Reproduction and Lipid Utilization of Tropical Populations of Sceloporus variabilis

Abstract

Reproductive characteristics and lipid cycles of two tropical populations of the insectivorous lizard Sceloporus variabilis inhabiting different elevations were compared. Compared to phylogenetically related temperate zone species, S. variabilis demonstrates reproductive characteristics predicted in the literature for lizards inhabiting relatively aseasonal environments: small clutch size (4.3-4.6) relative to body size (60-61 mm SVL), highest clutch frequency (4.5-6), earliest age at maturity (4-7 months), longest reproductive season (8-9.5 months) and smaller relative clutch mass (0.203-0.212). Most of these trends are also found in the comparison of lizards from the high elevation population (1000 m above sea level), where seasonality is more conspicuous, with lizards from the low elevation population (45 m above sea level) where the environment is more equable. At low elevation, the reproductive season is longer, permitting reproductive potential to be higher. In addition, incubation time of eggs is shorter at low elevation and thus, some females are able to reproduce at the end of the same reproductive season in which they were born. Seasonal shifts in egg size in the high elevation population are analyzed regarding the bet-hedging and the parental investment models. Lizards at both elevations store lipids in fat bodies and in body tissues that are used at the beginning of the reproductive season. Higher and more suitable ambient temperature and abundant food later in the reproductive season allow lizards to get the energy necessary for reproduction directly from the environment, until the "nortes" (northern storms) season restricts lizard activity. Juveniles use all energy from food for growth and do not store lipids until shortly before reaching maturity.