scholarly journals Diversity patterns in parasite populations capable for persistence and reinfection with a view towards thehuman cytomegalovirus

2019 ◽  
Author(s):  
Cornelia Pokalyuk ◽  
Irene Görzer
Keyword(s):  
Balancing Selection ◽  
Parasite Population ◽  
Substantial Fraction ◽  
Diversity Patterns ◽  
Coding Regions ◽  
Evolutionary Advantage ◽  
Parasite Reproduction ◽  
Host Parasite ◽  
Parasite Populations ◽  
High Diversity

AbstractMany parasites like thecytomegalovirus, HIVandEscherichia coliare capable to persist in and reinfect its host. The evolutionary advantage (if so) of these complicated mechanisms have not been quantitatively analyzed so far. Here we take a first step by investigating a host-parasite model for which these mechanisms are driving the evolution of the parasite population. We consider two variants of the model. In one variant parasite reproduction is directed by balancing selection, in the other variant parasite reproduction is neutral. In the former scenario reinfection and persistence have been shown to sustain the maintenance of diversity in the parasite population in certain parameter regimes (Pokalyuk and Wakolbinger, 2018). Here we analyse the diversity patterns in the latter, neutral scenario. We evaluate the biological relevance of both model variants with respect to thehuman cytomegalovirus(HCMV), an ancient herpesvirus that is carried by a substantial fraction of mankind and manages to maintain a high diversity in its coding regions.

HOST LARVAL MORTALITY IN AN EXPERIMENTAL HOST–PARASITE POPULATION

1964 ◽  
Vol 42 (5) ◽  
pp. 745-765 ◽  
Author(s):  
T. Burnett
Keyword(s):  
Larval Mortality ◽  
Trialeurodes Vaporariorum ◽  
Parasite Population ◽  
Rapid Decline ◽  
Encarsia Formosa ◽  
Host Protection ◽  
Host Mortality ◽  
Host Parasite ◽  
Parasite Populations ◽  
Two Populations

Two populations of Trialeurodes vaporariorum (Westw.) and its chalcid parasite Encarsia formosa Gahan were reared on tomato plants in the greenhouse at 72–76 °F for 26 weeks. Although the abundance of both species fluctuated with peaks of increasing amplitude, the population that was initially larger remained so throughout the period of sampling because the parasite inflicted similar rates of mortality in both cases. The fluctuations of the two separate populations were synchronized throughout the period of propagation. Host mortality, which resulted either from almost immediate killing of host scales following attack by adult parasites or from death of host larvae following parasitization and development of parasite progeny, was determined by parasite density, host size, and possibly by a number of other factors such as the age structure of host larval populations, age of adult parasites, and succulence of leaves on which the host larvae developed. The interaction of host and parasite produced cycles in the age structures of host and parasite populations that, in turn, influenced the interaction of the two species. The death of host larvae following attack by adult parasites was a form of host protection, as it ensured the rapid decline in the abundance of the parasite population and was, therefore, the primary factor in the maintenance of the host–parasite system.

scholarly journals Host “cleansing zone” at secondary contact: a new pattern in host-parasite population genetics

2020 ◽  
Author(s):  
Jana Martinů ◽  
Jan Štefka ◽  
Anbu Poosakkannu ◽  
Václav Hypša
Keyword(s):  
Population Genetics ◽  
Generation Time ◽  
Population Genetic ◽  
Parasite Population ◽  
Secondary Contact ◽  
Mitochondrial Genomes ◽  
Isolated Populations ◽  
Host Parasite ◽  
Parasite Populations ◽  
Complete Mitochondrial Genomes

AbstractWe introduce a new pattern of population genetic structure in a host-parasite system that can arise after secondary contact (SC) of previously isolated populations. Due to different generation time and therefore different tempo of molecular evolution the host and parasite populations reach different degrees of genetic differentiation during their separation (e.g. in refugia). Consequently, during the SC the host populations are able to re-establish a single panmictic population across the whole recolonized area, while the parasite populations stop their dispersal at the SC zone and create a narrow hybrid zone (HZ). From the host’s perspective, the parasite’s HZ functions on a microevolutionary scale as a “host-cleansing filter”: while passing from area A to area B, the hosts are rid of the area A parasites and acquire the area B parasites. We demonstrate this novel pattern on a model composed of Apodemus mice and Polyplax lice by comparing maternally inherited markers (complete mitochondrial genomes, and complete genomes of vertically transmitted symbiont Legionella polyplacis) with SNPs derived from the louse genomic data. We discuss circumstances which may lead to this pattern and possible reasons why it has been overlooked in the studies on host-parasite population genetics.

