When similar beginnings lead to different ends: Constraints and diversity in cirripede larval development

Summary

Cirripedes are fascinating models for studying both functional constraints and diversity in larval development. Adult cirripedes display an amazing variation in morphology from sessile suspension feeders that still retain many crustacean characters to parasites that have lost virtually all arthropod traits. In contrast, cirripede larval development follows a common scheme with pelagic larvae comprising a series of nauplii followed by a cyprid. Variations are mostly concerned with whether or not the nauplii are feeding and the degree of abbreviation of development, culminating in species where the larvae hatch as cyprids. The cypris larvae are very similar among the ingroups of the Cirripedia, but interesting variations occur in structures used for substrate location and attachment. The cyprid is specialized to both swim through the water and actively explore the substratum by walking on the antennules and using an array of sensory organs in search for a suitable site to attach. This unique morphology and behavior of the cyprid have enabled the Cirripedia to colonize widely different habitats ranging from hard rock to soft animal tissue. Yet, the cyprid can metamorphose into juveniles as different as a setose feeding barnacle and the vermiform stages of the parasitic forms. This emphasizes the importance of the cyprid as one of the key features for the evolutionary success of the Cirripedia.     

Intravital microscopy: Imaging host–parasite interactions in the brain

Intravital fluorescence microscopy (IVM) is a powerful technique for imaging multiple organs, including the brain of living mice and rats. It enables the direct visualisation of cells in situ providing a real‐life view of biological processes that in vitro systems cannot. In addition, to the technological advances in microscopy over the last decade, there have been supporting innovations in data storage and analytical packages that enable the visualisation and analysis of large data sets. Here, we review the advantages and limitations of techniques predominantly used for brain IVM, including thinned skull windows, open skull cortical windows, and a miniaturised optical system based on microendoscopic probes that can be inserted into deep tissues. Further, we explore the relevance of these techniques for the field of parasitology. Several protozoan infections are associated with neurological symptoms including Plasmodium spp., Toxoplasma spp., and Trypanosoma spp. IVM has led to crucial findings on these parasite species, which are discussed in detail in this review.     

Histopathological alterations and parasite infection in fish: indicators of multiple stress factors

Within the scope of the multidisciplinaryresearch project Valimar (1995–1999), thepresent study emphasizes the use ofhistopathological investigations to evaluatethe effects of the different chemical impactof two small streams on the general health andcondition of the two sentinel fish species,brown trout (Salmo trutta f.fario) and loach (Barbatula barbatula).Parasitological investigations were alsoincluded to assess a possible relationshipbetween toxicant exposure, parasitic load, andthe occurence of histopathological organchanges. According to the multitiered approachof the Valimar project, fish from the field,individuals exposed to stream water undersemi-field conditions, and fish fromlaboratory experiments were investigated.Under semi-field conditions, thehistopathological responses in brown troutproved to reflect the different levels ofcontamination of the two small streams moreclearly than those detected in loach. Whencaptured from the field, both fish speciesrevealed, in most cases, a higher degree ofhistopathological alterations than thoseindividuals exposed at the respective siteunder semi-field conditions. Simulation of thetoxic load of the more polluted stream in alaboratory experiment did not result in thesame kind of tissue lesions in brown trout asin the field and semi-field investigations.Whereas results from the laboratoryexperiments could be specified astoxicant-induced, the histopathologicalalterations in fish from both semi-field andfield studies represent stress responses whichintegrate the effects of various abiotic andbiotic stress factors including both toxicantsand parasitic diseases.     

Some but not All Tetrahymena Species Destroy Monolayer Cultures of Cells from a Wide Range of Tissues and Species

The activities of Tetrahymena corlissi, Tetrahymena thermophila, and Tetrahymena canadensis were studied in coculture with cell lines of insects, fish, amphibians, and mammals. These ciliates remained viable regardless of the animal cell line partner. All three species could engulf animal cells in suspension. However, if the animal cells were monolayer cultures, the monolayers were obliterated by T. corlissi and T. thermophila. Both fibroblast and epithelial monolayers were destroyed but the destruction of human cell monolayers was done more effectively by T. thermophila. By contrast, T. canadensis was unable to destroy any monolayer. At 4 °C T. thermophila and T. corlissi did not carryout phagocytosis and did not destroy monolayers, whereas T. canadensis was able to carryout phagocytosis but still could not destroy monolayers. Therefore, monolayer destruction appeared to require phagocytosis, but by itself this was insufficient. In addition, the ciliates expressed a unique swimming behavior. Tetrahymena corlissi and T. thermophila swam vigorously and repeatedly into the monolayer, which seemed to loosen or dislodge cells, whereas T. canadensis swam above the monolayer. Therefore, differences in swimming behavior might explain why T. corlissi has been reported to be a pathogen but T. canadensis has not.     

Noninvasive Assessment of Gastrointestinal Parasite Infections in Free-Ranging Primates

Recent evidence of emerging human diseases with origins or likely transmission to humans, or both, that involve primates and a greater recognition of the risk of human pathogen transmission to free-ranging primates have raised awareness of the potential impact of zoonotic pathogen transmission on primate conservation and nonhuman primate and human health. As human population density continues to increase exponentially, speeding the reduction and fragmentation of primate habitats, greater human-primate contact is inevitable and even higher rates of pathogen transmission are likely. Thus interest has grown in collecting baseline data on patterns of parasitic infections in wild primate populations to provide an index of population health and to begin to assess and, to manage disease risks. Primatologists traditionally have been involved with such surveys through noninvasive assessment of gastrointestinal parasites. Unfortunately, previous studies have tended toward divergent methodologies, compromising the potential for longitudinal and comparative work. Here, I provide practical guidelines and standardized methodologies for the noninvasive assessment of gastrointestinal parasites of primates.

Gut microbiota instead of host genotype drive the specificity in the interaction of a natural host-parasite system

Specific interactions between parasite genotypes and host genotypes (G_p × G_h) are commonly found in invertebrate systems, but are largely lacking a mechanistic explanation. The genotype of invertebrate hosts can be complemented by the genomes of microorganisms living on or within the host (‘microbiota’). We investigated whether the bacterial gut microbiota of bumble bees (Bombus terrestris) can account for the specificity of interactions between individuals from different colonies (previously taken as host genotype proxy) and genotypes of the parasite Crithidia bombi. For this, we transplanted the microbiota between individuals of six colonies. Both the general infection load and the specific success of different C. bombi genotypes were mostly driven by the microbiota, rather than by worker genotype. Variation in gut microbiota can therefore be responsible for specific immune phenotypes and the evolution of gut parasites may be driven by interactions with ‘microbiota types’ as well as with host genotypes.     

‘Big data’ from shrinking pathogen populations

Falling costs for genome sequencing and genotyping mean that population genomic data sets are becoming commonplace for a wide variety of species. Once these data are used for the initial tasks of investigating population structure and demographic history, however, is there reason to go back for more? In this issue of Molecular Ecology, Nkhoma et al. (2013) explore the applications of longitudinal genomic diversity data for detecting changes in the prevalence and transmission of the Plasmodium falciparum malaria parasite in South‐East Asia. While this study finds several genetic signatures indicative of reduced disease transmission, other measures, such as short‐term effective population size, geographical population structure and heterozygosity, were not informative. These results indicate the potential contribution of genomic data to the surveillance of small, dynamic populations, whether they are at risk of extinction or targeted for elimination. The interpretation of such data will require close consideration of biological context, however, at both the species and the population level.