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Among the many Callinectes spp. across the western Atlantic, the blue crab C. sapidus has the broadest latitudinal distribution, encompassing both tropical and temperate climates. Its life history varies latitudinally, from extended overwintering at high latitudes to year-round activity in tropical locations. Callinectes sapidus reovirus 1 (CsRV1) is a pathogenic virus first described in North Atlantic C. sapidus and has recently been detected in southern Brazil. Little information exists about CsRV1 prevalence at intervening latitudes or in overwintering blue crabs. Using a quantitative reverse transcription PCR (RT-qPCR) method, this study investigated CsRV1 prevalence in C. sapidus across latitudinal differences in temperature and crab life history, as well as in additional Callinectes spp. and within overwintering C. sapidus. CsRV1 prevalence in C. sapidus was significantly correlated with high water temperature and blue crab winter dormancy. Prevalence of CsRV1 in C. sapidus on the mid-Atlantic coast was significantly lower in winter than in summer. CsRV1 infections were not detected in other Callinectes spp. These findings revealed that CsRV1 is present in C. sapidus across their range, but not in other Callinectes species, with prevalence associated with temperature and host life history. Such information helps us to better understand the underlying mechanisms that drive marine virus dynamics under changing environmental conditions.

The amphipod Dikerogammarus haemobaphes is a high-risk carrier of parasites that impact wildlife in its non-native range. Studies using the mitochondrial genes, Cytochrome Oxidase Sub-Unit 1 (cox1) and small-subunit ribosomal RNA gene (16S), provide some nucleotide detail for understanding the evolution and phylogeography of this species. Despite this, the origins of the invasion remain unknown, as do the origins of its parasites. This study provides the full annotated mitochondrial genome (15,460 bp) of D. haemobaphes, consisting of 2 rRNAs, 24 tRNAs and 14 protein coding genes. Mitochondrial genes from the UK isolate are compared to existing data on NCBI and are used in a concatenated phylogenetic approach and identify D. haemobaphes as an early member of the Gammaridae (Amphipoda). Viral, bacterial, protistan and microsporidian parasites are present across the Gammaridae, including D. haemobaphes, suggesting the ancestor of the Gammaridae harboured related diseases, and that further screening of amphipods is likely to reveal further microparasite diversity. This correlation suggests that other gammarid invaders have the potential to harbour a range of microparasites. The mitochondrial genome of this species will act a resource to facilitate our understanding of geneflow, disease epidemiology and evolutionary history in this invasion-disease model.

Crustaceans suffer from diseases that can alter their survival and ecology with additional economic consequences for fisheries and aquaculture. Many parasites have been described from crustaceans and with the advent of novel technologies such as next generation sequencing, the discovery of novel parasites has become increasingly efficient. Molecular techniques are beginning to surpass more conventional tools for parasite discovery, but they typically do not provide information on pathology. Histopathology remains one of the least expensive methods for parasite discovery and allows for both detection of parasites and descriptions of the pathology they cause. When used in concert with modern molecular and electron microscopy techniques, the approach is powerful; however, there are few informational tools for the interpretation of histological slides from crustaceans. Those available do not provide comprehensive images of all organs and early works were limited to lower resolution than currently available. More recent texts provide in-depth details of infection in histological section, but few provide images of healthy material or describe a baseline from which to compare. Here, we provide a series of image plates derived from histologically processed tissues from three palinurid lobsters: Panulirus argus, Palinurus elephas and Panulirus guttatus. Histology from these lobsters shows high visual similarity in all tissue types. We provide a histological atlas of healthy tissue that can be used as a baseline resource for pathobiologists working on these common species (and related crustaceans) and we discuss how disease may result in visual aberrations to these tissues.

