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Crustaceans are a valuable resource globally, both ecologically and economically, and investigations into their health are becoming increasingly important as exploitation rises. The microbiome plays a crucial role in crustacean immunity, and understanding its composition and structure can provide insights into the health of an organism and its interactions with various factors. In this study, we investigated the hepatopancreas microbiome of the velvet swimming crab, Necora puber, and compared its composition and structure with several study factors, including two different sampling points and infection with a paramyxid parasite, Paramarteilia canceri. To our knowledge, we provide the first description of a velvet crab microbiome, highlighting the dominance of a single microorganism, Candidatus hepatoplasma. We identified variations in microbiome composition between sampling points and discussed the possible processes affecting microbiome assembly. We also outline a core microbiome for the velvet crab hepatopancreas, consisting of 12 core phyla. Our study adds to the growing literature on crustacean microbiomes and provides a baseline for future investigations into the velvet crab microbiome and the health of this crustacean species. [ABSTRACT FROM AUTHOR]

Decapod crustaceans and their associated fisheries are an important resource globally, and demand for seafood continues to grow alongside a growing human population. With a combined 2023 value of €36 million in Ireland, three species of brachyuran crabs, the velvet crab (Necora puber Linnaeus, 1767), edible crab (Cancer pagurus Linnaeus, 1758), spider crab (Maja squinado Herbst, 1788)), and the European lobster (Homarus gammarus Linnaeus, 1758) are decapods of commercial importance. These species are also important components of their respective ecosystems. Parasite infection can affect the health of crustaceans and may affect population productivity. Microparasites, including paramyxids (Hematodinium spp.) and microsporidians can infect decapod crustaceans and have a range of effects on their hosts. We assessed three microparasites in four crustacean species. Paramarteilia canceri was found in all three crab species, and we provide the first genetic confirmation in spider crabs. A microsporidian associated with cotton crab disease, Ameson sp. was identified in N. puber , along with a second species of microsporidian which will require further classification. None of the three parasite groups were identified in Homarus gammarus. Species of Hematodinium were not identified in any of the species studies. Our work highlights the need for parasite surveys to uncover parasite diversity and prevalence in crustaceans to help elucidate host-parasite interactions, and the potential impacts of parasites. [ABSTRACT FROM AUTHOR]

Parasites represent a ubiquitous threat for most organisms, requiring potential hosts to invest in a range of strategies to defend against infection—these include both behavioural and physiological mechanisms. Avoidance is an essential first line of defence, but this behaviour may show a trade-off with host investment in physiological immunity. Importantly, while environmental stressors can lead to elevated hormones in vertebrates, such as glucocorticoids, that can reduce physiological immunity in certain contexts, behavioural defences may also be compromised. Here, we investigate anti-parasite behaviour and immune responses against a trematode (flatworm) parasite by larval amphibians (tadpoles) exposed or not to a simulated general stressor in the form of exogenous corticosterone. Tadpoles that were highly active in the presence of the trematode infectious stage (cercariae) had lower infection loads, and parasite loads from tadpoles treated only with dechlorinated water were significantly lower than those exposed to corticosterone or the solvent control. However, treatment did not affect immunity as measured through white blood-cell profiles, and there was no relationship between the latter and anti-parasite behaviour. Our results suggest that a broad range of stressors could increase host susceptibility to infection through altered anti-parasite behaviours if they elevate endogenous glucocorticoids, irrespective of physiological immunity effects. How hosts defend themselves against parasitism in the context of multiple challenges represents an important topic for future research, particularly as the risk posed by infectious diseases is predicted to increase in response to ongoing environmental change. [ABSTRACT FROM AUTHOR]

The biodiversity of freshwater ecosystems globally still leaves much to be discovered, not least in the trematode parasite fauna they support. Echinostome trematode parasites have complex, multiple-host life-cycles, often involving migratory bird definitive hosts, thus leading to widespread distributions. Here, we examined the echinostome diversity in freshwater ecosystems at high latitude locations in Iceland, Finland, Ireland and Alaska (USA). We report 14 echinostome species identified morphologically and molecularly from analyses of nad1 and 28S rDNA sequence data. We found echinostomes parasitising snails of 11 species from the families Lymnaeidae, Planorbidae, Physidae and Valvatidae. The number of echinostome species in different hosts did not vary greatly and ranged from one to three species. Of these 14 trematode species, we discovered four species (Echinoparyphium sp. 1, Echinoparyphium sp. 2, Neopetasiger sp. 5, and Echinostomatidae gen. sp.) as novel in Europe; we provide descriptions for the newly recorded species and those not previously associated with DNA sequences. Two species from Iceland (Neopetasiger islandicus and Echinoparyphium sp. 2) were recorded in both Iceland and North America. All species found in Ireland are new records for this country. Via an integrative taxonomic approach taken, both morphological and molecular data are provided for comparison with future studies to elucidate many of the unknown parasite life cycles and transmission routes. Our reports of species distributions spanning Europe and North America highlight the need for parasite biodiversity assessments across large geographical areas.

