AFLP-PCR and RAPD-PCR evidences of the transmission of the pathogen Aphanomyces astaci (Oomycetes) to wild populations of European crayfish from the invasive crayfish species, Procambarus clarkii

Influence of temperature on embryonic development of Pontastacus leptodactylus freshwater crayfish, and characterization of growth and osmoregulation related genes

Narrow clawed crayfish, Pontastacus (Astacus) leptodactylus, represents an ecologically and economically valuable freshwater species. Despite the high importance of artificial breeding for conservation purpose and aquaculture potential, hatching protocols have not been developed so far in this species. Further, limited knowledge exists regarding the artificial egg incubation, the temperature effect on embryonic development, hatching synchronization and hatching rate. In the present study we investigated the temperature increase (from 17 oC to 22oC) effects in two different embryonic developmental stages of P. leptodactylus. Furthermore, two primer pairs for the Fibroblast Growth Factor Receptor 4 (FGFR4) gene cDNA amplification were successfully designed, characterising for the first time the FGFR4 gene in P. leptodactylus in relation to different developmental stages and temperatures. Apart from the FGFR4 gene, the Na+/K+-ATPase α-subunit expression was also explored. Both the FGFR4 and Na+/K+-ATPase α-subunit expression levels were higher in embryos closer to hatching. Egg incubation at 22oC for seven days led to significant increase of FGFR4 expression in embryos from earlier developmental stages. Nevertheless, temperature increase did not affect FGFR4 expression in eggs from latter developmental stages and Na+/K+-ATPase α-subunit expression in all developmental stages. Temperature increase represents therefore probably a promising strategy for accelerating hatching in freshwater crayfish particularly in early developmental stages. Specifically, our results indicate that FGFR4 expression increased in embryonic stages closer to hatching and that temperature influences significantly its expression in embryos from earlier developmental stages. Overall, these findings can provide a better understanding of artificial egg incubation of P. leptodactylus, and therefore can be employed for the effective management of this species, both for economic and biodiversity retention reasons.

Protocols for studying the crayfish plague pathogen, Aphanomyces astaci, and its host-pathogen interactions

The crayfish plague caused by the pathogen Aphanomyces astaci has decimated the European and Asian populations of freshwater crayfish and represents an important threat to the other highly susceptible crayfish species in the world, such as the Australian, Madagascar, and South American species. The development and application of molecular methods addressed to the identification of A. astaci has increased exponentially during the last decades in contrast to a slow trend of the pathogen biology and host interaction. There is still a need for a better comprehension of the A. astaci-crayfish interactions, specifically the resistance and tolerance immune mechanism. These types of studies required a robust basic knowledge on the developmental biology of the pathogen in order to reproduce life stages and to perform infection experiments. A great piece of work in this area was carried out during the 1960 s to 80 s in University of Uppsala. Thus, the purpose of this work was to update previous protocols as well as to generate new guidelines to reproduce key developmental biology stages of A. astaci, to eventually identify crayfish populations with higher resistance and tolerance to this pathogen. This work also refers to other methodologies and guidelines for the diagnosis of crayfish plague, the pathogen isolation, and the in vitro production of zoospores.

Austropotamobius pallipes can be infected by two haplotypes of Aphanomyces astaci: A key example from an outbreak at an ex-situ conservation facility

The crayfish plague, caused by the pathogen Aphanomyces astaci, is a pandemic disease endemic to North America that has been devastating susceptible crayfish populations in Europe since the 19th century. In Spain, this disease has decimated populations of the native crayfish species Austropotamobius pallipes due to introductions of North American crayfish, which act as vectors of the pathogen. To combat against these losses, several regional governments have established ex-situ breeding programs to restock wild populations of the species. In this study, we report on an outbreak of A. astaci that occurred in one of the most important A. pallipes aquaculture centers in Spain. Using a variety of detection methods, we analyzed affected crayfish and environmental samples from the facilities over a period of six months and determined that the outbreak was caused by two haplotypes of A. astaci, d1 and d2, which are both associated with the North American crayfish species Procambarus clarkii. To our knowledge, this is the first report of a two-haplotype coinfection of A. astaci outside the native range of this pathogen.

