Head shape and bite performance in xenosaurid lizards

Abstract

Bite performance in lizards influences many aspects of the animal's lifestyle. During feeding, inter- and intrasexual interactions, and defensive behavior, the ability to bite hard might be advantageous. Although biomechanical considerations predict clear relations between head shape and bite performance, this has rarely been tested. Here we investigate the effect of head shape on bite performance in three closely related species of xenosaurid lizards. Our data show that in this family of lizards, bite performance is mainly determined by head height, with high headed animals biting harder than flat headed ones. Species clearly differ in head shape and bite performance and show a marked sexual dimorphism. The dimorphism in head shape also results in an intersexual difference in bite performance. As head height is the major determinant of bite performance in xenosaurid lizards, trade offs between a crevice dwelling life-style and bite performance seem to occur. The evolutionary implications of these results are discussed. J. Exp. Zool. 290:101-107, 2001.

Multivariate and geometric morphometrics in the analysis of sexual dimorphism variation in Podarcis lizards

“…Moreover, it has been stated by various authors that characters that present positive allometry with body size in one of the two sexes, probably represent sexually selected traits (Green, 1992;Petrie, 1992;Bonduriansky and Day, 2003). Given that head dimensions, and especially head height, have been shown to be directly related to the volume and power of the jaw muscle (Herrel et al, 1996(Herrel et al, , 1999(Herrel et al, , 2001a, the positive allometry of HH in these two Podarcis species suggests sexual selection. This hypothesis is corroborated by the sexual differences present in the shape of the lateral view of the head involving the tympanic area, but the relation between lateral head shape and jaw musculature should be further explored in the future.…”

“…In many lacertid lizards, as in other lizard families, males present larger body size and head dimensions (Cooper and Vitt, 1989;Anderson and Vitt, 1990;Mouton and van Wyk, 1993;Andersson, 1994;Brañ a, 1996;Herrel et al, 1996Herrel et al, , 1999Herrel et al, , 2001aKratochvil et al, 2003;Molina-Borja, 2003;Uller and Olsson, 2003), while females have a longer trunk (Andersson, 1994;Brañ a, 1996;Butler and Losos, 2002;Olsson et al, 2002;Schwarzkopf, 2005). Moreover, both head dimensions and trunk length have been shown to present a positive allometric relationship with total size in males and females, respectively, offering indirect support of sex-specific selection for these traits (Carothers, 1984;Brañ a, 1996;Hews, 1996;Olsson et al, 2002;Kratochvil et al, 2003).…”

“…Moreover, both head dimensions and trunk length have been shown to present a positive allometric relationship with total size in males and females, respectively, offering indirect support of sex-specific selection for these traits (Carothers, 1984;Brañ a, 1996;Hews, 1996;Olsson et al, 2002;Kratochvil et al, 2003). Abdomen length has been shown to be positively correlated to clutch size in various lacertid species (Brañ a, 1996;Olsson et al, 2002), while head dimensions are directly related to the jaw musculature and affect jaw force, a structure implicated not only in competitive behavior and copulation, but also in feeding, antipredatory behavior, and refuge use (Herrel et al, 1996(Herrel et al, , 1999(Herrel et al, , 2001a.…”

Comparative analysis of methods for determining bite force in the spiny dogfish Squalus acanthias

“…Bite force in particular, which is one of the least investigated aspects of feeding in sharks , is an informative measure of ecological performance 1 because successful prey capture and processing are critical to an animal's existence (Wainwright and Reilly, '94;Binder and Van Valkenburgh, 2000;Herrel et al, 2001a). Bite force has been shown to affect the timing of ontogenetic diet shifts (Hernandez and Motta,'97;Clifton and Motta,'98), breadth of dietary diversity (Wainwright,'87,'88;Clifton and Motta,'98), niche diversification (Kiltie, '82;Herrel et al, 2001b), exemplify patterns of sexual dimorphism (Herrel et al,'99), and has been used to indicate the functional effects of morphological transitions in muscle placement throughout evolution (Dechow and Carlson,'83;Thomason and Russell,'86).…”

Sex-specific variation in morphology and performance in the Asian house gecko

“…Vocalisation, dominance and aggressive behaviours have been found to increase with increasing temperature and the overall density of a population (Marcellini, 1971(Marcellini, , 1974Frenkel, 2006). This geographic variation in intensity of territoriality is suggested to lead to differing degrees of sexual selection for larger body size and head size in males (Cooper and Vitt, 1989;Herrel et al, 1999b;Herrel, 2001;Lappin et al, 2006). Thus, over the average five-year live span of H. freantus males and females in warmer more tropical climates may be under greater sexual selection pressure compared to their conspecific in the more temperate distributions.…”