Temporal variation in the prevalence of the crayfish plague pathogen,Aphanomyces astaci, in three Czech spiny-cheek crayfish populations

Abstract

Key-words:Orconectes limosus, oomycete, infection prevalence, molecular detection, crayfish plagueNorth American crayfish species are natural hosts of the crayfish plague pathogen Aphanomyces astaci. The spiny-cheek crayfish Orconectes limosus, widespread in Central Europe, is the main reservoir of A. astaci in Czech Republic. We tested if there are temporal changes in the prevalence of infected individuals (i.e., the proportion of individuals in which the pathogen is detected) in spiny-cheek crayfish populations. Crayfish from three populations shown previously to be infected to different extents (high, intermediate and low), were repeatedly sampled in different years (2004−2010) and seasons. The presence of A. astaci in the soft abdominal crayfish cuticle was tested by specific amplification of the pathogen DNA. There was no substantial temporal variation in pathogen prevalence in the highly and very lowly infected populations. However, a significant long-term as well as seasonal decrease was found in the intermediately infected population. This decline could be related to a decrease in population density over the studied years, and to crayfish seasonal moulting, respectively. A reliable estimate of pathogen prevalence in American crayfish populations thus requires repeated monitoring over years, preferably during the same season before the main period of crayfish moulting. RÉSUMÉVariation temporelle de la prévalence de l'agent de la peste de l'écrevisse, Aphanomyces astaci, dans trois populations tchèques d'écrevisses américaines Mots-clés :

Spiny-cheek crayfish Orconectes limosus carry a novel genotype of the crayfish plague pathogen Aphanomyces astaci

“…Selection of a suitable source of crayfish for parasite isolation was based on data of its prevalence in Czech populations of O. limosus . We chose a pond in Smečno (Central Bohemia, 50°11.3 0 N, 14°02.8 0 E), as the vast majority (ca 95%) of individuals sampled repeatedly from this locality were found to be infected by A. astaci (Matasová et al, 2011). Furthermore, the infection dose in some local crayfish individuals was high (up to agent level A5 after Vrålstad et al, 2009).…”

Absence of the crayfish plague pathogen (Aphanomyces astaci) facilitates coexistence of European and American crayfish in central Europe

“…The lower prevalence limit for an obligate crayfish parasite like A. astaci remains unknown. It has been shown that the pathogen prevalence in a weakly infected population decreases from April to November, whereas the prevalence in a highly infected population remains high over several years and during different seasons (Matasová et al, 2011).…”

“…This, together with the catastrophic decline of native European crayfish (Bohman, Nordwall & Edsman, 2006;Holdich et al, 2009) suggests that the stable coexistence of American and European crayfish species is unlikely. Indications of pathogen-free American crayfish populations have also been found sporadically (Matasová et al, 2011;Skov et al, 2011). Indications of pathogen-free American crayfish populations have also been found sporadically (Matasová et al, 2011;Skov et al, 2011).…”

“…However, examples of apparently long-term coexistence have been found occasionally: for signal crayfish and noble crayfish (Astacus astacus) in Finland (Westman & Savolainen, 2001;Westman, Savolainen & Julkunen, 2002) and Sweden (Söderbäck, 1994), for spiny-cheek crayfish and native narrow-clawed crayfish (Astacus leptodactylus) in Romania and for spiny-cheek crayfish and noble crayfish in lakes from Poland (Schulz et al, 2006). Indications of pathogen-free American crayfish populations have also been found sporadically (Matasová et al, 2011;Skov et al, 2011). Schulz et al (2006) suggest that the displacement of noble crayfish by spiny-cheek crayfish in some lakes in Poland is caused by direct competition instead of via A. astaci infection of the European species.…”

Prevalence of the Crayfish Plague Pathogen Aphanomyces astaci in Populations of the Signal Crayfish Pacifastacus leniusculus in France: Evaluating the Threat to Native Crayfish

“…Providing conclusive evidence that some populations of potential A. astaci hosts (North American invasive crayfish) are likely to be uninfected requires much more intensive sampling effort [49]. Temporal fluctuations of the pathogen prevalence (or detectability) could also influence our results, as was shown for a Czech Orconectes limosus population studied over several seasons [54]. Thus, low A. astaci prevalence detected in some French signal crayfish populations does not mean that those pose a lower threat than other more infected populations of the same species.…”