Long-term changes in the prevalence of the crayfish plague pathogen and its genotyping in invasive crayfish species in Czechia

The widespread presence of North American alien crayfish in Europe is a major driver of native crayfish population declines, mainly because they are chronic carriers of the oomycete Aphanomyces astaci responsible for crayfish plague. Screening for the crayfish plague pathogen in host populations has become a common practice across Europe, but sampling usually covers spatial but not temporal variation. Our study focuses on the current situation in Czechia, where screening for A. astaci was first conducted in the mid-2000s. We provide data about the distribution and prevalence of this pathogen at almost 50 sites with three host crayfish: the spiny-cheek crayfish Faxonius limosus, signal crayfish Pacifastacus leniusculus, and marbled crayfish Procambarus virginalis. Among these sites were 20 localities that were resampled several years (usually more than a decade) after the original screening for A. astaci. We did not detect any A. astaci infection in two studied P. virginalis populations but documented several new hotspots of highly infected P. leniusculus in Czechia, and the first site with the coexistence of the latter with F. limosus. Our data suggest that despite some fluctuations, A. astaci prevalence in North American host populations generally does not tend to change significantly over time; we only observed two cases of a significant increase and one of a significant decrease. We no longer detected A. astaci in several originally weakly infected populations, but our data suggest it likely still persists in these areas and threatens native crayfish populations. At the single known site in the country where P. leniusculus and F. limosus coexist, we documented the presence of the same A. astaci genotype group in both crayfish species, likely due to interspecific transmission of the pathogen from the former host to the latter. However, genotyping of A. astaci in infected host individuals still supported the link between specific pathogen genotypes and crayfish hosts, suggesting that assessment of sources of mass mortalities from the pathogen genotyping is feasible in European regions where the mutual contact of different American crayfish species is uncommon.

Money Kills Native Ecosystems: European Crayfish as an Example

Native European crayfish conservation was triggered by invasion of crayfish plague disease agent, Aphanomyces astaci, starting 1860s in Northern Italy. Resulting crayfish plague epidemics quickly spread over Continental Europe, then to Finland, Sweden and finally, after running amok around Europe, A. astaci was discovered also in Iberian Peninsula, Norway, Ireland, and United Kingdom in 1970s and 1980s. By that time significant proportion of native crayfish stocks had been lost, and while crayfish plague epidemics were still recorded, also industrialization and waterways construction were causing damage to remaining native crayfish stocks. While alien crayfish introductions, at least Faxonius limosus, already gave rise to first wave of crayfish plague epidemics in late 19th century, later in 1960s it was decided that introductions of alien Pacifastacus leniusculus should be initiated to replace native European crayfish populations. Decisions were based on presumed advantages for fishery, suitable habitat requirements and supposed immunity against A. astaci. Furthermore, conservation of native European crayfish species was sidelined and focus shifted toward alien crayfish stocking routine and consumption. Alien crayfish species introductions resulted in repeated waves of crayfish plague epidemics among remaining native crayfish stocks. It was soon discovered that alien crayfish of North American origin were, as suspected, permanent reservoirs for A. astaci, that some of those alien species were losing their resistance against selected strains of A. astaci and struggled in European aquatic ecosystems. In this article, we introduce numerous motives behind grand mistake of introducing alien crayfish species to Europe and then promoting their stocks instead of focusing on conservation of native crayfish species. We outline how false economical, biological and ecologic assumptions were used to justify a hasty introduction of alien crayfish, which has further devastated native crayfish and also permanently changed European aquatic ecosystems, both with disastrous consequences. Lesson to be learnt is that science-based warnings about alien species damage to native ecosystems and native crayfish must be taken with utmost caution. Protection of native European crayfish should be core issue, not commercial activities. Finally, we summarize main threats and actions needed to protect remaining native freshwater crayfish fauna in Europe.

Real-Time PCR Assays for Rapid Identification of Common Aphanomyces astaci Genotypes

The oomycete Aphanomyces astaci is the etiologic agent of crayfish plague, a disease that has seriously impacted the populations of European native crayfish species. The introduction of non-indigenous crayfish of North American origin and their wide distribution across Europe have largely contributed to spread of crayfish plague in areas populated by indigenous crayfish. Tracking A. astaci genotypes may thus be a useful tool for investigating the natural history of crayfish plague in its European range, as well as the sources and introduction pathways of the pathogen. In this study, we describe the development of real-time PCR TaqMan assays aiming to distinguish the five genotype groups of A. astaci (A–E) previously defined by their distinct RAPD patterns. The method was evaluated using DNA extracts from pure A. astaci cultures representing the known genotype groups, and from A. astaci-positive crayfish clinical samples collected mostly during crayfish plague outbreaks that recently occurred in Central Italy and Czechia. The assays do not cross-react with each other, and those targeting genotype groups A, B, D, and E seem sufficiently specific to genotype the pathogen from infected crayfish in the areas invaded by A. astaci (particularly Europe). The unusual A. astaci genotype “SSR-Up” documented from crayfish plague outbreaks in Czechia and chronically infected Pontastacus leptodactylus in the Danube is detected by the group B real-time PCR. The assay originally developed to detect group C (one not yet documented from crayfish plague outbreaks) showed cross-reactivity with Aphanomyces fennicus; the A. astaci genotype “rust1” described in the United States from Faxonius rusticus is detected by that assay as well. Analyses of additional markers (such as sequencing of the nuclear internal transcribed spacer or mitochondrial ribosomal subunits) may complement such cases when the real-time PCR-based genotyping is not conclusive. Despite some limitations, the method is a robust tool for fast genotyping of A. astaci genotype groups common in Europe, both during crayfish plague outbreaks and in latent infections.

