Birds are islands for parasites

Understanding the mechanisms driving the extraordinary diversification of parasites is a major challenge in evolutionary biology. Co-speciation, one proposed mechanism that could contribute to this diversity is hypothesized to result from allopatric co-divergence of host–parasite populations. We found that island populations of the Galápagos hawk (Buteo galapagoensis) and a parasitic feather louse species (Degeeriella regalis) exhibit patterns of co-divergence across variable temporal and spatial scales. Hawks and lice showed nearly identical population genetic structure across the Galápagos Islands. Hawk population genetic structure is explained by isolation by distance among islands. Louse population structure is best explained by hawk population structure, rather than isolation by distance per se, suggesting that lice tightly track the recent population histories of their hosts. Among hawk individuals, louse populations were also highly structured, suggesting that hosts serve as islands for parasites from an evolutionary perspective. Altogether, we found that host and parasite populations may have responded in the same manner to geographical isolation across spatial scales. Allopatric co-divergence is likely one important mechanism driving the diversification of parasites.     

Trap for tephritid fruit fly parasites

A sticky trap for capturing the adults of tephritid fruit fly parasites was designed. This trap consisted of an outer and inner cylinder made of hardware cloth. Host fruits of fruit flies were placed in the inner cylinder and the outer one was sprayed with tanglefoot. Fruit fly adults and parasites attracted to the fruit were captured on the sticky outer cylinder.     

The genetic toolbox for Leishmania parasites

Leishmania parasites cause a variety of devastating diseases in tropical areas around the world. Due to the lack of vaccines and limited availability of drugs, new therapeutic targets are urgently needed. A variety of genetic tools have been developed to investigate the complex biology of this parasite and its interactions with the host. One of the main techniques is the generation of knock-out parasites via targeted gene replacement, a process that takes advantage of the parasites ability to undergo homologous recombination. Studying the effect of gene deletions in vitro and in infectivity models in vivo allows understanding the function of a target gene and its potential as a therapeutic target. Other genetic manipulations available include episomal and chromosomal complementation and the generation of overproducer strains. However, there are also limitations, such as the lack of RNA interference machinery in most Leishmania species and limited options for inducible expression systems. The genomes of several Leishmania species have now been sequenced and will provide powerful resources in combination with the genetic tools that are available. The increasing knowledge of parasite biology and host parasite interactions derived from these studies will raise the number of potential therapeutic targets, which are sorely needed to combat leishmaniasis.     

Social parasites

Protozoan parasites cause tremendous human suffering worldwide, but strategies for therapeutic intervention are limited. Recent studies illustrate that the paradigm of microbes as social organisms can be brought to bear on questions about parasite biology, transmission and pathogenesis. This review discusses recent work demonstrating adaptation of social behaviors by parasitic protozoa that cause African sleeping sickness and malaria. The recognition of social behavior and cell-cell communication as a ubiquitous property of bacteria has transformed our view of microbiology, but protozoan parasites have not generally been considered in this context. Works discussed illustrate the potential for concepts of sociomicrobiology to provide insight into parasite biology and should stimulate new approaches for thinking about parasites and parasite-host interactions.     

Ultimate parasites

Evolutionary Ecology of Parasites. From Individuals to Communities by Robert Poulin, Chapman & Hall, 1998. £55.00 hbk (x+212 pages) ISBN 0 412 80560 X     

Food webs: a plea for parasites

Parasites have the capacity to regulate host populations and may be important determinants of community structure, yet they are usually neglected in studies of food webs. Parasites can provide much of the information on host biology, such as diet and migration, that is necessary to construct accurate webs. Because many parasites have complex life cycles that involve several different hosts, and often depend on trophic interactions for transmission, parasites provide complementary views of web structure and dynamics. Incorporation of parasites in food webs can substantially after baste web properties, Including connectance, chain length and proportions of top and basal species, and can allow the testing of specific hypotheses related to food-web dynamics.     

A risk assessment for managing non-native parasites

The spread of non-native parasites with the movement of animals is a primary cause of disease emergence worldwide. Such introductions can threaten native biodiversity, hinder conservation efforts and limit the socio-economic development of natural resources. Evaluating the threats from alien parasites can represent a considerable challenge, due to the limited information that often accompanies their introduction. We present a comprehensive modular risk assessment scheme that supports the management of non-native fish parasites in their pre- and post-introduction phases. This scheme addresses some of the shortcomings of current risk analysis, including the risk management of non-notifiable pathogens and impact assessment of parasites following establishment. An initial procedure for hazard identification promotes a rapid assessment of disease risk and prompt imposition of management measures. This is followed by a longer-term assessment of impact that accommodates available and emerging knowledge on the pathogen and its distribution. Consideration is given to ecological and economic consequences of disease at the host, population and fishery levels. Each module provides an easily interpreted output that underpins management responses, ranging from monitoring parasite distribution to their attempted eradication. A final module ensures clear communication of disease risk to relevant stakeholders, using the other modules as a framework. Outputs of this risk assessment will inform the prioritisation of available resources and provides a scientifically robust foundation on which to base practical and proportionate management measures to protect native environments. The scheme presented here was specifically developed for freshwater fisheries in England and Wales, but may be modified for use globally and for the non-native parasite fauna of other taxa.     

Antlers and parasites

Development of ornamental characters exposed to directional selection may be particularly sensitive to the effect of parasitic infections. Antlers are ornamental characters of importance in intraspecific interactions, and are in reindeer (Rangifer) developed by both males and females. By antihelmintic treatment of naturally infected female reindeer we show that parasite intensities affect development of antler asymmetry, but not antler length. These results suggest that asymmetry in antlers may reflect parasite intensities and thus be of importance in intraspecific assessment of genetic resistance towards infectious organisms.     

Genetic engineering of attenuated malaria parasites for vaccination

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Highlights? Genetically attenuated parasites (GAPs) as potential vaccines against malaria. ? Attenuated Plasmodium sporozoites confer sustained sterile immunity against malaria. ? Rodent malaria models are an important in vivo platform to delineate GAP safety and potency. ? Late liver-arresting GAPs elicit superior protective immunity than early arresting parasites. ? P. falciparum GAP vaccine candidates need ultimately to be validated in clinical studies.     

Diversity increases biomass production for trematode parasites in snails

Increasing species diversity typically increases biomass in experimental assemblages. But there is uncertainty concerning the mechanisms of diversity effects and whether experimental findings are relevant to ecological process in nature. Hosts for parasites provide natural, discrete replicates of parasite assemblages. We considered how diversity affects standing-stock biomass for a highly interactive parasite guild: trematode parasitic castrators in snails. In 185 naturally occurring habitat replicates (individual hosts), diverse parasite assemblages had greater biomass than single-species assemblages, including those of their most productive species. Additionally, positive diversity effects strengthened as species segregated along a secondary niche axis (space). The most subordinate species--also the most productive when alone--altered the general positive effect, and was associated with negative diversity effects on biomass. These findings, on a previously unstudied consumer class, extend previous research to illustrate that functional diversity and species identity may generally both explain how diversity influences biomass production in natural assemblages of competing species.     

Sex-specific genetic structure: new trends for dioecious parasites

In dioecious parasite species, genetic structure can differ between sexes, as recently demonstrated for the digenetic trematode Schistosoma mansoni and the ectoparasitic tick Ixodes ricinus. This article presents some of the methods that allow detecting such a pattern in natural populations. The proximate and ultimate factors that potentially generate a sex-specific genetic structure are discussed, as are evolutionary and epidemiological consequences for dioecious parasites and vectors.