The different aspects in motion of the three reproductive stages of Pseudodiaptomus annandalei (Copepoda, Calanoida)

Abstract

Individual variation in morphology is linked to organism displacement in numer-ous taxa. This relationship among adult copepods has previously received littleattention. In this study, we questioned whether the swimming behaviour of threemorphologically different adult states of Pseudodiaptomus annandalei (i.e. males, non-ovigerous and ovigerous females) could be differentiated. Two-dimensional videoobservations revealed that some swimming patterns were common to all adultstates, whereas others were more specific to one of the adult states. Males swim ina straight way, ovigerous females exhibit jerky swimming behaviour, and non-ovigerous females exhibit slow and steady gliding, interrupted occasionally byjumps. Direct measures of the swimming behaviour (i.e. mean, maximal and prob-ability density of speed) for a large number of trajectories were considered first.Deeper comparisons of each sexual state were conducted using scale-dependant(i.e. net-to-gross displacement ratio), scale-independent (power spectrum, multi-fractal) metrics and symbolic analysis. The combined analysis emphasized thedifferences (e.g. male swimming patterns were slower and less complex, both ovi-gerous and non-ovigerous female swimming patterns were faster and morecomplex) and similarities (e.g. all swimming patterns were different from theBrownian motion) between adult swimming patterns. The multi-fractal approachidentified differences between the two sexes suggesting differential swimming be-haviour. In an ecological discussion, we relate these differences to mating andpredator avoidance strategies.KEYWORDS: swimming behaviour; sexual dimorphism; calanoid copepod;Pseudodiaptomus annandalei