Phenotypic Plasticity in Desert Rodents Harderian Glands Under Seasonal Steroids Control

Sex hormones activate reproductive behaviors throughout the Harderian glands (HG) in desert rodents. It appears that gonadal hormones have both organizational and activational effects on epithelial cells. This study, thus represents a significant advance in our understanding of the steroid actions that regulate cellular differentiation and thereby pheromones production. Our results reveal that HG of two desert rodents having an opposite lifestyle, Psammomys obesus (diurne) and Gerbillus tarabuli (nocturne) are capable of undergoing significant morphological changes from season to season. In both species, during the mating season, HG exhibit remarkable phenotypic responsiveness in order to produce chemical cues that promote sexual interaction. Small specimens from the HG were processed for light and transmission electron microscopic study. Obvious structural differences were observed between diurnal and nocturnal species. The gland is compound tubulo-alveolar, being characterized by a single layer of vacuolated columnar cells in Psammomys obeus, whereas two cells types were found in Gerbillus tarabuli, vacuolated columnar cells and pyramidal basal cells. In breeding season, a new cellular type (the same for both species) appears characterized by large lipid vacuoles. Porphyrins and cellular debris were observed in the glandular lumens indicating that important cellular remodelling occurs in the HG of desert rodents. The possible functional significance of this new cellular type was discussed. These results suggest, that phenotypic plasticity is an important means by which HG cope with environmental lighting.