PARENT SESSION
Contributed Oral Session 104: Predator - Prey Ecology: Communities; Defenses
Wednesday, August 10, 1:30 PM - 5:00 PM, Meeting Room 521 A, Level 5, Palais des congrès de Montréal
Manipulating predation risk and pathogens to understand the evolution of Schreckstoff.
Chivers, Douglas 1, Kusch, Robin1, Michalk, Tracy1, Wisenden, Brian2, Mirza, Reehan 3, Brown, Grant3, 1 Biology Department, University of Saskatchewan, Saskatoon, CANADA2 Department of Biology, Minnesota State University Moorhead, Moorhead, USA3 Biology Department, Concordia University, Montreal, CANADA
ABSTRACT- Upon being captured many species of prey fishes release chemical substances from specialized epidermal club cells. These substances have been termed alarm cues or Schreckstoff (literally fear substances) because conspecifics that detect them often show dramatic anti-predator responses. For the past 60+ years it has been assumed that these chemicals evolved in the context of predation, yet few data are available to make this conclusion. We used a series of laboratory and field experiments to demonstrate that manipulating predation risk does not result in a facultative adjustment in alarm cell investment. In contrast, exposure to pathogens causes significant changes in investment. Minnows exposed to pathogenic oomycetes (Saprolegnia ferax or S. parasitica) show dramatic increases in alarm cell number. This has considerable implications as the growth of Saprolegnia is significantly reduced when in the presence of minnow skin but not the skin of other fish that does not contain Ostariophysan alarm cues. In a field survey, we found a positive correlation between the number of club cells in yellow perch (Perca flavescens) with the incidence of blackspot disease, metacercarial cysts of the trematode Uvulifer ambloplites. In a manipulative experiment we found that exposure of minnows to larval trematodes causes a dramatic increase in alarm cell investment. Our results provide strong evidence to suggest that at least some alarm cues may have evolved as protective agents against epidermal damage that benefits the sender directly, and that these chemical compounds have only secondarily acquired an ecological role as alarm cues.
Key words: Schreckstoff, alarm cells, pathogens, predation