Contextual chemosensory urine signaling in an African cichlid fish

Abstract

Chemosensory signaling is crucial for communication in many fish species, but little is known about how signalers modulate chemical output in response to sensory information and social context. Here, we tested the hypothesis that dominant male African cichlid fish (Astatotilapia burtoni) use urine signals during social interactions, and demonstrate that this signaling depends on social context (reproductive; territorial) and on available sensory information (visual cues; full interaction). We injected males with dye to visualize urine pulses and exposed them to full sensory information or visual cues alone of four types: (1) dominant male; (2) gravid (reproductively receptive) females; (3) mouth-brooding (non-receptive) females; or (4) control (no fish). We found that males released urine sooner and increased their urination frequency when visually exposed to gravid females as compared with mouth-brooding females and or no-fish controls. While males could distinguish female reproductive states using visual cues alone, courtship behavior rates were ∼10-fold higher when they fully interacted with gravid females compared with receiving visual cues alone. Males also increased their urination and territorial behaviors when exposed to another male, suggesting that chemical signals may convey information on dominance status. These data support the hypothesis that dominant males use urine as a chemical signal and adjust the frequency of their urine output based on contextual information.

Fig. 1.

Experimental protocol and example of pulsatile urine release from a dominant male Astatotilapia burtoni. (A) Experimental tank set-up during stimulus trials. On the day of the experiment, the dye-injected subject dominant male in the center compartment was isolated from the acclimation fish (left) with an opaque barrier (pre-stimulus isolation) and then exposed to one of four different stimulus conditions (right). The subject male was also exposed to the stimulus fish in two different sensory protocols: (1) the opaque barrier separating the subject and stimulus fish was removed to provide only visual cues to the subject, while keeping the fish separated by an impermeable transparent barrier, or (2) the stimulus fish were introduced into the subject males' compartment, providing full sensory information and physical interaction. (B) Example of a urine pulse (arrow) released from a dominant male that was visually exposed to another dominant male.

Fig. 2.

Urine pulses from dominant male A. burtoni were not coincident with courtship or territorial behavioral displays. Examples of the temporal sequence of urine pulses and reproductive or territorial behaviors produced by individual dominant males when exposed to gravid females (A, full sensory interaction) or another dominant male (B, visual cues only). Each vertical mark represents a single urine pulse or behavioral display across the 30 min trial. Quantified behaviors were either reproductive courtship displays (A) or territorial displays (B).

Fig. 3.

Dominant male A. burtoni alter their chemical urine signaling in response to contextual sensory social cues. The percentage change in urination rate (pulses min^–1 between pre-stimulus isolation and stimulus condition) was higher when dominant males were exposed to either another dominant male or to gravid females than when they were exposed to mouth-brooding females or an empty compartment (no-fish control). Urination rates were also higher during the visual only compared with full interaction trials when males were exposed to either gravid females or a dominant male. Lines and asterisks indicate statistical differences: *P<0.05; **P<0.01. N=10 different subject males for each condition. Control bars are the same data set plotted next to both female and male exposure conditions for comparison.

Fig. 4.

Dominant male A. burtoni change their latency to start chemical urine signaling in response to contextual sensory social cues. Males released their first urine pulse sooner (reduced latency) when exposed to either another dominant male or gravid females, but there was no difference between visual only and full interaction trials for either stimulus. Males also showed a shorter latency when fully exposed to brooding females compared with visual only trials. Lines and asterisks indicate statistical differences: *P<0.05; **P<0.01. N=10 different subject males for each condition. Control bars are the same data set plotted next to both female and male exposure conditions for comparison.

Fig. 5.

Dominant male A. burtoni alter their rate of courtship and territorial behaviors in response to contextual sensory social cues. The total number of behaviors (mean ± s.e. per 30 min stimulus trial) was highest when dominant males were fully exposed to either gravid females or another dominant male compared with brooding females or control conditions. Male A. burtoni increased their behaviors when only visually exposed to both gravid females and another dominant male, but rates of these behaviors were ∼3- to 10-fold higher in the full sensory interaction trials. Behaviors quantified for female exposure conditions were courtship quivers and leads, while behaviors for male exposure were lateral displays and frontal threats. Lines and asterisks indicate statistical differences: *P<0.05; **P<0.01. N=10 different stimulus males for each condition. Control bars are the same data set plotted next to both female and male exposure conditions for comparison.