Dishonest signalling of fighting ability and multiple performance traits in the fiddler crab Uca mjoebergi

Abstract

Abstract1. Signals used during male combat are expected to be honest indicators of fighting ability. However, recent studies show that dishonesty in male signalling is more prevalent than previously believed. 2. Here we show that regenerated (leptochelous) claws in male Uca mjoebergi fiddler crabs are not only dishonest signals of two types of whole-organism performance capacities that are likely to be useful during fights (claw closing force and pull-resisting force), but they are also less effective as weapons in situations where males are unable to bluff. 3. Original (brachychelous) male claws are statistically significant predictors (independent of body size) of both closing force and the force required to pull a male out of a tunnel. By contrast, leptochelous claw size does not convey information on those performance capacities following control for body size. 4. Furthermore, claw size affects fighting ability such that leptochelous residents are at a significant competitive disadvantage to brachychelous residents, although claw type does not affect the ability of non-resident males to win fights. 5. This study is among the first to show that male armaments can dishonestly signal performance traits that are likely important for winning fights, and is the first to show evidence for dishonest signalling of multiple components of fighting ability.

A performance-based cost to honest signalling in male green anole lizards (Anolis carolinensis)

“…Thus, while allocating resources away from bite force development may allow males to bluff rivals during the early stages of competitive interactions where bite force is important (cf. [21,23]), it may also result in decrease in fitness in other selective contexts (but see [66]). The fitness costs to expressing a poor bite force in terms of total selection (see [67,68] for discussion) might therefore outweigh the energetic costs of bite force development.…”

“…Since our results show that bite force does not appear to be 'protected' from resource allocation in this way, a more likely possibility is that honesty may be maintained in nature via receiver-dependent costs if deceptive signallers are exposed through escalated combat with 'honest' individuals (cf. [21]). The costs of such escalated combat can be substantial in A. carolinensis, resulting in severe injury or even death [15,69], and hence may be an important factor limiting the evolution of dishonesty in this system.…”

“…The resulting partial regression coefficients express the relationships between dewlap size and bite force, with body size effects statistically removed [54]. This approach is analogous to residual analysis but has the advantage of not losing a degree of freedom ( [43,55]; see [21,56] for examples). Separate multiple regressions were conducted for the restricted and unrestricted diet treatments.…”

Rapid regeneration of the major cheliped in relation to its function in male-male contests in the hermit crab Pagurus middendorffii

“…In fiddler crabs, individuals with regenerated chelipeds have an improved performance in comparison with individuals without the cheliped during contests for territory (Backwell et al 2000, Reaney et al 2008. Although a regenerated cheliped of a male fiddler crab is lighter and less robust than the original (Backwell et al 2000, Reaney et al 2008, Lailvaux et al 2009), it allows crabs to bluff in male-male contests and for attracting potential mates (Backwell et al 2000). However, such a cheliped may not be effective in species where males aggressively use their major chelipeds as a substantial weapon during physical combat (e.g.…”

“…Male fiddler crabs also regenerate a slender and less robust cheliped than their original cheliped after losing the original one (Lailvaux et al 2009). While their original robust chelipeds are used both as display to their rivals and mates and as physical weapons in male-male contests, the regenerated slender chelipeds are considered to function as dishonest signals during the pre-fight phase and courtship behavior for females (Backwell et al 2000).…”