First Detection of the Crayfish Plague Pathogen Aphanomyces astaci in Costa Rica: European Mistakes Should Not Be Repeated

The crayfish plague pathogen Aphanomyces astaci is one of the main factors responsible for the decline in European and Asian native crayfish species. This pathogen was transported to these regions through its natural carriers, North American crayfish species, which were introduced during the last century. Since then, the carrier species and the pathogen have spread worldwide due to globalization and the highly invasive nature of these species. In Europe, five carrier species have been categorized as high-risk as they are responsible for the loss of provisioning services, which endangers freshwater ecosystems. The red swamp crayfish Procambarus clarkii, in particular, is currently one of the most concerning species as its spread threatens crayfish biodiversity and freshwater ecosystems worldwide. In this study, we describe the first detection of A. astaci in an introduced population of P. clarkii in Central America, specifically in Costa Rica. Using molecular approaches, we analyzed 48 crayfish samples collected from Reservoir Cachí and detected the presence of A. astaci in four of these samples. The introduction of P. clarkii and the incorrect management of the species (related to its fishery and the commercialization of live specimens) over the past decades in Europe are mistakes that should not be repeated elsewhere. The detection of the pathogen is a warning sign about the dangerous impact that the introduction of this invasive crayfish may have, not only as a carrier of an emerging disease but also as a direct risk to the invaded ecosystems. Our results may serve to (1) assess current and future consequences, and (2) direct future research activities, such as determining the potential impacts of A. astaci on native decapod species, or on other introduced crayfish species that are used for aquaculture purposes, such as Cherax quadricarinatus.

Tracing the origin of the crayfish plague pathogen, Aphanomyces astaci, to the Southeastern United States

The oomycete Aphanomyces astaci is an emerging infectious pathogen affecting freshwater crayfish worldwide and is responsible for one of the most severe wildlife pandemics ever reported. The pathogen has caused mass mortalities of freshwater crayfish species in Europe and Asia, and threatens other susceptible species in Madagascar, Oceania and South America. The pathogen naturally coexists with some North American crayfish species that are its chronic carriers. Presumptions that A. astaci originated in North America are based on disease outbreaks that followed translocations of North American crayfish and on the identification of the pathogen mainly in Europe. We studied A. astaci in the southeastern US, a center of freshwater crayfish diversity. In order to decipher the origin of the pathogen, we investigated (1) the distribution and haplotype diversity of A. astaci, and (2) whether there are crayfish species-specificities and/or geographical restrictions for A. astaci haplotypes. A total of 132 individuals, corresponding to 19 crayfish species and one shrimp species from 23 locations, tested positive for A. astaci. Mitochondrial rnnS and rnnL sequences indicated that A. astaci from the southeastern US exhibited the highest genetic diversity so far described for the pathogen (eight haplotypes, six of which we newly describe). Our findings that A. astaci is widely distributed and genetically diverse in the region supports the hypothesis that the pathogen originated in the southeastern US. In contrast to previous assumptions, however, the pathogen exhibited no clear species-specificity or geographical patterns.

Coexistence of Two Invasive Species, Procambarus clarkii and Aphanomyces astaci, in Brackish Waters of a Mediterranean Coastal Lagoon

Procambarus clarkii is a worldwide freshwater invasive crustacean from North America and was first introduced into Europe the 1970s. Along with P. clarkii, another invasive alien species was also spreading: Aphanomyces astaci. This pathogen is listed among the 100 World’s worst invasive species and involved in the European native crayfish decline. Although both species live in freshwater ecosystems, P. clarkii can withstand brackish waters and inhabit estuarine habitats. However, the presence of A. astaci associated to North American crayfishes has never been described in brackish waters. In this study, we have investigated the presence of A. astaci in a P. clarkii population of a Mediterranean coastal lagoon in the Albufera Natural Park, Valencia, Spain introduced in 1976. Our study confirmed the presence of this pathogen, and suggests that A. astaci has been spreading for more than four decades in the mentioned estuarine environment. Mitochondrial ribosomal rnnS and rnnL indicated that the isolated pathogen belongs to d1-haplotype (i.e., D-haplogroup) typically hosted by P. clarkii. The presence of this pathogen in a brackish environment may suggest a better adaptation than other A. astaci strains to adverse conditions, such as high salinity levels. This is a matter of concern for the conservation of European native freshwater crayfish and highlights once more the risk of introducing invasive alien crustaceans.

