Dishonest signalling in a fiddler crab

Abstract

Animal communication theory predicts that low-frequency cheating should be common in generally honest signalling systems. However, perhaps because cheats are designed to go undetected, there are few examples of dishonest signals in natural populations. Here we present what we believe is the first example of a dishonest signal which is used commonly by males to attract mates and fight sexual rivals. After losing their large claw male fiddler crabs (Uca annulipes) grow a new one which has less mass, is a less effective weapon and costs less to use in signalling than an equivalent-length claw of the original form. Males with original claws do not differentially fight males with regenerated claws even though they are likely to win. Regenerated claws effectively bluff fighting ability and deter potential opponents before they fight. During mate searching, females do not discriminate against males with low-mass, regenerated claws, indicating that they are deceived as to the true costs males pay to produce sexual signals. Up to 44% of males in natural populations have regenerated claws, a level unanticipated by current signalling theory. The apparent rarity of cheating may be an artefact of the usual difficulty of detecting cheats and dishonesty may be quite common.

Cryptic asymmetry: unreliable signals mask asymmetric performance of crayfish weapons

“…The widespread occurrence of unreliable signals in crayfish suggests one of two conditions: either crayfish receive great benefits by making deceptive chelae or crayfish incur great costs to identify deceitful opponents. Such conditions could occur when individuals must regenerate a chela after injury, as documented in fiddler crabs (Uca annulipes) [18]. In this case, we should expect only the regenerated chela in a pair to be an unreliable signal of strength.…”

What determines direction of asymmetry: genes, environment or chance?

“…They tend to be smaller, they lack some dentition characteristic of major claws and they are often weaker [117,122,123,128,129].…”

Comparison of body size, relative growth and size at onset sexual maturity ofUca uruguayensis(Crustacea: Decapoda: Ocypodidae) from different latitudes in the south-western Atlantic

“…This may be a very important growth strategy and might be a response, in part, to the differences in the relative size of morphological sexual maturity for males between the populations. Behaviour in this genus is predominantly visual (Crane, 1975), and rapid development of the chelipeds may also ensure that a male could more rapidly and effectively participate in reproductive processes, and interact with other males for territory and/or food (Christy, 1978(Christy, , 1983Christy & Salmon, 1984;Backwell et al, 2000). Large claws and the waving activity of males are important criteria for mate selection and it is primarily directed at receptive females (Oliveira & Custódio, 1998;Latruffe et al, 1999).…”