Playing to an audience

Posted on March 28, 2013

Behavioural interactions between individual animals are sometimes influenced by their social history.  For example, the strength of displays between neighbouring territory-holders often falls as the individuals concerned become more familiar with one another, and it’s likely that this adaptation keeps unnecessary energy expenditure to a minimum.  It also seems that some animals alter their behaviour in response to the broader social context, for example, when they are in the presence of “eavesdropping” members of the same species.  This behavioural flexibility raises the possibility that interacting animals gain benefits by controlling the signals that they send to their audience as well as their opponent.  The “audience effect” has been associated with a wide range of behaviours, including aggression, courtship, mate choice, foraging and anti-predator responses.  What’s less well understood is how social history and the audience effect combine to shape behavioural interactions.  This topic has been explored through experiments on male Siamese fighting fish (Betta splendens), which carry out aggressive displays in the presence of other males and are known to be sensitive both to the familiarity of opponents and to the presence of eavesdroppers.   Experiments were carried out using two “opponent” aquarium tanks placed side by side lengthwise, and a third “audience” tank placed widthwise against both opponent tanks.  The opponent tanks each housed a single male fish, while a transparent container within the audience tank contained a single male, a single female, or no fish, depending on the trial.  Opponents were either unfamiliar with one another or had undergone mutual exposure prior to the main trial.  During each ten-minute trial the numbers of gill protrusions and tail beats performed by opposing fish, and their location in the tank, were recorded.  Opponent-directed gill-protrusion (a typical feature of male aggressive displays) occurred significantly more often when the audience was male and the opponent was unfamiliar.  In contrast, opponent-directed tail beating (where a fish orientates side-on to another individual and moves the tail suddenly towards it), was performed more often when the audience was female and the opponent unfamiliar.  Because tail beating is a prominent feature of courtship, competing males may increase its use to boost their attractiveness when they are being watched by a female audience and when the worth of their opponent is unknown.  These results show that fish are capable of balancing the threat of opponents against the benefits or costs of being seen by different types of audience, and then modifying their behaviour accordingly.

Reference:  Dzieweczynski, T.L., Gill, C.E. & Perazio, C.E.  2012.  Opponent familiarity influences the audience effect in male-male interactions in Siamese fighting fish.  Animal Behaviour 83, 1219-1224.