Aphanomyces astaci mtDNA: insights into the pathogen's differentiation and its genetic diversity from other closely related oomycetes

The causative agent of crayfish plague, Aphanomyces astaci (Saprolegniales, Oomycota), is one of the 100 world's worst invasive alien species and represents a major threat to freshwater crayfish species worldwide. A better understanding of the biology and epidemiology of A. astaci relies on the application of efficient tools to detect the pathogen and assess its genetic diversity. In this study, we validated the specificity of two recently developed PCR-based approaches used to detect A. astaci groups. The first relies on the analysis of mitochondrial ribosomal rnnS (small) and rnnL (large) subunit sequences and the second, of sequences obtained by using genotype-specific primers designed from A. astaci whole genome sequencing. For this purpose, we tested the specificity against 76 selected isolates, including other oomycete species and the recently described species Aphanomyces fennicus, which, when used in nrITS-based specific tests for A. astaci, is known to result in a false positive. Under both approaches, we were able to efficiently and accurately identify A. astaci and its genetic groups in both pure cultures and clinical samples. We report that sequence analysis of the rnnS region alone is sufficient for the identification of A. astaci and a partial characterization of haplogroups. In contrast, the rnnL region alone is not sufficiently informative for A. astaci identification as other oomycete species present sequences identical to those of A. astaci.

Multilocus Sequence Typing (MLST) and Random Polymorphic DNA (RAPD) Comparisons of Geographic Isolates of Neoparamoeba perurans, the Causative Agent of Amoebic Gill Disease

Neoparamoba perurans, is the aetiological agent of amoebic gill disease (AGD), a disease that affects farmed Atlantic salmon worldwide. Multilocus sequence typing (MLST) and Random Amplified Polymorphic DNA (RAPD) are PCR-based typing methods that allow for the highly reproducible genetic analysis of population structure within microbial species. To the best of our knowledge, this study represents the first use of these typing methods applied to N. perurans with the objective of distinguishing geographical isolates. These analyses were applied to a total of 16 isolates from Australia, Canada, Ireland, Scotland, Norway, and the USA. All the samples from Australia came from farm sites on the island state of Tasmania. Genetic polymorphism among isolates was more evident from the RAPD analysis compared to the MLST that used conserved housekeeping genes. Both techniques consistently identified that isolates of N. perurans from Tasmania, Australia were more similar to each other than to the isolates from other countries. While genetic differences were identified between geographical isolates, a BURST analysis provided no evidence of a founder genotype. This suggests that emerging outbreaks of AGD are not due to rapid translocation of this important salmonid pathogen from the same area.

Mapping 15 years of crayfish plague in the Iberian Peninsula: The impact of two invasive species on the endangered native crayfish

Crayfish plague, caused by the pathogen Aphanomyces astaci, is one of the main factors responsible for the decimation of the native European crayfish species Austropotamobius pallipes. In Spain, two North American freshwater crayfish species, Procambarus clarkii and Pacifastacus leniusculus, were intentionally introduced during the 1970s for aquaculture and fishery purposes. Since then, incidences of crayfish plague have been continually reported. In this work, we evaluated more than 50 diagnosed cases of crayfish plague that have occurred in the Iberian Peninsula since 2004 by performing a microscopic examination of infected specimens and by molecularly identifying and haplotyping the pathogen. Our results showed that (i) the pathogen A. astaci has been active 45 years since the first introductions of the invasive North American crayfish species in the Iberian Peninsula, and (ii) P. clarkii and P. leniusculus are chronic reservoirs of the crayfish plague pathogen. Moreover, our data confirmed a correspondence between pathogen origin and spread and the specific haplotypes carried by the North American invasive crayfish located in the vicinity of each outbreak. We generated a crayfish plague incidence map of the Iberian Peninsula that shows (i) a northern area, mainly inhabited by alien P. leniusculus, where crayfish plague cases are associated with the b-haplotype specific to P. leniusculus, and (ii) southern, central and eastern areas that are basically inhabited by alien P. clarkii, where crayfish plague cases are associated with the d1- and d2-haplotypes specific to P. clarkii. The results presented here are evidence of the long standing and negative impact of the two invasive crayfish species on the native species, indicating the need for more extensive control measures.

