Evol Ecol Res 19: 517-527 (2018)     Full PDF if your library subscribes.

The location of damage-released alarm cues in a cichlid fish

Denis Meuthen^1,2, Patrick Flege¹, Ronja Brandt¹ and Timo Thünken¹

¹Institute for Evolutionary Biology and Ecology, University of Bonn, Bonn, Germany and ²Department of Biology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada

Correspondence: D. Meuthen, Department of Biology, University of Saskatchewan, 112 Science Place, Saskatoon, Saskatchewan S7N 5E2, Canada. email: denis.meuthen@usask.ca

ABSTRACT

Background: Damage-released alarm cues are reliable indicators of predation risk for prey fishes. Based on observations early in the twentieth century, alarm cues were for a long time assumed to be produced and located exclusively within skin-based club or sacciform cells. However, recent studies have suggested that these cells may be unrelated to the alarm function and that fish respond similarly to blood cues, mucus or to muscle tissue extracts as they do to skin extracts. Continuing to assume that alarm cues are primarily located within the skin and using skin extracts in contemporary alarm cue research may thus be problematic.

Hypothesis: In fish, damage-released alarm cues are not located exclusively within the skin but are also present elsewhere in the body.

Organism: Pelvicachromis taeniatus, a Western African river cichlid.

Site of experiments: Nine-litre (30 x 20 x 20 cm) experimental tanks in the wet lab of the Institute for Evolutionary Biology and Ecology at the University of Bonn, Germany.

Methods: Since reduced activity is a common adaptation to reduce predation risk in prey animals, we measured the change in activity of individual fish in response to extracts obtained from skin, muscle tissue, blood, mucus, liver tissue, intestine tissue, and spleen tissue, as well as to a distilled water control. First, we measured individual responses when extracts were diluted proportional to their contribution to a whole-body extract concentration that is known to induce a change in activity. Then, in a second experiment, we exposed fish to the same extracts but now diluted to have the same concentration for each tissue. Furthermore, we histologically analysed the P. taeniatus epidermis.

Results and conclusion: Only muscle tissue extracts induced a significant reduction in activity relative to the water control in both experiments. Although P. taeniatus possesses sacciform cells in its epidermis, the effects of skin extracts and other tissue extracts on activity remain ambiguous in this species. Consequently, our research provides support for other studies indicating that alarm cues are not exclusively located in skin tissue and suggests a more careful approach to future alarm cue research such as applying whole-body extracts instead of skin extracts until the identity of alarm cues has been elucidated.

Keywords: alarm cues, club cells, Pelvicachromis taeniatus, predation risk, predator, skin extract.

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