The salmon louse Lepeophtheirus salmonis (Copepoda: Caligidae) life cycle has only two chalimus stages

Each year the salmon louse (Lepeophtheirus salmonis Krøyer, 1838) causes multi-million dollar commercial losses to the salmon farming industry world-wide, and strict lice control regimes have been put in place to reduce the release of salmon louse larvae from aquaculture facilities into the environment. For half a century, the Lepeophtheirus life cycle has been regarded as the only copepod life cycle including 8 post-nauplius instars as confirmed in four different species, including L. salmonis. Here we prove that the accepted life cycle of the salmon louse is wrong. By observations of chalimus larvae molting in incubators and by morphometric cluster analysis, we show that there are only two chalimus instars: chalimus 1 (comprising the former chalimus I and II stages which are not separated by a molt) and chalimus 2 (the former chalimus III and IV stages which are not separated by a molt). Consequently the salmon louse life cycle has only six post-nauplius instars, as in other genera of caligid sea lice and copepods in general. These findings are of fundamental importance in experimental studies as well as for interpretation of salmon louse biology and for control and management of this economically important parasite.publishedVersio

Le Liknon, le "Masque" et le Poteau. Images du rituel dionysiaque

Bérard Claude, Bron Christiane. Le Liknon, le "Masque" et le Poteau. Images du rituel dionysiaque. In: Mélanges Pierre Lévêque. Tome 4 : Religion. Besançon : Université de Franche-Comté, 1990. pp. 29-44. (Annales littéraires de l'Université de Besançon, 413

Le Liknon, le "Masque" et le Poteau. Images du rituel dionysiaque

Bérard Claude, Bron Christiane. Le Liknon, le "Masque" et le Poteau. Images du rituel dionysiaque. In: Mélanges Pierre Lévêque. Tome 4 : Religion. Besançon : Université de Franche-Comté, 1990. pp. 29-44. (Annales littéraires de l'Université de Besançon, 413

The Salmon Louse Lepeophtheirus salmonis (Copepoda: Caligidae) Life Cycle Has Only Two Chalimus Stages

Each year the salmon louse (Lepeophtheirus salmonis Kroyer, 1838) causes multi-million dollar commercial losses to the salmon farming industry world-wide, and strict lice control regimes have been put in place to reduce the release of salmon louse larvae from aquaculture facilities into the environment. For half a century, the Lepeophtheirus life cycle has been regarded as the only copepod life cycle including 8 post-nauplius instars as confirmed in four different species, including L. salmonis. Here we prove that the accepted life cycle of the salmon louse is wrong. By observations of chalimus larvae molting in incubators and by morphometric cluster analysis, we show that there are only two chalimus instars: chalimus 1 (comprising the former chalimus I and II stages which are not separated by a molt) and chalimus 2 (the former chalimus III and IV stages which are not separated by a molt). Consequently the salmon louse life cycle has only six post-nauplius instars, as in other genera of caligid sea lice and copepods in general. These findings are of fundamental importance in experimental studies as well as for interpretation of salmon louse biology and for control and management of this economically important parasite

Size measurements for <i>L</i><i>. salmonis</i> larvae incubated in hatching wells.

<p>Pre-incubation measurements for incubated samples are shown as blue circles (chalimus I/II category) and red triangles (chalimus III/IV category). The post-incubation measurements are shown as blue triangles (chalimus III-IV category) and red diamonds (preadults). For molted individuals the pre- and post-incubation measurements are connected with a dotted line. Frames I-IV represent the sizes for the chalimus I-IV stages as reported by Schram [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0073539#B19" target="_blank">19</a>] and durations as reported by Johnson and Albright [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0073539#B28" target="_blank">28</a>].</p

Cluster analysis and cluster number selection for chalimi.

<p>The proportion of unexplained variability in the dataset as a function of the number of chalimus clusters is shown in A. Total length (TL), cephalothorax length (CL) and cephalothorax width (CW) for experiment 2 (mm) are shown in B. Chalimus larvae assigned to chalimus cluster 1 are shown as diamonds. Chalimus larvae assigned to chalimus cluster 2 are shown as circles. Preadult 1samples are shown as triangles. Color codes: black=sex not determined, blue=male, red=female. Post-incubation measurements are not shown except for preadult I females (red triangles). The assignments to cluster (chalimus cluster 1 and 2) and morphological group (chalimus I/II, chalimus III/IV or preadult category) were congruent for all samples except the individual marked with an arrow.</p

Chalimus larvae and shed exuviae.

<p>Chalimus larvae and shed exuviae belonging to the chalimus I/II category (A,B) and the chalimus III/IV category (C,D). The exuviae shown are the actual exuviae shed by the depicted larvae. The total length (TL), cephalothorax length (CL) and cephalothorax width (CW) measurements are shown in A.</p