The signal crayfish (Pacifastacus leniusculus) in Lake Tahoe (USA) hosts multiple Aphanomyces species

The genus Aphanomyces (Oomycetes) comprises approximately 50 known species of water molds in three lineages. One of the most notorious is Aphanomyces astaci, the causative agent of crayfish plague. In this study, fresh isolates of Aphanomyces were collected from 20 live specimens of the signal crayfish Pacifastacus leniusculus (Dana, 1852) from Lake Tahoe, California, providing 35 axenic cultures of A. astaci as well as two apparently undescribed Aphanomyces spp. isolates. Based on the results of ITS-, chitinase-, mitochondrial rnnS- and rnnL-sequences and microsatellite markers combined, the Lake Tahoe A. astaci isolates were identical to isolates of A. astaci B-haplogroup commonly detected in Europe, and infection experiments confirmed their high virulence towards noble crayfish. One of the two undescribed Aphanomyces spp. isolates was highly similar to an Aphanomyces lineage detected previously in crustacean zooplankton (Daphnia) in Central Europe, while the other was distinct and most closely related (ITS sequence similarity of 93%) to either A. astaci or to Aphanomyces fennicus isolated recently from Astacus astacus in Finland. Neither of the two Aphanomyces spp. isolates caused crayfish mortality under experimental conditions. Our results indicate that the populations of North American signal crayfish can act as carriers of both pathogenic and non-pathogenic Aphanomyces at the same time. Furthermore, considering that a limited number of crayfish individuals from a single location yielded multiple distinct Aphanomyces isolates, our results suggest that substantial species diversity within this genus remains undescribed.

Improved method for genotyping the causative agent of crayfish plague (Aphanomyces astaci) based on mitochondrial DNA

Aphanomyces astaci causes crayfish plague, which is a devastating disease of European freshwater crayfish. The likely first introduction of A. astaci into Europe was in the mid-19th century in Italy, presumably with the introduction of North American crayfish. These crayfish can carry A. astaci in their cuticle as a benign infection. Aphanomyces astaci rapidly spread across Europe causing the decline of the highly susceptible indigenous crayfish species. Random amplified polymorphic DNA-PCR analysis of A. astaci pure cultures characterized five genotype groups (A, B, C, D and E). Current A. astaci genotyping techniques (microsatellites and genotype-specific regions, both targeting nuclear DNA) can be applied directly to DNA extracted from infected cuticles but require high infection levels. Therefore, they are not suitable for genotyping benign infections in North American crayfish (carriers). In the present study, we combine bioinformatics and molecular biology techniques to develop A. astaci genotyping molecular markers that target the mitochondrial DNA, increasing the sensitivity of the genotyping tools. The assays were validated on DNA extracts of A. astaci pure cultures, crayfish tissue extractions from crayfish plague outbreaks and tissue extractions from North American carriers. We demonstrate the presence of A. astaci genotype groups A and B in UK waters.

Aphanomyces astaci genotypes involved in recent crayfish plague outbreaks in central Italy

The oomycete Aphanomyces astaci is the causative agent of crayfish plague in native European freshwater crayfish. Molecular analyses showed that several distinct genotype groups of this pathogen, apparently associated with different original host taxa, are present in Europe. Tracking their distribution may contribute to understanding the introduction pathways of A. astaci. We used microsatellite markers to genotype the pathogen strains involved in 7 mass mortalities of the endangered indigenous crayfish Austropotamobius pallipes that occurred between 2009 and 2016 in the Abruzzi and Molise regions, central Italy. Three A. astaci genotype groups (A, B, and D, with the latter represented by 2 distinct multilocus genotypes) were identified, suggesting the existence of multiple infection sources even in a relatively small area. Most crayfish plague episodes were due to genotype groups associated with the North American host species Pacifastacus leniusculus and Procambarus clarkii, although these crayfish are not widespread in the study area. A. astaci genotype group A was detected not only in crayfish plague outbreaks but also in apparently healthy Astacus leptodactylus imported for human consumption from Armenia and kept alive in an aquaculture facility. Imports of chronically infected A. leptodactylus from Armenia, Turkey, and possibly Eastern Europe are an underestimated introduction pathway for A. astaci. Although we cannot exclude the presence of latently infected native populations of A. pallipes in the region, A. astaci infections in legally imported crayfish species considered vulnerable to crayfish plague may represent further reservoirs of A. astaci; this should be reflected in the policies regulating the trade of live crayfish.

New genotyping method for the causative agent of crayfish plague (Aphanomyces astaci) based on whole genome data

