EFFECTS OF CROWDING ON REPRODUCTIVE TRAITS OF WESTERN FENCE LIZARDS, SCELOPORUS OCCIDENTALIS

Research on the natural history of lizards often involves attempting to identify sources of variation in life-history traits among different populations. Studying lizards under controlled laboratory conditions is a useful method for evaluating the relative effects of phenotypic plasticity and underlying genetic constraints on variable reproductive parameters. Therefore, there is a need to determine the best techniques for maintaining various species under laboratory conditions to avoid biasing data as much as possible. The purpose of our study was to determine if housing female Western Fence Lizards, Sceloporus occidentalis, in different sized breeding groups increased variability in reproductive parameters. We randomly assigned each of 96 healthy females to a control or one of three different sized groups, i.e. one female per cage (control), two females per cage, four females per cage, and eight females per cage. One male was randomly assigned to each cage. There were no statistical differences between the controls and females in the two-female groups for any parameter measured. Housing females in four-and eight-female groups decreased the mean number of clutches laid by females and decreased reproductive effort in terms of relative clutch mass (clutch mass divided by maternal body mass). Housing four or eight females together also increased the number of days before the first clutch was laid and increased the percentage of infertile eggs per clutch.