Infection cycle of Marteilia pararefringens in blue mussels Mytilus edulis in a heliothermic marine oyster lagoon in Norway.

Agapollen is a traditional heliothermic marine oyster lagoon in western Norway, representing the northernmost site of any Marteilia sp. protists detected in Europe. The semi-closed lagoon is a unique site to study the life cycle and development of M. pararefringens in naïve mussels. Two baskets with uninfected mussels were deployed in the lagoon outlet in May and October 2018, respectively, and sampled every 6 wk. The parasite was first detected in the mussels by PCR in early July and by histology in late August. By then, M. pararefringens had developed into mature stages, indicating a rapid development during mid-summer. Sporulation occurred during autumn. Mussels deployed in October never became infected, indicating that transmission was restricted to the warmest period of the year. Pronounced pathology was observed in infected mussels, including degenerated digestive tubules and infiltration of haemocytes. Mussel mortality was observed in the baskets, but whether this was due to infections of M. pararefringens or other environmental factors could not be determined. Plankton samples from the lagoon were also collected for PCR analysis. These samples, dominated by copepods, were positive for M. pararefringens in summer. In sorted samples, M. pararefringens was detected in the Acartia spp. and Paracartia grani fractions between July and October. These plankton copepods are therefore potentially involved in the life cycle of M. pararefringens.

The salmon louse genome: Copepod features and parasitic adaptations.

Copepods encompass numerous ecological roles including parasites, detrivores and phytoplankton grazers. Nonetheless, copepod genome assemblies remain scarce. Lepeophtheirus salmonis is an economically and ecologically important ectoparasitic copepod found on salmonid fish. We present the 695.4 Mbp L. salmonis genome assembly containing ≈60% repetitive regions and 13,081 annotated protein-coding genes. The genome comprises 14 autosomes and a ZZ-ZW sex chromosome system. Assembly assessment identified 92.4% of the expected arthropod genes. Transcriptomics supported annotation and indicated a marked shift in gene expression after host attachment, including apparent downregulation of genes related to circadian rhythm coinciding with abandoning diurnal migration. The genome shows evolutionary signatures including loss of genes needed for peroxisome biogenesis, presence of numerous FNII domains, and an incomplete heme homeostasis pathway suggesting heme proteins to be obtained from the host. Despite repeated development of resistance against chemical treatments L. salmonis exhibits low numbers of many genes involved in detoxification.

Parasites, pathogens, and other symbionts of copepods.

There is a large diversity of eukaryotic symbionts of copepods, dominated by epizootic protists such as ciliates, and metazoan parasites. Eukaryotic endoparasites, copepod-associated bacteria, and viruses are less well known, partly due to technical limitations. However, new molecular techniques, combined with a range of other approaches, provide a complementary toolkit for understanding the complete symbiome of copepods and how the symbiome relates to their ecological roles, relationships with other biota, and responses to environmental change. In this review we provide the most complete overview of the copepod symbiome to date, including microeukaryotes, metazoan parasites, bacteria, and viruses, and provide extensive literature databases to inform future studies.

Morphological and molecular characterization of Udonella brasiliensis n. sp. (Monogenoidea), an epibiont on Caligus sp. parasite of Ariidae from the southeastern coast of Brazil.

The present study describes Udonella brasiliensis n. sp., an epibiont found on Caligus sp., a parasite the ariids Genidens barbus (Lacepède) and Aspistor luniscutis (Valenciennes), caught on the coast of the state of São Paulo, Brazil. Morphological and molecular analyses (partial 18S rDNA) were carried out. The morphological data showed that U. brasiliensis n. sp. can be distinguished from current valid species by its morphometric attributes (e.g., body, pharynx, ovary and testis), while the molecular information supports the proposal of a new species. The 18S rDNA phylogenetic analysis shows a close relationship between the new species and Udonella australis Carvajal & Sepulveda, in a subclade formed of species that parasitize South American fish. Finally, this study also discusses a scenario of initial irradiation for udonellids.

Trophic relationship between the Patinga hybrid (Piaractus mesopotamicus x Piaractus brachypomus) and Echinorhynchus gomesi Machado Filho, 1948 in fish farms.

A total of 122 Patinga specimens were collected from fish farms (P1, P2 and P3), and only those from fish farm P1 were shown to be infected with Echinorhynchus gomesi. In addition, fish in this study were shown to have diets that consisted of 21 different food items, and Notodiaptomus sp. (Copepoda: Calanoida) was identified as a potential intermediate host for E. gomesi.

