Evolution of host resistance to parasite infection in the snail–schistosome–human system

The evolutionary strategies that emerge within populations can be dictated by numerous factors, including interactions with other species. In this paper, we explore the consequences of such a scenario using a host-parasite system of human concern. By analyzing the dynamical behaviors of a mathematical model we investigate the evolutionary outcomes resulting from interactions between Schistosoma mansoni and its snail and human hosts. The model includes two types of snail hosts representing resident and mutant types. Using this approach, we focus on establishing evolutionary stable strategies under conditions where snail hosts express different life-histories and when drug treatment is applied to an age-structured population of human hosts. Results from this work demonstrate that the evolutionary trajectories of host-parasite interactions can be varied, and at times, counter-intuitive, based on parasite virulence, host resistance, and drug treatment.     

A comparison of diversity estimators applied to a database of host–parasite associations

Understanding the drivers of biodiversity is important for forecasting changes in the distribution of life on earth. However, most studies of biodiversity are limited by uneven sampling effort, with some regions or taxa better sampled than others. Numerous methods have been developed to account for differences in sampling effort, but most methods were developed for systematic surveys in which all study units are sampled using the same design and assemblages are sampled randomly. Databases compiled from multiple sources, such as from the literature, often violate these assumptions because they are composed of studies that vary widely in their goals and methods. Here, we compared the performance of several popular methods for estimating parasite diversity based on a large and widely used parasite database, the Global Mammal Parasite Database (GMPD). We created artificial datasets of host–parasite interactions based on the structure of the GMPD, then used these datasets to evaluate which methods best control for differential sampling effort. We evaluated the precision and bias of seven methods, including species accumulation and nonparametric diversity estimators, compared to analyzing the raw data without controlling for sampling variation. We find that nonparametric estimators, and particularly the Chao2 and second-order jackknife estimators, perform better than other methods. However, these estimators still perform poorly relative to systematic sampling, and effect sizes should be interpreted with caution because they tend to be lower than actual effect sizes. Overall, these estimators are more effective in comparative studies than for producing true estimates of diversity. We make recommendations for future sampling strategies and statistical methods that would improve estimates of global parasite diversity.     

Histone lactylation: a new epigenetic axis for host–parasite signalling in malaria?

Epigenetic modifications play important roles in the biology of malaria parasites. The new epigenetic mark histone lactylation, discovered only recently in humans, is also present in malaria parasites. It may have important functions as a key player in the epigenetic repertoire of Plasmodium.     

Temporal variations of Microsporidia diversity and discovery of new host–parasite interactions in a lake ecosystem

Microsporidia are a large group of obligate intracellular eukaryotic parasites related to Fungi. Recent studies suggest that their diversity has been greatly underestimated and little is known about their hosts other than metazoans, and thus about their impact on the communities at the base of the food web. In this work, we therefore studied the diversity of Microsporidia over one year and identified potential new hosts in small-sized fractions (<150 μm) in a lake ecosystem using a metabarcoding approach coupled with co-occurrence networks and tyramide signal amplification-fluorescent in situ hybridization. Our analysis shows a great Microsporidia diversity (1 472 OTUs), with an important part of this diversity being unknown. Temporal variations of this diversity have been observed, which might follow temporal variations of their potential hosts such as protists and microzooplankton. New hosts among them were identified as well as associations with phytoplankton. Indeed, repeated infections were observed in Kellicottia (rotifers) with a prevalence of 38% (infected individuals). Microsporidia inside a Stentor (ciliate) were also observed. Finally, potential infections of the diatom Asterionella were identified (prevalence <0.1%). The microsporidian host spectrum could be therefore even more important than previously described, and their role in the functioning of lake ecosystems is undoubtedly largely unknown.     

What has become of the refugia hypothesis to explain biological diversity in Amazonia?