The oomycete Aphanomyces astaci causes crayfish plague, the most important disease of European freshwater crayfish species. Presumably introduced into Europe 150 years ago with the import of North American crayfish, A. astaci is highly pathogenic to European crayfish species. Five genotypes (A, B, C, D, and E) have been defined based on random amplified polymorphic DNA analysis (RAPD-PCR) from A. astaci pure cultures. The distinction of genotypes is an essential tool to conduct molecular epidemiological studies on crayfish plague and it has been used to clarify and better understand the history and spread of this disease in Europe. Whereas RAPD-PCR requires DNA from pure culture isolates, the development of genotyping tools that can be applied to DNA extracted from clinical samples allows a much wider application of genotyping studies, including revisiting historic samples. In this study, we present a new approach that adds to currently available methods for genotyping A. astaci strains directly from clinical crayfish samples. Whole-genome sequencing of A. astaci strains representing all currently known genotypes was employed, genomic regions unique to the respective genotype identified, and a PCR-based genotyping assay designed, which focuses on the presence/absence of PCR product after amplification with the genotype-specific primers. Our diagnostic methodology was tested using DNA extracts from pure A. astaci cultures, other Aphanomyces species and additional oomycetes, samples from a recent Italian crayfish plague outbreak and additional historical samples available in the Centre for Environment, Fisheries and Aquaculture Science laboratory. The new markers were reliable for pure culture and clinical samples from a recent outbreak and successfully discriminated genotype A, B, D, and E. The marker for genotype C required an additional sequencing step of the generated PCR product to confirm genotype.

Hidden sites in the distribution of the crayfish plague pathogen Aphanomyces astaci in Eastern Europe: Relicts of genetic groups from older outbreaks?

The crayfish plague agent Aphanomyces astaci is one of the world's most threatening invasive species. Originally from North America, the pathogen is being imported alongside American crayfish species, which are used for various purposes. In this study, we investigated the marginal, currently known distribution area of the pathogen in Eastern Europe by sampling narrow-clawed crayfish (Astacus leptodactylus) and spiny-cheek crayfish (Orconectes limosus) populations. In addition, using specific real-time PCR, we tested several marine decapod species, which also occur in brackish waters of the Danube at the West coast of the Black Sea and the Dniester River basin. By sequencing the nuclear chitinase gene, mitochondrial rnnS/rnnL DNA and by genotyping using microsatellite markers, we identified the A. astaci haplogroups of highly infected specimens. The A. astaci DNA was detected in 9% of the investigated A. leptodactylus samples, both in invaded and non-invaded sectors, and in 8% of the studied O. limosus samples. None of the marine decapods tested positive for A. astaci. The results revealed that narrow-clawed crayfish from the Dniester River carried the A. astaci B-haplogroup, while A. astaci from the Danube Delta belonged to the A- and B-haplogroups. In the invaded sector of the Danube, we also identified the A-haplogroup. Microsatellite analysis revealed a genotype identical to the genotype Up. It might be that some of the detected A. astaci haplogroups are relics from older outbreaks in the late 19th century, which may have persisted as a chronic infection for several decades in crayfish populations.

Crayfish plague in Japan: A real threat to the endemic Cambaroides japonicus

Global introductions of aquatic species and their associated pathogens are threatening worldwide biodiversity. The introduction of two North American crayfish species, Procambarus clarkii and Pacifastacus leniusculus, into Japan in 1927 seems to have negatively affected native Japanese crayfish populations of Cambaroides japonicus. Several studies have shown the decline of these native populations due to competition, predation and habitat colonization by the two invasive North American crayfish species. Here, we identify an additional factor contributing to this decline. We report the first crayfish plague outbreaks in C. japonicus populations in Japan, which were diagnosed using both histological and molecular approaches (analyses of the internal transcribed spacer region). Subsequent analyses of the mitochondrial ribosomal rnnS and rnnL regions of diseased specimens indicate that these outbreaks originated from a P. clarkii population and identify a novel haplotype of Aphanomyces astaci, d3-haplotype, hosted by P. clarkii. Overall, our findings demonstrate the first two cases of crayfish plague in Japan, and the first case in a non-European native crayfish species, which originated from the red swamp crayfish P. clarkii. This finding is a matter of concern for the conservation of the native freshwater species of Japan and also highlights the risk of introducing crayfish carrier species into biogeographic regions harboring species susceptible to the crayfish plague.

MtDNA allows the sensitive detection and haplotyping of the crayfish plague disease agent Aphanomyces astaci showing clues about its origin and migration

The oomycete Aphanomyces astaci, the causative agent of crayfish plague, is listed as one of the 100 worst invasive species in the world, destroying the native crayfish populations throughout Eurasia. The aim of this study was to examine the potential of selected mitochondrial (mt) genes to track the diversity of the crayfish plague pathogen A. astaci. Two sets of primers were developed to amplify the mtDNA of ribosomal rnnS and rnnL subunits. We confirmed two main lineages, with four different haplogroups and five haplotypes among 27 studied A. astaci strains. The haplogroups detected were (1) the A-haplogroup with the a-haplotype strains originating from Orconectes sp., Pacifastacus leniusculus and Astacus astacus; (2) the B-haplogroup with the b-haplotype strains originating from the P. leniusculus; (3) the D-haplogroup with the d1 and d2-haplotypes strains originating from Procambarus clarkii; and (4) the E-haplogroup with the e-haplotype strains originating from the Orconectes limosus. The described markers are stable and reliable and the results are easily repeatable in different laboratories. The present method has high applicability as it allows the detection and characterization of the A. astaci haplotype in acute disease outbreaks in the wild, directly from the infected crayfish tissue samples.

