Daily Activity Cycles of Gerbils and Guinea Pigs: Implications for the Temporal Design Of Comparative Studies

Summary The species-specific daily activity cycles for five male gerbils (Meriones unquiculatus) and five male guinea pigs (Cavia porcellus) were established. Activity was measured every hour for 24 consecutive hours with the use of an activity wheel for the gerbils and a stabilimeter cage for the guinea pigs. Ss were observed in a light-dark (LD) 12/12 condition and an LD 24/0 condition. In the 12/12 condition gerbils were primarily nocturnal and guinea pigs primarily diurnal. For the 24/0 condition gerbils exhibited a free running rhythm of about 23 hours. However, the guinea pig did not exhibit any consistent overall pattern, showing instead a tendency to go in three- to five-hour cycles. These results are related to the temporal design of comparative studies, and the implications for experimental design are discussed.