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Results for “Host-Parasite Interactions”

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PubMed1979

The evolution of genetic diversity.

The existence within natural populations of large amounts of genetic variation in molecules and morphology presents an evolutionary problem. The 'neutralist' solution to this problem, that the variation is usually unimportant to the organism displaying it, has now lost much of its strength. Interpretations that assume widespread heterozygous advantage also face serious difficulties. A resolution is possible in terms of frequency-dependent selection by predators, parasites and competitors. The evidence for pervasive frequency-dependent selection is now very strong. It appears to follow naturally from the behaviour of predators, from the evolutionary lability of parasites, from the ecology of competition and, at the molecular level, from the phenomena of enzyme kinetics. Such selection can explain the maintenance not only of conventional polymorphism but also of continuous variation in both molecular and morphological characters. It can account for the occurrence of diversity within groups of haploid and self-fertilizing organisms, and for the evolution of differences between individuals in their systems of genetic control.

Alleles↗
PubMed1979

Arms races between and within species.

An adaptation in one lineage (e.g. predators) may change the selection pressure on another lineage (e.g. prey), giving rise to a counter-adaptation. If this occurs reciprocally, an unstable runaway escalation or 'arms race' may result. We discuss various factors which might give one side an advantage in an arms race. For example, a lineage under strong selection may out-evolve a weakly selected one (' the life-dinner principle'). We then classify arms races in two independent ways. They may be symmetric or asymmetric, and they may be interspecific or intraspecific. Our example of an asymmetric interspecific arms race is that between brood parasites and their hosts. The arms race concept may help to reduce the mystery of why cuckoo hosts are so good at detecting cuckoo eggs, but so bad at detecting cuckoo nestlings. The evolutionary contest between queen and worker ants over relative parental investment is a good example of an intraspecific asymmetric arms race. Such cases raise special problems because the participants share the same gene pool. Interspecific symmetric arms races are unlikely to be important, because competitors tend to diverge rather than escalate competitive adaptations. Intraspecific symmetric arms races, exemplified by adaptations for male-male competition, may underlie Cope's Rule and even the extinction of lineages. Finally we consider ways in which arms races can end. One lineage may drive the other to extinction; one may reach an optimum, thereby preventing the other from doing so; a particularly interesting possibility, exemplified by flower-bee coevolution, is that both sides may reach a mutual local optimum; lastly, arms races may have no stable and but may cycle continuously. We do not wish necessarily to suggest that all, or even most, evolutionary change results from arms races, but we do suggest that the arms race concept may help to resolve three long-standing questions in evolutionary theory.

Adaptation, Biological↗
PubMed2025

Biomathematical enzyme kinetics model of prebiotic autocatalytic RNA networks: degenerating parasite-specific hyperparasite catalysts confer parasite resistance and herald the birth of molecular immunity.

Catalysis and specifically autocatalysis are the quintessential building blocks of life. Yet, although autocatalytic networks are necessary, they are not sufficient for the emergence of life-like properties, such as replication and adaptation. The ultimate and potentially fatal threat faced by molecular replicators is parasitism; if the polymerase error rate exceeds a critical threshold, even the fittest molecular species will disappear. Here we have developed an autocatalytic RNA early life mathematical network model based on enzyme kinetics, specifically the steady-state approximation. We confirm previous models showing that these second-order autocatalytic cycles are sustainable, provided there is a sufficient nucleotide pool. However, molecular parasites become untenable unless they sequentially degenerate to hyperparasites (i.e. parasites of parasites). Parasite resistance-a parasite-specific host response decreasing parasite fitness-is acquired gradually, and eventually involves an increased binding affinity of hyperparasites for parasites. Our model is supported at three levels; firstly, ribozyme polymerases display Michaelis-Menten saturation kinetics and comply with the steady-state approximation. Secondly, ribozyme polymerases are capable of sustainable auto-amplification and of surmounting the fatal error threshold. Thirdly, with growing sequence divergence of host and parasite catalysts, the probability of self-binding is expected to increase and the trend towards cross-reactivity to diminish. Our model predicts that primordial host-RNA populations evolved via an arms race towards a host-parasite-hyperparasite catalyst trio that conferred parasite resistance within an RNA replicator niche. While molecular parasites have traditionally been viewed as a nuisance, our model argues for their integration into the host habitat rather than their separation. It adds another mechanism-with biochemical precision-by which parasitism can be tamed and offers an attractive explanation for the universal coexistence of catalyst trios within prokaryotes and the virosphere, heralding the birth of a primitive molecular immunity.

Kinetics↗
PubMed2025

Widespread release of translational repression across Plasmodium's host-to-vector transmission event.

Malaria parasites must respond quickly to environmental changes, including during their transmission between mammalian and mosquito hosts. Therefore, female gametocytes proactively produce and translationally repress mRNAs that encode essential proteins that the zygote requires to establish a new infection. While the release of translational repression of individual mRNAs has been documented, the details of the global release of translational repression have not. Moreover, changes in the spatial arrangement and composition of the DOZI/CITH/ALBA complex that contribute to translational control are also not known. Therefore, we have conducted the first quantitative, comparative transcriptomics and DIA-MS proteomics of Plasmodium parasites across the host-to-vector transmission event to document the global release of translational repression. Using female gametocytes and zygotes of P. yoelii, we found that ~200 transcripts are released for translation soon after fertilization, including those encoding essential functions. Moreover, we identified that many transcripts remain repressed beyond this point. TurboID-based proximity proteomics of the DOZI/CITH/ALBA regulatory complex revealed substantial spatial and/or compositional changes across this transmission event, which are consistent with recent, paradigm-shifting models of translational control. Together, these data provide a model for the essential translational control mechanisms that promote Plasmodium's efficient transmission from mammalian host to mosquito vector.