Mikrocytos mytilicoli n.sp. (Cercozoa, Mikrocytida, Mikrocytiidae) infecting the copepod Mytilicola intestinalis (Arthropoda, Cyclopoida, Mytilicolidae), a symbiont of Mytilus galloprovincialis in Galicia (NW Spain).

During a histopathological survey of Mytilus galloprovincialis in Galicia (NW Spain), microcells were observed infecting several organs of the symbiont copepod Mytilicola intestinalis. Positive results of PCR assay with specific primers for genus Mikrocytos and a clear signal of in situ hybridization with MACKINI-1 digoxigenin- labelled DNA probe (DIG-ISH) indicated a protozoan parasite of Mikrocytos genus. The ultrastructural study revealed intra and extracellular locations, polymorphic nuclei, intracellular round vesicles in the cytoplasm and absence of mitochondria. The present paper reports the characterization of the Mikrocytos sp. infecting M. intestinalis and proposes a novel species in the genus: Mikrocytos mytilicoli n. sp. A sequence of 18S-28S rDNA was obtained with 95.6% maximum identity (query cover 100%) with Mikrocytos mackini. Phylogenetic analysis showed that M. mytilicoli n. sp. and M. mackini share a common ancestor. However, comparison of the ITS1 rDNA region showed low similarity (75.8%) with M. mackini, which, combined with differences in ultrastructural details, host and geographic location, support the designation of a new species. This is the first description of a microcytid parasite of the genus Mikrocytos from a non-bivalve host.

A pond-side test for Guinea worm: Development of a loop-mediated isothermal amplification (LAMP) assay for detection of Dracunculus medinensis.

Guinea worm Dracunculus medinensis causes debilitating disease in people and is subject to an ongoing global eradication programme. Research and controls are constrained by a lack of diagnostic tools. We developed a specific and sensitive LAMP method for detecting D. medinensis larval DNA in copepod vectors. We were able to detect a single larva in a background of field-collected copepods. This method could form the basis of a "pond-side test" for detecting potential sources of Guinea worm infection in the environment, in copepods, including in the guts of fish as potential transport hosts, enabling research, surveillance and targeting of control measures. The key constraint on the utility of this assay as a field diagnostic, is a lack of knowledge of variation in the temporal and spatial distribution of D. medinensis larvae in copepods in water bodies in the affected areas and how best to sample copepods to obtain a reliable diagnostic sample. These fundamental knowledge gaps could readily be addressed with field collections of samples across areas experiencing a range of worm infection frequencies, coupled with field and laboratory analyses using LAMP and PCR.

Morphology, molecular phylogeny, and taxonomy of trichodinids (Ciliophora, Mobilida) from Calanoid copepods.

Trichodinid ciliates were isolated from calanoid copepods and were characterized by morphological and molecular techniques. The trichodinids found in this study were morphologically similar to Trichodina acuta, but morphometric differences were observed between our specimens and T. acuta. The T. acuta specimens, isolated from fish in several geographical locations around the world, were slightly larger than specimens in our population. In fact, our morphological and morphometric data are more similar to Trichodina diaptomi populations, also found on copepods. Moreover, our phylogenetic analyses revealed that the 18S rRNA gene sequence from our samples emerged in a clade with two T. acuta sequences, infesting fish hosts in China. These three sequences showed 100% identity. Our data, along with a taxonomic review, suggest that the species T. diaptomi, described recently, is actually a synonym of T. acuta and that this species may be related to fish and copepod hosts. In conclusion, we highlight the urgent need to better investigate the polymorphism and host specificity within the Mobilida, as this data may represent important characters to better understand the evolution into this order.

Passenger for millenniums: association between stenothermic microcrustacean and suctorian epibiont - the case of Eurytemora lacustris and Tokophyra sp.

Epibionts often colonize the exoskeleton of crustaceans, which sometimes results in the development of a long-term relationship between them. Our present work confirmed that a specific epibiont is closely associated with the pelagic calanoid copepod Eurytemora lacustris, regardless of the region, which suggests a preserved interaction between these species. Molecular analyses revealed that the epibiont belongs to the genus Tokophrya. We also found that the level of basibiont colonization is related to its size and identified that the most intensely inhabited body parts are those located near the center of the copepod body. We hypothesize that the relationship between Eurytemora (basibiont) and Tokophrya (epibiont) was established during the Quaternary period, following which these two populations were fragmented into lakes where they survived in close interaction. In addition, we suppose that the close relationship between the two species indicates the coevolution of stenotherms. Further studies on the interactions between Eurytemora lacustris and Tokophrya are required in order to gain insight into the long-term relationship between the copepods and the epibionts.