scholarly journals Recombination and Selection at Brassica Self-Incompatibility Loci

Genetics ◽  
1999 ◽  
Vol 152 (1) ◽  
pp. 413-425 ◽  
Author(s):  
Philip Awadalla ◽  
Deborah Charlesworth
Keyword(s):  
Linkage Disequilibrium ◽  
Balancing Selection ◽  
Brassica Species ◽  
Selective Constraint ◽  
Intragenic Recombination ◽  
Self Incompatibility ◽  
History Of ◽  
Unknown Gene ◽  
Slg Gene ◽  
High Diversity

Abstract In Brassica species, self-incompatibility is controlled genetically by haplotypes involving two known genes, SLG and SRK, and possibly an as yet unknown gene controlling pollen incompatibility types. Alleles at the incompatibility loci are maintained by frequency-dependent selection, and diversity at SLG and SRK appears to be very ancient, with high diversity at silent and replacement sites, particularly in certain “hypervariable portions of the genes. It is important to test whether recombination occurs in these genes before inferences about function of different parts of the genes can be made from patterns of diversity within their sequences. In addition, it has been suggested that, to maintain the relationship between alleles within a given S-haplotype, recombination is suppressed in the S-locus region. The high diversity makes many population genetic measures of recombination inapplicable. We have analyzed linkage disequilibrium within the SLG gene of two Brassica species, using published coding sequences. The results suggest that intragenic recombination has occurred in the evolutionary history of these alleles. This is supported by patterns of synonymous nucleotide diversity within both the SLG and SRK genes, and between domains of the SRK gene. Finally, clusters of linkage disequilibrium within the SLG gene suggest that hypervariable regions are under balancing selection, and are not merely regions of relaxed selective constraint.

scholarly journals How host phenology impacts multi-season epidemic cycles

2021 ◽  
Author(s):  
Hannelore MacDonald ◽  
Dustin Brisson
Keyword(s):  
Mathematical Model ◽  
Population Dynamics ◽  
Population Cycles ◽  
Seasonal Activity ◽  
Host Interactions ◽  
Host Phenology ◽  
Demographic Impact ◽  
Host Parasite ◽  
Parasite Populations ◽  
Parasite Dynamics

Parasite-host interactions can result in periodic population dynamics when parasites over-exploit host populations. The timing of host seasonal activity, or host phenology, determines the frequency and demographic impact of parasite-host interactions which may govern if the parasite can sufficiently over-exploit their hosts to drive population cycles. We describe a mathematical model of a monocyclic, obligate-killer parasite system with seasonal host activity to investigate the consequences of host phenology on host-parasite dynamics. The results suggest that parasites can reach the densities necessary to destabilize host dynamics and drive cycling in only some phenological scenarios, such as environments with short seasons and synchronous host emergence. Further, only parasite lineages that are sufficiently adapted to phenological scenarios with short seasons and synchronous host emergence can achieve the densities necessary to over-exploit hosts and produce population cycles. Host-parasite cycles can also generate an eco-evolutionary feedback that slows parasite adaptation to the phenological environment as rare advantageous phenotypes are driven to extinction when introduced in phases of the cycle where host populations are small and parasite populations are large. The results demonstrate that seasonal environments can drive population cycling in a restricted set of phenological patterns and provides further evidence that the rate of adaptive evolution depends on underlying ecological dynamics.

Heterogeneity in helminth infections: factors influencing aggregation in a simple host–parasite system

Parasitology ◽  
2019 ◽  
Vol 147 (1) ◽  
pp. 65-77 ◽  
Author(s):  
Richard C. Tinsley ◽  
Hanna Rose Vineer ◽  
Rebecca Grainger-Wood ◽  
Eric R. Morgan
Keyword(s):  
Post Infection ◽  
Evolutionary Biology ◽  
Negative Binomial ◽  
Parasite Population ◽  
Trout Population ◽  
Helminth Infections ◽  
Transmission Period ◽  
Binomial Parameter ◽  
Host Parasite ◽  
Direct Life Cycle

