ONTOGENETIC CHANGES IN RESPONSE TO HETEROSPECIFIC ALARM CUES BY JUVENILE LARGEMOUTH BASS ARE PHENOTYPICALLY PLASTIC

Abstract

AbstractJuvenile largemouth bass (Micropterus salmoides) undergo an ontogenetic change in their response to chemical alarm cues of a heterospecific prey guild member (finescale dace, Phoxinus neogaeus), shifting from an antipredator to a foraging response at a standard length of 50 to 55 mm. We conducted a laboratory study to determine if: (1) this shift is fixed or phenotypically plastic, and (2) juvenile bass respond to the alarm cues of a non-Ostariophysan prey guild member. Juvenile bass were reared on high versus low food diets for 10 weeks prior to the experiment, and then exposed to heterospecific skin extracts (the source of chemical alarm cues). When exposed to the skin extracts of finescale dace or green sunfish (Lepomis cyanellus), juvenile bass exhibited a significant positive relationship between standard length and horizontal and vertical area use and time spent moving. In addition, there was a significant effect of body type, with bass with deeper body morphs shifting from antipredator to foraging responses earlier than those with shallower body morphs. Bass exhibited no change in behaviour to swordtail (Xiphophorus helleri) skin extracts, which lack a chemical alarm cue recognized by bass. These data strongly suggest that the developmental point at which bass switch from an antipredator to a foraging response is phenotypically plastic and dependant upon body morphology, and that bass are capable of using the chemical alarm cue of at least two, taxonomically diverse, heterospecific prey guild members as social information cues.