Parasitic copepods of the family Lernanthropidae Kabata, 1979 (Copepoda: Siphonostomatoida) from Australian fishes, with descriptions of seven new species.

The total number of species of Lernanthropidae previously recorded from Australian waters is 15 (i.e., one species each of Aethon Krøyer, 1837, Lernanthropodes Bere, 1936, and Lernanthropsis Do, in Ho Do, 1985; 10 species of Lernanthropus de Blainville, 1822; and two species of Sagum Wilson, 1913), and all of these records are reviewed. We report here the presence of three species of Aethon. One species, A. garricki Hewitt, 1968, is reported from Australian waters for the first time and a new species, A. bicamera sp. nov., is described from the latrid, Latris lineatus (Forster, 1801) caught off South Australia. The genus Lernanthropodes is represented by a single species, L. trachinoti Pillai, 1962. We recognize Chauvanium Kazachenko, Kovaleva, Nguyen Ngo, 2017 as a subjective synonym of Lernanthropodes and transfer its type and only species C. chauvani Kazachenko, Kovaleva, Nguyen Ngo, 2017 which becomes Lernanthropodes chauvani (Kazachenko, Kovaleva, Nguyen Ngo, 2017) n. comb. Lernanthropsis mugilii (Shishido, 1898) is reported here from Mugil cephalus Linnaeus, 1758 sampled in Queensland and in New South Wales. The genus Lernanthropus is the most species rich and we report the presence of 20 nominal species on Australian marine fishes. This total includes six new species: L. alepicolus sp. nov. from Alepes apercna Grant, 1987, L. elegans sp. nov. from Atractoscion aequidens (Cuvier, 1830), L. gnathanodontus sp. nov. from Gnathanodon speciosus (Forsskål, 1775), L. paracruciatus sp. nov. from Protonibea diacanthus (Lacepède, 1802), L. pemphericola sp. nov. from Pempheris compressa (White, 1790), and L. selenotoca sp. nov. from Selenotoca multifasciata (Richardson, 1846). In addition, we report the presence of another four species in Australian waters for the first time: L. abitocephalus Tripathi, 1962, L. cadenati Delamare Deboutteville Nuñes-Ruivo, 1954, L. microlamini Hewitt, 1968, and L. pomadasysis Rangnekar Murti, 1961. After reexamination of the types of L. paenulatus Wilson, 1922 held in the USNM, we relegate this species to subjective synonymy with L. seriolii Shishido, 1898. Previous records of L. paenulatus from Australian Seriola species should be reassigned to L. seriolii. Lernanthropus ecclesi Kensley Grindley, 1973 is recognized as a junior subjective synonym of L. micropterygis Richiardi, 1884, and L. delamarei Marques, 1960, which is based on the male only, is tentatively considered to be a junior subjective synonym of L. micropterygis. Males are described for the first time for three species; L. breviculus Kabata, 1979, L. microlamini and L. mollis Kabata, 1979. A member of the genus Mitrapus Song Chen, 1976, M. oblongus (Pillai, 1964), is reported from Australia for the first time, on Herklotsichthys castelnaui (Ogilby, 1897) caught off Queensland and New South Wales. Finally, two species of Sagum were previously known from Australia and here we add three more. Two of the newly reported species were originally described as species of Lernanthropus but we formally transfer them here to Sagum as S. lativentris (Heller, 1865) n. comb. and S. sanguineus (Song, in Song Chen, 1976) n. comb. The males of S. lativentris and S. vespertilio Kabata, 1979 are described for the first time. A key to the females of the 31 species of lernanthropids found in Australian waters is provided.

Odds ratios and hurdle models: a long-term analysis of parasite infection patterns in endangered young-of-the-year suckers from Upper Klamath Lake, Oregon, USA.

