Testosterone has opposite effects on male growth in lizards(Sceloporusspp.) with opposite patterns of sexual size dimorphism

Abstract

Sexual size dimorphism (SSD) is a widespread biological phenomenon in which members of one sex are characteristically larger than those of the opposite sex for a given population or species. Studies of the selective forces shaping SSD have figured prominently in the evolutionary literature since Darwin (1871). However, relatively little is known about the proximate physiological mechanisms underlying sex differences in growth (Badyaev, 2002;Cox et al., 2005;Duvall and Beaupre, 1998). Testosterone (T) is commonly regarded as an anabolic steroid that promotes skeletal and muscular growth, but most of the evidence supporting this generalization comes from studies of mammals, fishes and birds with male-larger SSD (Borski et al., 1996; Fennel and Scanes, 1992a;Ford and Klindt, 1989;Gatford et al., 1998;Holloway and Leatherland, 1998;Huggard et al., 1996;Kuwaye et al., 1993;Wehrenberg and Giustina, 1992). Interestingly, T inhibits growth in some reptiles with femalelarger SSD (Abell, 1998a;Cox et al., 2005;Crews et al., 1985;Lerner and Mason, 2001). Collectively, these studies suggest that opposite patterns of SSD may develop in part because of underlying differences in the hormonal regulation of male growth. However, comparisons among these studies are complicated by the taxonomic and biological disparity of the study organisms and by significant differences in methodology. In the present study, we provide the first direct comparison of the effects of T on male growth in two closely related species with opposite patterns of SSD.Life history ecologists have long recognized that growth may be constrained by the preferential allocation of available energy to reproduction (Fisher, 1930;Reznick, 1985;Williams, 1966). More recently, behavioral endocrinologists have begun to explore the role of hormones as proximate mediators of such trade-offs (Ketterson et al., 1992;Ricklefs and Wikelski, 2002). For example, in male lizards, T increases activity, endurance, locomotor performance, territorial aggression and home range size DeNardo and Sinervo, 1994;John-Alder et al., 1996;Klukowski et al., 1998Klukowski et al., , 2004Marler and Moore, 1988;Moore, 1988;Moore and Marler, 1987). These behavioral and physiological effects of T presumably enhance male reproductive success, but they also Sexual size dimorphism (SSD) has received considerable attention from evolutionary biologists, but relatively little is known about the physiological mechanisms underlying sex differences in growth that lead to SSD. Testosterone (T) stimulates growth in many male-larger vertebrates, but inhibits growth in the female-larger lizard Sceloporus undulatus. Thus, opposite patterns of SSD may develop in part because of underlying differences in the hormonal regulation of male growth. In the present study, we examined the effects of T on male growth in two sympatric congeners with opposite patterns of SSD (S. virgatus: female-larger; S. jarrovii: male-larger). During the mating season, yearling males of both species have higher plasma T levels than fem...

Ovarian control of growth and sexual size dimorphism in a male-larger gecko

“…Squamate reptiles represent a particularly interesting group for studies of evolutionary changes in SSD, as they include both malelarger and female-larger species, often even among closely related species (Kratochvíl and Frynta, 2002;Cox and John-Alder, 2005;Starostová et al, 2010; see also Cox et al, 2009, for review). Similar to most other vertebrates (Badyaev, 2002), male and female squamates are nearly identical in size at birth/hatching, with SSD being developed only later in ontogeny (Kratochvíl and Frynta, 2002;Taylor and DeNardo, 2005;Frynta et al, 2010;Starostová et al, 2010;Bonnet et al, 2011;Kubicǩa et al, 2013).…”

“…This hypothesis suggests that female-biased SSD should occur in species where males are forced to expend energy in demanding activities such as territory defence in order to obtain mating opportunities (e.g. Cox and John-Alder, 2005). In contrast, malebiased SSD should be present in species where females allocate substantially more energy to reproduction than males, and hence it is impossible for them to sustain male-typical growth.…”

“…One such endogenous mechanism potentially explaining evolutionary shifts in SSD in squamates was proposed by Cox and John-Alder (2005). Based on the results of hormonal manipulations in the iguanian genus Sceloporus, these authors suggested that male gonadal androgens can masculinize growth and have positive effects on growth in male-larger species, but a negative influence in female-larger species.…”

Study of Latent Toxoplasma gondii Role in Level of Testosterone, DHEA, Cortisol and Prolactin Hormones of Young Persons

“…Excessive levels of testosterone (social hormone) can lead to depression and anxiety. Individuals with increased level of cortisol (stress hormone) may suffer from emotional disorders like depression, paranoia and anxiety (Cox and John-Alder, 2005;Karrer-Voegeli et al, 2009). Based on the present research findings Toxoplasma infection can induce elevation of testosterone and cortisol level in infected patients and by this manner this protozoan parasite probably effects on human behavior, personality and phenotypic traits.…”

“…It is produced in adrenal gland. The DHEA serves as precursor to estrogens and testosterone (Cox and John-Alder, 2005;Tuck and Francis, 2009).…”