Animals↗
PubMed2026

Epigenetic and metabolic reprogramming of innate immune cells establishes immunological memory in the Schistosomiasis vector snail Biomphalaria glabrata.

Innate immune memory enables non-vertebrates to mount faster and more effective immune responses upon re-exposure to a previously encountered pathogen, yet its cellular and molecular bases remain poorly understood. The freshwater snail Biomphalaria glabrata, intermediate host of the human parasite Schistosoma mansoni, provides a powerful model to investigate this phenomenon. Here, we show that innate immune memory in B. glabrata is carried by hemocytes and relies on profound metabolic and epigenetic reprogramming initiated during primary infection. Using an integrative multi-omics approach combining transcriptomics, chromatin accessibility profiling, whole-genome bisulfite sequencing and targeted metabolomics, we reveal that the first parasite encounter induces a stable rewiring of hemocyte metabolism and chromatin landscape. This reprogramming primes hemocytes for a massive and rapid transcriptional response upon secondary challenge, characterized by an immune shift toward highly specific humoral effector pathways. Metabolic analyses demonstrate an early switch toward aerobic glycolysis, altered tricarboxylic acid cycle activity and amino acid metabolism, consistent with a Warburg-like metabolic state previously described in vertebrate trained immunity. Notably, metabolic and epigenetic remodeling occurs primarily during the primary infection and remains stable upon secondary exposure, suggesting that immune memory is encoded prior to pathogen re-encounter. Together, our results identify conserved metabolic and epigenetic mechanisms underlying innate immune memory in a non-vertebrate host and provide direct evidence that hemocyte-mediated innate immune memory in B. glabrata shares core features with trained immunity described in vertebrates.

Animals↗
PubMed1979

Haematobium schistosomiasis in the squirrel monkey (Saimiri sciureus).

The squirrel monkey (Saimiri sciureus) accommodates Schistosoma haematobium moderately well. Adults occur in the major viscera but the extent of tissue egg deposits and associated pathology is variable. Pathologic involvement of the urogenital system occurs in a large proportion of hosts exposed to moderate to heavy infections, and bladder pathology is indicative of conditions associated with bladder carcinoma.

Animals↗
PubMed1979

The host/parasite relationships of Xenopsylla astia and X. cheopis on Bandicota bengalensis in Rangoon, Burma.

In Rangoon, Burma, over half the commensal B. bengalensis taken in live traps were found to be infested with Xenopsylla species fleas. X. astia infestations were twice as common as those of the classic plague vector X. cheopis. In terms of absolute numbers X. astia outnumbered X. cheopis by 10 to 1. X. astia was more commonly found as a monospecific infestation, and X. cheopis was more commonly found mixed with X. astia. The flea indicies were high, with a specific index of 2.4 for X. cheopis and 10.2 for X. astia. The flea indicies and flea sex ratios remained stable across the host population and could not be correlated to changes in the head and body length of the host and were not different on male or female hosts. The evidence of this and other surveys is that X. cheopis is not as well adapted for parasitism on free ranging B. bengalensis as is X. astia.

Animals↗
PubMedDate not supplied

[The lice of the gerbils of Tajikistan].

2606 gerbils of four species from Tajikistan were examined. On them there were found over 14 thousand sucking lice of 10 species, four of which are typical to gerbils. Hoplopleura merionidis Ferris is a Mongolian-Turkestan species, which in Central Asia parasitizes Meriones meridianus Pallas and M. unguiculatus Milne-Edw. and in Middle Asia--M. meridianus and M. erythrourus Gray, seldom M. tamariscinus Pallas. Polyplax chinensis Ferris, a parasite of M. meridianus, is a Mongolian-Turkestan species the distribution of which, apparently, corresponds to that of the host. P. paradoxa Johnson, a parasite of M. erythrourus, is an Afro-Asiatic species. P. opimi Sosnina, a parasite of Rhombomys opimus Lichtenstein, is apparently an Asiatic species, the distribution of which is closely associated with the host's distribution area.

Animals↗
PubMedDate not supplied

[The assimilation by Eimeria tenella coccidia of DNA and RNA precursors from the host cell].

The assimilation of purine and pyrimidine bases, their nucleosides and orotic acid from the host cell by coccidian E. tenella was studied by means of radioactive precursors of DNA and RNA. It has been established that within their development and reproduction the parasites use selectively different precursors of DNA and RNA from the host cell. Coccidians use intensively the purine base 14C-adenine, assimilate negligibly the pyrimidine base 14C-uracil and nucleoside 14C-uridine and do not use at all 14C-thymidine and 14C-thymine. The coccidians were found to assimilate most intensively 14C-orotic acid, the lower precursor of pyrimidine bases.

Animals↗