Weapon size is a reliable indicator of strength and social dominance in female slender crayfish (Cherax dispar)

Abstract

Summary 1.Weapons are specialized structures that are commonly used by animals to signal fighting ability and resource holding potential during agonistic encounters. Current theory predicts weapon size should reliably indicate weapon strength and unreliable signals should only occur at very low frequencies in nature. However, a recent study found weapon size was an unreliable signal of strength during agonistic interactions among males of the slender crayfish ( Cherax dispar ). 2. In this study, we investigated the relationship between morphology, performance and social dominance in females of C. dispar . Based on current theory, we predicted chela size would reliably indicate chela strength and would relate indirectly to dominance via its influence on strength. 3. We found females that possessed large chelae were more likely to possess stronger chelae, and those individuals with stronger chelae were more likely to win competitive bouts. The best predictive model of the relationships among morphology, performance and dominance indicated chela size indirectly affected social dominance via its influence on strength, thus demonstrating displays of weaponry are reliable signals of fighting ability. 4. Reliable signals of strength among females of C. dispar supports current theory predicting stable signalling systems should largely consist of honest displays of strength. However, this contrasts with previous work demonstrating that male C. dispar routinely uses unreliable signals of weapon strength during agonistic encounters.

Social control of unreliable signals of strength in male but not female crayfish,Cherax destructor

“…similar to that previously reported for C. dispar (males, CV75%; females, CV31%) Bywater et al, 2008). It is this variation between signal and an individual's actual performance (or potential to inflict a cost on an opponent) that forms the basis or opportunity for unreliable signals of strength to be used to determine dominance.…”

“…Despite such theoretical expectations, there are many reported cases of unreliable signals of both fighting ability and mate choice across a range of species, including fiddler crabs (Backwell et al, 2000;Lailvaux et al, 2009), hermit crabs (Elwood et al, 2006), snapping shrimp (Hughes, 2000), stomatopods (Steger and Caldwell, 1983;Adams and Caldwell, 1990) and freshwater crayfish (Seebacher and Wilson, 2006;Wilson et al, 2007). Moreover, recent studies of male slender crayfish, Cherax dispar, revealed dishonest signals are routinely used during agonistic interactions and are far more common than previously predicted Bywater et al, 2008). In this system, male slender crayfish use relative chela size to determine dominance , but chela size is a poor predictor of chela strength (a measure of fighting ability), and strength is unrelated to social dominance .…”

“…It is important to note that when fights do occur between males of the slender crayfish it is the individuals with the stronger chelae that win the disputes . For female C. dispar, in contrast, there is a strong correlation between chela size and strength, suggesting that a female's chelae provide a reliable signal of potential fighting ability (Bywater et al, 2008).…”

Cryptic asymmetry: unreliable signals mask asymmetric performance of crayfish weapons

“…Previous analyses have focused on either the properties of individual chelae or the average properties of paired chelae [15,20,21,22], ignoring the role of asymmetry in dominance. These analyses indicated that stronger individuals were more likely to win disputes that escalated into fighting.…”

Metabolic incentives for dishonest signals of strength in crustaceans

“…To reduce these potential costs animals often seek to resolve disputes without fighting by signalling intent, and using assessments of weapon size, body mass and/or aggressive displays (Bywater et al, 2008;Smith and Harper, 1995). Visual signals, and the intrinsic quality they represent, are used by receivers to assess the likelihood of combat success should physical confrontation ensue (Bradbury and Vehrencamp, 2011;Hughes, 2000).…”