Dimethyl sulfide triggers search behavior in copepods

The oceans are nutritionally dilute, and finding food is a major challenge for many zooplanktonic predators. Chemodetection is necessary for successful preycapture, but little is known about the infochemicals involved in the interaction between herbivorous copepods and their phytoplankton prey. We used females of Temora longicornis to investigate chemodetection of dimethyl sulfide (DMS) in this calanoid copepod and quantified its behavioral response to plumes of DMS using video-microscopy in combination with laser-sheet particle image velocimetry (PIV). Slow injection of a 1-mmol L21 DMS plume into the feeding current resulted in a characteristic behavioral pattern (‘‘tailflapping’’), a redirection of flow equivalent to 30% of the average current velocity, and changes in the location of flow-induced vortices. In free-swimming individuals, this likely results in somersault-type movements that are associated with search behavior in copepods. In comparison to seawater controls, DMS injections significantly increased the average number of tail-flaps per copepod during the first 2 s after exposure to DMS gradients. Our results demonstrate that copepods can detect and react to plumes of DMS and suggest that this biogenic trace gas can influence the structure and function of pelagic foodwebs. Calanoid copepods (average size range 0.5–2 mm) show a variety of behavioral patterns related to vertical migration, swarming, feeding, mating, and swimming (Mauchline 1998). Jumping and escape reactions involve fast and rhythmical beating of the swimming legs that propel the copepods at velocities of 10–100 mm s21 (van Duren and Videler 2003). Various swimming modes are found in suspension feeders that create regular feeding currents with their mouth appendages (Fig. 1; Koehl and Strickler 1981; Malkiel et al. 2003) and result in swimming velocities of a few mm s21 when foraging (van Duren and Videler 2003). This linkage between feeding and swimming greatly increases the prospects of encountering prey (Gerritsen and Strickler 1977). Instead of depending on random encounters with other organisms, however, behavioral studies (Poulet and Marsot 1978; Koehl and Strickler 1981; Gill and Poulet 1988), ultrastructural analyses (Gill 1986), and modeling efforts (Moore et al. 1999; Jiang et al. 2002; Jackson and Kiørboe 2004) suggest that copepods use mechanoreception and chemoreception when searching