We used odds ratios and a hurdle model to analyze parasite co-infections over 25 years on >20,000 young-of-the year of endangered Shortnose and Lost River Suckers. Host ecologies differed as did parasite infections. Shortnose Suckers were more likely to be caught inshore and 3-5 times more likely to have Bolbophorus spp. and Contracaecum sp. infections, and Lost River Suckers were more likely to be caught offshore and approximately three times more likely to have Lernaea cyprinacea infections. An observed peak shift seems likely to be due to a lower host size limit for Bolbophorus spp. (13.6 mm) compared with L. cyprinacea (23.4 mm). The large data set allowed us to generate strong hypotheses: (i) that a major marsh restoration project had unintended consequences that resulted in an increase in infections; (ii) that co-infection with Bolbophorus spp. increased the odds of infection by L. cyprinacea and Contracaecum sp.; (iii) that significant declines in the odds of infection over approximately 25 days were due to parasite-induced host mortality; (iv) that the fish's small size relative to L. cyprinacea and Contracaecum sp. might be directly lethal; (v) that the absence of L. cyprinacea infections in the early 1990s was associated with good year-class production of the suckers; and (vi) that parasites might increase the odds of vagrancy from the nursery ground.

Cooking copepods: The survival of cyclopoid copepods (Crustacea: Copepoda) in simulated provisioned water containers and implications for the Guinea Worm Eradication Program in Chad, Africa.

INTRODUCTION: The global Guinea Worm Eradication Program has reduced numbers of human infections of Guinea worm disease (dracunculiasis) to 49 cases in four countries. However, infections of domestic animals (dogs and cats) have recently been recognized and are increasing. Typically, Guinea worm (Dracunculus medinensis) transmission occurs via the ingestion of copepods from water. Despite several interventions, including tethering of dogs while worms emerge, the number of infected dogs continue to increase. One hypothesis is that dogs could be infected through the ingestion of copepods in provisioned water. OBJECTIVES: The purpose of this study was to determine whether copepods can survive in water containers under typical Chadian temperatures. METHODS: Four container types (plastic, glass, gourd, and metal) were seeded with copepods and exposed to simulated Chadian temperatures. RESULTS: All copepods in the metal containers died within 4 h. Conversely, after 8 h live copepods were still present in plastic, glass, and gourd containers. CONCLUSIONS: If provisioned water is provided to potential hosts of D. medinensis, metal containers create the most inhospitable environment for copepods. Plastic containers have little effect on copepod mortality. The use of metal containers for water provisions could be a useful tool assisting with the interruption of D. medinensis transmission among dogs.

Dracunculiasis: water-borne anthroponosis vs. food-borne zoonosis.

Dracunculiasis is the first parasitic disease set for eradication. However, recent events related to the Dracunculus medinensis epidemiology in certain African countries are apparently posing new challenges to its eradication. Two novel facts have emerged: the existence of animal reservoirs (mainly dogs but also cats and baboons), and possibly a new food-borne route of transmission by the ingestion of paratenic (frogs) or transport (fish) hosts. Therefore, instead of being exclusively a water-borne anthroponosis, dracunculiasis would also be a food-borne zoonosis. The existence of a large number of infected dogs, mainly in Chad, and the low number of infected humans, have given rise to this potential food-borne transmission. This novel route would concern not only reservoirs, but also humans. However, only animals seem to be affected. Dracunculus medinensis is on the verge of eradication due to the control measures which, classically, have been exclusively aimed at the water-borne route. Therefore, food-borne transmission is probably of secondary importance, at least in humans. In Chad, reservoirs would become infected through the water-borne route, mainly in the dry season when rivers recede, and smaller accessible ponds, with a lower water level containing the infected copepods, appear, whilst humans drink filtered water and, thus, avoid infection. The total absence of control measures aimed at dogs (or at other potential reservoirs) up until the last years, added to the stimulating reward in cash given to those who find parasitized dogs, have presumably given rise to the current dracunculiasis scenario in Chad.

Experimental evolution of parasitic host manipulation.

Host manipulation is a parasite-induced alteration of a host's phenotype that increases parasite fitness. However, if genetically encoded in the parasite, it should be under selection in the parasite. Such host manipulation has often been assumed to be energetically costly, which should restrict its evolution. Evidence of such costs, however, remains elusive. The trophically transmitted cestode Schistocephalus solidus manipulates the activity of its first intermediate copepod host to reduce its predation susceptibility before the parasite is ready for transmission. Thereafter, S. solidus increases host activity to facilitate transmission to its subsequent fish host. I selected S. solidus for or against host manipulation over three generations to investigate the evolvability of manipulation and identify potential trade-offs. Host manipulation responded to selection, confirming that this trait is heritable in the parasite and hence can present an extended phenotype. Changes in host manipulation were not restrained by any obvious costs.