The Caribbean spiny lobster Panulirus argus is susceptible to infection by Panulirus argus Virus 1 (PaV1), the only virus known to naturally infect any lobster species. However, P. argus is able to mitigate PaV1 transmission risk by avoiding infected individuals. White Spot Syndrome Virus (WSSV) has a particularly wide host range. WSSV has not been documented in wild populations of spiny lobsters, but has been experimentally transmitted to six other lobster species from the genus Panulirus spp. While WSSV has been detected intermittently in wild populations of shrimp in the Caribbean region, the risk to P. argus has not been evaluated. Potential emergence of the disease could result in fisheries losses and ecological disruption. To assess the risk to P. argus, we tested its susceptibility to WSSV via injection and waterborne transmission. We also tested whether healthy lobsters can detect and avoid conspecifics with qPCR-quantifiable WSSV infections. We found P. argus to be highly susceptible to WSSV via intramuscular injection, with mortality reaching 88% four weeks post inoculation. Panulirus argus was also susceptible to WSSV via waterborne transmission, but WSSV burden was low after four weeks via qPCR. Behavioral assays indicated that P. argus can detect and avoid conspecifics infected with WSSV and the avoidance response was strongest for the most heavily infected individuals – a response comparable to PaV1-infected conspecifics. Panulirus argus is the first spiny lobster found to be susceptible to WSSV in the Americas, but it is possible that a generalized avoidance response by healthy lobsters against infected conspecifics provides a behavioral defense and may reduce WSSV infection potential and prevalence. Such avoidance may extend to other directly transmitted pathogens in spiny lobster populations preventing them from becoming common in their population.Author SummaryErica P. Ross is a PhD candidate at the University of Florida, studying the disease ecology of the Caribbean spiny lobster, with a focus on chemosensory ecology. Donald C. Behringer is an associate professor at the University of Florida and his research focuses on disease ecology, epidemiology, and fishery ecology, with a focus on crustaceans and other marine invertebrates. Jamie Bojko received his PhD from the University of Leeds and is currently a post-doctorate associate at the University of Florida studying experimental and systemic crustacean pathology.

Invasive crayfish and the introduction of non-native diseases pose a significant risk for the conservation of endangered, white-clawed crayfish (Austropotamobius pallipes). Continued pollution of waterways is also of concern for native species and may be linked with crayfish disease dynamics. We explore whether crayfish species or environmental quality are predictors of infection presence and prevalence in native A. pallipes and invasive signal crayfish (Pacifastacus leniusculus). We use a seven-year dataset of histology records, and a field survey comparing the presence and prevalence of infectious agents in three isolated A. pallipes populations; three isolated P. leniusculus populations, and three populations where the two species had overlapped in the past. We note a lower diversity of parasites (Simpson’s Index) in P. leniusculus (‘Pacifastacus leniusculus Bacilliform Virus’ - PlBV) (n = 1 parasite) relative to native A. pallipes (n = 4 parasites), which host Thelohania contejeani, ‘Austropotamobius pallipes bacilliform virus’ (ApBV), Psorospermium haeckeli and Branchiobdella astaci, at the sites studied. The infectious group present in both species was an intranuclear bacilliform virus of the hepatopancreas. The prevalence of A. astaci in A. pallipes populations was higher in more polluted water bodies, which may reflect an effect of water quality, or may be due to increased chance of transmission from nearby P. leniusculus, a species commonly found in poor quality habitats.

Jennings, Lucas A., Bojko, Jamie, Rotjan, Randi D., Behringer, Donald C. (2021): Cirolana westbyi, (Isopoda: Cirolanidae) a new species in the 'Cirolana parva-group' from the Turneffe Atoll, Belize. Journal of Natural History 54 (31-32): 2053-2069, DOI: 10.1080/00222933.2020.1837273, URL: http://dx.doi.org/10.1080/00222933.2020.1837273

The blue crab Callinectes sapidus is one of the most widely studied marine crustaceans due to its high economic value and ecological significance. Despite extensive research on the blue crab in North America, many questions remain about the distribution and abundance of the species in the subtropics and tropics. In many places, C. sapidus is sympatric with morphologically similar Callinectes spp., which has implications for seafood mislabeling. To enable rapid identification of the species, we designed and tested two PCR-based assays targeting the 12S rRNA mitochondrial gene. The first assay discriminates C. sapidus from other Callinectes spp. via post-PCR restriction digestion (PCR-RFLP) and the second assay discriminates among multiple Callinectes spp. through High Resolution Melting (HRM) analysis and supervised machine learning analyses. A total of 58 DNA samples from five Callinectes spp. (validated via 12S gene sequencing) were used for assay testing. The PCR RFLP assay was 100% accurate identifying C. sapidus from other Callinectes spp. HRM analysis of amplicons showed good discrimination among species, with distinct clusters formed between species with higher sequence homology. Linear discriminant analysis (LDA) classification of HRM curves was quite successful given the small dataset available, producing ~90-91% mean accuracy in classification over all species with 100-fold cross validation. Much of the error came from misclassifications between C. similis and C. danae, which are ~99% similar in sequence for the amplicon; collapsing them into a single class increased overall classification success to 94%. Error also arose from C. bocourti classifications, which had a reference set containing only three samples. Classification accuracy of C. sapidus alone via HRM was 97.5%. Overall, these assays show great promise as rapid and inexpensive methods to identify Callinectes spp. and have application for both ecological research and seafood identification or labeling.

