Gaping Displays Reveal and Amplify a Mechanically Based Index of Weapon Performance

Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ 86011, USA.
The American Naturalist (Impact Factor: 3.83). 08/2006; 168(1):100-13. DOI: 10.1086/505161
Source: PubMed


Physical prowess, a key determinant of fight outcomes, is contingent on whole-organism performance traits. The advertisement of performance, via display, is poorly understood because it is unclear how information about performance is encoded into display characteristics. Previous studies have shown that weapon performance (i.e., bite force) predicts dominance and reproductive success in male lizards. We tested the hypothesis that gaping displays by adult male collared lizards (Crotaphytus) can provide an index of weapon performance by exposing the major jaw-adductor muscle complex and that white patches at the mouth corners amplify this index. For territorial adult males, the breadth of the muscle complex, which is not correlated with body size, was a strong predictor of bite force. For nonterritorial yearling males and females, however, measures of body and head size predicted bite force. The patches are highly conspicuous, exhibit UV-reflecting properties within the visual range of lizards, and provide size-independent information about bite force only in adult males. We conclude that exposure of the muscle complex during gaping displays can provide rival males with a reliable, body-size independent, biomechanically based index of weapon performance, an index that the mouth-corner patches amplify. Indexes that transmit information through mechanistic links to performance are expected to be widespread among animals.

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Available from: Darrell J. Kemp, Oct 10, 2015
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    • "Even though we did not increase UV reflectance and measure costs of aggression to test this hypothesis, the fact that intruders with UV-reduced coloration were more often challenged by control residents suggests that this explanation is implausible. Finally, another alternative possibility is that UV signals have no information content but act as amplifier signals enabling an easier evaluation of head size, as previously suggested for UV-blue mouth-corner patches of the collared lizards (Lappin et al. 2006). Yet again, our behavioral data do not support this hypothesis. "
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    ABSTRACT: Ultraviolet (UV) colors are visual signals potentially involved in territorial conflicts. However, the role of UV signals remains unclear relative to the prior resident effect and familiarity with the opponent, and the reliability of UV signals is still controversial. Male common lizards Zootoca vivipara exhibit substantial variation in the reflectance of their throat UV color patch. We tested whether UV reflectance was correlated with indicators of individual condition. We further manipulated throat UV reflectance of resident and intruder lizards and staged repeated encounters in the laboratory during the mating season. We found no evidence of condition-dependence of the UV colors expression. During the first encounter among unfamiliar males, a reduction of UV reflectance of one of the two opponents influenced agonistic behaviors and the contest outcome, such that there was a significant advantage for residents over intruders. This advantage disappeared when both opponents were UV-reduced. During the subsequent encounters among familiar males, fighting was more aggressive when opponents displayed similar UV signals, but UV signals did not influence the contest outcome. These results demonstrate that UV reflectance acted as a badge of status in male common lizards whose effects on the behavioral response were modulated, but not overridden, by the prior resident effect and by the familiarity effect. Male-male interactions are therefore mediated by UV signaling and competition for mates should play a major role in the evolutionary maintenance of this ornament. We discuss putative functions and reliability of UV signals.
    Behavioral Ecology 09/2015; DOI:10.1093/beheco/arv149 · 3.18 Impact Factor
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    • "donck et al . , 2005 ; Lail - vaux & Irschick , 2007 ) , and a positive correlation between mean dewlap size and the likely intensity of competition experienced by males has been found across populations in at least one Anolis species ( Van - hooydonck et al . , 2009 ) . Given that combat in lizards is centred on inflicting injury through biting ( Lappin et al . , 2006 ) , these data would suggest the size of the extended dewlap in Anolis signals potential fighting ability ( Vanhooydonck et al . , 2005 , 2009 ; Lailvaux & Irschick , 2007 ) . Similarly , in agamids , the colour of the large , extendible frill in male frillneck lizards determi - nes contest outcome between size - matched territorial mal"
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    ABSTRACT: The existence of elaborate ornamental structures in males is often assumed to reflect the outcome of female mate choice for showy males. However, female mate choice appears weak in many iguanian lizards, but males still exhibit an array of ornament-like structures around the throat. We performed a phylogenetic comparative study to assess whether these structures have originated in response to male-male competition or the need for improved signal efficiency in visually difficult environments. We found little evidence for the influence of male-male competition. Instead, forest species were more likely to exhibit colourful throat appendages than species living in open habitats, suggesting selection for signal efficiency. On at least three independent occasions, throat ornamentation has become further elaborated into a large, conspicuously coloured moving dewlap. Although the function of the dewlap is convergent, the underlying hyoid apparatus has evolved very differently, revealing the same adaptive outcome has been achieved through multiple evolutionary trajectories. More generally, our findings highlight that extravagant, ornament-like morphology can evolve in males without the direct influence of female mate choice, and that failure to consider alternative hypotheses for the evolution of these structures can obscure the true origins of signal diversity among closely related taxa. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
    Journal of Evolutionary Biology 08/2015; DOI:10.1111/jeb.12709 · 3.23 Impact Factor
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    • "Flight performance is likely to be of crucial importance for male butterflies in terms of mate location, conquering and defending territories, aerial fights, and courtship (Kemp & Wiklund, 2001; Tiple et al., 2010). Larger body size is often positively related to mating success (Marden & Waage, 1990; Kemp & Wiklund, 2001; Candolin, 2005; Lappin et al., 2006). Larger wing size reduces wing loading and therefore typically increases flight performance in insects (Van Dyck et al., 1997; Martinez-Lendech et al., 2007). "
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