Sexual Dimorphism in Lizard Body Shape: The Roles of Sexual Selection and Fecundity Selection

Abstract

Sexual dimorphism is widespread in lizards, with the most consistently dimorphic traits being head size (males have larger heads) and trunk length (the distance between the front and hind legs is greater in females). These dimorphisms have generally been interpreted as follows: (1) large heads in males evolve through male-male rivalry (sexual selection); and (2) larger interlimb lengths in females provide space for more eggs (fecundity selection). In an Australian lizard (the snow skink, Niveoscincus microlepidotus), we found no evidence for ongoing selection on head size. Trunk length, however, was under positive fecundity selection in females and under negative sexual selection in males. Thus, fecundity selection and sexual selection work in concert to drive the evolution of sexual dimorphism in trunk length in snow skinks.

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

“…Head size is known to be a sexually selected trait in lacertids and in lizards in general-males usually presenting bigger heads than females (Brañ a, 1996;Olsson et al, 2002). The head is involved in mating in the Lacertidae both directly, males grabbing females in order to immobilize them and copulate with them (Verbeek, 1972;Heulin 1988; 1990; Gvozdik and Van Damme, 2003), and indirectly when fights between males for territory defense take place (Verbeek, 1972;Stamps, 1983;Heulin 1988;Gvozdik andVan Damme, 2003, Perry et al, 2004).…”

“…However, most of them can be summarized by three major forces differentially acting on males and females of a population: sexual, fecundity, and natural selection. In those species where males engage in fights and copulation is forced, sexual selection may act via male-male combats or/and female choice and thus favor bigger male body size, whereas fecundity selection may favor bigger female body size (Olsson et al, 2002;Cox et al, 2003). Moreover, natural selection acting on both sexes might pose constraints to the evolution of certain characters, for example via habitat use.…”

“…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). 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.…”

“…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.…”

Fluctuating asymmetry and preferences for sex-typical bodily characteristics

“…I n humans, as in other species, sex differences in size and shape are attributed to divergent effects of morphology on the survival or reproductive success of each sex (1)(2)(3)(4)(5)(6)(7)(8)(9)(10). For human females, smaller waist relative to hips (WHR), larger breasts, and longer legs relative to height have been attributed to fecundity selection and are perceived as attractive by males (8,11,12).…”