Invasive non-native species (INNS) pose a risk as vectors of parasitic organisms (Invasive Parasites). Introducing invasive parasites can result in ecological disturbances, leading to biodiversity loss and native species illness/mortality, but occasionally can control INNS limiting their impact. Risks to human health and the economy are also associated with INNS and invasive parasites; however, we understand little about the diversity of symbiotic organisms co-invading alongside INNS. This lack of clarity is an important aspect of the ‘One Health’ prerogative, which aims to bridge the gap between human, wildlife, and ecosystem health. To explore symbiont diversity associated with the invasive crustacean group (including: crab, lobster, crayfish, shrimp, amphipod, isopod, copepod, barnacle, other) (n = 323) derived from 1054 aquatic invertebrates classed as INNS across databases, we compile literature (year range 1800–2017) from the native and invasive range to provide a cumulative symbiont profile for each species. Our search indicated that 31.2% of INN crustaceans were known to hold at least one symbiont, whereby the remaining 68.8% had no documented symbionts. The symbiont list mostly consisted of helminths (27% of the known diversity) and protists (23% of the known diversity), followed by bacteria (12%) and microsporidians (12%). Carcinus maenas, the globally invasive and extremely well-studied green crab, harboured the greatest number of symbionts (n = 72). Additional screening is imperative to become more informed on invasive symbiont threats. We reveal that few studies provide truly empirical data that connect biodiversity loss with invasive parasites and suggest that dedicated studies on available systems will help to provide vital case studies. Despite the lack of empirical data, co-invasive parasites of invasive invertebrates appear capable of lowering local biodiversity, especially by causing behavioural change and mortality in native species. Alternatively, several invasive parasites appear to protect ecosystems by controlling the impact and population size of their invasive host. We provide a protocol that could be followed to explore symbiont diversity in invasive groups as part of our case studies. The consequence of limited parasite screening of INNS, in addition to the impacts invasive parasites impart on local ecologies, are explored throughout the review. We conclude in strong support of the ‘One Health’ prerogative and further identify a need to better explore disease in invasion systems, many of which are accountable for economic, human health and ecological diversity impacts.

Littorina saxatilis is a common intertidal gastropod on shores of the North Atlantic, and an 24 important study species for evolutionary investigations. Its congener L. arcana is much less 25 widely distributed, but both species are common at Old Peak, Yorkshire, UK. The parasite 26 profiles of L. saxatilis and L. arcana from this shore were determined histologically, revealing 27 a ciliated protist, Protophrya ovicola, an unidentified apicomplexan (present in

Crayfish are a vital ecological asset in their native range but can be highly damaging as invasive species. Knowledge of their diseases, including high levels of research on Aphanomyces astaci (crayfish plague), show that disease plays a vital role during crayfish invasions. Microsporidian diseases in crayfish are less studied but are thought to have important links to crayfish health and invasion dynamics. In this study we provide a systematic description of a novel microsporidian parasite from the Floridian crayfish, Procambarus paeninsulanus, with additional genetic identification from related Microsporidia from Procambarus fallax, Cambarellus shufeldtii and Cambarellus blacki. This novel microsporidium from P. paeninsulanus is described in a new genus, Cambaraspora, and species, Cambaraspora floridanus, and represents a novel member of the Clade V Microsporidia within the Glugeidae. The parasite develops in the muscle tissue of P. paeninsulanus, within a sporophorous vesicle, and produces a spore with 19–21 turns of the polar filament measuring 6.136 ± 0.84 µm in length and 2.12 ± 0.23 µm in width. The muscle-infecting nature of the parasite suggests that it is horizontally transmitted. Genetic data for the 18S of the parasite from all hosts confirms its assignment to Clade V and reveal it to be a relative of multiple fish-infecting parasites. It shows closest genetic relationship to Glugea plecoglossi, but branches alongside multiple microsporidia from fish, crustaceans and eDNA isolates. The information presented here suggests that this novel parasite may have the potential to infect piscine hosts and is a likely mortality driver in the P. paeninsulanus population. Its potential as a control agent or wildlife disease invasion threat is explored, as well as the placement of this novel microsporidium within the Glugeidae.

