Zoogeography of marine parasites

Latitudinal gradients in species numbers of marine parasites, differences between the Atlantic and Indo-Pacific Oceans, latitudinal gradients in frequency and intensity of infection, in host range and specificity, and in fluctuations of infection are discussed, as well as differences between shallow and deep water, parasite endemicity at remote oceanic islands, and importance of temperature for parasite distribution. Examples are given to demonstrate the usefulness of marine parasites as biological tags and as indicators of the geographical origin of hosts.     

Parasites as biological tags for stock discrimination in marine fish from South American Atlantic waters

The use of parasites as biological tags in population studies of marine fish in the south-western Atlantic has proved to be a successful tool for discriminating stocks for all species to which it has been applied, namely: Scomber japonicus, Engraulis anchoita, Merluccius hubbsi and Cynoscion guatucupa, the latter studied on a broader geographic scale, including samples from Uruguayan and Brazilian waters. The distribution patterns of marine parasites are determined mainly by temperature-salinity profiles and by their association with specific masses of water. Analyses of distribution patterns of some parasite species in relation to gradients in environmental (oceanographic) conditions showed that latitudinal gradients in parasite distribution are common in the study area, and are probably directly related to water temperature. Indeed, temperature, which is a good predictor of latitudinal gradients of richness and diversity of species, shows a latitudinal pattern in south-western Atlantic coasts, decreasing southwards, due to the influence of subtropical and subantarctic marine currents flowing along the edge of the continental slope. This pattern also determines the distribution of zooplankton, with a characteristic specific composition in different water masses. The gradient in the distribution of parasites determines differential compositions of their communities at different latitudes, which makes possible the identification of different stocks of their fish hosts. Other features of the host-parasite systems contributing to the success of the parasitological method are: (1) parasites identified as good biological tags (i.e. anisakids) are widely distributed in the local fauna; (2) many of these species show low specificity and use paratenic hosts; and (3) the structure of parasite communities are, to a certain degree, predictable in time and space.     

海洋动物档案式标志及其定位方法研究进展

档案式标志是一种可存储数据档案的电子标志,应用于水生动物尤其是大洋高度洄游性鱼类的研究,是获取海洋动物长时间、大空间尺度的活动信息和环境数据的有力工具.自20世纪90年代以来,档案式标志被大量用于海洋动物研究,取得了一系列成果,其不足之处在于需要回收标志来获取采样数据.90年代末,分离式卫星档案标志的问世解决了数据回收的问题,不再依赖于渔业捕捞,扩展了海洋动物研究的广度和深度.基于光亮度定位是研究海洋动物洄游路线的关键,其重点在于匹配光亮度与特定天顶角(如日出、日落),有3种方法：固定参照法、可变参照法和映射法.在过去的20年内,光亮度定位方法有所发展,并取得了一定的成果,但纬度向的定位还不够精确,有继续发展的空间.本文还总结了档案式标志定位的现存问题,展望了档案式标志及其定位方法的研究方向,并认为存在档案式标志小型化和传感器集成化、定位方法由单一光亮度反演向多因子反演的趋势.     

Recombinant protein expression and purification: a comprehensive review of affinity tags and microbial applications

Protein fusion tags are indispensible tools used to improve recombinant protein expression yields, enable protein purification, and accelerate the characterization of protein structure and function. Solubility-enhancing tags, genetically engineered epitopes, and recombinant endoproteases have resulted in a versatile array of combinatorial elements that facilitate protein detection and purification in microbial hosts. In this comprehensive review, we evaluate the most frequently used solubility-enhancing and affinity tags. Furthermore, we provide summaries of well-characterized purification strategies that have been used to increase product yields and have widespread application in many areas of biotechnology including drug discovery, therapeutics, and pharmacology. This review serves as an excellent literature reference for those working on protein fusion tags.     

Local variability in metazoan parasites of the pelagic fish species, Engraulis ringens: implications for fish stock assessment using parasites as biological tags

Parasites have been used successfully as biological tags in population studies, mainly in marine fishes, but also in marine mammals, crustaceans and molluscs. Almost all published information dealing with parasites as biological tags evaluates differences between localities. However, local variability in the component community has not been assessed. In this work, we examined whether local variation of the metazoan parasite fauna of Engraulis ringens, extracted from five independent samples from two nearby localities in northern Chile, can be a factor causing bias in stock identification. Our results show that local variability, as estimated by a single sample, may suffice to represent component community variability with no need for replicated data.     

