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Host Generations (host + generation)
Selected AbstractsSecondary host generation of the gall aphid Cerataphis jamuritsu (Homoptera)ENTOMOLOGICAL SCIENCE, Issue 4 2004Utako KUROSU Abstract Colonies of a Cerataphis species with well-developed horns were found on the rattan Calamus quinquesstinervis in southern Taiwan. The morphology of first instar nymphs from the colonies accorded well with the morphology of first instar nymphs laid by alates of Cerataphis jamuritsu from galls on Styrax suberifolia, indicating that the rattan aphids are the secondary host generation of C. jamuritsu. Although the aphid colonies were attended by ants, the sharp horns of the first instar nymphs suggest that they might attack predators. [source] Inference of parasite local adaptation using two different fitness componentsJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2007D. REFARDT Abstract Estimating parasite fitness is central to studies aiming to understand parasite evolution. Theoretical models generally use the basic reproductive rate R0 to express fitness, yet it is very difficult to quantify R0 empirically and experimental studies often use fitness components such as infection intensity or infectivity as substitutes. These surrogate measures may be biased in several ways. We assessed local adaptation of the microsporidium Ordospora colligata to its host, the crustacean Daphnia magna using two different parasite fitness components: infection persistence over several host generations in experimental populations and infection intensity in individual hosts. We argue that infection persistence is a close estimator of R0, whereas infection intensity measures only a component of it. Both measures show a pattern that is consistent with parasite local adaptation and they correlate positively. However, several inconsistencies between them suggest that infection intensity may at times provide an inadequate estimate of parasite fitness. [source] Strain-specific regulation of intracellular Wolbachia density in multiply infected insectsMOLECULAR ECOLOGY, Issue 12 2003L. Mouton Abstract Vertically transmitted symbionts suffer a severe reduction in numbers when they pass through host generations, resulting in genetic homogeneity or even clonality of their populations. Wolbachia endosymbionts that induce cytoplasmic incompatibility in their hosts depart from this rule, because cytoplasmic incompatibility actively maintains multiple infection within hosts. Hosts and symbionts are thus probably under peculiar selective pressures that must shape the way intracellular bacterial populations are regulated. We studied the density and location of Wolbachia within adult Leptopilina heterotoma, a haplodiploid wasp that is parasitic on Drosophila and that is naturally infected with three Wolbachia strains, but for which we also obtained one simply infected and two doubly infected lines. Comparison of these four lines by quantitative polymerase chain reaction using a real-time detection system showed that total Wolbachia density varies according to the infection status of individuals, while the specific density of each Wolbachia strain remains constant regardless of the presence of other strains. This suggests that Wolbachia strains do not compete with one another within the same host individual, and that a strain-specific regulatory mechanism is operating. We discuss the regulatory mechanisms that are involved, and how this process might have evolved as a response to selective pressures acting on both partners. [source] Epigenetic effects of infection on the phenotype of host offspring: parasites reaching across host generationsOIKOS, Issue 3 2008Robert Poulin Parasite-induced changes in host phenotype are now well-documented from a wide range of taxa. There is a growing body of evidence indicating that parasites can also have trans-generational consequences, with infection of a host leading to changes in the phenotype of its offspring, though the latter are not parasitised. Several proximate mechanisms have been put forward to explain these ,maternal' effects, most involving hormonal or other physiological pathways, ultimately leading to offspring that are pre-adapted to the parasites they are most likely to encounter based on their mother's experience. Here, we propose that all these trans-generational effects on offspring phenotype must involve epigenetic phenomena. Epigenetics concerns the appearance and inheritance of seemingly new phenotypic traits without changes in the underlying DNA sequence. Since diet and other environmental factors experienced by a mother can affect gene expression in her offspring by turning genes ,on' or ,off' (for example, via DNA methylation), why couldn't parasites do it? Although epigenetic effects have not been explicitly invoked to account for trans-generational impacts of parasites on the phenotype of host offspring, the existing evidence is fully compatible with their involvement. We argue that epigenetic mechanisms must play a central role; we also discuss their evolutionary implications and suggest questions for future investigations in this new and exciting research direction. [source] | ||||||||||