co-auteur étranger; International audience; The Trematoda are a group of phylogenetically diverse metazoan parasites that exhibit complex life cycles that often pass through invertebrate and vertebrate hosts. Some trematodes influence their host's behaviour to benefit transmission. Their parasitic influence may impact host population size by inhibiting an individual's reproductive capacity. We assessed the impact of infection by Podocotyle atomon on the reproductive behaviour and fecundity of its amphipod intermediate host, Gammarus zaddachi, using laboratory and field studies. Parasite prevalence was high in the field, with males more likely to be infected (prevalence in males 64%, in females 39%). Males also suffered a higher parasite burden than females. Infected females were less active, but we found no evidence for a reduction in female reproductive success. Infected females also had comparable pairing success to uninfected females. In males, infection reduced survival and fecundity, with mortality being highest, and sperm numbers lowest, in heavily infected individuals. Trematode parasites are sometimes associated with altered host fecundity, but studies often lack the relevant experimental data to explore the evolution of the trait. We discuss this among information specific to the effect of P. atomon infection in G. zaddachi.

A positive, single-stranded RNA virus is identified from the transcriptome of Probopyrinella latreuticola Gissler, 1882; a bopyrid isopod parasite of the Sargassum shrimp, Latreutes fucorum Fabricius, 1789. The viral sequence is 13,098 bp in length (including polyA), encoding four open reading frames (ORF). ORF-1 encodes a polyprotein, with three computationally discernible functional domains: viral methyltransferase; viral helicase; and RNA-directed RNA polymerase. The remaining ORFs encode a transmembrane protein, a capsid protein and a protein of undetermined function. The raw transcriptomic data reveal a low level of background single nucleotide mutations within the data. Comparison of the protein sequence data and synteny with other viral isolates reveals that the greatest protein similarity (39%) is shared with the Negevirus group, a group that exclusively infects insects. Phylogenetic assessment of the individual polyprotein domains revealed a mixed prediction of phylogenetic origins, suggesting with low confidence that the novel +ssRNA virus could be present in multiple places throughout the individual gene trees. A concatenated approach strongly suggested that this new virus is an early diverging isolate, branching before the Negevirus and Cilevirus groups. Alongside the new isolate are other marine viruses, also present toward the base of the tree. The isopod virosphere, with the addition of this novel virus, is discussed relative to viral genomics/systematics. A great diversity of nege-like viruses appears to be present in marine invertebrate hosts, which require greater efforts for discovery and identification.

Ovipleistophora diplostomuri (Microsporidia) is an obligate parasite of fish and trematodes in the US. In April 2019, an individual crayfish, Procambarus bivittatus (Escambia River, Florida), with a high-intensity microsporidian infection was delivered to the Emerging Pathogens Institute. Histological analysis determined that infection was restricted to the muscle tissue. Molecular diagnostics (PCR) provided 952 bp of the parasite SSU (18S) sequence. The isolate was 99.16% similar to O. diplostomuri identified from blue gill and their trematode parasites in Washington, USA. This discovery increases our understanding of Microsporidia within aquatic trophic networks, supporting the theory that the Ovipleistophora share complex relationships with vertebrates, invertebrates and helminth parasites.

Parasites, including macroparasites, protists, fungi, bacteria and viruses, can impose a heavy burden upon host animals. However, hosts are not without defences. One aspect of host defence, behavioural avoidance, has been studied in the terrestrial realm for over 50 years, but was first reported from the aquatic environment approximately 20 years ago. Evidence has mounted on the importance of parasite avoidance behaviours and it is increasingly apparent that there are core similarities in the function and benefit of this defence mechanism between terrestrial and aquatic systems. However, there are also stark differences driven by the unique biotic and abiotic characteristics of terrestrial and aquatic (marine and freshwater) environments. Here, we review avoidance behaviours in a comparative framework and highlight the characteristics of each environment that drive differences in the suite of mechanisms and cues that animals use to avoid parasites. We then explore trade-offs, potential negative effects of avoidance behaviour and the influence of human activities on avoidance behaviours. We conclude that avoidance behaviours are understudied in aquatic environments but can have significant implications for disease ecology and epidemiology, especially considering the accelerating emergence and re-emergence of parasites. This article is part of the Theo Murphy meeting issue ‘Evolution of pathogen and parasite avoidance behaviours'.