Effects of the vertically transmitted microsporidian Facilispora margolisi and the parasiticide emamectin benzoate on salmon lice (Lepeophtheirus salmonis)

Abstract

BackgroundMicrosporidia are highly specialized, parasitic fungi that infect a wide range of eukaryotic hosts from all major taxa. Infections cause a variety of damaging effects on host physiology from increased stress to death. The microsporidian Facilispora margolisi infects the Pacific salmon louse (Lepeophtheirus salmonis oncorhynchi), an economically and ecologically important ectoparasitic copepod that can impact wild and cultured salmonids.ResultsVertical transmission of F. margolisi was demonstrated by using PCR and in situ hybridization to identify and localize microsporidia in female L. salmonis and their offspring. Spores and developmental structures of F. margolisi were identified in 77% of F1 generation copepods derived from infected females while offspring from uninfected females all tested negative for the microsporidia. The transcriptomic response of the salmon louse to F. margolisi was profiled at both the copepodid larval stage and the pre-adult stage using microarray technology. Infected copepodids differentially expressed 577 transcripts related to stress, ATP generation and structural components of muscle and cuticle. The infection also impacted the response of the copepodid to the parasiticide emamectin benzoate (EMB) at a low dose of 1.0 ppb for 24 h. A set of 48 transcripts putatively involved in feeding and host immunomodulation were up to 8-fold underexpressed in the F. margolisi infected copepodids treated with EMB compared with controls or either stressor alone. Additionally, these infected lice treated with EMB also overexpressed 101 transcripts involved in stress resistance and signalling compared to the other groups. In contrast, infected pre-adult lice did not display a stress response, suggesting a decrease in microsporidian virulence associated with lice maturity. Furthermore, copepodid infectivity and moulting was not affected by the microsporidian infection.ConclusionsThis study demonstrated that F. margolisi is transmitted vertically between salmon louse generations and that biological impacts of infection differ depending on the stage of the copepod host. The infection caused significant perturbations of larval transcriptomes and therefore must be considered in future studies in which impacts to host development and environmental factors are assessed. Fitness impacts are probably minor, although the interaction between pesticide exposure and microsporidian infection merits further study.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-017-4040-8) contains supplementary material, which is available to authorized users.

Analysis of Predicted Host–Parasite Interactomes Reveals Commonalities and Specificities Related to Parasitic Lifestyle and Tissues Tropism

“…In the analysis, we found the biological process Protein folding enriched across 14 interactomes (Figure 2A). This biological process has been identified already as enriched and crucial in several host–pathogen systems, including mouse– P. falciparum (18); human– M. tuberculosis (42); B. glabrata – S. mansoni (43); L. salmonis – F. margolisi (44), based on transcriptomics and proteomics data. The protein folding biological process appears to be a conserved natural response to the infection and is related to a response to stress.…”

Evaluating the potential for sea lice to evolve freshwater tolerance as a consequence of freshwater treatments in salmon aquaculture

“…Going one step further, Borchel et al (2018) noted that 2 of the HSPs expressed by L. salmonis salmonis copepodids in response to salinity stress were also induced following exposure to the anti-louse treatment hydrogen peroxide. Poley et al (2017) also showed that HSc70 and HSP60 were induced in L. salmonis oncorhynchi copepodids infected with the microsporidian Facilispora margolisi and exposed to the anti-louse treatment emamectin benzoate. Other known pathways for freshwater tolerance in crustaceans include reduced cuticular permeability, ability to excrete urine that is more dilute than hemolymph and adaptation to lower hemolymph osmolality relative to stenohaline species (Pequeux 1995).…”

Population Genetics of Parasites and Their Arthropod Hosts

“…If the parasite traces the same route as the host's genetic information-is vertically transmitted-then co-structuring can be expected. Vertical transmission may occur transovarially, such as in many Microsporidia, for example Facilispora margolisi Jones et al parasitising the copepod Lepeophtheirus salmonis (Krøyer) [15]. Vertical transmission may also occur if the parasite from parent host taints the egg integument which is then ingested by the offspring [16].…”