Costs of reproduction in male lizards, Sceloporus virgatus

Models of life history evolution typically assume a balance between the ben efits of current reproductive activity and the costs to future reproductive success or survivorship, but empirical studies often find positive correla tions between such components of fitness in undisturbed animal populations. I examined possible survivorship costs of reproduction in free-ranging mal e lizards, Sceloporus virgatus, and found that males with low levels of mat ing success were less likely to survive to the following breeding season. I also investigated two possible indicators of reproductive effort, increase in ectoparasite load and decrease in body weight during the breeding seaso n. Levels of parasitism with trombiculid mites at the end of the breeding s eason were not associated with any measure of fitness or body condition (ma ting success, survivorship to the following year, relative weight loss). Ye arling males (which have low levels of mating success) usually gained weigh t during the breeding season, while older males generally lost weight durin g this period. This suggests that young males may have postponed reproducti on in favor of body growth and that seasonal weight loss of older males mig ht reflect reproductive effort. Within the group of older males, individual s with the highest levels of mating success did nor. have high levels of ei ther weight loss or mortality. Mate guarding behavior, an alternative to th e aggressive territorial behavior typical of many lizard species, may allow certain males to obtain mates without expending large amounts of energy or exposing themselves to great mortality risks.