Local adaptation in host use among marine invertebrates

The study of interactions between small invertebrates and their larger plant and animal hosts has a long tradition. One persistent theme within this literature is that spatially‐segregated populations of terrestrial and freshwater invertebrates commonly adapt to local hosts across their geographic ranges. Marine examples are rare, which leaves the impression that marine populations are less likely to adapt to locally abundant hosts and more likely to evolve generalized or phenotypically‐plastic strategies. Here, I review a short but growing list of marine invertebrates that appear to display local adaptation in host use. As expected, most of the marine examples are brooded animals with weak dispersal potential. However, some species with pelagically dispersed larvae have apparently adapted to local hosts. This surprising result is consistent with recent evidence that pelagically‐dispersed larvae are not always broadly dispersed, that strong selective pressures maintain local differences in host use, or both. The presence of host‐mediated adaptation in the sea alters predictions on how marine communities respond to disturbance, supports the notion that marine consumer‐prey interactions can coevolve, and indicates that hosts play fundamental roles in the differentiation and perhaps speciation of small marine invertebrates.     

The Gut Bacterial Community of Mammals from Marine and Terrestrial Habitats

After birth, mammals acquire a community of bacteria in their gastro-intestinal tract, which harvests energy and provides nutrients for the host. Comparative studies of numerous terrestrial mammal hosts have identified host phylogeny, diet and gut morphology as primary drivers of the gut bacterial community composition. To date, marine mammals have been excluded from these comparative studies, yet they represent distinct examples of evolutionary history, diet and lifestyle traits. To provide an updated understanding of the gut bacterial community of mammals, we compared bacterial 16S rRNA gene sequence data generated from faecal material of 151 marine and terrestrial mammal hosts. This included 42 hosts from a marine habitat. When compared to terrestrial mammals, marine mammals clustered separately and displayed a significantly greater average relative abundance of the phylum Fusobacteria. The marine carnivores (Antarctic and Arctic seals) and the marine herbivore (dugong) possessed significantly richer gut bacterial community than terrestrial carnivores and terrestrial herbivores, respectively. This suggests that evolutionary history and dietary items specific to the marine environment may have resulted in a gut bacterial community distinct to that identified in terrestrial mammals. Finally we hypothesize that reduced marine trophic webs, whereby marine carnivores (and herbivores) feed directly on lower trophic levels, may expose this group to high levels of secondary metabolites and influence gut microbial community richness.     

Experimental transmission of Enteromyxum leei to freshwater fish

The myxosporean Enteromyxum leei is known to infect a wide range of marine fish hosts. The objective of the present study was to determine whether freshwater fish species are also receptive hosts to this parasite. Seventeen species of freshwater fish were experimentally fed E. leei-infected gut tissue from donor gilthead sea bream Sparus aurata obtained from a commercial sea bream cage farm. Four of the tested species, tiger barb Puntius tetrazona, zebra danio Danio rerio, oscar Astronotus ocellatus and Mozambique tilapia Oreochromis mossambicus, were found to be susceptible with prevalences ranging from 53 to 90%. The course of infection and pathology was limited to the gut mucosa epithelium and was similar to that observed in marine hosts. Little is known of the differences in physiological conditions encountered by a parasite in the alimentary tract of freshwater vs. marine teleost hosts, but we assume that a similar osmotic environment is maintained in both. Parasite infectivity may be influenced by differences in the presence or absence of a true stomach, acidic gastric pH and digestive enzyme activity both in the stomach and intestine. Variability in susceptibility among species may also stem from differences in innate immunity. Dimensions of spores produced in the donor sea bream and recipient freshwater species are variable in size, as previously observed in other captive marine host species.     

Approaches to studying climatic change and its role on the habitat selection of antarctic pinnipeds

Top predators integrate resources over time and space, and depending on the particular species they represent, different components of the marine environment. The habitat utilization of top predators has been studied using electronic tags to follow their movements and foraging behavior. In addition, these tags provide information on the physical characteristics of the water column (temperature and salinity) at a scale and resolution that is coincident with the animals' behavior. In addition to data on the animals' behavior, these tags provide physical oceanographic data in regions or at times they cannot be collected using other currently available technologies. These data inform us on how these important top predators are likely to respond to climatic change, as well as about how the Southern Ocean is changing.     

The phylogeny of the Gregarinia (Sporozoa)

The Gregarinia, all parasitic in invertebrates have appeared in marine hosts (Polychaeta). The most primitive are the Archigregarinida (Selenidium) which are intestinal parasites. The Eugreganida (intestinal or coelomic) are found in various marine invertebrates as well as in terrestrial or fresh water arthropods. The Neogregarinida which parasitize only insects have a very reduced number of spores compensated by a schizogony (merogony). The Gregarinia constitute a perfect example of a concomitant evolution between a group of parasites and their hosts.     

