PATTERNS OF PAIR FORMATION AND MATING IN AN ECTOPARASITIC CALIGID COPEPOD LEPEOPHTHEIRUS-SALMONIS (KROYER 1837) - IMPLICATIONS FOR ITS SENSORY AND MATING BIOLOGY

Non-invasive observations of single cohort and manipulated populations of the sealouse on laboratory-maintained salmon established the seque nce of reproductive events and mating. Protandry occurs with adult mal e emergence synchronized with pre-adult II female emergence, the stage at which most pair formation and pre-copular guarding takes place. Ma le competence for pair formation and mating was achieved within 24h of the final moult and pairing occurred according to the preference hier archy, virgin adult females > pre-adult II females much greater than p re-adult I females. This hierarchy broke down when the adult male to u nmated female ratio increased rapidly. Males mated successfully not on ly with newly moulted adult females, but also with older virgin female s in which enlargement of the genital complex and premature extrusion of egg strings had occurred. Multiple mating by adult males was demons trated and may be widespread. Significant inter-host transfer was also demonstrated. Adult males were more mobile than adult females and sho wed significantly more inter-host transfer. Ablation of the distal tip of the antennules significantly reduced the success of host-finding, pair formation and males' mating.