Polyandry in the ectoparasitic copepod Lepeophtheirus salmonis despite complex precopulatory and postcopulatory mate-guarding

Lepeophtheirus salmonis (Kroyer) is an economically important pest on cultured salmonids in the North Atlantic, and has been implicated in declines of some wild salmonid populations. Males inseminate newly-moulted adult females following the cementing of a pair of spermatophores to the female's genital complex. Females can produce multiple pairs of eggstrings over a period of months, but this species is reported to be monogamous as a result of blockage of the female's copulatory ducts by the spermatophore tubules. On wild and farmed Atlantic salmon Salmo salar L., respectively, 88 and 78% adult females sea lice bore the typical pair of spermatophores, while 11 and 19 % lacked spermatophores. A very few individuals (1 % wild, 3 % farmed) bore 3 or 4 spermatophores, showing that apparently successful multiple mating is possible. Multiple paternity was confirmed by dual-locus microsatellite typing of offspring for 3 of 7 females carrying 4 spermatophores, but also for 2 of 3 females carrying a single pair of spermatophores. Probably most females on wild fish lose their initial spermatophores and are polygamous during their extended ovigerous lifetime, although effective blockage of the copulatory ducts by the first male almost certainly assures single paternity of the first few pairs of eggstrings. The total level of polyandry or sperm competition faced by males may be relatively low. The ecological implications of multiple paternity are discussed within the context of integrated pest management as a strategy of ameliorating L. salmonis infestations impacting both wild and farmed salmonids