SEASONAL-CHANGES OF LOCOMOTOR-ACTIVITY PATTERNS IN RUIN LIZARDS PODARCIS-SICULA .1. ENDOGENOUS CONTROL BY THE CIRCADIAN SYSTEM

The daily pattern of locomotor activity of the ruin lizard Podarcis si cula in its natural environment changes from unimodal in spring (with only one activity peak per day) to bimodal in summer (with two well-se parated activity peaks per day) and it becomes unimodal again in autum n. In order to establish whether such seasonal changes in pattern migh t be at least in part controlled by endogenous temporal programs, liza rds were collected at different times of the year and immediately afte r capture their locomotor behavior was tested in the laboratory under constant temperature (29-degrees-C) and in darkness. For some individu als tested in the laboratory the locomotor pattern previously expresse d in the field was known. Seasonal differences in pattern have been un equivocally found to have an endogenous component, as most lizards in constant conditions retained the locomotor pattern shown in the field during the same season. Besides, in the bimodal lizards the freerunnin g period of locomotor rhythms (tau) Was significantly shorter and circ adian activity time (alpha) longer than in the unimodal ones. Altogeth er the data are compatible with the idea that both the interdependent changes Of tau and alpha and the changes in locomotor pattern occurrin g seasonally in the circadian activity rhythms of P. sicula would depe nd on changes in the phase relationship between mutually coupled oscil lators which drive these rhythms.