Abstract
The evolution of alarm signals has puzzled evolutionary ecologists for decades. This is particularly true for alarm cues (‘Schreckstoff’) which are present in many fishes. They are passively released through injuries and signal the presence of a predator. Although the benefits for conspecific receivers are obvious (they can adjust their behavior to avoid predation), those for the senders are not which is, however, a necessary requirement for the evolution of alarm signals. Several hypotheses relying on potential direct benefits for the senders have been suggested. Alarm cues might attract secondary predators which in turn might increase the escape probability of the sender. A primary immune enhancing role was suggested as well. An alternative explanation is based on Hamilton’s inclusive fitness theory stating that individuals can indirectly increase their fitness by increasing the survival of genetically related individuals (‘kin selection theory’). If related individuals preferentially benefit from alarm signals, for instance by being more receptive to kin-alarm cues, senders could increase their inclusive fitness. Here, we investigate whether individuals of the cichlid fish Pelvicachromis taeniatus respond differentially to alarm cues derived from kin and non-kin. P. taeniatus possesses alarm cues and is known to adjust its behavior when exposed to alarm cues. We measured the change in activity after the addition of alarm cues (derived from kin- and non-kin) relative to a control treatment. Reduced activity is a widespread behavioral adaptation to reduce predation risk in prey organisms. Fish of the alarm cue treatments significantly reduced their activity relative to control fish. However, fish did not respond differentially to alarm cues derived from kin and non-kin suggesting that potential inclusive fitness benefits are not mediated by responses specific to individual alarm cues. We discuss alternative mechanisms such as kin-related grouping and mating preferences potentially leading to kin-biased alarm cue perception.
Highlights
Alarm signals are signals that are emitted by individuals in the presence of predators
The change in activity of female P. taeniatus was significantly affected by the treatment (χ2 = 10.057, p = 0.007, Figure 1)
Generally, activity of female P. taeniatus was affected by the presence of conspecific alarm cues
Summary
Alarm signals are signals that are emitted by individuals in the presence of predators. These signals may divert predator attention or discourage it to attack and alert conspecifics[1]. Chemical alarm signals are widespread especially due to the large number of water-soluble compounds[8] (insects[9], crustaceans[10], asteroids[11,12], gastropods[13,14], amphibians[15,16] and fishes[17]). Signaling is usually costly for the individual sender[18] and often appears to primarily benefit the receivers. To evolve and be maintained by natural selection, the fitness benefits for the signaling individual must override its costs
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