ABSTRACT
The endocrine system comprises a diverse array of hormonal signaling pathways that regulate the expression of key life-history traits, such as developmental and growth rates, and timing and magnitude of reproductive effort. The role of hormones in the expression of life-history traits has become increasingly of interest in the field of evolutionary ecology, which seeks to understand the genetic and physiological mechanisms underlying the evolution of life-history strategies (Ketterson and Nolan 1992; Finch and Rose 1995; Zera and Bottsford 2001; Ricklefs and Wikelski 2002). The hormone insulin-like growth factor-1 (IGF-1) is particularly of interest in this regard, as it can exert far-reaching pleiotropic effects on organismal growth, reproduction, and lifespan. As a member of the insulin-like family of signaling molecules found throughout the vertebrate and invertebrate phylogeny, IGF-1 has been the subject of intense research in domesticated and model species, including those of great commercial interest. Little, however, is known regarding the physiology of IGF-1 in reptiles, or in wild species in general. Reptiles display various combinations of terrestrial ectothermy, determinate or indeterminate growth, diversity in reproductive mode, metabolic flexibility, and remarkable plasticity in lifehistory strategy, which make them a particularly intriguing focus for IGF-1 study. Nevertheless, IGF-1 function has been examined in only five reptile species to date: the Loggerhead Sea Turtle (Caretta caretta), Pond Slider (Trachemys picta), American Alligator (Alligator mississippiensis), Terrestrial
Gartersnake (Thamnophis elegans), and Brown House Snake (Lamprophis fuliginosus) (Crain et al. 1995a,b; Guillette et al. 1996; Sparkman et al. 2009; Sparkman et al. 2010). Though these few studies have done much to show both consistencies and disparities in activity of IGF-1 with that in other taxa, many questions remain.