The spatial distribution of biodiversity and related processes is the core of Biogeography. Amazonia is the world's most diverse rainforest and the primary source of diversity to several Neotropical regions. The origins of such diversity continue to be an unresolved question in evolutionary biology. Among many competing hypotheses to explain the evolution of the Amazonian biodiversity, one stands out as the most influential: the refugia hypothesis by Jürgen Haffer. Here, we provide a chronological overview on how the refugia hypothesis evolved over the decades and how the criticism from different fields affected its acceptance. We conclude that the refugia hypothesis alone cannot explain the diversification of the complex Amazonian diversity, and perhaps it was not the most important diversification mechanism. However, the debate provoked by refugia has produced a great amount of knowledge on Amazonian climatic, geological, and evolutionary processes, as well as on species distributions, movements, and history.     

A fundamental plant evolutionary problem: the origin of land-plant sporophyte; is a new hypothesis possible?

The origin of the sporophyte in land plants represents a fundamental phase in the plant evolution. Today this subject is controversial and, in my opinion, scarcely considered in our textbooks and journals of botany, in spite of its importance. There are two conflicting theories concerning the origin of the alternating generations in land plants: the "antithetic" and the "homologous" theory. These have never been fully resolved. The antithetic theory maintains that the sporophyte and gametophyte generations are fundamentally dissimilar and that the sporophyte originated in an ancestor organism with haplontic cycle by the zygote dividing mitotically rather than meiotically, and with a developmental pattern not copying the developmental events of the gametophyte. The sporophyte generation was an innovation of critical significance for the land-plant evolution. By contrast, the homologous theory simply stated that a mass of cells forming mitotically from the zygote adopted the same developmental plan of the gametophyte, but giving origin to a diploid sporophyte. In this context, a very important question concerns the possible ancestor or ancestors of the land plants. Considerable evidences at morphological, cytological, ultrastructural, biochemical and, especially, molecular level, strongly suggest that the land plants or Embryophyta (both vascular and non-vascular) evolved from green algal ancestor(s), similar to those belonging to the genus Coleochaete, Chara and Nitella, living today. Their organism is haploid for most of their life cycle, and diploid only in the zygote phase (haplontic cycle). On the contrary, the land plants are characterized by a diplo-haplontic life cycle. Several questions are implied in these theories, and numerous problems remain to be solved, such as, for example, the morphological difference between gametophyte and sporophyte (heteromorphism, already present in the first land plants, the bryophytes), and the strong gap existing between these last with a sporophyte dependent on the gametophyte, and the pteridophytes having the gametophyte and sporophyte generations independent. On the ground of all of the evidences on the ancestors of the land plants, the antithetic theory is considered more plausible than the homologous theory. Unfortunately, no phylogenetic relationship exists between some green algae with diplontic life cycle and the land plants. Otherwise, perhaps, it should be possible to hypothesize another scenario in which to place the origin of the alternating generations of the land plants. In this case, could the gametophyte be formed by gametes produced from the sporophyte, through their mitoses or a delayed fertilization process?     

Can the source–sink hypothesis explain macrofaunal abundance patterns in the abyss? A modelling test

Low food availability is a major structuring force in deep-sea benthic communities, sustaining only very low densities of organisms in parts of the abyss. These low population densities may result in an Allee effect, whereby local reproductive success is inhibited, and populations are maintained by larval dispersal from bathyal slopes. This slope–abyss source–sink (SASS) hypothesis suggests that the abyssal seafloor constitutes a vast sink habitat with macrofaunal populations sustained only by an influx of larval ‘refugees'' from source areas on continental slopes, where higher productivity sustains greater population densities. Abyssal macrofaunal population densities would thus be directly related to larval inputs from bathyal source populations. We evaluate three predictions derived from the SASS hypothesis: (i) slope-derived larvae can be passively transported to central abyssal regions within a single larval period, (ii) projected larval export from slopes to the abyss reproduces global patterns of macrofaunal abundance and (iii) macrofaunal abundance decreases with distance from the continental slope. We find that abyssal macrofaunal populations are unlikely to be sustained solely through influx of larvae from slope sources. Rather, local reproduction probably sustains macrofaunal populations in relatively high-productivity abyssal areas, which must also be considered as potential larval source areas for more food-poor abyssal regions.     

