Analysis of repeated signals during shell fights in the hermit crab Pagurus bernhardus

Abstract

Shell exchanges between hermit crabs may occur after a period of shell rapping, when the initiating or attacking crab brings its shell rapidly and repeatedly into contact with the shell of the non-initiator or defender, in a series of bouts. There are two opposing models of hermit crab shell exchange and the function of shell rapping. The negotiation model views shell exchange as a mutualistic activity, in which the initiator supplies information about the quality of its shell via the fundamental frequency of the rapping sound. The aggression model views shell rapping as either detrimental to the defending crab, or as providing it with information about the initiator's ability or motivation to continue, or both. The negotiation model makes no predictions about the temporal pattern of rapping, but under the aggression model it would be expected that crabs that rapped more vigorously would be more likely to e¡ect an exchange. Repeating the signal could be expected under either model. Crabs that achieve an exchange rap more vigorously, rapping is more persistent when a clear gain in shell quality may be achieved, and the vigour is greater when the relative resource-holding potential (or`¢ghting ability') is high. These ¢ndings support the aggression model rather than the negotiation model. Contrary to the predictions of game theory, crabs that do not e¡ect an exchange appear to signal that they are about to give up. The data suggest that rapping is performed repeatedly because the accumulation of all of the performances acts as a signal of stamina.

Cumulative or sequential assessment during hermit crab shell fights: effects of oxygen on decision rules

“…Previous studies (Bri¡a et al 1998;Bri¡a & Elwood 2000a,b) have clearly demonstrated a relationship between the vigour of rapping and the likelihood of the defender being evicted and indicate that defenders use the pattern of rapping to assess the ability of the attacker. One possible reason for the di¡erence between the e¡ects of hypoxia on the two roles is that, in reaching the decision to release the shell, defenders compare the rate of rapping in attackers with an absolute threshold rate, rather than with a relative one.…”

“…Previous analysis of the temporal pattern of shell rapping demonstrates both escalation and de-escalation in vigour as predicted by the energetic war of attrition model (Payne & Pagel 1997), and shows that attackers that evict the opponent rap with greater vigour than those that are unsuccessful (Bri¡a et al 1998). Furthermore, analysis of the within-bout structure of rapping shows that vigour decreases both within individual bouts and from bout to bout (Bri¡a & Elwood 2000a) suggesting that vigour could be determined by the level of fatigue.…”

Social rules govern vocal competition in the barn owl

“…produces louder begging calls in nestling birds) usually gains easier access to these limited resources (Godfray, 1991;Kilner, Noble, & Davies, 1999), but, for transient signals, this average signal level can vary over short periods of time, independently of variation in need or condition (Briffa, Elwood, & Dick, 1998;Greenfield, Tourtellot, & Snedden, 1997). The contest outcome is then the result of an interactive process settled during repeated interactions (Briffa et al, 1998;Enquist & Leimar, 1983;Enquist, Leimar, Ljungberg, Mallner, & Segerdahl, 1990;Payne & Pagel, 1996). These variations in signal level during competitive interactions raise the possibility that animals assess the temporal dynamics of signal production and not only the absolute signalling level of conspecifics to adjust their behaviour (Patricelli, Uy, Walsh, & Borgia, 2002).…”

“…These variations in signal level during competitive interactions raise the possibility that animals assess the temporal dynamics of signal production and not only the absolute signalling level of conspecifics to adjust their behaviour (Patricelli, Uy, Walsh, & Borgia, 2002). Game theory has dominated the way evolutionary biologists envisage social interactions (Dobler & Kolliker, 2009;McNamara et al, 1999), and the dynamic process leading animals to behave in a certain way has hardly been investigated empirically (Briffa et al, 1998;Van Dyk, Taylor, & Evans, 2007). Much remains to be done to pinpoint the social factors that induce an individual to increase or decrease investment in signalling over short periods of time in the course of competitive interactions.…”

“…Game theory has dominated the way evolutionary biologists envisage social interactions (Dobler & Kolliker, 2009;McNamara et al, 1999), and the dynamic process leading animals to behave in a certain way has hardly been investigated empirically (Briffa et al, 1998;Van Dyk, Taylor, & Evans, 2007). Much remains to be done to pinpoint the social factors that induce an individual to increase or decrease investment in signalling over short periods of time in the course of competitive interactions.…”