AbstractThe almost universally-occurring aggregated distributions of helminth burdens in host populations have major significance for parasite population ecology and evolutionary biology, but the mechanisms generating heterogeneity remain poorly understood. For the direct life cycle monogenean Discocotyle sagittata infecting rainbow trout, Oncorhynchus mykiss, variables potentially influencing aggregation can be analysed individually. This study was based at a fish farm where every host individual becomes infected by D. sagittata during each annual transmission period. Worm burdens were examined in one trout population maintained in isolation for 9 years, exposed to self-contained transmission. After this year-on-year recruitment, prevalence was 100% with intensities 10–2628, mean 576, worms per host. Parasite distribution, amongst hosts with the same age and environmental experience, was highly aggregated with variance to mean ratio 834 and negative binomial parameter, k, 0.64. The most heavily infected 20% of fish carried around 80% of the total adult parasite population. Aggregation develops within the first weeks post-infection; hosts typically carried intensities of successive age-specific cohorts that were consistent for that individual, such that heavily-infected individuals carried high numbers of all parasite age classes. Results suggest that host factors alone, operating post-infection, are sufficient to generate strongly overdispersed parasite distributions, rather than heterogeneity in exposure and initial invasion.

Regulation and Stability of Host-Parasite Population Interactions: II. Destabilizing Processes

10.2307/3934 ◽  
1978 ◽  
Vol 47 (1) ◽  
pp. 249 ◽  
Author(s):  
Robert M. May ◽  
Roy M. Anderson
Keyword(s):  
Parasite Population ◽  
Population Interactions ◽  
Host Parasite

scholarly journals Rapid change in parasite infection traits over the course of an epidemic in a wild host-parasite population

Oikos ◽  
2013 ◽  
Vol 123 (2) ◽  
pp. 232-238 ◽  
Author(s):  
Stuart K. J. R. Auld ◽  
Philip J. Wilson ◽  
Tom J. Little
Keyword(s):  
Rapid Change ◽  
Parasite Infection ◽  
Parasite Population ◽  
Wild Host ◽  
Host Parasite

The regulation of host population growth by parasitic species

Parasitology ◽  
1978 ◽  
Vol 76 (2) ◽  
pp. 119-157 ◽  
Author(s):  
R. M. Anderson
Keyword(s):  
Population Growth ◽  
Reproductive Potential ◽  
Parasite Burden ◽  
Host Population ◽  
Parasitic Species ◽  
Regulatory Influence ◽  
Host Mortality ◽  
Parasite Reproduction ◽  
Over Dispersion ◽  
Host Parasite

SummaryThe nature of parasitism at the population level is defined in terms of the parasite's influence on the natural intrinsic growth rate of its host population. It is suggested that the influence on this rate is related to the average parasite burden/host and hence to the statistical distribution of parasites within the host population.Theoretical models of host–parasite associations are used to assess the regulatory influence of parasitic species on host population growth. Model predictions suggest that three specific groups of population processes are of particular importance: over-dispersion of parasite numbers/host, density dependence in parasite mortality or reproduction and parasite-induced host mortality that increases faster than linearly with the parasite burden. Other population mechanisms are shown to have a destabilizing influence, namely: parasite-induced reduction in host reproductive potential, direct parasite reproduction within the host and time delays in the development of transmission stages of the parasite.These regulatory and destabilizing processes are shown to be commonly observed features of natural host-parasite associations. It is argued that interactions in the real world are characterized by a degree of tension between these regulatory and destabilizing forces and that population rate parameter values in parasite life-cycles are very far from being a haphazard selection of all numerically possible values. It is suggested that evolutionary pressures in observed associations will tend to counteract a strong destabilizing force by an equally strong regulatory influence. Empirical evidence is shown to support this suggestion in, for example, associations between larval digeneans and molluscan hosts (parasite-induced reduction in host reproductive potential counteracted by tight density-dependent constraints on parasite population growth), and interactions between protozoan parasites and mammalian hosts (direct parasite reproduction counteracted by a well-developed immunological response by the host).The type of laboratory and field data required to improve our understanding of the dynamical properties of host–parasite population associations is discussed and it is suggested that quantitative measurement of rates of parasite-induced host mortality, degrees of over-dispersion, transmission rates and reproductive and mortality rates of both host and parasite would provide an important first step. The value of laboratory work in this area is demonstrated by reference to studies which highlight the regulatory influence of parasitic species on host population growth.

The Effect of Temperature on an Insect Host-Parasite Population

Ecology ◽  
1949 ◽  
Vol 30 (2) ◽  
pp. 113-134 ◽  
Author(s):  
Thomas Burnett
Keyword(s):  
Parasite Population ◽  
Effect Of Temperature ◽  
Insect Host ◽  
Host Parasite
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