Horizons in plant pathology I. The “host” and the “parasite”: Need for a broadened outlook

Summary A critical appraisal of the celebrated couplet of plant pathology host and parasite is presented in the preceding pages. Author's own evaluation opens new vistas, displays several new ideas and an altogether new interpretation of this central theme of plant pathology incorporating biochemical concepts.     

Differential virulence in a multiple‐host parasite of bumble bees: resolving the paradox of parasite survival?

Parasite virulence determines both the impact that parasites have on their hosts and parasite fitness. While most studies of virulence have involved single-species host–parasite interactions, the majority of parasites are likely to use multiple concurrent host species. Our understanding of how this impacts on parasite epidemiology and virulence is limited. Using the bumble bee Bombus lucorum , which exists in sympatry with B. terrestris in multi-species assemblages, and their generalist micosporidian parasite Nosema bombi , we tested whether the apparent paradox of parasite maintenance due to parasite virulence in a single host, B. terrestris , could be resolved through understanding the parasite's virulence in this sympatric host species. Nosema bombi significantly impacted colony growth, individual longevity, and individual development in B. lucorum . However, these effects were different both qualitatively and quantitatively to the parasite's impact in B. terrestris . Infected colonies of B. lucorum successfully produced both male and female reproductives, and infected female reproductives were capable of successful mating. Variation in life-history across host species may explain differences in the virulence, or impact of the parasite in B. terrestris and B. lucorum , with species with shorter life-cycles being more likely to transfer the parasite from one annual generation to the next. These results suggest that to understand the virulence and epidemiology of multi-host parasites we need to examine their ecological interactions across their various host species.     

A tritrophic approach to the preference–performance hypothesis involving an exotic and a native plant

Exotic plants often generate physical and chemical changes in native plant communities where they become established. A major challenge is to understand how novel plants may affect trophic interactions in their new habitats, and how native herbivores and their natural enemies might respond to them. We compared the oviposition preference and offspring performance of the crucifer specialist, Pieris brassicae, on an exotic plant, Bunias orientalis, and on a related native plant, Sinapis arvensis. Additionally, we studied the response of the parasitoid, Cotesia glomerata to herbivore-induced plant volatiles (HIPV) and determined the volatile blend composition to elucidate which compound(s) might be involved in parasitoid attraction. On both host plants we also compared the parasitism rate of P. brassicae by C. glomerata. Female butterflies preferred to oviposit on the native plant and their offspring survival and performance was higher on the native plant compared to the exotic. Although, headspace analysis revealed qualitative and quantitative differences in the volatile blends of both plant species, C. glomerata did not discriminate between the HIPV blends in flight-tent bioassays. Nevertheless, parasitism rate of P. brassicae larvae was higher on the native plant under semi-field conditions. Overall, P. brassicae oviposition preference may be more influenced by bottom-up effects of the host plant on larval performance than by top-down pressure exerted by its parasitoid. The potential for dietary breadth expansion of P. brassicae to include the exotic B. orientalis and the role of top-down processes played by parasitoids in shaping herbivore host shifts are further discussed.     

Fluid preservation causes minimal reduction of parasite detectability in fish specimens: A new approach for reconstructing parasite communities of the past?

