Sexual Dimorphism in Physiological Performance of Whiptail Lizards (GenusCnemidophorus)

Abstract

Numerous studies have examined sexual dimorphism in the morphology and behavior of vertebrates; very few, however, have explicitly investigated the possibility of gender differences in physiological performance, despite the observations of such differences in humans. In this study, I investigated physiological sexual dimorphism in the lizard genus Cnemidophorus by measuring five whole-animal traits, all of which are likely to influence fitness in these species: burst speed, endurance, maximal exertion capacity, standard metabolic rate, and evaporative water loss rate. Because at least some of these traits are known to be strongly influenced by body size, I tested for dimorphism using both absolute and size-corrected trait values. An examination of six Cnemidophorus species and subspecies revealed a strong trend toward higher absolute trait values in males for all variables except endurance. Most of the dimorphism in standard metabolic rate and evaporative water loss rate could be explained by differences in body mass between males and females; for the locomotor traits, however, body size explained only a small fraction of the overall sexual dimorphism. The portion of trait differences not explained by body size was likely due to gender differences in physiology, such as differences in relative muscularity and fat content.

Escape strategy of Schreiber’s green lizards (Lacerta schreiberi) is determined by environment but not season or sex

“…In Platysaurus broadley, there was no difference on predation risk between males and females, which could explain the lack of differences between sexes on FID and RD (Whiting, 2002). The lack of sexual differences in L. schreiberi might be also explained if the more conspicuous males could escape faster than the more cryptic females, as it occurs in many other species (Cullum, 1998;Lailvaux et al, 2005). However, in the agamid lizard Phrynocephalus vlangalii, a species without sexual dimorphism, FID do not differ between the sexes and is unrelated to individual escape performance capacity, although males flee farther than females (Qi et al, 2014).…”

Neither season nor sex affects the cost of terrestrial locomotion in a circumpolar diving duck: the common eider (Somateria mollissima)

“…Supporting and transporting relatively more organ mass with relatively less muscle potentially requires relatively more energy (Taylor et al 1980;Tickle et al 2010); however, no studies to date have linked male and female energetic and kinematic data with such morphological measurements. Sexual dimorphisms like these are associated with male-male (intraspecific) aggressive competition for females in some vertebrate species (Cullum 1998;Hammond et al 2000;Bonnet et al 2005). Since inter-(rather than intra-) specific sexual selection is important in the common eider, and since male and female eiders shared identical top attainable U, it may be that the sexes also share similar visceral and muscle proportions.…”

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

“…Morphological variation often translates into variation in performance capacity and therefore comparable differences in whole-organism performance between males and females (Arnold, 1983;Bennett and Huey, 1990;Cullum, 1998;Herrel et al, 2010). From a theoretical perspective, the intensity of selection should be stronger on the actual capacities of individuals rather than their underlying morphology .…”

“…These studies have established that males and females frequently differ in whole-organism performance, as they do in sexually dimorphic traits (Cullum, 1998;Lailvaux et al, 2003;Krasnov et al, 2004). While a significant proportion of these differences can be explained by SSD, the remaining fraction of variation in male and female performance is suggested to result from the physiological differences associated with each sex (Abouheif and Fairbairn, 1997;Cullum, 1998;Krasnov et al, 2004;Lailvaux, 2007). Cullum (1998) conducted a study on the locomotor performance of several species of sexually dimorphic Cnemidophorus lizards and found that males were consistently faster than females.…”

“…While a significant proportion of these differences can be explained by SSD, the remaining fraction of variation in male and female performance is suggested to result from the physiological differences associated with each sex (Abouheif and Fairbairn, 1997;Cullum, 1998;Krasnov et al, 2004;Lailvaux, 2007). Cullum (1998) conducted a study on the locomotor performance of several species of sexually dimorphic Cnemidophorus lizards and found that males were consistently faster than females. Another perspective on the interaction between morphology and performance is that sex differences in body size and shape may be the product of selection on one or several interrelated performance traits .…”