Mobile receivers: releasing the mooring to ‘see’ where fish go

Much has been learned from the large scale deployment of acoustic tags on aquatic species and associated networks of riverine and marine receivers. While effective in the linear environment of river systems, marine systems limit the ability to provide spatial information on fish movements and distributions due to a combination of costs, logistics, and lack of off-shore technology. At the same time, each year millions of dollars worth of tags are being released into the aquatic environment with extended battery/transmission life, yet detections are limited to coastal arrays. Here we explore new methods of tracking acoustically tagged species in the marine environment. A new miniaturized acoustic receiver, the Vemco Mobile Transceiver (VMT) can be carried by large marine organisms. In combination with satellite and archival tag technology, VMTs were deployed on northern elephant seals to monitor acoustic tags encountered during their migrations across the Northeast Pacific. Early results include acoustic detections of tagged great white sharks, salmon sharks, Chinook salmon, steelhead, lingcod, green sturgeon and other elephant seals. We also propose several alternative directions for future effort: 1) analyzing the growing number of passive acoustic survey recordings made from hydrophone arrays for acoustic tag detections, 2) working with acoustic technology providers to develop hull-mounted receiver systems for the thousands of ocean going vessels around the world and 3) integrating acoustic receiver technology into the thousands of moored and drifting oceanographic buoy arrays.     

Crepidula fornicata is not a first intermediate host for trematodes: who is?

Trematode larvae must generally invade a molluscan intermediate host, usually a gastropod, before they can reach reproductive maturity in another definitive host. The research literature to date has focused almost exclusively on the documented specificity between particular trematode species and particular molluscan hosts; little attention has been paid to gastropod species that do not appear to serve as hosts. We sampled Rhode Island and Massachusetts populations of the marine gastropod Crepidula fornicata to determine whether this widespread species serves as a first intermediate host for trematodes. We also sampled from the same habitat populations of Littorina littorea and Ilyanassa obsoleta, gastropods known to serve as first intermediate hosts for several trematode species. All individuals were examined by dissection for the presence of sporocysts, rediae, or developing cercariae. Although 4-28% of L. littorea (N=112) and I. obsoleta (N=84) were infected by larvae of at least one trematode species, no individuals of C. fornicata sampled from the same locations were so infected (N=136). A survey of the Biological Abstracts computer database indicates that snails in only about 10% of marine gastropod families are known to serve as first intermediate hosts for trematodes. We suggest that more attention be paid to marine gastropods that appear not to be infected by trematode miracidia. Such species may productively serve as new models for understanding trematode host specificity and gastropod resistance to infection.     

Pathogenic fungi of marine animals: A taxonomic perspective

Fungi cause diseases in a variety of marine animal hosts. After a thorough review of published literature, we identified 225 fungal species causing infections of 193 animal species, for a total of 357 combinations of pathogenic fungi and marine animal hosts. Among the 193 animal host species, Chordata (100 species, 51.8 %) and Arthropoda (68 species, 35.2 %) were discovered to be the most frequently reported hosts of fungal pathogens. Microsporidia (111 species, 49.3 %) constitutes over half of the described pathogenic fungal species of marine animals, followed by Ascomycota (85 species, 37.8 %), Mucoromycota (22 species, 9.8 %), Basidiomycota (6 species, 2.7 %) and Chytridiomycota (1 species, 0.4 %). Microsporidia primarily parasitize marine arthropods and Teleostei fish, while Basidiomycota are primarily known to cause respiratory diseases of marine mammals. Ascomycota has a diverse host range, from mammals, fish, crustaceans, soft corals and sea turtle. Few Mucoromycota and Chytridiomycota were reported to infect marine animals. Fungal diseases documented in this review likely represent a fraction of fungal diseases in the ocean, where it was estimated to be inhabited by 2.15 million animal species. Intensification of aquaculture practices, global warming and marine pollution may increase fungal disease outbreak of marine animals. All the topics mentioned above will be discussed in greater details in this review.     

Marine parasites: an Australian perspective

A review is given of major studies in marine parasitology in Australia. Aspects discussed include: geographical distribution of parasites in Australian coastal waters and their affinities to parasites of other zoogeographical regions; species diversity in Australian coastal surface and deep waters; use of marine parasites for stock discrimination; use of marine parasites as ecological models; ultrastructural and phylogenetic studies of marine parasites; and effects of marine parasites on their hosts.     