Resistance to the crayfish plague, Aphanomyces astaci (Oomycota) in the endangered freshwater crayfish species, Austropotamobius pallipes

The pathogen Aphanomyces astaci Schikora 1906 is responsible for the decline of the native crayfish species of Europe, and their current endangered status. This pathogenic species is native to North America and only colonizes aquatic decapods. The North American crayfish species have a high resistance to this pathogen, while species from other regions are highly susceptible. However, recent field and laboratory observations indicate that there might exist some populations with resistance against this disease. The objective of this study was to test the susceptibility of 8 selected native European crayfish populations of Austropotamobius pallipes Lereboullet 1858 from the Pyrenees. We challenged them against the genome sequenced strain AP03 of A. astaci isolated from a North American red swamp crayfish, Procambarus clarkii Girard 1852, in the Garrotxa Natural Park, Girona. The results showed that there are significant differences (P<0,001) among populations, although most of them show high mortality rates after the zoospore challenge with A. astaci. However, one population from Girona exhibited a 100% survival during a four-month monitoring period under the experimental conditions tested. Histological analyses revealed a high immune reaction in tissues examined, i.e., encapsulation and melanization of hyphae, similar to that found in North American resistant crayfish species. These results represent the first observation of a native European crayfish population showing high resistance towards the most virulent genotype of this pathogen, i.e., genotype Pc. The identification of this population is of key importance for the management of these endangered species, and represents a crucial step forward towards the elucidation of the factors involved in the immune reaction against this devastating pathogen.

Hosts and transmission of the crayfish plague pathogen Aphanomyces astaci: a review

The crayfish plague pathogen, Aphanomyces astaci Schikora, has become one of the most well-studied pathogens of invertebrates. Since its introduction to Europe in the mid-19th century, it has caused mass crayfish mortalities, resulting in drastic declines of local populations. In contrast, North American crayfish usually serve as latent carriers, although they may also be negatively affected by A. astaci infections under some circumstances. Recent research benefiting from molecular tools has improved our knowledge about various aspects of A. astaci biology. In this review, we summarize these advances, particularly with respect to the host range and transmission. We highlight several aspects that have recently received particular attention, in particular newly confirmed or suspected A. astaci hosts, latent A. astaci infections in populations of European crayfish, and the relationship between A. astaci genotype groups and host taxa.

Mitochondrial genomes and comparative genomics of Aphanomyces astaci and Aphanomyces invadans

The genus Aphanomyces (Saprolegniales, Oomycetes) includes species with a variety of ecologies from saprotrophs to plant and animal parasites. Two important species in this genus are A. astaci, the cause of crayfish plague and its close relative, A. invadans, which causes the epizootic ulcerative syndrome on fish. In this study, we have assembled and annotated the mitochondrial (mt) genomes of A. astaci and A. invadans from the whole genome shotgun sequence reads (PRJNA187372; PRJNA258292, respectively). The assembly was generated from A. astaci Pc-genotype strain APO3 and A. invadans strain NJM9701. The sizes of the mtDNAs were 49,489 bp and 49,061 bp for A. astaci and A. invadans, respectively. The species shared similar genetic content and organization encoding 35 proteins, two ribosomal RNAs, three putative open reading frames and 33 transfer RNAs of 19 amino acids for peptide synthesis. Both species also had a large inverted repeat region (LIR) of approximately 12 kb, the LIR contained large and small ribosomal RNAs and eight protein coding genes. These annotated mt genomes serve as a valuable genetic backbone for further development of diagnostic methods and phylogenetic and migration studies of the animal parasitic species of Aphanomyces.

Comparison of ITS, RAPD and ISSR from DNA-based genetic diversity techniques

ITS, RAPD-PCR and ISSR-PCR are most popular DNA-based techniques that are extensively applied in the determination of the genetic diversity of species among populations. However, especially for organisms having high genetic polymorphism, phylogenetic trees drawn from the results of these techniques may be different. For finding a meaningful phylogenetic tree, it should be compared phylogenetic trees obtained from these different techniques with geographic locations of populations. Lichens have a high genetic polymorphism and tolerance against different environmental conditions. In this study, these three DNA-based genetic diversity techniques were compared, using different populations of a lichen species (Xanthoria parietina). X. parietina was especially chosen because of its high genetic diversity in narrow zones. Lichen samples were collected from ten different locations in a narrow transition climate zone Bilecik (Turkey). Statistical analyses of all results were calculated using UPGMA analysis. Phylogenic trees for each technique were drawn and transferred to the Bilecik map for comparative analysis. The results of three techniques allowed us to verify that populations of X. parietina have high genetic variety in a narrow zone. But phylogenetic trees obtained from these results were found to be very different. Our comparative analysis demonstrated that the results of these techniques are not similar and have critical differences. We observed that the ITS method provides more clear data and is more successful in genetic diversity analyses of more asunder populations, in contrast to ISSR-PCR and RAPD-PCR methods.