Crowding in the first intermediate host does not affect infection probability in the second host in two helminths.

When many worms co-infect the same host, their average size is often reduced. This negative density-dependent growth is called the crowding effect. Crowding has been reported many times for worms in their intermediate hosts, but rarely have the fitness consequences of crowding been examined. This study tested whether larval crowding reduces establishment success in the next host for two parasites with complex life cycles, the nematode Camallanus lacustris and the cestode Schistocephalus solidus. Infected copepods, the first host, were fed to sticklebacks, the second host. Fish received a constant dose, but the infection intensity in copepods was varied (e.g. giving two singly infected copepods or one doubly infected copepod). Worms from higher-intensity infections did not have significantly reduced infection success in fish. However, crowded treatments had a disproportionate number of low and high infection rates, and although this trend was not significant, it hints at the possibility that multiple worms within a copepod are more likely to either all infect or all die when transmitted to the next host. These results indicate that a smaller larval size due to crowding need not reduce the establishment probability of a worm in the next host.

A partly stage-structured model for the abundance of salmon lice in salmonid farms.

The parasitic salmon louse constrains growth in the Norwegian salmon farming industry through density dependent host-parasite interaction. Hence, there is a need for insight into how increases in salmon production, varying spatial organisation of the production and pest control strategies affect salmon louse population dynamics. Here we present a new salmon louse model for exploring effects of varying salmon farming conditions on spatio-temporal abundances of the parasite. The salmon louse model is partly stage-structured, comprising of (i) adult female lice and (ii) other mobile stages of lice. The abundance of adult females depend on survival of females from previous weeks and recruitment from the other mobile group of lice. The other mobiles also depend on survival of other mobiles from previous weeks, as well as recruitment from the previous generation of reproducing adult females from the same farm or from farms in the neighbourhood. In addition, expected abundances of the two stage-groups are modelled as functions of biological and physical covariates. The model is fitted to weekly salmon farm data covering all marine farms producing salmonids along the Norwegian cost over the years 2012-2016. Among novel results from fitting the model are estimates of the time-lag structure representing recruitment of other mobile lice from the previous generation adult females for different temperatures. Furthermore, the model estimates how various factors affect the susceptibility of fish on farms to louse infection and effects of treatments to control infection. Finally, the model estimates density dependent effects of increasing the number of fish in farms and of increasing the numbers of farms, on the rate of recruitment of other mobile lice. Analytically, the parameters representing density dependencies suggest that few farms with many fish and large between farm distances is effective in terms of minimising the overall output of salmon lice infection.

Phylogeny, Evidence for a Cryptic Plastid, and Distribution of Chytriodinium Parasites (Dinophyceae) Infecting Copepods.

Spores of the dinoflagellate Chytriodinium are known to infest copepod eggs causing their lethality. Despite the potential to control the population of such an ecologically important host, knowledge about Chytriodinium parasites is limited: we know little about phylogeny, parasitism, abundance, or geographical distribution. We carried out genome sequence surveys on four manually isolated sporocytes from the same sporangium, which seemed to be attached to a copepod nauplius, to analyze the phylogenetic position of Chytriodinium based on SSU and concatenated SSU/LSU rRNA gene sequences, and also characterize two genes related to the plastidial heme pathway, hemL and hemY. The results suggest the presence of a cryptic plastid in Chytriodinium and a photosynthetic ancestral state of the parasitic Chytriodinium/Dissodinium clade. Finally, by mapping Tara Oceans V9 SSU amplicon data to the recovered SSU rRNA gene sequences from the sporocytes, we show that globally, Chytriodinium parasites are most abundant within the pico/nano- and mesoplankton of the surface ocean and almost absent within microplankton, a distribution indicating that they generally exist either as free-living spores or host-associated sporangia.

Oomycete parasites in freshwater copepods of Patagonia: effects on survival and recruitment.