Integrating fish and parasite data as a holistic solution for identifying the elusive stock structure of Pacific sardines (Sardinops sagax)

There is an urgent need to clarify how different stocks, or subpopulations of fish species, are vulnerable to fishing pressure and unfavorable ocean conditions because of the increasing demand on fisheries for human consumption. For marine fishes, the potential for high gene flow increases the difficulty in determining the number of subpopulations managed in a specific fishery. Although the use of molecular data has become a common method in the past 15 years to identify fish subpopulations, no single technique or suite of techniques has been established for fish stock structure studies. We review the use of fish morphometrics, artificial tags, fish genetics, parasite genetics, and parasites as biological tags to identify subpopulations of marine fishes with a focus on the Pacific sardine (Sardinops sagax) fishery off the west coast of North America. We suggest an integration of fish- and parasite-based techniques for future stock structure studies, particularly for pelagic fish species whose stock structure can be elusive. An integration of techniques may also resolve fish stock structure over small geographic areas by increasing the number of spatial and temporal scales studied simultaneously leading to methods for successful management of marine fish species.     

Natural experiments and long-term monitoring are critical to understand and predict marine host–microbe ecology and evolution

Marine multicellular organisms host a diverse collection of bacteria, archaea, microbial eukaryotes, and viruses that form their microbiome. Such host-associated microbes can significantly influence the host’s physiological capacities; however, the identity and functional role(s) of key members of the microbiome (“core microbiome”) in most marine hosts coexisting in natural settings remain obscure. Also unclear is how dynamic interactions between hosts and the immense standing pool of microbial genetic variation will affect marine ecosystems’ capacity to adjust to environmental changes. Here, we argue that significantly advancing our understanding of how host-associated microbes shape marine hosts’ plastic and adaptive responses to environmental change requires (i) recognizing that individual host–microbe systems do not exist in an ecological or evolutionary vacuum and (ii) expanding the field toward long-term, multidisciplinary research on entire communities of hosts and microbes. Natural experiments, such as time-calibrated geological events associated with well-characterized environmental gradients, provide unique ecological and evolutionary contexts to address this challenge. We focus here particularly on mutualistic interactions between hosts and microbes, but note that many of the same lessons and approaches would apply to other types of interactions.

This Essay argues that in order to truly understand how marine hosts benefit from the immense diversity of microbes, we need to expand towards long-term, multi-disciplinary research focussing on few areas of the world’s ocean that we refer to as “natural experiments,” where processes can be studied at scales that far exceed those captured in laboratory experiments.     

Using CRISPRs as a metagenomic tool to identify microbial hosts of a diffuse flow hydrothermal vent viral assemblage

Metagenomic analyses of viruses have revealed widespread diversity in the viriosphere, but it remains a challenge to identify specific hosts for a viral assemblage. To address this problem, we analyze the viral metagenome of a northeast Pacific hydrothermal vent with a comprehensive database of spacers derived from the clustered regularly interspaced short palindromic repeat (CRISPR) putative immune system. CRISPR spacer matches to the marine vent virome suggest that viruses infecting hosts from diverse taxonomic groups are present in this vent environment. Comparative virome analyses show that CRISPR spacers from vent isolates and from thermophiles in general have a higher percentage of matches to the vent virome than to other marine or terrestrial hot spring viromes. However, a high percentage of hits to spacers from mesophilic hosts, combined with a moderately high modeled alpha diversity, suggest that the marine vent virome is comprised of viruses that have the potential to infect diverse taxonomic groups of multiple thermal regimes in both the bacterial and the archaeal domains.     

Structural and biochemical insights into His-tag-induced higher-order oligomerization of membrane proteins by cryo-EM and size exclusion chromatography

Structural and functional characterization of proteins as well as the design of targeted drugs heavily rely on recombinant protein expression and purification. The polyhistidine-tag (His-tag) is among the most prominent examples of affinity tags used for the isolation of recombinant proteins from their expression hosts. Short peptide tags are commonly considered not to interfere with the structure of the tagged protein and tag removal is frequently neglected. This study demonstrates the formation of higher-order oligomers based on the example of two His-tagged membrane proteins, the dimeric arginine-agmatine antiporter AdiC and the pentameric light-driven proton pump proteorhodopsin. Size exclusion chromatography revealed the formation of tetrameric AdiC and decameric as well as pentadecameric proteorhodopsin through specific interactions between their His-tags. In addition, single particle cryo-electron microscopy (cryo-EM) allowed structural insights into the three-dimensional arrangement of the higher-order oligomers and the underlying His-tag-mediated interactions. These results reinforce the importance of considering the length and removal of affinity purification tags and illustrate how neglect can lead to potential interference with downstream biophysical or biochemical characterization of the target protein.