Crayfish plague Aphanomyces astaci detected in redclaw crayfish, Cherax quadricarinatus in Taiwan

Between December 2013 and January 2014, five outbreaks of an unknown disease with moderate to high cumulative mortality were observed among the freshwater redclaw crayfish (Cherax quadricarinatus) populations at four crayfish farms in Miaoli and Changhua counties (northern Taiwan) and at one crayfish farm in Pingtung County (southern Taiwan). Polymerase chain reaction (PCR) analysis allowed the detection of Aphanomyces astaci DNA in dead crayfish. Histopathological examination revealed an infection of host tissue by fungal hyphae that presented as typical non-septate hyphae within the soft abdominal cuticle from the first to second segment and in the tail fan. In PCR assays completed for the detection of crayfish plague, an expected 568-bp product, specific for the A. astaci ITS gene, was obtained from all sub-adults and adults examined. In a comparison of our strains with the known strains of A. astaci in Europe, nucleotide sequence identities were very similar, with 99.8-100% sequence similarity in that gene region. Positive reactions to in situ hybridization, using a digoxigenin (DIG)-labelled DNA probe, further confirmed A. astaci as the causative agent. This is the first report concerning natural infection of A. astaci in freshwater redclaw crayfish in Asia.

Prevalence of the pathogen Aphanomyces astaci in freshwater crayfish populations in Croatia

The Oomycete Aphanomyces astaci is an obligate crayfish parasite that co-evolved with American crayfish species, and they therefore generally live in a balanced relationship. On the contrary, European native crayfish are highly susceptible to A. astaci, and infestation with it causes development of the lethal disease termed crayfish plague. Until now, 5 A. astaci strains have been described from the freshwater crayfish present in Europe. In this study we aimed to investigate the occurrence of the pathogen A. astaci in Croatian native and non-native crayfish populations, as well as to genotype established strains using microsatellite markers and obtain information on the pathogen's epidemiology. Our results showed that the pathogen is widespread in both native and non-native crayfish populations. Agent level, when positive, in non-native crayfish was generally low; in native species it was higher. Genotyping from microsatellites proved the presence of the B (Ps) strain in non-native species (Pacifastacus leniusculus), while the A (As) strain was detected from viable native species (Astacus astacus and Austropotamobius torrentium) that are distributed in areas lacking non-native crayfish. The genotype from A. torrentium differed from a typical A (As) by 1 allele. Strain B (Ps) was identified in native Astacus leptodactylus from the population that co-occurs with P. leniuscuslus. Interestingly, in 1 A. leptodactylus population both A (As) and B (Ps) strains were present.

Molecular cloning and expression of a GABA receptor subunit from the crayfish Procambarus clarkii

Molecular cloning has introduced an unexpected, large diversity of neurotransmitter hetero- oligomeric receptors. Extensive research on the molecular structure of the γ-aminobutyric acid receptor (GABAR) has been of great significance for understanding how the nervous system works in both vertebrates and invertebrates. However, only two examples of functional homo-oligomeric GABA-activated Cl(-) channels have been reported. In the vertebrate retina, the GABAρ1 subunit of various species forms homo-oligomeric receptors; in invertebrates, a cDNA encoding a functional GABA-activated Cl(-) channel has been isolated from a Drosophila melanogaster head cDNA library. When expressed in Xenopus laevis oocytes, these subunits function efficiently as a homo-oligomeric complex. To investigate the structure-function of GABA channels from the crayfish Procambarus clarkii, we cloned a subunit and expressed it in human embryonic kidney cells. Electrophysiological recordings show that this subunit forms a homo-oligomeric ionotropic GABAR that gates a bicuculline-insensitive Cl(-) current. The order of potency of the agonists was GABA > trans-4-amino-crotonic acid = cis-4-aminocrotonic acid > muscimol. These data support the notion that X-organ sinus gland neurons express at least two GABA subunits responsible for the formation of hetero-oligomeric and homo-oligomeric receptors. In addition, by in situ hybridization studies we demonstrate that most X-organ neurons from crayfish eyestalk express the isolated pcGABAA β subunit. This study increases the knowledge of the genetics of the crayfish, furthers the understanding of this important neurotransmitter receptor family, and provides insight into the evolution of these genes among vertebrates and invertebrates.