Abstract
BackgroundSalmon lice, Lepeophtheirus salmonis (Copepoda: Caligidae), are highly important ectoparasites of farmed and wild salmonids, and cause multi-million dollar losses to the salmon aquaculture industry annually. Salmon lice display extensive sexual dimorphism in ontogeny, morphology, physiology, behavior, and more. Therefore, the identification of transcripts with differential expression between males and females (sex-biased transcripts) may help elucidate the relationship between sexual selection and sexually dimorphic characteristics.ResultsSex-biased transcripts were identified from transcriptome analyses of three L. salmonis populations, including both Atlantic and Pacific subspecies. A total of 35-43 % of all quality-filtered transcripts were sex-biased in L. salmonis, with male-biased transcripts exhibiting higher fold change than female-biased transcripts. For Gene Ontology and functional analyses, a consensus-based approach was used to identify concordantly differentially expressed sex-biased transcripts across the three populations. A total of 127 male-specific transcripts (i.e. those without detectable expression in any female) were identified, and were enriched with reproductive functions (e.g. seminal fluid and male accessory gland proteins). Other sex-biased transcripts involved in morphogenesis, feeding, energy generation, and sensory and immune system development and function were also identified. Interestingly, as observed in model systems, male-biased L. salmonis transcripts were more frequently without annotation compared to female-biased or unbiased transcripts, suggesting higher rates of sequence divergence in male-biased transcripts.ConclusionsTranscriptome differences between male and female L. salmonis described here provide key insights into the molecular mechanisms controlling sexual dimorphism in L. salmonis. This analysis offers targets for parasite control and provides a foundation for further analyses exploring critical topics such as the interaction between sex and drug resistance, sex-specific factors in host-parasite relationships, and reproductive roles within L. salmonis.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2835-7) contains supplementary material, which is available to authorized users.
Highlights
Salmon lice, Lepeophtheirus salmonis (Copepoda: Caligidae), are highly important ectoparasites of farmed and wild salmonids, and cause multi-million dollar losses to the salmon aquaculture industry annually
Two of the populations were from the Atlantic subspecies L. salmonis salmonis and were collected from separate bay management areas (BMA-2a and Bay Management Area (BMA)-2b) in the Bay of Fundy, New Brunswick [37], and the third was from the Pacific subspecies L. salmonis oncorhynchi [38] collected from the Broughton Archipelago, British Columbia (BC)
Including only the transcripts expressed in both sexes, a Principal Component Analysis (PCA) separated male and female samples along the first principal component (PC1; explaining the most variation) in all three populations, representing 50.2, 39.5 and 53.4 % of the transcriptional variation in Bay Management Area 2a (BMA-2a), BMA-2b, and Pacific lice, respectively (Fig. 1)
Summary
Lepeophtheirus salmonis (Copepoda: Caligidae), are highly important ectoparasites of farmed and wild salmonids, and cause multi-million dollar losses to the salmon aquaculture industry annually. Sexual dimorphism describes the phenotypic differences between sexes of the same species It is ubiquitous across the animal kingdom and is favored through a combination of sexual selection, intersexual competition for resources, and fundamental differences in reproductive roles [1,2,3]. Crustaceans are one of the most diverse animal taxa, comprising more than 850 families with approximately 67,000 species [18, 19] They are ecologically important, serving essential roles in the food chain and primary production in marine ecosystems [20]. Drug resistant strains of L. salmonis (and other sea lice species) have emerged globally (reviewed by [25]), threatening the sustainability and productivity of the industry
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