand (refugium for H. stephenseni). Without sand, infection levels were significantly higher in H. stephenseni than in P. novizealandiae. With sand, H. stephenseni was able to hide, offsetting the parasite's intrinsic preferences for this host. These results demonstrate the existence of genetic variation in host preferences, as well as the effect of environmental variables on observed patterns of host use.

The shell morphology of mud snails, Zeacumantus subcarinatus, both uninfected and infected by trematodes, was compared to determine if different trematode species induce different degrees of alteration in host shell shape. Snails harbouring either the echinostomatid Acanthoparyphium sp., or a double infection by the microphallid Maritrema novaezealandensis and an undescribed philophthalmid species, had a wider shell base relative to the rest of the shell spire, than uninfected snails or snails infected by only one of the latter two trematode species. These results are independent of any differences in shell length among the different infection groups. The findings of this study suggest that alterations in host shell morphology are species-specific trematode manipulations of host phenotype rather than a generalized host response to castrating trematodes.

SUMMARYTrematodes form clonal colonies in their first intermediate host. Individuals are, depending on species, rediae or sporocysts (which asexually reproduce) and cercariae (which develop within rediae or sporocysts and infect the next host). Some species use a division of labour within colonies, with 2 distinct redial morphs: small rediae (non-reproducing) and large rediae (individuals which produce cercariae). The theory of optimal caste ratio predicts that the ratio of caste members (small to large rediae) responds to environmental variability. This was tested in Philophthalmus sp. colonies exposed to host starvation and competition with the trematode, Maritrema novaezealandensis. Philophthalmus sp. infected snails, with and without M. novaezealandensis, were subjected to food treatments. Reproductive output, number of rediae, and the ratio of small to large rediae were compared among treatments. Philophthalmus sp. colonies responded to host starvation and competition; reproductive output was higher in well-fed snails of both infection types compared with snails in lower food treatments and well-fed, single infected snails compared with well-fed double infected snails. Furthermore, the caste ratio in Philophthalmus sp. colonies was altered in response to competition. This is the first study showing caste ratio responses to environmental pressures in trematodes with a division of labour.

Abstract. This article describes a potentiometric ocean acidification simulation system which automatically regulates pH through the injection of 100% CO2 gas into temperature-controlled seawater. The system is ideally suited to long-term experimental studies of the effect of acidification on biological processes involving small-bodied (10–20 mm) calcifying or non-calcifying organisms. Using hobbyist-grade equipment, the system was constructed for approximately USD 1200 per treatment unit (tank, pH regulation apparatus, chiller, pump/filter unit). An overall tolerance of ±0.05 pHT units (SD) was achieved over 90 days in two acidified treatments (7.60 and 7.40) at 12 °C using glass electrodes calibrated with synthetic seawater buffers, thereby preventing liquid junction error. The performance of the system was validated through the independent calculation of pHT (12 °C) using dissolved inorganic carbon and total alkalinity data taken from discrete acidified seawater samples. The system was used to compare the shell growth of the marine gastropod Zeacumantus subcarinatus infected with the trematode parasite Maritrema novaezealandensis with that of uninfected snails at pH levels of 7.4, 7.6, and 8.1.

SUMMARYIndividual animals are often infected not only by different parasite species, but also by multiple genotypes of the same parasite species. Genetic relatedness among parasites sharing a host is expected to modulate their strategies of resource exploitation, growth and virulence. We experimentally examined the effects that genetic diversity and infection intensity had on host mortality, infectivity and growth of the marine trematode Maritrema novaezealandensis in amphipod hosts. The presence of 2 versus 1 parasite genotype during infection did not influence subsequent host mortality, had different effects on infectivity among genotypes and did not influence growth or variation in parasite growth. Density-dependent growth reductions revealed that the number of parasites infecting a host was more important than their genetic relatedness. Temperature, host size, and host sex influenced the degree to which density-dependent factors affected parasite growth. Our results suggest that the effects of parasite relatedness vary among parasite genotypes in this trematode species, and reveal that many factors play an important role during parasite development and transmission.

Most, if not all, animals will at some stage in their lives encounter parasites. Some of the most widespread and abundant parasites belong to the Class Trematoda. Trematodes often have a substantial negative impact on individual intermediate host ecology. In this thesis, I investigate ecological and evolutionary consequences of the interaction between the microphallid trematode, Maritrema novaezealandensis, and its intermediate snail and crustacean hosts. Parasites often show a heterogeneous spatial distribution pattern in natural animal host populations. In this study, factors determining the spatial distribution of larval trematodes in Zeacumantus subcarinatus were investigated at two spatial scales (within and among bays). The distribution of shorebird definitive hosts explained a significant amount of the variation in the distribution of trematodes among bays. However, within a bay, other factors override the effect of bird distribution. The influence of larval trematodes on reproduction, survival and population density of Z. subcarinatus was investigated using laboratory and field studies. In the laboratory, it was found that larval trematodes induce castration and mortality of Z. subcarinatus. The field study revealed that the local prevalence of trematodes had a significant negative effect on population density of Z. subcarinatus. Through castration, trematodes act as strong selective agents on snail host life history. The effect of trematodes on life history characteristics (reproductive effort, juvenile growth, size at maturity and susceptibility to trematode infections) were investigated among natural populations of Z subcarinatus. Reproductive effort was not higher for uninfected females from populations where the risk of becoming infected was high. However, offspring from those populations were significantly larger, and laboratory-reared juveniles grew significantly faster than conspecifics from other populations. In addition, size at maturity was negatively correlated with trematode prevalence across snail populations. Z. subcarinatus thus adapts to a high local risk of trematode infection by reaching maturity early, thereby increasing the chance of reproducing. The influence of M. novaezealandensis on the survial of the amphipod host, Paracalliope novizealandiae was examined using experimental infections and field observations. The experimental infections demonstrated that parasite-induced mortality was intensity-dependent. The number of M. novaezealandensis per amphipod was too low to significantly induce host mortality in the field. However, the transmission strategy of this parasite allows it to affect host populations during weather conditions ideal for trematode transmission. Trematode strategies in the second intermediate host are important to the understanding of host-parasite co-evolution and the evolution of parasite life cycles. In this study, potential density-dependent effects at the metacercarial stage on size and fecundity of in vitro adult M. novaezealandensis was examined in both experimentally infected P. novizealandiae and naturally infected Macrophthalmus hirtipes. For this purpose, a method to excyst and cultivate M. novaezealandensis metacercariae to an egg producing stage, was developed. Naturally infected M. hirtipes also harboured larval stages of three other helminths. Crowding effects in the two crustacean hosts were expressed as a decreased volume and smaller egg production of in vitro adult M. novaezealandensis. In addition, interspecific interactions among parasite species were observed in crab hosts. The work in this thesis provides evidence that M. novaezealandensis significantly and negatively affect intermediate host ecology. The heterogeneous distribution of trematodes causes differential effects among host populations with subsequent effects on the life history of snail hosts. In addition, this study demonstrates that parasites interact within their second intermediate host with possible implications for the way parasites exploit their hosts.