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

Abstract

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.

Preliminary survey of Aphanomyces sp. associated with native and invasive crayfish in the Lower Susquehanna watershed of South Central Pennsylvania

“…Morbid A. astaci infections occur when short-lived encysted zoospores attach to the host surface and germinate; the resulting hyphae penetrate the cuticle, and in a susceptible host, will invade the surrounding tissue leading to necrosis and eventual death (Rezinciuc et al 2015). High mortality rates, up to 100%, have been observed for many native European species (Unestam 1969;Alderman et al 1987), although variation has been documented (Mart ın-Torrijos et al 2017;Svoboda et al 2017). Conversely, North American crayfish species show reduced susceptibility to A. astaci infection by encapsulating the penetrating hyphae in melanin; higher constitutive expression of the prophenoloxidase pathway is thought to account for this defense mechanism (Cerenius et al 2003;.…”

Microbial pathogens of freshwater crayfish: A critical review and systematization of the existing data with directions for future research

“…In addition, pathogenicity is a result of interaction between the microbe and host's immune system, which may have an exaggerated response (i.e., exhibit “immunopathology”) and can also adapt the level of response to an infection. Such adaptation in host–microbe interactions is visible in the case of effects of A. astaci on some European ICS: in the past, certain crayfish plague strains expressed high virulence in populations of highly susceptible native crayfish, however, chronically infected ICS populations were observed over the last few years (e.g., A. astacus : Jussila et al., 2011; Makkonen et al., 2012; A. pallipes : Martín‐Torrijos et al., 2017; A. torrentium : Kušar et al., 2013; P. leptodactylus : Kokko et al., 2018). However, none of the studies analysed the underlying causes of observed adaptations to the host– A. astaci co‐existence, but only speculate that they could be driven by changes in the A. astaci virulence, host response or both (Kokko et al., 2012; Kušar et al., 2013; Martín‐Torrijos et al., 2017).…”

“…We briefly present some of the most well‐established crayfish diseases. The crayfish plague is one of the most researched and the most detrimental crayfish diseases that causes significant declines of crayfish populations in Europe and other regions (Martín‐Torrijos et al., 2017, 2018). The causative agent of this disease, oomycete Aphanomyces astaci Schikora, 1906, spreads through water by viable zoospores (Oidtmann et al., 2002).…”

Ecological plasticity and commercial impact of invasive marbled crayfish populations in Madagascar

“…These findings suggest that either the marbled crayfish in Madagascar do not transmit the crayfish plague agent or that the (as yet unidentified) A. astaci strain is not very virulent. It is also possible that Astacoides is resistant to the disease, similar the American crayfish species and the European freshwater crayfish Autropotamobius pallipes [37, 38]. It will be important to clarify the infection status of Astacoides in future studies.…”