Abstract
BackgroundThe salmon louse Lepeophtheirus salmonis is a parasitic copepod that infects salmonids in the Pacific and Atlantic oceans. Although considered as a single species, morphological and biological differences have been reported between lice from the two oceans. Likewise, studies based on nucleotide sequencing have demonstrated that sequence differences between Atlantic and Pacific L. salmonis are highly significant, albeit smaller than the divergence observed between congeneric copepod species.ResultsWe demonstrated reproductive compatibility between L. salmonis from the two oceans and successfully established F2 hybrid strains using separate maternal lines from both the Pacific and Atlantic. The infection success for the F2 hybrid strains were similar to results typically observed for non hybrid lice strains in the rearing facility used. Lepeophtheirus salmonis COI and 16S sequences divergence between individuals from the Pacific and the Atlantic oceans was high compared to what may be expected within a copepod species and phylogenetic analysis showed that they consistently formed monophyletic clades representing their origin from the Pacific or Atlantic oceans.ConclusionsLepeophtheirus salmonis from the Pacific and Atlantic oceans are reproductively compatible at least until adults at the F2 hybrid stage, and should not be regarded as separate species based on reproductive segregation or sequence divergence levels. Reported biological and genetic differences in L. salmonis seen in conjunction with the reported genetic diversity commonly observed between and within species demonstrate that Atlantic and Pacific L. salmonis should be regarded as two subspecies: Lepeophtheirus salmonis salmonis and L. salmonis oncorhynchi subsp. nov.
Highlights
The salmon louse Lepeophtheirus salmonis is a parasitic copepod that infects salmonids in the Pacific and Atlantic oceans
The number of adult females used to produce the copepodids founding each generation and the numbers of copepodids and resulting offspring for the hybrid strains are given in Tables 1 and 2
We suggest that Atlantic and Pacific L. salmonis should be regarded as two subspecies: Lepeophtheirus salmonis salmonis and Lepeophtheirus salmonis oncorhynchi subsp. nov. urn:lsid:zoobank.org:pub:8CABA147FB3D-4DFA-AF37-7FFB74AFB454
Summary
The salmon louse Lepeophtheirus salmonis is a parasitic copepod that infects salmonids in the Pacific and Atlantic oceans. The salmon louse (Lepeophtheirus salmonis Krøyer, 1838) is a marine ectoparasitic copepod found on salmonids in the northern hemisphere This parasite causes large economic losses in commercial cage-based salmon aquaculture [1,2], and has been causatively associated with declines in wild salmonid populations [3]. Lepeophtheirus salmonis displays a life cycle comprising eight stages: Two planktonic nauplius stages, an infective copepodid stage, two host-anchored chalimus stages and two motile preadult stages, before they molt into reproductive adults [7]. It displays considerable potential for dispersal, passively with ocean currents or while attached to its highly migratory hosts. At more modest infection levels, L. salmonis causes the host stress and initiates a cascade of gene regulation associated with stress response functions [14,15]
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