A tale of two jirds: The locomotory activity patterns of the King jird (Meriones rex) and Lybian jird (Meriones lybicus) from Saudi Arabia

The animal–environment interaction is complex, and the ability to temporally organise locomotor activity provides adaptive and survival advantages. We investigated daily and circadian locomotor activity patterns of two jird species from Arabia occurring in dramatically different environments to determine the environmental effect on activity. The King jird occurs in mountainous regions of Azir where climatic conditions are cool and wet, while the Libyan jird inhabits low-lying hot sandy deserts where temperatures exceed 45 °C during summer.Six King jirds and nine Libyan jirds were subjected to a 12L:12D light cycle, a period of constant darkness (DD) and an inversed 12D:12L light cycle. Five of six King jirds and all Libyan jirds showed entrainment of their activity to the light cycles, most animals exhibited nocturnal activity. All entraining jirds showed circadian rhythmicity, with the periods of the rhythms very close to 24 h. Entraining jirds inversed their activity patterns when the light cycle was inversed. The two jird species displayed comparable amounts of nocturnal activity in all light cycles presented. The King jird showed larger intraspecific variability than the Libyan jird, which may reflect more plasticity in its circadian clock, allowing it to adapt quicker to environmental changes.

► Both species entrain their locomotor activity to light cycles.
► Both species have free-running rhythms around 24 h.
► King jird display more flexible activity patterns than the Lybian jird.
► Activity profiles may be related to habitat differences.
► Could enhance quick adaptation to changes in environment.