Costs of bearing a sexually selected ornamental weapon in a fiddler crab

Abstract

Summary1. Sexually selected structures with dual function of combat and display are likely to be honest signals of male quality to opponents and mates, but should be costly to produce and maintain. 2. Male fiddler crabs use a single greatly enlarged claw as both a weapon in agonistic contests with other males and an ornament to attract females for mating. Given the extreme size of this structure (up to half the total body mass), there is surprisingly little evidence for costs as predicted by theory. 3. We experimentally investigated several potential costs of the large claw to male sand fiddler crabs Uca pugilator . Mass-specific metabolic rates were significantly higher and treadmill endurance capacity significantly lower for males bearing an intact major claw compared with those without. 4. In contrast, presence of the claw did not affect maximal sprint speeds, suggesting that the massive structure does not compromise the ability of male crabs to evade predators. These counterintuitive results conform to recent theoretical models of energy costs of locomotion. 5. Our study provides empirical support for a key assumption of sexual selection theoryenergetic and endurance-related locomotor costs incurred while bearing this ornamental weapon act in opposition to sexual selection favouring larger claws.

Male nutritional history affects female fecundity in a male-dimorphic mite: Evidence for a nuptial gift?

“…Furthermore, because minor males are not impaired in their locomotion (e.g. Basolo and Alcaraz 2003;Allen and Levinton 2007;Goyens et al 2015), they can obtain larger energy reserves than major males in complex habitats. Females have previously been found to prefer well-fed males over starved males as mates (e.g.…”

“…This is because major's physical weaponry often makes locomotion less efficient (e.g. Basolo and Alcaraz 2003;Allen and Levinton 2007;Goyens et al 2015) and because size-for-size, majors likely suffer higher maintenance costs than minors as they have a larger body volume on account of their weaponry (Kooijman and Metz 1983;Parker 1983;Emlen 2008;Stuglik et al 2014). When compounds that increase female fecundity are costly to produce (Cordero 1995;Vahed 1998), having weaponry leads to a lower maximum investment in compounds to increase female fecundity.…”

Cost of flight and the evolution of stag beetle weaponry

“…The costs of bearing weapons become more evident when the armaments are heavier. Walking around with hermit crab chelipeds (30% of body mass), fiddler crab claws (50% of body mass) or stag beetle mandibles and their musculature (18% of body mass) is energetically very costly [8][9][10]. Stag beetle males need their robust mandibles and the associated massive muscles to bite extremely forcefully (three times as forcefully as scaled female bites) in their aggressive battles [11] (figure 1).…”

Female monopolization mediates the relationship between pre- and postcopulatory sexual traits

“…Producing and maintaining weapons used in precopulatory contest competition and ejaculate traits important in postcopulatory sperm competition can be energetically demanding [9][10][11][12] . Consequently, sperm competition models assume that energy allocated to mate acquisition limits investment in ejaculate production, leading to the prediction that investment in testes should trade off against the investment in weaponry used in male-male contest over access to mates 13 .…”