Parasite fecundity decreases with increasing parasite load in the salmon louse Lepeophtheirus salmonis infecting Atlantic salmon Salmo salar

Abstract

Aggregation is common amongst parasites, where a small number of hosts carry a large proportion of parasites. This could result in density-dependent effects on parasite fitness. In a laboratory study, we explored whether parasite load affected parasite fecundity and survival, using ectoparasitic salmon lice (Lepeophtheirus salmonis Krøyer, 1837) infecting Atlantic salmon (Salmo salar) hosts. We found a significant reduction in fecundity with higher parasite load, but no significant effect on survival. Together with previous findings, this suggests that stronger competition amongst female lice under high parasite load is a more likely explanation than increased host immune response.

Invest more and die faster: The life history of a parasite on intensive farms

“…It is somehow unclear at this stage what consequences such adaptive changes may have in epidemiological terms, and knowledge about the life history of salmon lice is still expanding (e.g., (Ugelvik, Mo, et al., ; Ugelvik, Skorping, et al., ). From earlier studies, it seems that faster life histories correlate with higher levels of virulence (Mennerat et al., ), which is consistent with virulence evolution theory and more specifically the existence of a virulence—transmission tradeoff (Alizon, Hurford, Mideo, & Van Baalen, ; Cressler, Mc, Rozins, Van den Hoogen, & Day, ).…”

“…The total number of eggs contained in each egg string was estimated by dividing total egg string length by average egg length, and fecundity was calculated as the sum for each pair of egg strings (Mennerat et al., ; Ugelvik, Skorping, & Mennerat, ). Fecundity of wild and farmed salmon lice was compared using a linear mixed‐effect model ( lmer ) with status (farmed vs. wild) and reproductive event (from 1 to 5) as factors.…”

“…Fecundity of wild and farmed salmon lice was compared using a linear mixed‐effect model ( lmer ) with status (farmed vs. wild) and reproductive event (from 1 to 5) as factors. Because parasite load varied across fish hosts and is known to negatively affect salmon lice fecundity (Ugelvik, Mo, Mennerat, & Skorping, ; Ugelvik, Skorping, et al., ), we also included the number of female lice on each fish as a covariate. Room (1 vs. 2) and Tank (nested within Room) were used as random effect factors.…”

Statistical modelling of sea lice count data from salmon farms in the Faroe Islands

“…Considering model limitations this can to some extent distort the conclusions derived; for example, if mobile males in fish farms can leave their hosts to seek out females, this possibly leads to a higher reproduction at low densities. At higher densities the lice fecundity—but not the lice survival—is found to be reduced (Ugelvik, Skorping, & Mennerat, ). However, this effect is most important at high parasite loads, above 2–4 female lice/fish, and before reaching these levels in fish farms, the various treatments reduce the densities.…”

Production, mortality, and infectivity of planktonic larval sea lice, Lepeophtheirus salmonis (Krøyer, 1837): current knowledge and implications for epidemiological modelling

“…Host-related and abiotic conditions may not be the only factors governing salmon louse fecundity. As an example, intraspecific competition between lice on a given host is suggested to result in reduced fecundity with increasing salmon louse infection densities (Ugelvik et al, 2017). Louse fecundity is clearly the product of a number of biotic and abiotic factors, most of which remain to be fully characterised.…”