Parasites and pathogens (hereafter parasites) commonly challenge organisms, but the extent to which their infections are physiologically stressful to hosts remains unclear. Importantly, vertebrate hormones, glucocorticoids (GCs), have been reported to increase, decrease or show no alterations stemming from infections, challenging the generality of parasite‐associated GC responses and motivating a search for important moderator variables.We undertook the first meta‐analysis of changes in vertebrate GCs following experimental infection with parasites, extracting 146 effect sizes from 42 studies involving 32 host and 32 parasite species to test for general patterns of GC following infection, as well as the influence of moderators.Overall, infection increased GCs relative to preliminary or control levels when the single largest effect sizes from repeated measures studies were examined, suggesting that parasites of vertebrate hosts can be thought of generally as physiological stressors by elevating GCs.When all effect sizes were included along with the moderator of sampling time post‐infection (tPI), parasite infection still had a positive effect on host GCs. However, the strength of that effect did not relate consistently to tPI, illustrating temporal differences in GC changes during the course of infection among parasite taxa (e.g. arthropod vs. bacterial infections). Other moderator variables examined did not influence GC responses.Studies broadening the range of host and parasite taxa, and sampling during critical time windows, would aid in our understanding of variation in the host stress response and its consequences for fitness of both vertebrate hosts and their parasites. [ABSTRACT FROM AUTHOR]

We investigated for the first time the digenean parasites of Austrolittorina unifasciata Gray (Gastropoda: Littorinidae), a periwinkle snail inhabiting the rocky shores of Australia. Here we present detailed morphological descriptions and molecular data (sequences for the mitochondrial cox1 and the nuclear 28S rRNA gene) for the cercariae and intramolluscan stages of the digenean parasites found. Five species, one each of the families Notocotylidae Lühe, 1909, Gorgocephalidae Manter, 1966 and Philophthalmidae Looss, 1899, and two of the family Renicolidae Dollfus, 1939, were recorded and characterised molecularly. Phylogenetic analyses at the superfamily level provided evidence for the familial and generic affiliation of the species and their relationships with congeners. This study is the first to provide data on the life cycle of a species of the family Gorgocephalidae, a parasite of kyphosid fish for which only adult stages had, thus far, been described. The relatively high prevalence of this species allowed mapping of the cox1 haplotype distribution of Gorgocephalus sp. Aus along the southern coast of New South Wales. [ABSTRACT FROM AUTHOR]

Littorinid snails are one particular group of gastropods identified as important intermediate hosts for a wide range of digenean parasite species, at least throughout the Northern Hemisphere. However nothing is known of trematode species infecting these snails in the Southern Hemisphere. This study is the first attempt at cataloguing the digenean parasites infecting littorinids in New Zealand. Examination of over 5,000 individuals of two species of the genus Austrolittorina Rosewater, A. cincta Quoy & Gaimard and A. antipodum Philippi, from intertidal rocky shores, revealed infections with four digenean species representative of a diverse range of families: Philophthalmidae Looss, 1899, Notocotylidae Lühe, 1909, Renicolidae Dollfus, 1939 and Microphallidae Ward, 1901. This paper provides detailed morphological descriptions of the cercariae and intramolluscan stages of these parasites. Furthermore, partial sequences of the 28S rRNA gene and the mitochondrial gene cytochrome c oxidase subunit 1 ( cox1) for varying numbers of isolates of each species were obtained. Phylogenetic analyses were carried out at the superfamily level and along with the morphological data were used to infer the generic affiliation of the species. [ABSTRACT FROM AUTHOR]

ABSTRACT Although a small set of external factors account for much of the spatial variation in plant and animal diversity, the search continues for general drivers of variation in parasite species richness among host species. Qualitative reviews of existing evidence suggest idiosyncrasies and inconsistent predictive power for all proposed determinants of parasite richness. Here, we provide the first quantitative synthesis of the evidence using a meta-analysis of 62 original studies testing the relationship between parasite richness across animal, plant and fungal hosts, and each of its four most widely used presumed predictors: host body size, host geographical range size, host population density, and latitude. We uncover three universal predictors of parasite richness across host species, namely host body size, geographical range size and population density, applicable regardless of the taxa considered and independently of most aspects of study design. A proper match in the primary studies between the focal predictor and both the spatial scale of study and the level at which parasite species richness was quantified (i.e. within host populations or tallied across a host species' entire range) also affected the magnitude of effect sizes. By contrast, except for a couple of indicative trends in subsets of the full dataset, there was no strong evidence for an effect of latitude on parasite species richness; where found, this effect ran counter to the general latitude gradient in diversity, with parasite species richness tending to be higher further from the equator. Finally, the meta-analysis also revealed a negative relationship between the magnitude of effect sizes and the year of publication of original studies (i.e. a time-lag bias). This temporal bias may be due to the increasing use of phylogenetic correction in comparative analyses of parasite richness over time, as this correction yields more conservative effect sizes. Overall, these findings point to common underlying processes of parasite diversification fundamentally different from those controlling the diversity of free-living organisms. [ABSTRACT FROM AUTHOR]

Most bopyrid isopod parasites, which are crustaceans themselves, settle in the branchial chamber of decapod crustaceans and feed on host haemolymph. Here we report the results of an experiment on the common prawn Palaemon serratus and the parasite Bopyrus squillarum. Infected and uninfected prawns were stimulated with pokes of a plastic rod until an escape response was triggered; the number of pokes was recorded as an indicator of prawn responsiveness, whereas the time spent moving following stimulation was used as an indicator of prawn activity. Our results show that bopyrid infection affects both prawn responsiveness and activity, with infected prawns requiring more pokes to move, and moving for less time compared to uninfected prawns. In nature, such behavioural changes may impact defence mechanisms and survival of infected prawns. This could contribute to decreases in P. serratus abundance, thereby affecting the coastal ecosystems home to this species and the fisheries reliant on it, such as the Irish shrimp fishery.