Long‐term datasets are needed to evaluate temporal patterns in wildlife disease burdens, but historical data on parasite abundance are extremely rare. For more than a century, natural history collections have been accumulating fluid‐preserved specimens, which should contain the parasites infecting the host at the time of its preservation. However, before this unique data source can be exploited, we must identify the artifacts that are introduced by the preservation process. Here, we experimentally address whether the preservation process alters the degree to which metazoan parasites are detectable in fluid‐preserved fish specimens when using visual parasite detection techniques. We randomly assigned fish of three species (Gadus chalcogrammus, Thaleichthys pacificus, and Parophrys vetulus) to two treatments. In the first treatment, fish were preserved according to the standard procedures used in ichthyological collections. Immediately after the fluid‐preservation process was complete, we performed parasitological dissection on those specimens. The second treatment was a control, in which fish were dissected without being subjected to the fluid‐preservation process. We compared parasite abundance between the two treatments. Across 298 fish individuals and 59 host–parasite pairs, we found few differences between treatments, with 24 of 27 host–parasite pairs equally abundant between the two treatments. Of these, one pair was significantly more abundant in the preservation treatment than in the control group, and two pairs were significantly less abundant in the preservation treatment than in the control group. Our data suggest that the fluid‐preservation process does not have a substantial effect on the detectability of metazoan parasites. This study addresses only the effects of the fixation and preservation process; long‐term experiments are needed to address whether parasite detectability remains unchanged in the months, years, and decades of storage following preservation. If so, ecologists will be able to reconstruct novel, long‐term datasets on parasite diversity and abundance over the past century or more using fluid‐preserved specimens from natural history collections.     

How do secretory products cross the plant cell wall to be released? A new hypothesis involving cyclic mechanical actions of the protoplast

Background In plants, the products of secretory activity leave the protoplast and cross the plasma membrane by means of transporters, fusion with membranous vesicles or, less commonly, as result of disintegration of the cell. These mechanisms do not address an intriguing question: How do secretory products cross the cell wall? Furthermore, how do these substances reach the external surface of the plant body? Such diverse substances as oils, polysaccharides or nectar are forced to cross the cell wall and, in fact, do so. How are chemical materials that are repelled by the cell wall or that are sufficiently viscous to not cross passively released from plant cells?Scope and Conclusions I propose a cell-cycle model developed based on observations of different secreting systems, some unpublished results and an extensive literature review, aiming to understand the processes involved in both the secretory process and the release of secretion products. In the absence of facilitated diffusion, a mechanical action of the protoplast is necessary to ensure that some substances can cross the cell wall. The mechanical action of the protoplast, in the form of successive cycles of contraction and expansion, causes the material accumulated in the periplasmic space to cross the cell wall and the cuticle. This action is particularly relevant for the release of lipids, resins and highly viscous hydrophilic secretions. The proposed cell-cycle model and the statements regarding exudate release will also apply to secretory glands not elaborated upon here. Continuous secretion of several days, as observed in extrafloral nectaries, salt glands and some mucilage-producing glands, is only possible because the process is cyclical.     

Testing the ‘plant domestication-reduced defense’ hypothesis in blueberries: the role of herbivore identity

Domestication is predicted to reduce resistance of agricultural crops against insect herbivores; however, its impact on herbivores with different feeding modes and evolutionary histories needs investigation. To this end, we conducted greenhouse experiments to explore the effects of domestication of blueberries (Vaccinium corymbosum), a crop native to North America, on the performance of two chewing herbivores [the native Sparganothis fruitworm (Sparganothis sulfureana (Clemens)) and non-native gypsy moth (Lymantria dispar L.)], and one piercing-sucking herbivore [the blueberry aphid (Illinoia azaleae (Mason))]. Lymantria dispar performed better (i.e., larvae gained more mass, damaged more leaves, and had greater survival) on cultivated V. corymbosum than on its wild counterpart. In contrast, domestication had no impact on the native S. sulfureana larval mass, consumption, and survivorship. Domestication increased survivorship, but not offspring production, of the aphid I. azaleae. To examine changes in plant chemistry due to domestication, we measured phenolic and nutrient (macro- and micro-elements) content in wild and cultivated V. corymbosum leaves. Although there were no differences in total phenolic content, two compounds were absent, while two were at lower and one at higher concentration in domesticated than in wild plants. Wild V. corymbosum leaves had higher amounts of phosphorus, sulfur, and sodium than cultivated leaves; the opposite was found for aluminum. While our findings provide support for the ‘plant domestication-reduced defense’ hypothesis, the effects of domestication were dependent on feeding modes and adaptations of the herbivores such that the non-native chewing species was more positively affected than the chewing and the piercing-sucking natives.