Thyroid hormones play an important role in all tissues of the body, including gonadal function. In Sundevall’s jird, Meriones crassus (Rodentia, Gerbillinea), caught in its natural biotope in the Algerian Sahara Desert, the testis activity was evaluated by testicular and seminal vesicles weights and plasma testosterone level. The thyroid activity was evaluated by plasma concentrations of total triiodothyronine (T3) and thyroxin (T4) using the radioimmunoassay (RIA) method. The testis activity is characterized by a maximum in spring, a regression during summer, a minimum in autumn, and a lower activity in winter. The plasma concentrations of total T3 and T4 varied non-significantly during the seasons. However, thyroid activity varied in contrast to testicular structure, especially during the breeding season when the testis activity is maximum. In order to specify the implication of thyroid function in testis seasonal variations, we investigated the relationship between both activities. This study could further explain the seasonal regulation of testicular function concerning the environmental cues in this jird.