Copepods are hosts to various oomycete parasite species, but the effects of pathogens on copepod populations have rarely been studied. This study aimed to characterize oomycete infection in the freshwater copepod Parabroteas sarsi in a temporary pond in Patagonia (Argentina). A complete hydroperiod was monitored, evaluating environmental variables as influencing factors in the oomycete infections. Laboratory experiments were performed to evaluate the susceptibility of infected copepods to consumption by predators. Although 5 species of copepods were present in the pond, only ovigerous P. sarsi females were parasitized by oomycetes. Two species of oomycetes were always found together: Aphanomyces ovidestruens and Pythium flevoense. Infections were detected at water temperatures >20°C, with a positive relationship between temperature and parasite prevalence. Infection occurred after a decrease in large filter-feeder densities. The pathogens were not lethal to P. sarsi females in the short-term, but did produce mortality of entire egg sacs, thus negatively impacting subsequent recruitment. Mean prevalence of infection in females was 53%, reaching 83% in December. Females have the capacity to release an infected egg sac and generate a new one in a few days. This infection does not affect the susceptibility of P. sarsi to the predator Notonecta vereertbruggheni. The decrease in female abundance registered towards the end of the hydroperiod could be related to a combination of factors that may have a differential effect on female survival, such as increasing temperature, the energy cost of egg sac development and carrying and oomycete infection.

Amblyospora khaliulini (Microsporidia: Amblyosporidae): Investigations on its life cycle and ecology in Aedes communis (Diptera: Culicidae) and Acanthocyclops vernalis (Copepoda: Cyclopidae) with redescription of the species.

A multi-year study was conducted to examine the natural ecology of the microsporidium Amblyospora khaliulini and more fully characterize parasite development and histopathology in all stages of its primary mosquito host, Aedes communis and intermediate copepod host, Acanthocyclops vernalis with redescription of the species. A. khaliulini exhibits polymorphic development, produces three morphologically and functionally distinct spores, and is both horizontally and vertically transmitted. Development in A. vernalis is restricted to females, occurs within the ovaries and results in death of the host. Development is haplophasic with division by binary and multiple fission producing rosette-shaped sporogonial plasmodia and conical uninucleate spores that are orally infectious to Ae. communis larvae. Both sexes are equally susceptible and infections are confined to testes in males and ovaries in females. Initial stages of development include uninucleate schizonts that undergo karyokinesis forming diplokaryotic meronts that divide repeatedly by binary fission. Sporogony occurs in both host sexes, but sporogenesis does not progress normally in adult males and elliptical, thin walled binucleate spores that function in vertical transmission of the microsporidium via infection of the ovaries and eggs are formed in adult females only. Development of vertically acquired infections in larval Ae. communis hosts occurs within fat body tissue, leads to the production of meiospores in male hosts only and results in death during the 4th larval stadium. Initial development is characterized by merogonial multiplication of diplokarya by synchronous binary division producing additional diplokarya. The cessation of merogony and the onset of sporogony are characterized by the simultaneous secretion of a sporophorous vesicle and meiotic division of diplokarya resulting in the formation of octonucleate sporonts that undergo cytokinesis and sporogenesis to form eight uninucleate, broadly ovoid meiospores enclosed within a sporophorous vesicle. The natural prevalence of patent vertically acquired fat body infections in field populations of Ae. communis ranged from 1.6% to 3.6%. Yearly infection rates in A. vernalis copepods ranged from 57.1% to 15.0%. Prevalence rates of horizontally acquired infections in emerging adult Ae. communis ranged from 69.0% to 11.9% in males and 50.0% to 16.4% in females.

Differences between populations in host manipulation by the tapeworm Schistocephalus solidus - is there local adaptation?

Host manipulation whereby a parasite increases its transmission to a subsequent host by altering the behaviour of its current host is very far spread. It also occurs in host-parasite systems that are widely distributed. This offers the potential for local adaptation. The tapeworm Schistocephalus solidus modifies its first intermediate copepod host's predation susceptibility to suit its own needs by reducing its activity before it becomes infective and increasing it thereafter. To investigate potential differences in host manipulation between different populations and test for potential local adaptation with regard to host manipulation, I experimentally infected hosts from two distinct populations with parasites from either population in a fully crossed design. Host manipulation differed between populations mostly once the parasite had reached infectivity. These differences in infective parasites were mostly due to differences between different parasite populations. In not yet infective parasites, however, host population also had a significant effect on host manipulation. There was no evidence of local adaptation; parasites were able to manipulate foreign and local hosts equally well. Likewise, hosts were equally poor at resisting host manipulation by local and foreign parasites.